title:
Six Peaks Visible in the Redshift Distribution of 46,400 SDSS Quasars
  Agree with the Preferred Redshifts Predicted by the Decreasing Intrinsic
  Redshift Model

abstract:
  The redshift distribution of all 46,400 quasars in the Sloan Digital Sky
Survey (SDSS) Quasar Catalog III, Third Data Release, is examined. Six Peaks
that fall within the redshift window below z = 4, are visible. Their positions
agree with the preferred redshift values predicted by the decreasing intrinsic
redshift (DIR) model, even though this model was derived using completely
independent evidence. A power spectrum analysis of the full dataset confirms
the presence of a single, significant power peak at the expected redshift
period. Power peaks with the predicted period are also obtained when the upper
and lower halves of the redshift distribution are examined separately. The
periodicity detected is in linear z, as opposed to log(1+z). Because the peaks
in the SDSS quasar redshift distribution agree well with the preferred
redshifts predicted by the intrinsic redshift relation, we conclude that this
relation, and the peaks in the redshift distribution, likely both have the same
origin, and this may be intrinsic redshifts, or a common selection effect.
However, because of the way the intrinsic redshift relation was determined it
seems unlikely that one selection effect could have been responsible for both.


title: The Anisoplanatic Point Spread Function in Adaptive Optics

abstract:
  The effects of anisoplanatism on the adaptive optics point spread function
are investigated. A model is derived that combines observations of the guide
star with an analytic formulation of anisoplanatism to generate predictions for
the adaptive optics point spread function at arbitrary locations within the
field of view. The analytic formulation captures the dependencies of
anisoplanatism on aperture diameter, observing wavelength, angular offset,
zenith angle and turbulence profile. The predictions of this model are compared
to narrowband 2.12 um and 1.65 um images of a 21 arcsec binary (mV=7.3, 7.6)
acquired with the Palomar Adaptive Optics System on the Hale 5 meter telescope.
Contemporaneous measurements of the turbulence profile made with a DIMM/MASS
unit are used together with images of the primary to predict the point spread
function of the binary companion. Predicted companion Strehl ratios are shown
to match measurements to within a few percent, whereas predictions based on the
isoplanatic angle approximation are highly discrepant. The predicted companion
point spread functions are shown to agree with observations to 10%. These
predictions are used to measure the differential photometry between binary
members to an accuracy of 1 part in 10^{3}, and the differential astrometry to
an accuracy of 1 mas. Errors in the differential astrometry are shown to be
dominated by differential atmospheric tilt jitter. These results are compared
to other techniques that have been employed for photometry, astrometry, and
high contrast imaging.


title:
Scalar perturbations and the possible self-destruction of the phantom
  menace

abstract:
  Some analysis of the supernovae type Ia observational data seems to indicate
that the Universe today is dominated by a phantom field, for which all energy
conditions are violated. Such phantom field may imply a singularity in a future
finite time, called big rip. Studying the evolution of scalar perturbations for
such a field, we show that if the pressure is negative enough, the Universe can
become highly inhomogeneous and this phantom menace may be avoided.


title:
Formation of Small-Scale Condensations in the Molecular Clouds via
  Thermal Instability

abstract:
  A systematic study of the linear thermal instability of a self-gravitating
magnetic molecular cloud is carried out for the case when the unperturbed
background is subject to local expansion or contraction. We consider the
ambipolar diffusion, or ion-neutral friction on the perturbed states. In this
way, we obtain a non-dimensional characteristic equation that reduces to the
prior characteristic equation in the non-gravitating stationary background. By
parametric manipulation of this characteristic equation, we conclude that there
are, not only oblate condensation forming solutions, but also prolate solutions
according to local expansion or contraction of the background. We obtain the
conditions for existence of the Field lengths that thermal instability in the
molecular clouds can occur. If these conditions establish, small-scale
condensations in the form of spherical, oblate, or prolate may be produced via
thermal instability.


title: Methanol detection in M82

abstract:
  We present a multilevel study of the emission of methanol, detected for the
first time in this galaxy, and discuss the origin of its emission. The high
observed methanol abundance of a few 10^-9 can only be explained if injection
of methanol from dust grains is taken into account. While the overall
[CH3OH]/[NH3] ratio is much larger than observed towards other starbursts, the
dense high excitation component shows a similar value to that found in NGC 253
and Maffei 2. Our observations suggest the molecular material in M 82 to be
formed by dense warm cores, shielded from the UV radiation and similar to the
molecular clouds in other starbursts, surrounded by a less dense
photodissociated halo. The dense warm cores are likely the location of recent
and future star formation within M 82.


title: Impact of Supernova Explosions on Galaxy Formation

abstract:
  We study the effects of Supernova (SN) feedback on the formation of disc
galaxies. For that purpose we run simulations using the extended version of the
code GADGET-2 which includes a treatment of chemical and energy feedback by SN
explosions. We found that our model succeeds in setting a self-regulated star
formation process since an important fraction of the cold gas from the center
of the haloes is efficiently heated up and transported outwards. The impact of
SN feedback on galactic systems is also found to depend on virial mass: smaller
systems are more strongly affected with star formation histories in which
several starbursts can develop. Our implementation of SN feedback is also
successful in producing violent outflows of chemical enriched material.


title:
Tidally Triggered Star Formation in Close Pairs of Galaxies: Major and
  Minor Interactions

abstract:
  We study star formation in a sample of 345 galaxies in 167 pairs and compact
groups drawn from the original CfA2 Redshift Survey and from a follow-up search
for companions. We construct our sample with attention to including pairs with
luminosity contrast |\Delta m_R| >= 2. These 57 galaxies with |\Delta m_R| >= 2
provide a set of nearby representative cases of minor interactions, a central
feature of the hierarchical galaxy formation model. Here we report the
redshifts and positions of the 345 galaxies in our sample, and of 136 galaxies
in apparent pairs that are superpositions. In the pairs sample as a whole,
there are strong correlations between the equivalent width of the H\alpha
emission line and the projected spatial and the line-of-sight velocity
separation of the pair. For pairs of small luminosity contrast, |\Delta m_R| <
2, the member galaxies show a correlation between the equivalent width of
H\alpha and the projected spatial separation of the pair. However, for pairs
with large luminosity contrast, |\Delta m_R| >= 2, we detect no correlation
between the equivalent width of H\alpha and the projected spatial separation.
The relative luminosity of the companion galaxy is more important in a
gravitational tidal interaction than the intrinsic luminosity of the galaxy.
Central star formation across the entire pairs sample depends strongly on the
luminosity ratio, |\Delta m_R|, a reasonable proxy for the mass ratio of the
pair; pairs composed of similarly luminous galaxies produce the strongest
bursts of star formation. Pairs with |\Delta m_R| >= 2 rarely have EW(H\alpha)
>~ 70 Ang.


title:
Radio Observations of a Large Sample of Late-M, L, and T Dwarfs: The
  Distribution of Magentic Field Strengths

abstract:
  We present radio observations of a comprehensive sample of 90 dwarf stars and
brown dwarfs ranging from spectral type M5 to T8. We detect three radio active
sources in addition to the six objects previously detected in quiescence and
outburst, leading to an overall detection rate of about 10% for objects later
than M7. From the properties of the radio emission we infer magnetic field
strengths of ~100 G in quiescence and nearly 1 kG during flares, while the
majority of the non-detected objects have B<50 G. Depending on the
configuration and size of the magnetic loops, the surface magnetic fields may
approach 1 kG even in quiescence, at most a factor of few smaller than in
early-M dwarfs. With the larger sample of sources we find continued evidence
for (i) a sharp transition around spectral type M7 from a ratio of radio to
X-ray luminosity of log(L_R/L_X) ~ -15.5 to >-12, (ii) increased radio activity
with later spectral type, in contrast to H-alpha and X-ray observations, and
(iii) an overall drop in the fraction of active sources from about 30% for M
dwarfs to about 5% for L dwarfs, fully consistent with H-alpha and X-ray
observations. Taken together, these trends suggest that some late-M and L
dwarfs are capable of generating 0.1-1 kG magnetic fields, but the overall drop
in the fraction of such objects is likely accompanied by a change in the
structure of the chromospheres and coronae, possibly due to the increasingly
neutral atmospheres and/or a transition to a turbulent dynamo. A more extended
radio survey currently holds the best promise for measuring the magnetic field
properties of a large number of dwarf stars. [abridged]


title:
The DEEP2 Galaxy Redshift Survey: The Relationship Between Galaxy
  Properties and Environment at z ~ 1

abstract:
  We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey
as a function of rest-frame color, luminosity, and [OII] equivalent width. The
local galaxy overdensity for >14,000 galaxies at 0.75 < z < 1.35 is estimated
using the projected 3rd-nearest-neighbor surface density. Of the galaxy
properties studied, mean environment is found to depend most strongly on galaxy
color; all major features of the correlation between mean overdensity and
rest-frame color observed in the local universe were already in place at z ~ 1.
In contrast to local results, we find a substantial slope in the mean
dependence of environment on luminosity for blue, star-forming galaxies at z ~
1, with brighter blue galaxies being found on average in regions of greater
overdensity. We discuss the roles of galaxy clusters and groups in establishing
the observed correlations between environment and galaxy properties at high
redshift, and we also explore the evidence for a ``downsizing of quenching''
from z ~ 1 to z ~ 0. Our results add weight to existing evidence that the
mechanism(s) that result in star-formation quenching are efficient in group
environments as well as clusters. This work is the first of its kind at high
redshift and represents the first in a series of papers addressing the role of
environment in galaxy formation at 0 < z < 1.


title:
The signature of the magnetorotational instability in the Reynolds and
  Maxwell stress tensors in accretion discs

abstract:
  The magnetorotational instability is thought to be responsible for the
generation of magnetohydrodynamic turbulence that leads to enhanced outward
angular momentum transport in accretion discs. Here, we present the first
formal analytical proof showing that, during the exponential growth of the
instability, the mean (averaged over the disc scale-height) Reynolds stress is
always positive, the mean Maxwell stress is always negative, and hence the mean
total stress is positive and leads to a net outward flux of angular momentum.
More importantly, we show that the ratio of the Maxwell to the Reynolds
stresses during the late times of the exponential growth of the instability is
determined only by the local shear and does not depend on the initial spectrum
of perturbations or the strength of the seed magnetic. Even though we derived
these properties of the stress tensors for the exponential growth of the
instability in incompressible flows, numerical simulations of shearing boxes
show that this characteristic is qualitatively preserved under more general
conditions, even during the saturated turbulent state generated by the
instability.


