# Dwarf Galaxy Discoveries from the KMTNet Supernova Program III. the Milky-
Way Analog NGC 2997 Group

Tony Junjing Fan,1 Dae-Sik Moon,1 Hong Soo Park,2,3,4 Dennis Zaritsky,4 Sang
Chul Kim,2,3 Youngdae Lee,5 Ting S. Li,1 Yuan Qi Ni,1 Jeehye Shin,2,3 Sang-Mok
Cha,2,6 Yongseok Lee,2,6
1David A. Dunlap Department of Astronomy and Astrophysics, University of
Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
2Korea Astronomy and Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu,
Daejeon 34055, Republic of Korea
3Korea University of Science and Technology (UST), Daejeon 34113, Republic of
Korea
4Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson,
AZ 85719, USA
5Department of Astronomy and Space Science, Chungnam National University,
Daejeon 34134, Republic of Korea
6School of Space Research, Kyung Hee University, Yongin 17104, Republic of
Korea

(Accepted XXX. Received YYY; in original form ZZZ)

###### Abstract

We present the discovery of 48 new and the analysis of 55, including 7
previously discovered, dwarf galaxy candidates around the giant spiral galaxy
NGC 2997 using deep $BVI$ images from the KMTNet Supernova Program. Their
$V$-band central surface brightness and total absolute magnitudes range
between 20.3–26.7 mag arcsec-2 and –(8.02–17.69) mag, respectively, while the
$I$-band effective radii are between 0.14 and 2.97 kpc. We obtain $\alpha$
$\simeq$ –1.43 $\pm$ 0.02 for the faint-end slope of their luminosity
function, comparable to previously measured values but shallower than
theoretical predictions based on $\Lambda$CDM models. The distance-independent
distributions of their mass and color from the host galaxy NGC 2997 suggest
that the group could be dynamically young, prior to the development of
significant mass segregation or radial color gradients. The systematically
bluer colors of the brighter candidates than the fainter ones indicate higher
star formation activities in brighter members. We suggest that the higher-mass
dwarf galaxies in the group have maintained star-formation activities by
effectively retaining gas content, while environmental quenching is only
effective for the lower-mass galaxies. The interpretation of early
evolutionary stage of this group is also consistent with the overall
morphological distribution of the dwarf galaxy candidates showing a lack of
morphologically evolved candidates but a plethora of irregularly shaped ones.
Our detection rate of dwarf galaxy candidates in the NGC 2997 group and their
inferred star formation activities are largely comparable to those found in
Milky Way analog systems from the SAGA survey within the magnitude limit MV
$\lesssim$ –13 mag, as well as those found in the ELVES survey.

###### keywords:

galaxies: dwarf —- galaxies: individual (NGC 2997)

††pubyear: 2022††pagerange: Dwarf Galaxy Discoveries from the KMTNet Supernova
Program III. the Milky-Way Analog NGC 2997 Group–A

##  1 Introduction

The study of dwarf galaxies plays an important role in our understanding of
several important issues in astronomy. It provides critical insights into the
processes through which galaxy formation/evolution occurs, as well as
observational tests for the distribution of dark matter and the $\Lambda$CDM
model. For example, studies of dwarf galaxies based on large surveys have
shown that satellite galaxies form in more than one channel (e.g. Lisker et
al., 2007), and dwarf galaxies appear to show an extreme range in the amount
of dark matter content, from being almost free of dark matter to being almost
entirely made of dark matter (e.g. van Dokkum et al., 2016; Khalifeh &
Jimenez, 2021). Despite recent efforts, there exists a substantial gap in our
understanding of the origin and properties of dwarf galaxies, such as the
well-known discrepancies in central densities and abundance of dwarf galaxies
between observational data on the Milky Way system and the $\Lambda$CDM model
predictions, known as the “small-scale challenges” (Weinberg et al., 2015; Mao
et al., 2021), or whether “galactic conformity" is universal in which both
central host galaxies and satellite galaxies show similar properties in star-
formation or colors (Weinmann et al., 2006; Otter et al., 2020; Poulain et
al., 2021).