title:
Gravitational Instabilities in Gaseous Protoplanetary Disks and
  Implications for Giant Planet Formation

abstract:
  Protoplanetary gas disks are likely to experience gravitational instabilites
(GI's) during some phase of their evolution. Density perturbations in an
unstable disk grow on a dynamic time scale into spiral arms that produce
efficient outward transfer of angular momentum and inward transfer of mass
through gravitational torques. In a cool disk with rapid enough cooling, the
spiral arms in an unstable disk form self-gravitating clumps. Whether gas giant
protoplanets can form by such a disk instability process is the primary
question addressed by this review. We discuss the wide range of calculations
undertaken by ourselves and others using various numerical techniques, and we
report preliminary results from a large multi-code collaboration. Additional
topics include -- triggering mechanisms for GI's, disk heating and cooling,
orbital survival of dense clumps, interactions of solids with GI-driven waves
and shocks, and hybrid scenarios where GI's facilitate core accretion. The
review ends with a discussion of how well disk instability and core accretion
fare in meeting observational constraints.


title:
Fueling Low-Level AGN Activity Through the Stochastic Accretion of Cold
  Gas

abstract:
  Using a simple description of feedback from black hole (BH) growth, we
develop an analytic model for the fueling of Seyferts (low-luminosity AGN) and
their relation to their host galaxies, Eddington ratio distributions, and
cosmological evolution. We derive a solution for evolution of accretion rates
in a feedback-driven blast wave, applicable to large-scale outflows from bright
quasars in galaxy mergers, low-luminosity AGN, and BHs in supernova remnants.
Under the assumption that cold gas stochastically accretes onto a central SMBH
at a rate set by the dynamics of that gas, our solution determines the Seyfert
light curve evolution. We use this to predict the Seyfert luminosity function
(LF), duty cycles, lifetimes, and distribution of host morphologies, Eddington
ratios, and obscuration as a function of AGN luminosity and mass, and find
agreement with observations at z=0. We consider the breakdown of contributions
from this and stellar wind accretion and merger-driven activity. We make
specific predictions for the weak evolution of the Seyfert LF with redshift (LF
of non-merger driven activity), and for changes in both the slope and scatter
of the M_BH-sigma relation at low-M_BH. Quiescent fueling dominates over a wide
luminosity range (-14 > M_B > -22) at z=0, where most BH growth occurs around
M_BH~10^7 M_sun, in S0 and Sa/b galaxies. However, quasar activity from
gas-rich mergers evolves more rapidly with redshift, and by z=1 quiescent
fueling is important only at luminosities an order of magnitude or more below
the LF break. Although non-merger driven fueling is important for BH growth and
the M_BH-sigma relation at low M_BH, it does not significantly contribute to
the total BH mass density or cosmological backgrounds.


title:
High Quality Early Time Light Curves of GRB 060206: Implications for
  Gamma Ray Burst Environments and Energetics

abstract:
  The 2-m robotic Liverpool Telescope (LT) reacted promptly to the
high-redshift (z=4.048) gamma-ray burst GRB 060206. The afterglow was
identified automatically and multicolor r'i'z' imaging was triggered without
human intervention. Combining our data with those obtained from later
follow-ups provides a well-sampled optical light-curve from 5 minutes to >2d
after the gamma event. The light-curve is highly structured with at least three
bumps evident in the first 75 minutes, including a major rebrightening
(Delta_r'=-1.6 at t=3000s), interpreted as late energy injection. At early time
(t=440s), we find evidence for fast (Delta t_(rest)<4s<<t) variability,
indicating on-going internal-engine activity. We emphasise that a low redshift
GRB (z<1) with similar intrinsic properties would have been interpreted
completely differently due to undersampling of the light curve in the rest
frame at early times; the light-curve behaviour of GRB 060206 should therefore
not be considered peculiar. Finally, although the observed late-time steepening
of the optical light curve resembles a jet break if taken in isolation, the
lack of a corresponding change in the X-ray slope rules out a jet-break
interpretation. Traditionally, GRB jet breaks have been inferred from optical
data in the absence of simultaneous X-ray data. We suggest therefore that
current estimates of the jet opening angle distribution might be biased by
events like GRB060206. Consequently, the GRB explosion energy distribution and
event rates may have to be revised.


title:
GALEX Observations of "Passive Spirals" in the Cluster Cl 0024+17: Clues
  to the Formation of S0 Galaxies

abstract:
  We present new results from deep GALEX UV imaging of the cluster Cl 0024+17
at z~0.4. Rest-frame far UV emission is detected from a large fraction of
so-called ``passive spiral galaxies'' -a significant population which exhibits
spiral morphology with little or no spectroscopic evidence for ongoing star
formation. This population is thought to represent infalling galaxies whose
star formation has been somehow truncated by environmental processes, possibly
in morphological transition to S0 galaxies. Compared to normal cluster spirals,
we find that passive spirals are redder in FUV-optical color, while exhibiting
much stronger UV emission than cluster E/S0s - as expected for
recently-truncated star formation. By modeling the different temporal
sensitivities of UV and spectroscopic data to recent activity, we show that
star formation in passive spirals decayed on timescales of less than 1 Gyr,
consistent with `gas starvation' - a process where the cluster environment
prevents cold gas from accreting onto the spiral disk. Intriguingly, the
fraction of spirals currently observed in the passive phase is consistent with
the longer period expected for the morphological transformation and the
subsequent build-up of cluster S0s observed since z=0.4.


title: Simulating Diffuse Light in Galaxy Clusters

abstract:
  Using N-body simulations, we have modeled the production and evolution of low
surface brightness, diffuse intra-cluster light (ICL) in galaxy clusters. By
creating simulated observations of the clusters we have measured the evolution
of the ICL luminosity throughout the dynamical history of the clusters. We find
that ICL production tends to occur in short, discrete events, which correlate
very strongly with strong, small-scale interactions and accretions between
groups within the clusters.


title: 3D Models for High Velocity Features in Type Ia Supernovae

abstract:
  Spectral synthesis in 3-dimensional (3D) space for the earliest spectra of
Type Ia supernovae (SNe Ia) is presented. In particular, the high velocity
absorption features that are commonly seen at the earliest epochs ($\sim 10$
days before maximum light) are investigated by means of a 3D Monte Carlo
spectral synthesis code. The increasing number of early spectra available
allows statistical study of the geometry of the ejecta. The observed diversity
in strength of the high velocity features (HVFs) can be explained in terms of a
``covering factor'', which represents the fraction of the projected photosphere
that is concealed by high velocity material. Various geometrical models
involving high velocity material with a clumpy structure or a thick torus can
naturally account for the observed statistics of HVFs. HVFs may be formed by a
combination of density and abundance enhancements. Such enhancements may be
produced in the explosion itself or may be the result of interaction with
circumstellar material or an accretion disk. Models with 1 or 2 blobs, as well
as a thin torus or disk-like enhancement are unlikely as a standard situation.


title: The accretion-diffusion scenario for metals in cool white dwarfs

abstract:
  We calculated diffusion timescales for Ca, Mg, Fe in hydrogen atmosphere
white dwarfs with temperatures between 5000 and 25000 K. With these timescales
we determined accretion rates for a sample of 38 DAZ white dwarfs from the
recent studies of Zuckerman et al. (2003) and Koester et al. (2005). Assuming
that the accretion rates can be calculated with the Bondi-Hoyle formula for
hydrodynamic accretion, we obtained estimates for the interstellar matter
density around the accreting objects. These densities are in good agreement
with new data about the warm, partially ionized phase of the ISM in the solar
neighborhood.


title:
The discovery of an expanding X-ray source in the HH 154 protostellar
  jet

abstract:
  We have performed, in October 2005, a deep Chandra X-ray observation of HH
154. Comparison with the previous (2001) Chandra observation allows to detect
proper motion down to the level predicted by models of X-ray emitting shocks in
the jet. The 2005 Chandra observation of HH 154 shows unexpected morphological
changes of the X-ray emission in comparison with the 2001 data. Two components
are present: a stronger, point-like component with no detectable motion and a
weaker component which has expanded in size by approximately 300 AU over the 4
years time base of the two observations. This expansion corresponds to
approximately 500 km/s, very close to the velocity of the X-ray emitting shock
in the simple theoretical models. The 2005 data show a more complex system than
initially thought (and modeled), with multiple components with different
properties. The observed morphology is possibly indicating a pulsed jet
propagating through a non-homogeneous medium, likely with medium density
decreasing with distance from the driving source. Detailed theoretical modeling
and deeper X-ray observations will be needed to understand the physics of this
fascinating class of sources.


title:
Composite Dark Matter with Invisible Light from Almost-Commutative
  Geometry

abstract:
  Almost commutative geometry offers a specific way to unify general
relativity, quantum mechanics and gauge symmetries. The AC-model of elementary
particles, arising on this way, naturally embeds the Standard model and
predicts doubly charged AC-leptons, anion-like A^{--} and cathion-like C^{++},
which can bind in WIMP-like (AC)-atoms, being a nontrivial candidate for
cosmological dark matter. This state is reached in the early Universe along a
tail of more manifest secondary frozen blocks. They should be now here
polluting the surrounding matter. The main secondary relics are C^{++}
"anomalous helium" and a bound system of A^{--} with an ordinary helium ion
(^4He)^{++}, which is able to attract and capture (in thefirst three minutes)
all the free A^{--} fixing them into a neutral OLe-helium (OHe) nuclear
interacting "atom" (^4He^{++}A^{--}). The model naturally involves a new U(1)
gauge interaction, possessed only by the AC-leptons and providing a
Coulomb-like attraction between them. This attraction stimulates the effective
A-C recombination into AC-atoms inside dense matter bodies (stars and planets),
resulting in a decrease of anomalous isotopes below the experimental upper
limits. OLe-helium pollution of terrestrial matter and (OHe) catalysis of
nuclear reactions in it is one of the exciting problems (or advantages?) of the
present model.


title: Implications of the metallicity dependence of Wolf-Rayet winds

abstract:
  Aims: Recent theoretical predictions for the winds of Wolf-Rayet stars
indicate that their mass-loss rates scale with the initial stellar metallicity
in the local Universe.We aim to investigate how this predicted dependence
affects the models of Wolf-Rayet stars and their progeny in different chemical
environments. Methods: We compute models of stellar structure and evolution for
Wolf-Rayet stars for different initial metallicities, and investigate how the
scaling of the Wolf-Rayet mass-loss rates affects the final masses, the
lifetimes of the WN and WC subtypes, and how the ratio of the two populations
vary with metallicity. Results: We find significant effects of metallicity
dependent mass-loss rates for Wolf-Rayet stars. For models that include the
scaling of the mass-loss rate with initial metallicity, all WR stars become
neutron stars rather than black holes at twice the solar metallicity; at lower
$Z$, black holes have larger masses. We also show that our models that include
the mass-loss metallicity scaling closely reproduce the observed decrease of
the relative population of WC over WN stars at low metallicities.


title:
Chemical Self-Enrichment of HII Regions by the Wolf-Rayet Phase of an 85
  Msun star

abstract:
  It is clear from stellar evolution and from observations of WR stars that
massive stars are releasing metal-enriched gas through their stellar winds in
the Wolf-Rayet phase. Although HII region spectra serve as diagnostics to
determine the present-day chemical composition of the interstellar medium, it
is far from being understood to what extent the HII gas is already contaminated
by chemically processed stellar wind. Therefore, we analyzed our models of
radiative and wind bubbles of an isolated 85 Msun star with solar metallicity
(Kr\"oger et al. 2006) with respect to the chemical enrichment of the
circumstellar HII region. Plausibly, the hot stellar wind bubble (SWB) is
enriched with 14N during the WN phase and even much higher with 12C and 16O
during the WC phase of the star. During the short period that the 85 Msun star
spends in the WC stage enriched SWB material mixes with warm HII gas of solar
abundances and thus enhances the metallicity in the HII region. However, at the
end of the stellar lifetime the mass ratios of the traced elements N and O in
the warm ionized gas are insignificantly higher than solar, whereas an
enrichment of 22 % above solar is found for C. Important issues from the
presented study comprise a steeper radial gradient of C than O and a decreasing
effect of self-enrichment for metal-poor galaxies.


title: Deuterium astration in the local disc and beyond

abstract:
  (Abridged) Estimates of the interstellar deuterium abundance span a wide
range of values. Here we study the evolution of deuterium in the framework of
successful models for the chemical evolution of the Milky Way able to reproduce
the majority of the observational constraints for the solar neighbourhood and
for the Galactic disc. We show that, in the framework of our models, the lowest
D/H values observed locally cannot be explained in terms of simple astration
processes occurring during the Galaxy evolution. Indeed, the combination of a
mild star formation and a continuous infall of unprocessed gas required to fit
all the available observational data allows only a modest variation of the
deuterium abundance from its primordial value.


title:
The Outskrits of Spiral Galaxies: Evidence for Multiple Stellar
  Populations

abstract:
  We present an analysis of the metallicity distribution functions of fields
projected along the minor axis for a sample of inclined spiral galaxies in
order to search for evidence of the presence of multiple stellar populations.
In all cases, the stellar populations appear to have asymmetric metallicity
distributions with very high confidence levels. The mean metallicities of both
stellar subpopulations, determined from mixture modelling of the metallicity
distribution functions, correlate with parent galaxy luminosity. This suggests
that the vast majority of field stars have probably formed in galactic
fragments that were already embedded in the dark matter halo of the final
galaxy. The steeper correlation between the mean stellar metallicity and parent
galaxy luminosity is driven by an increasing fraction of metal-rich stars with
increasing galaxy luminosity. Metal-poor components show larger dispersion in
metallicity than metal-rich components. These properties are in striking
similarity with those of globular cluster subpopulations around early-type
galaxies. The properties of field stars along the minor axis are consistent
with a formation scenario in which the metal-poor stars formed in all galaxies,
possibly as a result of tidal disruption of dwarf-like objects. An additional
metal-rich component might be related to the formation of the bulge and/or the
disk.


title: Internal dynamics of the radio-halo cluster A2744

abstract:
  We present a detailed dynamical analysis of the rich galaxy cluster A2744,
containing a powerful diffuse radio halo.Our analysis is based on redshift data
for 102 galaxies, part of them recovered from unexplored spectra in the ESO
archive. We combine galaxy velocity and position information to select the
cluster members and determine global dynamical properties of the cluster. We
use a variety of statistical tests to detect possible substructures. We find
that A2744 appears as a well isolated peak in the redshift space at <z>=0.306,
which includes 85 galaxies recognized as cluster members. We compute the
line-of-sight (LOS) velocity dispersion of galaxies (~1750 km/sec), which is
significantly larger than what is expected in the case of a relaxed cluster
with an observed X-ray temperature of 8 keV. We find evidence that this cluster
is far from dynamical equilibrium, as shown by the non-Gaussian nature of the
velocity distribution, the presence of a velocity gradient and a significant
substructure. In particular, our results suggest a merging scenario of two
clumps with a mass ratio of 3:1 and a LOS impact velocity (rest frame) of ~3000
km/sec, likely observed just after the core passage. The merging is occuring
roughly in the NS direction with the axis close to the LOS. This scenario
agrees with that proposed on the basis of recent Chandra results in its general
lines, although suggesting a somewhat more advanced merging phase.


title:
Mass and Angular Momentum of Black Holes: An Overlooked Effect of
  General Relativity Applied to the Galactic Center Black Hole Sgr A*

abstract:
  I report the discovery of a new effect of General Relativity which is
important to understand very rapidly rotating (Kerr) black holes. The orbital
velocity of a test particle is no longer a monotonic function of the orbit
radius when the spin of the black hole is >0.9953, but displays a local
minimum-maximum structure for radii smaller than 1.8 gravitational radii. There
the rate of change of the orbital velocity per radius unit equals the radial
epicyclic frequency and is exactly one third of the polar epicyclic frequency,
suggesting a 3:1 resonant oscillatory motion of the particle. If associated
with the observed quasi-periods - including the most recent 2005/2006 data -
the mass of the supermassive black hole Sgr A* in the centre of the our Galaxy
is determined to 3.3 million solar masses and the spin is 0.99616.


title: Spectroscopic rotational velocities of brown dwarfs

abstract:
  We have obtained projected rotation velocities (vsini) of a sample of 19
ultracool dwarfs with spectral types in the interval M6.5-T8 using
high-resolution, near-infrared spectra obtained with NIRSPEC and the Keck II
telescope. Among our targets there are two young brown dwarfs, two likely field
stars, and fifteen likely brown dwarfs (30-72 Mjup) of the solar neighborhood.
Our results indicate that the T-type dwarfs are fast rotators in marked
contrast to M-type stars. We have derived vsini velocities between <15 and 40
km/s for them, and have found no clear evidence for T dwarfs rotating strongly
faster than L dwarfs. However, there is a hint for an increasing lower envelope
on moving from mid-M to the L spectral types in the vsini-spectral type diagram
that was previously reported in the literature; our vsini results extend it to
even cooler types. Assuming that field brown dwarfs have a size of 0.08-0.1
Rsol, we can place an upper limit of 12.5 h on the equatorial rotation period
of T-type brown dwarfs. In addition, we have compared our vsini measurements to
spectroscopic rotational velocities of very young brown dwarfs of similar mass
available in the literature. The comparison, although model-dependent, suggests
that brown dwarfs lose some angular momentum during their contraction; however,
their spin down time seems to be significantly longer than that of solar-type
to early-M stars.


title:
Radiative Hydrodynamic Models of Optical and Ultraviolet Emission from M
  Dwarf Flares

abstract:
  We report on radiative hydrodynamic simulations of M dwarf stellar flares and
compare the model predictions to observations of several flares. The flares
were simulated by calculating the hydrodynamic response of a model M dwarf
atmosphere to a beam of non-thermal electrons. Radiative backwarming through
numerous soft X-ray, extreme ultraviolet, and ultraviolet transitions are also
included. The equations of radiative transfer and statistical equilibrium are
treated in non-LTE for many transitions of hydrogen, helium and the Ca II ion
allowing the calculation of detailed line profiles and continuum radiation. Two
simulations were carried out, with electron beam fluxes corresponding to
moderate and strong beam heating. In both cases we find the dynamics can be
naturally divided into two phases: an initial gentle phase in which hydrogen
and helium radiate away much of the beam energy, and an explosive phase
characterized by large hydrodynamic waves. During the initial phase, lower
chromospheric material is evaporated into higher regions of the atmosphere
causing many lines and continua to brighten dramatically. The He II Lya line is
especially enhanced, becoming the brightest line in the flaring spectrum. The
hydrogen Balmer lines also become much brighter and show very broad line
widths, in agreement with observations. We compare our predicted Balmer
decrements to decrements calculated for several flare observations and find the
predictions to be in general agreement with the observations. During the
explosive phase both condensation and evaporation waves are produced. The
moderate flare simulation predicts a peak evaporation wave of 130 km/s and a
condensation wave of 30 km/s. The velocity of the condensation wave matches
velocities observed in several transition region lines.


title: Disk-Planet Interactions During Planet Formation

abstract:
  The discovery of close orbiting extrasolar giant planets led to extensive
studies of disk planet interactions and the forms of migration that can result
as a means of accounting for their location. Early work established the type I
and type II migration regimes for low mass embedded planets and high mass gap
forming planets respectively. While providing an attractive means of accounting
for close orbiting planets intially formed at several AU, inward migration
times for objects in the earth mass range were found to be disturbingly short,
making the survival of giant planet cores an issue. Recent progress in this
area has come from the application of modern numerical techniques which make
use of up to date supercomputer resources. These have enabled higher resolution
studies of the regions close to the planet and the initiation of studies of
planets interacting with disks undergoing MHD turbulence. This work has led to
indications of how the inward migration of low to intermediate mass planets
could be slowed down or reversed. In addition, the possibility of a new very
fast type III migration regime, that can be directed inwards or outwards, that
is relevant to partial gap forming planets in massive disks has been
investigated.


title: Radio Images of 3C 58: Expansion and Motion of its Wisp

abstract:
  New 1.4 GHz VLA observations of the pulsar-powered supernova remnant 3C 58
have resulted in the highest-quality radio images of this object to date. The
images show filamentary structure over the body of the nebula. The present
observations were combined with earlier ones from 1984 and 1991 to investigate
the variability of the radio emission on a variety of time-scales. No
significant changes are seen over a 110 day interval. In particular, the upper
limit on the apparent projected velocity of the wisp is 0.05c. The expansion
rate of the radio nebula was determined between 1984 and 2004, and is
0.014+/-0.003%/year, corresponding to a velocity of 630+/-70 km/s along the
major axis. If 3C 58 is the remnant of SN 1181, it must have been strongly
decelerated, which is unlikely given the absence of emission from the supernova
shell. Alternatively, the low expansion speed and a number of other arguments
suggest that 3C 58 may be several thousand years old and not be the remnant of
SN 1181.