The availability of recent wide-field deep survey data has made it possible to
study dwarf galaxies and their properties beyond the Milky Way (MW) and the
local group ($\;\buildrel<\over{\sim}\;$ 3 Mpc; Redd, 2018), furthering our
understanding of their luminosity functions (LFs) and star formation
activities to nearby groups. Dwarf galaxies identified in the fields of M81
(at 3.6 Mpc; Chiboucas et al., 2009), NGC 5128 (at 3.8 Mpc; Crnojević et al.,
2016), M83 (at 4.0 Mpc; Müller et al., 2015), M101 (at 7.0 Mpc; Bennet et al.,
2019), NGC 2784 (at 9.8 Mpc; Park et al., 2017), M96 (at 10.7 Mpc; Müller et
al., 2018), and NGC 3585 (at 20.4 Mpc; Park et al., 2019) have extended LFs of
dwarf satellites down to MV $\simeq$ –7 mag, showing discrepancies that the
observed faint-end slopes are still consistently flatter than the $\Lambda$CDM
model predictions (e.g., Klypin et al., 1999; Trentham & Tully, 2002; Springel
et al., 2008; Han et al., 2016; Li et al., 2019). The recent SAGA survey (Geha
et al., 2017; Mao et al., 2021), ELVES survey (Carlsten et al., 2021b, 2022),
as well as studies of nearby groups such as M101 (Bennet et al., 2019) and M94
(Bennet et al., 2020), on the other hand, have shown that star formation in
the faint (MV $\;\buildrel>\over{\sim}\;$ –12 mag) satellite galaxies of MW-
analog systems at $\;\buildrel<\over{\sim}\;$ 41 Mpc is significantly less
active than the massive ones, providing opportunities to understand the
effects of mass and environment on quenching processes (e.g., Samuel et al.,
2022). In addition, some studies have revealed the presence of apparent
magnitude “gaps” or “humps” in some of the observed LFs: the former wherein no
galaxies found (e.g., Bennet et al., 2019), while the latter with sudden
increase of the LF slopes (e.g., Park et al., 2019). They also show a
morphological diversity in dwarf galaxies, ranging from ultra-diffuse galaxies
to nucleated dwarf galaxies (e.g., van Dokkum et al., 2015; Park et al., 2017;
Müller et al., 2018; Bennet et al., 2019; Park et al., 2019). The origin of
these features may bear important clues to our understanding of gravitational
interactions among the members and the host of a galaxy group as well as the
environmental effects to their evolutionary paths.

We have recently begun a systematic search of dwarf galaxies around more than
100 nearby galaxies observable in the Southern Hemisphere using deep stacked
images from the Korea Microlensing Telescope Network (KMTNet, Kim et al.,
2016) Supernova Program (KSP, Moon et al., 2016). By stacking several hundred,
sometimes exceeding 1000, 60-s $BVI$ images obtained with the three wide-field
(= 2°$\times$ 2° at a pixel sampling of 0$\aas@@fstack{\prime\prime}$4 per
pixel) 1.6-meter telescopes located in Chile, South Africa and Australia that
are primarily dedicated to detecting supernovae and optical transients during
their early phases (e.g., Afsariardchi et al., 2019; Moon et al., 2021; Ni et
al., 2022a, b; Lee et al., 2022), we expect to discover a substantial number
of new dwarf galaxies on images that readily reach a limiting surface
brightness of $\;\buildrel>\over{\sim}\;$ 28 mag arcsec-2. In our previous two
studies of the NGC 2784 and NGC 3585 groups using the KSP data, we reported
discoveries of 30 (for NGC 2784) and 46 (NGC 3585) new dwarf galaxies (Park et
al., 2017, 2019). One particular advantage of the KSP-data based studies of
dwarf galaxies is the homogeneity of data obtained with three colors of $BVI$,
which can enable unprecedented systematic comparative studies and statistical
analyses of the discovered dwarf galaxies in different groups/clusters. This
can potentially lead to in-depth understanding of how different types of host
galaxies and environments influence differently to the evolution of satellite
galaxies in their structural, morphological and dynamical states.