title:
Mid-Infrared Identifications of SCUBA Galaxies in the CUDSS 14-Hour
  Field with the Spitzer Space Telescope

abstract:
  We identify 17 possible 8.0 micron-selected counterparts to the submillimeter
galaxies in the CUDSS 14-hour field, derived from deep imaging carried out with
the IRAC and MIPS instruments aboard the Spitzer Space Telescope. Ten of the 17
counterparts are not the same as those previously identified at shorter
wavelengths. We argue that 8.0 micron selection offers a better means for
identifying counterparts to submillimeter galaxies than near-infrared or
optical selection. Based on the panchromatic SEDs, most counterparts appear to
be powered by ongoing star formation. Power-law fits to the SEDs suggest that
five objects in the 8.0 micron-selected counterpart sample harbor dominant
AGNs; a sixth object is identified as a possible AGN. The 3.6 to 8.0 micron
colors of the infrared-selected counterparts are significantly redder than the
general IRAC galaxy population in the CUDSS 14-hour field.


title:
Cosmological Radiative Transfer Codes Comparison Project I: The Static
  Density Field Tests

abstract:
  Radiative transfer simulations are now at the forefront of numerical
astrophysics. They are becoming crucial for an increasing number of
astrophysical and cosmological problems; at the same time their computational
cost has come to the reach of currently available computational power. Further
progress is retarded by the considerable number of different algorithms
(including various flavours of ray-tracing and moment schemes) developed, which
makes the selection of the most suitable technique for a given problem a
non-trivial task. Assessing the validity ranges, accuracy and performances of
these schemes is the main aim of this paper, for which we have compared 11
independent RT codes on 5 test problems: (0) basic physics, (1) isothermal H II
region expansion and (2) H II region expansion with evolving temperature, (3)
I-front trapping and shadowing by a dense clump, (4) multiple sources in a
cosmological density field. The outputs of these tests have been compared and
differences analyzed. The agreement between the various codes is satisfactory
although not perfect. The main source of discrepancy appears to reside in the
multi-frequency treatment approach, resulting in different thicknesses of the
ionized-neutral transition regions and different temperature structure. The
present results and tests represent the most complete benchmark available for
the development of new codes and improvement of existing ones. To this aim all
test inputs and outputs are made publicly available in digital form.


title:
Habitability of known exoplanetary systems based on measured stellar
  properties

abstract:
  At present, because of observational selection effects, we know of no
exoplanetary systems with any planetary masses close to that of the Earth. We
have therefore used computer models to see whether such planets could be
dynamically stable in the presence of the more massive planets known to be
present, and in particular whether planets with roughly an Earth mass could
remain confined to the classical habitable zone (HZ) for long enough for life
to have emerged.
  Measured stellar properties have been used to determine for each system the
present location of the HZ. We have also determined the critical distances from
the orbit of each giant planet within which an Earth-mass planet would suffer
large orbital changes. We then evaluated the present habitability of each and
every exoplanetary system by examining the penetration of these critical
distances into the HZ. The critical distances can be obtained by extensive
computer modelling of an exoplanetary system. This is far too time consuming to
apply to all of the 150 or so systems already known, and to keep up with the
latest discoveries. Therefore, in earlier work we studied a few systems in
great detail, and developed a speedier means of obtaining the critical
distances. We summarize this comparatively quick method here. We can then
evaluate comparatively quickly the present habitability of each exoplanetary
system by examining the penetration of the critical distance(s) into the HZ.
The results are encouraging for astrobiology.


title: Discovery of Interstellar CF+

abstract:
  We discuss the first astronomical detection of the CF+ (fluoromethylidynium)
ion, obtained by observations of the J=1-0 (102.6 GHz), J=2-1 (205.2 GHz) and
J=3-2 (307.7 GHz) rotational transitions toward the Orion Bar region. Our
search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was
motivated by recent theoretical models that predict CF+ abundances of a few
times 1.E-10 in UV-irradiated molecular regions where C+ is present. The CF+
ion is produced by exothermic reactions of C+ with HF. Because fluorine atoms
can react exothermically with H2, HF is predicted to be the dominant reservoir
of fluorine, not only in well-shielded regions but also in the surface layers
of molecular clouds where the C+ abundance is large. The observed CF+ line
intensities imply the presence of CF+ column densities of at least 1.E+12 cm-2
over a region of size at least ~ 1 arcmin, in good agreement with theoretical
predictions. They provide support for our current theories of interstellar
fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous
in interstellar gas clouds and widely detectable in absorption by future
satellite and airborne observatories.


title: The VIMOS VLT Deep Survey: The build-up of the colour-density relation

abstract:
  We investigate the redshift and luminosity evolution of the galaxy
colour-density relation using the data from the First Epoch VIMOS-VLT Deep
Survey (VVDS). The size (6582 galaxies), depth (I_AB<=24) and redshift sampling
rate of the survey enable us to reconstruct the 3D galaxy environment on
relatively local scales (R=5 Mpc) up to z~1.5. Particular attention has been
devoted to calibrate a density reconstruction scheme, which factors out survey
selection effects and reproduces in an unbiased way the underlying `real'
galaxy environment. While at lower redshift we confirm the existence of a steep
colour-density relation, with the fraction of the reddest(/bluest) galaxies of
the same luminosity increasing(/decreasing) as a function of density, this
trend progressively disappears in the highest redshift bins investigated. The
rest frame u*-g' colour-magnitude diagram shows a bimodal pattern in both low
and high density environments up to z~1.5. We find that the bimodal
distribution is not universal but strongly depends upon environment: at lower
redshifts the colour-magnitude diagrams in low and high density regions are
significantly different while the progressive weakening of the colour-density
relation causes the two bimodal distributions to nearly mirror each other in
the highest redshift bin investigated. Both the colour-density and the
colour-magnitude-density relations appear to be a transient, cumulative product
of genetic and environmental factors operating over at least a period of 9 Gyr.
These findings support an evolutionary scenario in which star formation/gas
depletion processes are accelerated in more luminous objects and in high
density environments: star formation activity is shifting with cosmic time
towards lower luminosity (downsizing), and out of high density environments.


title: A SCUBA survey of L1689 - The dog that didn't bark

abstract:
  We present submillimetre data for the L1689 cloud in the rho-Ophiuchi
molecular cloud complex. We detect a number of starless and prestellar cores
and protostellar envelopes. We also detect a number of filaments for the first
time in the submillimetre continuum that are parallel both to each other, and
to filaments observed in the neighbouring L1688 cloud. These filaments are also
seen in the 13CO observations of L1689. The filaments contain all of the
star-formation activity in the cloud. L1689 lies next to the well studied L1688
cloud that contains the rho Oph-A core. L1688 has a much more active
star-formation history than L1689 despite their apparent similarity in 13CO
data. Hence we label L1689 as the dog that didn't bark. We endeavour to explain
this apparent anomaly by comparing the total mass of each cloud that is
currently in the form of dense material such as prestellar cores. We note
firstly that L1688 is more massive than L1689, but we also find that when
normalised to the total mass of each cloud, the L1689 cloud has a much lower
percentage of mass in dense cores than L1688. We attribute this to the
hypothesis of Loren (1989) that the star formation in the rho-Ophiuchi complex
is being affected and probably dominated by the external influence of the
nearby Upper Scorpius OB association and predominantly by sigma-Sco. L1689 is
further from sigma-Sco and is therefore less active. The influence of sigma-Sco
appears nonetheless to have created the filaments that we observe in L1689.
Accepted by MNRAS.


title: Getting a kick out of numerical relativity

abstract:
  Recent developments in numerical relativity have made it possible to follow
reliably the coalescence of two black holes from near the innermost stable
circular orbit to final ringdown. This opens up a wide variety of exciting
astrophysical applications of these simulations. Chief among these is the net
kick received when two unequal mass or spinning black holes merge. The
magnitude of this kick has bearing on the production and growth of supermassive
black holes during the epoch of structure formation, and on the retention of
black holes in stellar clusters. Here we report the first accurate numerical
calculation of this kick, for two nonspinning black holes in a 1.5:1 mass
ratio, which is expected based on analytic considerations to give a significant
fraction of the maximum possible recoil. We have performed multiple runs with
different initial separations, orbital angular momenta, resolutions, extraction
radii, and gauges. The full range of our kick speeds is 86--116 km s$^{-1}$,
and the most reliable runs give kicks between 86 and 97 km s$^{-1}$. This is
intermediate between the estimates from two recent post-Newtonian analyses and
suggests that at redshifts $z\gtrsim 10$, halos with masses $\lesssim 10^9
M_\odot$ will have difficulty retaining coalesced black holes after major
mergers.


title: A New Robust Low-Scatter X-ray Mass Indicator for Clusters of Galaxies

abstract:
  We present comparison of X-ray proxies for the total cluster mass, including
the spectral temperature (Tx), gas mass measured within r500 (Mg), and the new
proxy, Yx, which is a simple product of Tx and Mg and is related to the total
thermal energy of the ICM. We use mock Chandra images constructed for a sample
of clusters simulated with the eulerian N-body+gasdynamics adaptive mesh
refinement ART code in the concordance LCDM cosmology. The simulations achieve
high spatial and mass resolution and include radiative cooling, star formation,
and other processes accompanying galaxy formation. Our analysis shows that
simulated clusters exhibit a high degree of regularity and tight correlations
between the considered observables and total mass. The normalizations of the
M-Tx, Mg-Tx, and M-Yx relations agree to better than 10-15% with the current
observational measurements of these relations. Our results show that Yx is the
best mass proxy with a remarkably low scatter of only ~5-7% in M500 for a fixed
Yx, at both low and high redshifts and regardless of whether clusters are
relaxed or not. In addition, we show that redshift evolution of the Yx-M500
relation is close to the self-similar prediction, which makes Yx a very
attractive mass indicator for measurements of the cluster mass function from
X-ray selected samples.


title: Cosmological Parameters and Cosmic Topology

abstract:
  Geometry constrains but does not dictate the topology of the 3--dimensional
space. In a locally spatially homogeneous and isotropic universe, however, the
topology of its spatial section dictates its geometry. We show that, besides
determining the geometry, the knowledge of the spatial topology through the
circles--in--the--sky offers an effective way of setting constraints on the
density parameters associated with dark matter ($\Omega_m$) and dark energy
($\Omega_{\Lambda}$). By assuming the Poincar\'e dodecahedral space as the
circles--in--the--sky detectable topology of the spatial sections of the
Universe, we re-analyze the constraints on the density parametric plane
$\Omega_{m}$--$ \Omega_{\Lambda} $ from the current type Ia supenovae (SNe Ia)
plus X-ray gas mass fraction data, and show that a circles--in--the sky
detection of the dodecahedral space topology give rise to strong and
complementary constraints on the region of the density parameter plane
currently allowed by these observational data sets.