In this paper, we present our KSP based discoveries of dwarf galaxies in the
field of NGC 2997, which are our first dwarf galaxy discoveries around a
spiral-type host galaxy using the KSP data. NGC 2997 is a giant spiral galaxy
of type SAB(rs)c with a redshift of z $\simeq$ 0.003611 (Meyer et al., 2004)
and an inclination angle of 40°(Milliard & Marcelin, 1981). It is the largest
member of the loose galaxy group LGG 180 (Garcia, 1993) and is relatively
isolated from other major galaxies with no known companion within $\sim$ 110
kpc (Hess et al., 2009). The galaxy is reported to have a dynamical mass of
2.1 $\times$ 1011 M$\odot$, a gas accretion rate of 1.2 M$\odot$ yr-1, and a
thick H I disk (Hess et al., 2009). It has an $I$-band apparent magnitude of
$I$ $\simeq$ 9.88 mag (Doyle et al., 2005), and a $K$-band apparent magnitude
of 6.41 mag (Skrutskie et al., 2006). The distance to NGC 2997 has been
estimated to be in the range of 9.5–14.8 Mpc, including: (1) 9.5 Mpc using
tertiary distance indicators (magnitudes, luminosity index, and diameters) (de
Vaucouleurs, 1979; Larsen & Richtler, 1999), (2) 14.8 Mpc from the multi-
attractor velocity flow model (Masters, 2005) with $H_{0}$ = 72 km s-1 Mpc-1
(Pisano et al., 2011), and (3) 12.2 $\pm$ 0.9 Mpc based on the near-infrared
Tully-Fisher relation (Hess et al., 2009). We adopt the distance of 12.2 Mpc
from Hess et al. (2009) in this work. Its absolute $K$-band magnitude is
–24.02 mag, and it is within the range of –23 to –24.4 mag of the MW-analog
galaxies studied in the SAGA (Geha et al., 2017; Mao et al., 2021) or ELVES
survey (Carlsten et al., 2021b, 2022). Hence, this provides an opportunity of
comparing dwarf galaxies identified in another MW-analog host at a closer
distance with much deeper limiting magnitudes than those in the SAGA survey at
$>$ 25 Mpc. In §2, we provide the details of our observations and data
reduction process, while we describe the identification of dwarf galaxy
candidates (DGCs) and how we measure their photometric and morphological
properties in §3. §4 details group properties of the DGCs, including their
radial distributions, color and structural parameters, and luminosity
function. We discuss in §5 that the observed features of the NGC 2997 group
are compatible with it being a younger system. We summarize our conclusions in
§6.

##  2 Observations and Data Reduction

As part of the KSP (see above), we had monitored two 4 $\square\degr$ fields
around the giant spiral galaxy NGC 2997 between February 2017 and June 2019.
The wide field (= 2° $\times$ 2°) CCD cameras of the KMTNet consist of four
E2V CCD chips, with each chip covering 1 $\square\degr$ field at a pixel
sampling of 0$\aas@@fstack{\prime\prime}$4 per pixel. There is a gap of
3$\aas@@fstack{\prime}$1 between the chips in the east-west direction, while
that in the north-south direction is 6$\aas@@fstack{\prime}$2\. Figure 1 shows
the distribution of the two observed fields in $I$-band, composed of eight
sub-fields of 1 $\square\degr$, with two sub-fields largely overlapping near
the center of the entire field, where the host galaxy NGC 2997 is located. The
four sub-fields in the north-west of the image belong to the first field (F1)
observed mostly between February 2017 and January 2018, while those in the
south-east belong to the second field (F2) observed between February 2018 and
June 2019. As a result, the effective size of the field that we observed for
NGC 2997 is about 7 $\square\degr$, with the 1-$\square\degr$ sub-field
directly surrounding the galaxy observed almost 2$\times$ longer than the
other subfields. We stack 682, 716, and 798 individual frames of 60-second
exposures whose seeing is better than 2″ to create the deep stacked images for
F1 in the $B$, $V$, and $I$ bands using SWARP (Bertin et al., 2002). For F2,
we stack 761 ($B$), 810 ($V$), and 880 ($I$) frames. The final seeing in the
stacked images is in the range of
1$\aas@@fstack{\prime\prime}$3–1$\aas@@fstack{\prime\prime}$6 for the $BVI$
bands for all eight sub-fields, as shown in Table 1. The average point source
3-$\sigma$ limiting magnitudes in the stacked images of the first field are
$B$ = 25.14 $\pm$ 0.18 mag, $V$ = 24.69 $\pm$ 0.24 mag, and $I$ = 24.40 $\pm$
0.36 mag, while those of the second field are $B$ = 25.16 $\pm$ 0.24 mag, $V$
= 24.79 $\pm$ 0.31 mag and $I$ = 24.51 $\pm$ 0.36 mag.