title: The XMM-Newton view of GRS1915+105 during a "plateau"

abstract:
  Two XMM-Newton observations of the black-hole binary GRS1915+105 were
triggered in 2004 (April 17 and 21), during a long "plateau" state of the
source. We analyzed the data collected with EPIC-pn in Timing and Burst modes,
respectively. No thermal disc emission is required by the data; the spectrum is
well fitted by four components: a primary component (either a simple power law
or thermal Comptonization) absorbed by cold matter with abundances different
than those of standard ISM; reprocessing from an ionized disc; emission and
absorption lines; and a soft X-ray excess around 1 keV. The latter is not
confirmed by RGS (which were used in the second observation only); if real, the
excess could be due to reflection from the optically thin, photoionized plasma
of a disc wind, in which case it may provide a way to disentangle intrinsic
from interstellar absorption. Indeed, the former is best traced by the higher
abundances of heavier elements, while an independent estimate of the latter may
be given by the value we get for the disc wind component only, which roughly
coincides with what is found for lower-Z species.


title:
The Cosmic Infrared Background Resolved by Spitzer. Contributions of
  Mid-Infrared Galaxies to the Far-Infrared Background

abstract:
  Aims. We quantify the contributions of 24um galaxies to the Far-Infrared
(FIR) Background at 70 and 160um. We provide new estimates of the Cosmic
Infrared Background (CIB), and compare it with the Cosmic Optical Background
(COB). Methods. Using Spitzer data at 24, 70 and 160um in three deep fields, we
stacked more than 19000 MIPS 24um sources with S24>60uJy at 70 and 160um, and
measured the resulting FIR flux densities. Results. This method allows a gain
up to one order of magnitude in depth in the FIR. We find that the Mid-Infrared
(MIR) 24um selected sources contribute to more than 70% of the CIB at 70 and
160um. This is the first direct measurement of the contribution of MIR-selected
galaxies to the FIR CIB. Galaxies contributing the most to the total CIB are
thus z~1 luminous infrared galaxies, which have intermediate stellar masses. We
estimate that the CIB will be resolved at 0.9 mJy at 70 and 3 mJy at 160um. By
combining the extrapolation of the 24um source counts below 60uJy, with 160/24
and 70/24 colors as measured with the stacking analysis, we obtain lower limits
of 7.1+/-1.0 and 13.4+/-1.7 nW/m2/sr for the CIB at 70 and 160um, respectively.
Conclusions. The MIPS surveys have resolved more than three quarters of the MIR
and FIR CIB. By carefully integrating the Extragalactic Background Light (EBL)
SED, we also find that the CIB has the same brightness as the COB, around 24
nW/m2/sr. The EBL is produced on average by 115 infrared photons for one
visible photon. Finally, the galaxy formation and evolution processes emitted a
brightness equivalent to 5% of the primordial electromagnetic background (CMB).


title: Galaxy Formation and Dark Matter

abstract:
  The challenge of dark matter may be addressed in two ways; by studying the
confrontation of structure formation with observation and by direct and
indirect searches. In this review, I will focus on those aspects of dark matter
that are relevant for understanding galaxy formation, and describe the outlook
for detecting the most elusive component, non-baryonic dark matter. Galaxy
formation theory is driven by phenomenology and by numerical simulations of
dark matter clustering under gravity. Once the complications of star formation
are incorporated, the theory becomes so complex that the brute force approach
of numerical simulations needs to be supplemented by incorporation of such
astrophysical processes as feedback by supernovae and by active galactic
nuclei. I present a few semi-analytical perspectives that may shed some insight
into the nature of galaxy formation.


title:
High-frequency Quasi-Periodic Oscillations from GRS 1915+105 in its C
  state

abstract:
  We report the results of a systematic timing analysis of RXTE observations of
GRS 1915+105 when the source was in its variability class theta, characterized
by alternating soft and hard states on a time scale of a few hundred seconds.
The aim was to examine the high-frequency part of the power spectrum in order
to confirm the hecto-Hertz Quasi-Periodic Oscillations (QPO) previously
reported from observations from mixed variability behaviours. During the hard
intervals (corresponding to state C in the classification of Belloni et al.,
2000, A&A, 35, 271), we find a significant QPO at a frequency of ~170 Hz,
although much broader (Q~2) than previously reported. No other significant peak
is observed at frequencies >30 Hz. A time-resolved spectral analysis of
selected observations shows that the hard intervals from class theta show a
stronger and steeper (Gamma=2.8-3.0) power-law component than hard intervals
from other classes. We discuss these results in the framework of hecto-Hertz
QPOs reported from GRS 1915+105 and other black-hole binaries.


title:
Simulations of relativistic collisionless shocks: shock structure and
  particle acceleration

abstract:
  We discuss 3D simulations of relativistic collisionless shocks in
electron-positron pair plasmas using the particle-in-cell (PIC) method. The
shock structure is mainly controlled by the shock's magnetization ("sigma"
parameter). We demonstrate how the structure of the shock varies as a function
of sigma for perpendicular shocks. At low magnetizations the shock is mediated
mainly by the Weibel instability which generates transient magnetic fields that
can exceed the initial field. At larger magnetizations the shock is dominated
by magnetic reflections. We demonstrate where the transition occurs and argue
that it is impossible to have very low magnetization collisionless shocks in
nature (in more than one spatial dimension). We further discuss the
acceleration properties of these shocks, and show that higher magnetization
perpendicular shocks do not efficiently accelerate nonthermal particles in 3D.
Among other astrophysical applications, this may pose a restriction on the
structure and composition of gamma-ray bursts and pulsar wind outflows.


title: Pulsar electrodynamics: a time-dependent view

abstract:
  Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss
processes in many astrophysical objects including accretion disks and back
holes. In this paper we review the physics of pulsar magnetospheres,
concentrating on recent developments in force-free modeling of the
magnetospheric structure. In particular, we discuss a new method for solving
the equations of time-dependent force-free relativistic MHD in application to
pulsars. This method allows to dynamically study the formation of the
magnetosphere and its response to perturbations, opening a qualitatively new
window on pulsar phenomena. Applications of the method to other magnetized
rotators, such as magnetars and accretion disks, are also discussed.


title: Comments on "Dark matter: A phenomenological existence proof"

abstract:
  A recent paper by Ahluwalia-Khalilova (astro-ph/0601489) is examined where he
claims that the standard FRW cosmology with a $\Lambda$ predicts existence of
dark matter without invoking the data on galactic rotation curves and
gravitational lensing. However, we find that his claims are not correct. He has
already assumed (without realizing) in the very outset what he wants to prove.


title: On the Orbits and Masses of the Satellites of the Pluto-Charon System

abstract:
  (Abridged) The orbits of the recently discovered satellites of Pluto, S/2005
P2 and S/2005 P1, are significantly non-Keplerian, even if P2 and P1 have
negligible masses, because the mass ratio of Charon-Pluto is ~0.1. We present
an analytic theory with P2 and P1 treated as test particles. This analytic
theory shows that the azimuthal periods of P2 and P1 are shorter than the
Keplerian orbital periods and that the periapse and ascending node of each of
the satellites precess at nearly equal rates in opposite directions. The
deviation from Kepler's third law is already detected in the unperturbed
Keplerian fit of Buie and coworkers. We also present direct numerical orbit
integrations with different assumed masses for P2 and P1 within the ranges
allowed by the albedo uncertainties. If the albedos are as high as that of
Charon, the masses of P2 and P1 are sufficiently low that their orbits are well
described by the analytic theory. There is at present no evidence that P2 has
any significant epicyclic eccentricity. However, the orbit of P1 has a
significant epicyclic eccentricity, and its prograde periapse precession with a
period of 5300 days should be easily detectable. If the albedos are as low as
that of comets, the large inferred masses induce significant variations in the
epicyclic eccentricities and/or periapse longitudes on the 400-500-day
timescales, due to the proximity of P2 and P1 to the 3:2 mean-motion
commensurability. In fact, for the maximum inferred masses, P2 and P1 may be in
the 3:2 mean-motion resonance, with the resonance variable involving the
periapse longitude of P1 librating. Observations that sample the orbits of P2
and P1 well on the 400-500-day timescales should provide strong constraints on
the masses of P2 and P1 in the near future.


title:
Chemical abundances for Hf 2-2, a planetary nebula with the strongest
  known heavy element recombination lines

abstract:
  We present high quality optical spectroscopic observations of the planetary
nebula (PN) Hf 2-2. The spectrum exhibits many prominent optical recombination
lines (ORLs) from heavy element ions. Analysis of the H {\sc i} and He {\sc i}
recombination spectrum yields an electron temperature of $\sim 900$ K, a factor
of ten lower than given by the collisionally excited [O {\sc iii}] forbidden
lines. The ionic abundances of heavy elements relative to hydrogen derived from
ORLs are about a factor of 70 higher than those deduced from collisionally
excited lines (CELs) from the same ions, the largest abundance discrepancy
factor (adf) ever measured for a PN. By comparing the observed O {\sc ii}
$\lambda$4089/$\lambda$4649 ORL ratio to theoretical value as a function of
electron temperature, we show that the O {\sc ii} ORLs arise from ionized
regions with an electron temperature of only $\sim 630$ K. The current
observations thus provide the strongest evidence that the nebula contains
another previously unknown component of cold, high metallicity gas, which is
too cool to excite any significant optical or UV CELs and is thus invisible via
such lines. The existence of such a plasma component in PNe provides a natural
solution to the long-standing dichotomy between nebular plasma diagnostics and
abundance determinations using CELs on the one hand and ORLs on the other.


title: Automated Editing of Radio Interferometer Data with Pieflag

abstract:
  Editing of radio interferometer data, a process commonly known as
``flagging'', can be laborious and time-consuming. One quickly tends to flag
more data than actually required, sacrificing sensitivity and image fidelity in
the process. I describe a program, Pieflag, which can analyse radio
interferometer data to filter out measurements which are likely to be affected
by interference. Pieflag uses two algorithms to allow for data sets which are
either dominated by receiver noise or by source structure. Together, the
algorithms detect essentially all affected data whilst the amount of data which
is not affected by interference but falsely marked as such is kept to a
minimum. The sections marked by Pieflag are very similar to what would be
deemed affected by the observer in a visual inspection of the data. Pieflag
displays its results concisely and allows the user to add and remove flags
interactively. It is written in Python, is easy to install and use, and has a
variety of options to adjust its algorithms to a particular observing
situation. I describe how Pieflag works and illustrate its effect using data
from typical observations.