We carry out photometric calibration of KMTNet CCD images using standard
reference stars from the AAVSO Photometric All-Sky Survey (APASS)
111https://www.aavso.org/apass catalog in our fields, and the SuperNova
Analysis Package (SNAP) 222https://github.com/niyuanqi/SNAP. In order to
secure high signal-to-noise (S/N) ratios while avoiding CCD saturation and
non-linearity effects, only the reference stars whose apparent magnitudes are
in the range of 15–17 mag are used in the calibration. The APASS photometric
system is based on the standard Johnson $BV$ and the Sloan $i$ filter bands.
It has been known that the calibration of KMTNet instrumental magnitudes
against the Johnson $B$-band magnitudes requires a color correction of
$\simeq$ 0.27 $\times$ ($B\,-\,V$) (see Park et al., 2017, for details). After
confirming the presence of the same color dependence in our images, we made
the same color corrections on $B$-band magnitudes of the DGCs. No such color
dependence nor offset has been identified for the $V$-band. Although no color
dependence exists between the Sloan $i$-band and the KMTNet $I$-band either, a
0.4 mag offset is found between them from the comparison of the Landolt and
OGLE standard stars (Park et al., 2017, see §3.4 therein, and also Kim et al.
in preparation). We, therefore, adopt 0.4 magnitude difference between the
KMTNet $I$-band and APASS $i$-band photometry: $I$ = $i$ – 0.4 mag. Table 2
contains the zero-point magnitude offsets of our images. According to the
Galactic extinction model of Schlafly & Finkbeiner
(2011)333https://ned.ipac.caltech.edu/, the Galactic extinction in the
direction of NGC 2997 are $A_{B}=0.392$, $A_{V}=0.296$, and $A_{I}=0.163$ mag.
All the magnitudes that we provide in this study are corrected with these
extinction values.

[b]  Sub-field $B$ $V$ $I$ (arcsecs) (arcsecs) (arcsecs) NGC2997-F1-Q0
1.57$\pm$0.07 1.44$\pm$0.05 1.36$\pm$0.04 NGC2997-F1-Q1 1.53$\pm$0.06
1.43$\pm$0.05 1.34$\pm$0.04 NGC2997-F1-Q2 1.52$\pm$0.06 1.42$\pm$0.04
1.35$\pm$0.04 NGC2997-F1-Q3 1.48$\pm$0.04 1.40$\pm$0.04 1.34$\pm$0.04
NGC2997-F2-Q0 1.60$\pm$0.06 1.47$\pm$0.06 1.36$\pm$0.05 NGC2997-F2-Q1
1.55$\pm$0.06 1.44$\pm$0.05 1.34$\pm$0.05 NGC2997-F2-Q2 1.58$\pm$0.04
1.46$\pm$0.04 1.37$\pm$0.04 NGC2997-F2-Q3 1.52$\pm$0.04 1.42$\pm$0.03
1.34$\pm$0.06

Table 1: Seeings of the stacked images for the eight sub-fields

  * •

$\dagger$ F1 and F2 indicate the two observed fields, and Q0 to Q3 indicate
the 4 sub-fields in each field.

[b]  Sub-field $B$ $V$ $I$ NGC2997-F1-Q0 28.23 28.01 28.44 NGC2997-F1-Q1 28.30
28.00 28.41 NGC2997-F1-Q2 28.23 28.09 28.39 NGC2997-F1-Q3 28.29 28.05 28.37
NGC2997-F2-Q0 28.17 27.98 28.28 NGC2997-F2-Q1 28.22 27.93 28.39 NGC2997-F2-Q2
28.21 28.03 28.32 NGC2997-F2-Q3 28.23 28.00 28.35

Table 2: Zero-Point Instrumental Magnitude Offsets

  * •

$\dagger$ The 1-$\sigma$ uncertainties are 0.01 mag for all the sub-fields and
filters.

[b]  Name $B$-band Magnitudesa Redshift ($z$) ESO 434-33 13.19, 13.09 0.0032
ESO 434-27 15.22, 15.16 0.0031 LEDA 718707 17.24, 17.02 0.0034 ESO 434-39
15.55, 15.38 0.0034 ESO 434-34 14.06, 14.24 0.0033 IC 2507 13.12, 12.93 0.0042
ESO 434-41 14.69, 14.60 0.0033

Table 3: Previously Discovered Dwarf Galaxies and Their Properties

  * •

aThe previously measured magnitudes and the magnitudes obtained in this study
(see the text).