title:
Accurate photometric redshifts for the CFHT Legacy Survey calibrated
  using the VIMOS VLT Deep Survey

abstract:
  We present photometric redshifts for an uniquely large and deep sample of
522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep
Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241
spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a
calibration to derive these photometric redshifts. We devise a robust
calibration method which removes systematic trends in the photometric redshifts
and significantly reduces the fraction of catastrophic errors. We use our
unique spectroscopic sample to present a detailed assessment of the robustness
of the photometric redshift sample. For a sample selected at i'_{AB}<24, we
reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of
catastrophic error. The reliability of our photometric redshifts is lower for
fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%,
5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We
find that the photometric redshifts of starburst galaxies in our sample are
less reliable: although these galaxies represent only 18% of the spectroscopic
sample they are responsible for 54% of the catastrophic errors. We find an
excellent agreement between the photometric and the VVDS spectroscopic redshift
distributions at i'_{AB}<24. Finally, we compare the redshift distributions of
i' selected galaxies on the four CFHTLS deep fields, showing that cosmic
variance is already present on fields of 0.8 deg^2.


title: Star Formation in QSO Host Galaxies

abstract:
  Many of the conditions that are necessary for starbursts appear to be
important in the triggering of QSOs. However, it is still debatable whether
starbursts are ubiquitously present in galaxies harboring QSOs. In this paper
we review our current knowledge from observations of the role of starbursts in
different types of QSOs. Post-starburst stellar populations are potentially
present in the majority of QSO hosts. QSOs with far-infrared colors similar to
those of ultraluminous infrared galaxies invariably reside in merging galaxies
that have interaction-induced starbursts of a few hundred Myr or less. Similar,
but dramatically more luminous post-starburst populations are found in the
recently discovered class of QSOs known as post-starburst QSOs, or Q+A's. Both
of these classes, however, comprise only a small fraction (10-15%) of the total
QSO population. The so-called "red" QSOs generally suffer from strong
extinction at optical wavelengths, making them ideal candidates for the study
of hosts. Their stellar populations typically show a post-starburst component
as well, though with a larger range of ages. Finally, optical "classical" QSO
hosts show traces of major star formation episodes (typically involving >10% of
the mass of the stellar component) in the more distant past (1-2 Gyr). These
starbursts appear to be linked to past merger events. It remains to be
determined whether these mergers were also responsible for triggering the QSO
activity that we observe today.


title: HD 98618: A Star Closely Resembling our Sun

abstract:
  Despite the observational effort carried out in the last few decades, no
perfect solar twin has been found to date. An important milestone was achieved
a decade ago by Porto de Mello & da Silva, who showed that 18 Sco is almost a
solar twin. In the present work, we use extremely high resolution (R = 10^5)
high S/N Keck HIRES spectra to carry out a differential analysis of 16 solar
twin candidates. We show that HD 98618 is the second-closest solar twin and
that the fundamental parameters of both HD 98618 and 18 Sco are very similar
(within a few percent) to the host star of our solar system, including the
likelihood of hosting a terrestrial planet within their habitable zone. We
suggest that these stars should be given top priority in exoplanet and SETI
surveys.


title:
The Possibly Remnant Massive Outflow in G5.89-0.39: I - Observations and
  Initial MHD Simulations

abstract:
  We have obtained maps of the large scale outflow associated with the UCHII
regionG5.89-0.39 in CO and 13CO (J=3-2), SiO (J=8-7,J=5-4), SO2
(13(2,12)-13(1,13)) and H13CO+(J=4-3). From these maps we have been able to
determine the mass (3.3 M_sun), momentum (96 M_sun km/s), energy (3.5x10^{46}
erg), mechanical luminosity (141 L_sun), and mass loss rate
(~1x10^{-3}M_sun/yr) in the large scale outflow. The observationally derived
parameters were used toguide 3D magnetohydrodynamic models of the jet entrained
outflow. Through the combination of observations and simulations, we suggest
that the large scale outflowmay be inclined by approximately 45 deg to the line
of sight, and that the jet entraining the observed molecular outflow may have
been active for as little as 1000 years, half the kinematic age of the outflow.


title: Star Formation in the Northern Cloud Complex of NGC 2264

abstract:
  We have made continuum and spectral line observations of several outflow
sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope
(HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics
and outflow energetics of the young stellar systems observed and assesses the
impact star formation is having on the surrounding cloud environment. Our data
set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows
associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS
25 and 27, respectively, in the northern cloud complex. Complementary 870
micron continuum maps were made with the HHT 19 channel bolometer array. Our
results indicate that there is a weak (approximately less than 0.5%) coupling
between outflow kinetic energy and turbulent energy of the cloud. An analysis
of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining
their dynamical integrity except where outflowing material directly interacts
with the core, such as along the outflow axes.


title:
Dust Extinction of Gamma-ray Burst Host Galaxies: Identification of Two
  Classes?

abstract:
  Dust in the host galaxies of gamma-ray bursts (GRBs) dims and reddens their
afterglow spectra. Knowledge of the nature of this dust is crucial for
correcting for extinction, providing clues to the nature of GRB progenitors,
and probing the interstellar medium of high-redshift galaxies as well as the
nature of cosmic dust when the universe was much younger and galaxies were much
less evolved. The dust and extinction properties of GRB host galaxies are still
poorly known. Unlike previous work, we derive in this Letter the extinction
curves for 10 GRB host galaxies without a priori assumption of any specific
extinction types (such as that of the Milky Way, or the Small/Large Magellanic
Clouds). It is found that there appears to exist two different types of
extinction curves: one is relatively flat and gray, the other displays a
steeper dependence on inverse wavelength, closely resembling that of the Milky
Way but with the 2175$\Angstrom$ feature removed.


title: Numerical Studies of Diffusive Shock Acceleration at Spherical Shocks

abstract:
  We have developed a cosmic ray (CR) shock code in one dimensional spherical
geometry with which the particle distribution, the gas flow and their nonlinear
interaction can be followed numerically in a frame comoving with an expanding
shock. In order to accommodate a very wide dynamic range of diffusion length
scales in the CR shock problem, we have incorporated subzone shock tracking and
adaptive mesh refinement techniques. We find the spatial grid resolution
required for numerical convergence is less stringent in this code compared to
typical, fixed-grid Eulerian codes. The improved convergence behavior derives
from maintaining the shock discontinuity inside the same grid zone in the
comoving code. That feature improves numerical estimates of the compression
rate experienced by CRs crossing the subshock compared to codes that allow the
subshock to drift on the grid. Using this code with a Bohm-like diffusion model
we have calculated the CR acceleration and the nonlinear feedback at supernova
remnant shocks during the Sedov-Taylor stage. Similarly to plane-parallel
shocks, with an adopted thermal leakage injection model, about 10^{-3} of the
particles that pass through the shock and up to 60 % of the explosion energy
are transferred to the CR component. These results are in good agreement with
previous nonlinear spherical CR shock calculations of Berezhko and
collaborators.


title: The Evidence for a Binary origin of the Young Planetary Nebula HB 12

abstract:
  The young planetary nebulae play an important role in stellar evolution when
intermediate- to low-mass stars (0.8 $\sim$ 8 M$_\odot$) evolve from the
proto-planetary nebulae phase to the planetary nebulae phase. Many young
planetary nebulae display distinct bipolar structures as they evolve away from
the proto-planetary nebulae phase. One possible cause of their bipolarity could
be due to a binary origin of its energy source. Here we report our detailed
investigation of the young planetary nebula, Hubble 12, which is well-known for
its extended hourglass-like envelope. We present evidence with time-series
photometric observations the existence of an eclipsing binary at the center of
Hubble 12. Low-resolution spectra of the central source show, on the other
hand, absorption features such as CN, G-band & Mg b${\arcsec}$, which can be
suggestive of a low-mass nature of the secondary component.


title:
AGB star intershell abundances inferred from analyses of extremely hot
  H-deficient post-AGB stars

abstract:
  The hydrogen-deficiency in extremely hot post-AGB stars of spectral class
PG1159 is probably caused by a (very) late helium-shell flash or a AGB final
thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden
intershell region. Thus, the photospheric element abundances of these stars
allow to draw conclusions about details of nuclear burning and mixing processes
in the precursor AGB stars. We compare predicted element abundances to those
determined by quantitative spectral analyses performed with advanced non-LTE
model atmospheres. A good qualitative and quantitative agreement is found for
many species (He, C, N, O, Ne, F, Si) but discrepancies for others (P, S, Fe)
point at shortcomings in stellar evolution models for AGB stars.


title:
Non-Friedmann cosmology for the Local Universe, significance of the
  universal Hubble constant and short-distance indicators of dark energy

abstract:
  Basing on the increasing evidence for the cosmological relevance of the local
Hubble flow, we consider a simple analytical cosmological model for the Local
Universe. This is a non-Friedmann model with a non-uniform static space-time.
The major dynamical factor controlling the local expansion is the antigravity
produced by the omnipresent and permanent dark energy of the cosmic vacuum (or
the cosmological constant). The antigravity dominates at distances larger than
1-2 Mpc from the center of the Local Group. The model gives a natural
explanation of the two key quantitative characteristics of the local expansion
flow, which are the local Hubble constant and the velocity dispersion of the
flow. The observed kinematical similarity of the local and global flows of
expansion is clarified by the model. We demonstrate analytically the efficiency
of the vacuum cooling mechanism that allows one to see the Hubble flow so close
to the Local Group. Special significance is argued for the 'universal Hubble
constant' H_V, depending only on the vacuum density (H_V \approx 60 km/s/Mpc).
The model makes a number of testable predictions. It also shows unexpectedly
that it is the dwarf galaxies of the local flow with the shortest distances and
lowest redshifts that may be the most sensitive indicators of dark energy in
our neighborhood.


title:
M-type giants as optical counterparts of X-ray sources 4U 1700+24 and 4U
  1954+319

abstract:
  We observed with Chandra two peculiar galactic X-ray sources, 4U 1700+24 and
4U 1954+319, which are suspected to have a M-type giant star as optical
counterpart, in order to get an high-precision astrometric position for both of
them. The peculiarity of these sources lies in the fact that these are the only
two cases among low-mass X-ray binaries (LMXBs), besides the confirmed case of
GX 1+4, for which the companion can possibly be a M-type giant. We found that
in both cases the field M-type giant star is indeed the counterpart of these
X-ray sources. We also determined the distance to 4U 1954+319 to be about 1.7
kpc. This result suggests that a number of faint (L_X around 10^32-10^34 erg
s-1) Galactic X-ray sources are `symbiotic X-ray binaries', that is, wide-orbit
LMXBs composed of a compact object, most likely a neutron star, accreting from
the wind of a M-type giant.


title:
Early ComeOn+ Adaptive Optics Observation of GQ Lup and its Substellar
  Companion

abstract:
  An analysis of adaptive optics K-band imaging data of GQ Lup acquired in 1994
by the first generation adaptive optics system ComeOn+ at the ESO 3.6m optical
telescope in La Silla is presented. The data reveal a likely candidate for the
low-mass companion recently reported in the literature. An a posteriori
detection in the 11 year old data would provide a useful astrometric data point
for the very long period (~1000 yr) orbit of the GQ Lup system. However, the
data is severely contaminated by speckle noise at the given projected
separation, which decreases the confidence of the detection. Still, from the
data we can conclude that GQ Lup B is not an unrelated background source, but
instead a physical companion to GQ Lup A. We present here the reduction and
analysis of the ComeOn+ images, as well as the results. We also discuss the
nature of the companion based on data and models available in the scientific
literature and examine claims made regarding the classification of the object
as a planet.


title: On Multipolar Analytical Potentials for Galaxies

abstract:
  We present analytical potential-density pairs in three dimensions for the
gravitational field of galaxies, obtained by thickening the multipolar
expansion up to the quadrupole term. These may be interpreted as
generalizations of the Miyamoto and Nagai potential-density pairs. With a
suitable restriction on the possible values of the multipole moments, the
density distributions are positive and monotone decreasing functions of the
radial and axial coordinates.


title:
Triggered star formation in Bright-Rimmed Clouds: The Eagle Nebula
  revisited

abstract:
  A three dimensional Smoothed Particle Hydrodynamical (SPH) model has been
extended to study the radiative driven implosion effect of massive stars on the
dynamical evolutions of surrounding molecular clouds. The new elements in the
upgraded code are the inclusion of Lyman continuum in the incident radiation
flux and the treatment of hydrogen ionisation process; introducing ionisation
heating & recombination cooling effects; and adding a proper description of the
magnetic and turbulent pressures to the internal pressure of the molecular
cloud. The application of this newly developed model to the structure of the
middle Eagle Nebula finger suggests that the shock induced by the ionising
radiation at the front side of the head precedes an ionisation front moving
towards the center of the core, and that the core at the fingertip is at
transition stage evolving toward a state of induced star formation. The
dynamical evolution of the velocity field of the simulated cloud structure is
discussed to illustrate the role of the self-gravity and the different cloud
morphologies which appear at different stages in the evolutionary process of
the cloud. The modelled gas evaporation rate is consistent with that of current
other models and the density, temperature and chemical profiles are agreement
with the observed values. The relative lifetimes of different simulated cloud
morphologies suggests a possible answer to the question of why more
bright-rimmed clouds are observed to possess a flat-core than an elongated-core
morphology. [Abridged]


title:
Orientation dependency of broad-line widths in quasars and consequences
  for black-hole mass estimation

abstract:
  In this paper we report new evidence that measurements of the broad-line
widths in quasars are dependent on the source orientation, consistent with the
idea that the broad-line region is flattened or disc-like. This reinforces the
view derived from radio-selected samples, where the radio-core dominance has
been used as a measure of orientation. The results presented here show a highly
significant (>99.95%) correlation between radio spectral index (which we use as
a proxy for source orientation) and broad-line width derived from the H-beta
and MgII emission lines. This is the first time that this type of study has
used quasars derived from a large optically selected quasar sample, where the
radio-loud quasars (RLQs) and radio-quiet quasars (RQQs) have indistinguishable
distributions in redshift, bolometric luminosity and colour, and therefore
overcomes any biases which may be present in only selecting via radio emission.
We find that the mean FWHM for the flat-spectrum radio-loud quasars (FSQs) to
be <FWHM(FSQ)>= 4990 +/- 536km/s, which differs significant from the mean FWHM
of the steep-spectrum radio-loud quasars (SSQs), where <FWHM(SSQ)>=6464 +/-
506km/s. We also find that the distribution in FWHM for the FSQs is
indistinguishable from that of the radio-quiet quasars (RQQs), where
<FWHM(RQQ)>= 4831 +/-25km/s. Considering other observational results in the
literature we interpret this result in the context of a significant fraction of
the FSQs being derived from the underlying RQQ population which have their
radio flux Doppler boosted above the RLQ/RQQ divide. Under the assumption of a
disc-like broad-line region we find no evidence for a difference in the average
line-of-sight angle for RQQs and RLQs, implying that the difference is due to
black-hole mass. (abridged)


title: Integral-field studies of the high-redshift Universe

abstract:
  We present results from a new method of exploring the distant Universe. We
use 3-D spectroscopy to sample a large cosmological volume at a time when the
Universe was less than 3 billion years old to investigate the evolution of
star-formation activity. Within this study we also discovered a high redshift
type-II quasar which would not have been identified with imaging studies alone.
This highlights the crucial role that integral-field spectroscopy may play in
surveying the distant Universe in the future.


title: The Fragmentation of Cores and the Initial Binary Population

abstract:
  Almost all young stars are found in multiple systems. This suggests that
protostellar cores almost always fragment into multiple objects. The observed
properties of multiple systems such as their separation distribution and mass
ratios provide strong constraints on star formation theories. We review the
observed properties of young and old multiple systems and find that the
multiplicity of stars changes. Such an evolution is probably due to (a) the
dynamical decay of small-N systems and/or (b) the destruction of multiple
systems within dense clusters. We review simulations of the fragmentation of
rotating and turbulent molecular cores. Such models almost always produce
multiple systems, however the properties of those systems do not match
observations at all well. Magnetic fields appear to supress fragmentation,
prehaps suggesting that they are not dynamically important in the formation of
multiple systems. We finish by discussing possible reasons why theory fails to
match observation, and the future prospects for this field.


title: Cosmological Acceleration and Gravitational Collapse

abstract:
  The acceleration parameter defined through the local volume expansion is
negative for a pressureless, irrotational fluid with positive energy density.
In the presence of inhomogeneities or anisotropies the volume expansion rate
results from averaging over various directions. On the other hand, the
observation of light from a certain source in the sky provides information on
the expansion along the direction to that source. If there are preferred
directions in the underlying geometry one can define several expansion
parameters. We provide such definitions for the case of the Tolman-Bondi
metric. We then examine the effect of a localized inhomogeneity on the
surrounding cosmological fluid. Our framework is similar in spirit to the model
of spherical collapse. For an observer in the vicinity of a central
overdensity, the perceived local evolution is consistent with acceleration in
the direction towards the center of the overdensity, and deceleration
perpendicularly to it. A negative mass leads to deceleration along the radial
direction, and acceleration perpendicularly to it. If the observer is located
at the center of an overdensity the null geodesics are radial. The form of the
luminosity distance as a function of the redshift is consistent with
acceleration for a certain range of redshifts.


title: Diffusive Migration of Low-Mass Proto-planets in Turbulent Disks

abstract:
  Torque fluctuations due to magnetorotational turbulence in proto-planetary
disks may greatly influence the migration patterns and survival probabilities
of nascent planets. Provided that the turbulence is a stationary stochastic
process with finite amplitude and correlation time, the resulting diffusive
migration can be described with a Fokker-Planck equation, which we reduce to an
advection-diffusion equation. We calibrate the coefficients with existing
turbulent-disk simulations and mean-migration estimates, and solve the equation
both analytically and numerically. Diffusion tends to dominate over advection
for planets of low-mass and those in the outer regions of proto-planetary
disks, whether they are described by the Minimum Mass Solar Nebula (MMSN) or by
T-Tauri alpha disks. Diffusion systematically reduces the lifetime of most
planets, yet it allows a declining fraction of them to survive for extended
periods of time at large radii. Mean planet lifetimes can even be formally
infinite (e.g. in an infinite steady MMSN), though median lifetimes are always
finite. Surviving planets may linger near specific radii where the combined
effects of advection and diffusion are minimized, or at large radii, depending
on model specifics. The stochastic nature of migration in turbulent disks
challenges deterministic planet formation scenarios and suggests instead that a
wide variety of planetary outcomes are possible from similar initial
conditions. This would contribute to the diversity of (extrasolar) planetary
systems.


title: The Relic Neutrino Backround from the First Stars

abstract:
  We consider the relic neutrino background produced by Population III stars
coupled with a normal mode of star formation at lower redshift. The computation
is performed in the framework of hierarchical structure formation and is based
on cosmic star formation histories constrained to reproduce the observed star
formation rate at redshift z \la 6, the observed chemical abundances in damped
Lyman alpha absorbers and in the intergalactic medium, and to allow for an
early reionization of the Universe at z ~ 10-20. We consider both a burst and
non-burst model for Population III star formation. We find that although the
high redshift burst of Population III stars does lead to an appreciable flux of
neutrinos at relatively low energy (E_\nu \approx 1 MeV), the observable
neutrino flux is dominated by the normal mode of star formation. We also find
that predicted fluxes are at the present level of the SuperK limit. As a
consequence, the supernova relic neutrino background has a direct impact on
models of chemical evolution and/or supernova dynamics.


title: Impact of dark matter decays and annihilations on reionization

abstract:
  One of the possible methods to distinguish among various dark matter
candidates is to study the effects of dark matter decays. We consider four
different dark matter candidates (light dark matter, gravitinos, neutralinos
and sterile neutrinos), for each of them deriving the decaying/annihilation
rate, the influence on reionization, matter temperature and CMB spectra. We
find that light dark matter particles (1-10 MeV) and sterile neutrinos (2-8
keV) can be sources of partial early reionization (z<~100). However, their
integrated contribution to Thomson optical depth is small (<~0.01) with respect
to the three year WMAP results (tau_e=0.09+/-0.03). Finally, they can
significantly affect the behavior of matter temperature. On the contrary,
effects of heavy dark matter candidates (gravitinos and neutralinos) on
reionization and heating are minimal. All the considered dark matter particles
have completely negligible effects on the CMB spectra.


title:
The Origins and Evolutionary Status of B Stars Found Far From the
  Galactic Plane II: Kinematics and Full Sample Analysis

abstract:
  This paper continues the analysis of faint high latitude B stars from Martin
(2004). Here we analyze the kinematics of the stars and combine them with the
abundance information from the first paper to classify each one. The sample
contains 31 Population I runaways, fifteen old evolved stars (including five
BHB stars, three post-HB stars, a pulsating helium dwarf, and six stars of
ambiguous classification), one F-dwarf, and two stars which do not easily fit
in one of the other categories. No star in the sample unambiguously shows the
characteristics of a young massive star formed in situ in the halo. The two
unclassified stars are probably extreme Population I runaways. The low binary
frequency and rotational velocity distribution of the Population I runaways
imply that most were ejected from dense star clusters by DES (dynamic ejection
scenario). However we remain puzzled by the lack of runaway Be stars. We also
confirm that PB 166 and HIP 41979 are both nearby solar-metallicity BHB stars.


title:
Hubble Space Telescope Near-Infrared Snapshot Survey of 3CR radio source
  counterparts at low redshift

abstract:
  We present newly acquired images of the near-infrared counterpart of 3CR
radio sources. All the sources were selected to have a redshift of less than
0.3 to allow us to obtain the highest spatial resolution. The observations were
carried out as a snapshot program using the Near-Infrared Camera and
Multiobject Spectrograph (NICMOS) on-board the Hubble Space Telescope (HST). In
this paper we describe 69 radio galaxies observed for the first time with
NICMOS during HST cycle 13. All the objects presented here are elliptical
galaxies. However, each of them has unique characteristics such as close
companions, dust lanes, unresolved nuclei, arc-like features, globular clusters
and jets clearly visible from the images or with basic galaxy subtraction.


title: Dipole of the luminosity distance: a direct measure of H(z)

abstract:
  We show that the dipole of the luminosity distance is a useful observational
tool which allows us to determine the Hubble parameter as a function of the
redshift H(z). We determine the number of supernovae needed to achieve a given
precision for H(z) and to distinguish between different models for dark energy.
We analyse a sample of nearby supernovae and find a dipole consistent with the
cosmic microwave background at a significance of more than 2 sigma.


title: Diffuse Ionized Gas in irregular galaxies:I- GR 8 and ESO 245-G05

abstract:
  We have studied the spectral characteristics of the Diffuse Ionized Gas in
two irregular galaxies with low metallicities and intermediate Star Formation
Rates: ESO 245-G05 and Gr 8. The [OIII]/Hbeta in these galaxies is higher than
in the DIG of spiral galaxies but not as high as in other irregular galaxies
previously studied, such as IC 10 and NGC 6822. The [NII]/Halpha and
[SII]/Halpha ratios have very small values, indicating the absence of shocks as
the ionization source for this gas. This ionization can be explained in both
galaxies with photon leakage from the HII regions as the only source. The
percentage of photons escaped from the HII regions is small in ESO 245-G05, of
only 35%, but varies from 35% up to 60% in Gr 8. We also investigated if the
differences found between spiral and irregular galaxies in the [OIII]/Hbeta and
the [NII]/Halpha ratio are due to differences in the metal content between
these types of galaxies. Although the number of galaxies studied is not very
large, it can be concluded that the [OIII]/Hbeta is not related with the oxygen
content, while the situation is more ambiguous for the [NII]/Halpha ratio.


title:
The distribution of current helicity at the solar surface at the
  beginning of the solar cycle

abstract:
  A fraction of solar active regions are observed to have current helicity of a
sign that contradicts the polarity law for magnetic helicity; this law
corresponds to the well-known Hale polarity law for sunspots. A significant
excess of active regions with the "wrong" sign of helicity is seen to occur
just at the beginning of the cycle. We compare these observations with
predictions from a dynamo model based on principles of helicity conservation,
discussed by Zhang et al. (2006). This model seems capable of explaining only a
fraction of the regions with the wrong sign of the helicity. We attribute the
remaining excess to additional current helicity production from the twisting of
rising magnetic flux tubes, as suggested by Choudhuri et al. (2004). We
estimate the relative contributions of this effect and that connected with the
model based on magnetic helicity conservation.


title:
The ZEPLIN-III dark matter detector: performance study using an
  end-to-end simulation tool

abstract:
  We present results from a GEANT4-based Monte Carlo tool for end-to-end
simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase
detector which measures both the scintillation light and the ionisation charge
generated in liquid xenon by interacting particles and radiation. The software
models the instrument response to radioactive backgrounds and calibration
sources, including the generation, ray-tracing and detection of the primary and
secondary scintillations in liquid and gaseous xenon, and subsequent processing
by data acquisition electronics. A flexible user interface allows easy
modification of detector parameters at run time. Realistic datasets can be
produced to help with data analysis, an example of which is the position
reconstruction algorithm developed from simulated data. We present a range of
simulation results confirming the original design sensitivity of a few times
$10^{-8}$ pb to the WIMP-nucleon cross-section.


title: The Physical Nature of Lyman Alpha Emitting Galaxies at z=3.1

abstract:
  We selected 40 candidate Lyman Alpha Emitting galaxies (LAEs) at z ~=3.1 with
observed frame equivalent widths >150A and inferred emission line fluxes
>2.5x10^-17 ergs/cm^2/s from deep narrow-band and broad-band MUSYC images of
the Extended Chandra Deep Field South. Covering 992 sq. arcmin, this is the
largest ``blank field'' surveyed for LAEs at z ~3, allowing an improved
estimate of the space density of this population of 3+-1x10^-4 h_70^3/Mpc^3.
Spectroscopic follow-up of 23 candidates yielded 18 redshifts, all at z ~=3.1.
Over 80% of the LAEs are dimmer in continuum magnitude than the typical Lyman
break galaxy spectroscopic limit of R= 25.5 (AB), with a median continuum
magnitude R ~=27 and very blue continuum colors, (V-z) ~=0. Over 80% of the
LAEs have the right UVR colors to be selected as Lyman break galaxies, but only
10% also have R<=25.5. Stacking the UBVRIzJK fluxes reveals that LAEs have
stellar masses ~=5x10^8 h_70^-2 M_sun and minimal dust extinction, A_V < ~ 0.1.
Inferred star formation rates are ~=6 h_70^-2 M_sun/yr, yielding a cosmic star
formation rate density of 2x10^-3 h_70 M_sun/yr/Mpc^3. None of our LAE
candidates show evidence for rest-frame emission line equivalent widths
EW_rest>240A which might imply a non-standard IMF. One candidate is detected by
Chandra, implying an AGN fraction of 2+-2% for LAE candidate samples. In
summary, LAEs at z ~ 3 have rapid star formation, low stellar mass, little dust
obscuration and no evidence for a substantial AGN component.


title:
MUSYC: A Deep Square Degree Survey of the Formation and Evolution of
  Galaxies and Supermassive Black Holes

abstract:
  The Multiwavelength Survey by Yale-Chile (MUSYC) is optimized for the study
of galaxies at z=3, AGN demographics, and Galactic structure. MUSYC consists of
deep optical (UBVRIz') and near-infrared (JHK) imaging of four fields on the
sky covering 1.2 square degrees to AB limiting depths of U,B,V,R=26 and K=22.
Our optical catalog contains 277,341 objects detected in BVR images with median
seeing of 0.9''. Satellite coverage of our fields includes Chandra, XMM, GALEX,
HST-ACS, and Spitzer, with the Extended Chandra Deep Field South imaged at all
of these wavelengths plus the radio, making it the premier multiwavelength
field on the sky. Detailed follow-up spectroscopy is being performed with
VLT+VIMOS, Magellan+IMACS and Gemini+GNIRS. MUSYC provides ideal supporting
data for surveys with Z-Machines and rich target lists for spectroscopy with
ALMA. We are conducting a census of protogalaxies at redshift three (Lyman
break galaxies, Lyman-alpha emitters, Distant red galaxies, Sub-millimeter
galaxies and AGN) in order to separate physical properties from selection
effects. We discuss measurements of the dark matter halo masses and halo
occupation numbers of these populations and of the total cosmic star formation
rate at z=3. MUSYC publications and data releases are available at
http://www.astro.yale.edu/MUSYC .


title: The origin of cold fronts in the cores of relaxed galaxy clusters

abstract:
  Chandra X-ray observations revealed the presence of cold fronts (sharp
contact discontinuities between gas regions with different temperatures and
densities) in the centers of many, if not most, relaxed clusters with cool
cores. We use high-resolution simulations of idealized cluster mergers to show
that they are due to sloshing of the cool gas in the central gravitational
potential, which is easily set off by minor mergers and can persist for
gigayears. The only necessary condition is a steep entropy profile, as observed
in cooling flow clusters. Even if the infalling subcluster has no gas during
core passage, the gravitational disturbance sets the main mass peak (gas and
dark matter together) in motion relative to the surrounding gas. A rapid change
in the direction of motion causes a change in ram pressure, which pushes the
cool gas away from the dark matter peak and triggers sloshing. For nonzero
impact parameters, the cool gas acquires angular momentum, resulting in a
characteristic spiral pattern of cold fronts. There is little visible
disturbance outside the cool core in such a merger. If the subcluster retains
its gas during core passage, the cool central gas of the main cluster is more
easily decoupled from the dark matter peak. Subsequently, some of that gas, and
often the cool gas from the subcluster, falls back to the center and starts
sloshing. However, in such a merger, global disturbances are readily visible in
X-rays for a long time. We conclude that cold fronts at the centers of relaxed
clusters, often spiral or concentric-arc in shape, are probably caused by
encounters with small subhalos stripped of all their gas at the early infall
stages.


title:
Reduction of Cosmological Data for the Detection of Time-varying Dark
  Energy Density

abstract:
  We present a method for reducing cosmological data to constraints on the
amplitudes of modes of the dark energy density as a function of redshift. The
modes are chosen so that (1) one of them has constant density and (2) the
others are non-zero only if there is time-variation in the dark energy density
and (3) the amplitude errors for the time-varying modes are uncorrelated with
each other. We apply our method to various combinations of three-year WMAP
data, baryon acoustic oscillation data, the 'Gold' supernova data set, and the
Supernova Legacy Survey data set. We find no significant evidence for a
time-varying dark energy density or for non-zero mean curvature. Although by
some measure the limits on four of the time-varying mode amplitudes are quite
tight, they are consistent with the expectation that the dark energy density
does not vary on timescales shorter than a Hubble time. Since we do not expect
detectable time variation in these modes, our results should be viewed as a
systematic error test which the data have passed. We discuss a procedure to
identify modes with maximal signal-to-noise ratio.