##  3 Dwarf Galaxy Candidates and Basic Properties

###  3.1 Search of Dwarf Galaxy Candidates

We conduct a thorough visual inspection on stacked KMTNet images of the eight
sub-fields to identify DGCs around NGC 2997. We use the $I$-band images in
this search of DGCs, applying the selection criteria of being a diffuse source
extending more than 20 pixels (or $\simeq$ 8″) that is absent of any prominent
structures (e.g., spirals or bars), except for potential nucleated centers, as
was done in Park et al. (2017) and Park et al. (2019) for the NGC 2784 and NGC
3585 groups, respectively. Four444TJF, HSP, YDL and SCK from the author list
inspectors individually inspected the images and made a list of candidates of
their own. 44 dwarf galaxy candidates were co-selected by all the four members
in their independent identification, and 11 more are additionally added
unanimously after a second round of examination of candidates that were
originally selected by less than 4 inspectors. In addition to the $I$-band
images, the $B$\- and $V$-band images are also used to confirm the identified
DGCs. As a result, we identify 55 DGCs in total, with 80% of them being
selected in the first round. Figure 1 shows their locations around NGC 2997 on
the stacked $I$-band image. We note that there are more DGCs in the south-
eastern part of NGC 2997 than in the north-western part, especially in the
region $\gtrsim$ 1.3° away from the galaxy where there are twice as much DGCs
in the south-eastern corner. Figure 2 shows example cutout images of 8 DGCs,
while the images of all 55 DGCs is available in the appendix (Figure 14).

Figure 1: $I$-band stacked KMTNet images of about 7$\square\degr$ around the
galaxy NGC 2997 (cyan cross at the center). The blue open diamonds mark the
locations of 7 previously discovered dwarf galaxies (See § 3.1). The yellow
open squares mark the other 48 DGCs.

Figure 2: Example RGB cutout images of 8 (out of 55) DGCs in NGC 2997. North
is up and east is to the left. The blue horizontal bar at the bottom of each
image corresponds to the angular size of 0$\aas@@fstack{\prime}$5 (= 1.77 kpc
at the distance of 12.2 Mpc). The cutout images of all 55 DGCs are available
in Appendix (Figure 14).

Out of the 55 DGCs, seven were previously identified in the ESO and LEDA
catalogs (Lauberts & Valentijn, 1989; Paturel et al., 2003). Five of these
(i.e., ESO 434-27, ESO 434-31 [= IC 2507], ESO 434-33, ESO 434-34 and ESO
434-41) are known to be members of the loose galaxy group LGG 180 in which NGC
2997 is the largest member (Garcia, 1993). The redshifts of the other two
(i.e., ESO 434-39 and LEDA 718707) are similar to that of NGC 2997 (Jones et
al., 2009). Although we recovered three other dwarf galaxies (i.e., ESO
434-30, ESO 434-43, and LEDA 100726) that were previously presented in the
catalogs, we exclude them from our final list because their redshifts are
significantly larger than $z$ $\simeq$ 0.0036 of NGC 2997: 0.0071 (ESO 434-30;
Meyer et al., 2004), 0.0083 (ESO 434-43; Theureau et al., 1998), and 0.0080
(LEDA 100726; Matthews et al., 1995). Table 3 shows redshifts of the seven
previously discovered dwarf galaxies.

The two fields that we observed towards NGC 2997 are slightly different in the
total number of stacked images because the second field has about 10 % more
images and is therefore deeper than the first by $\;\buildrel<\over{\sim}\;$
0.1 mag (Table 2). The photometric depth difference is at the level of the
photometric uncertainties of the two fields, indicating that the difference in
depth is not significant. This conclusion is supported by our identification
of the exact same number of DGCs in the overlapping sub-fields between the
first and second field: NGC2997-F1-Q2 and NGC2997-F2-Q1. We measure the
completeness and limiting magnitudes of our stacked $I$-band images by
inserting 600 artificial galaxies in one of our sub-fields (NGC2997-F2-Q0).
For the properties (e.g. effective radius, total magnitude, effective
magnitude, positional angle, ellipticity, etc) of the artificial galaxies, we
adopt Gaussian random sampling on those of the identified dwarf galaxy
candidates. We then reapply the same visual identification procedure explained
above to recover the mock galaxies. As a result, we achieve a completeness
level of $\sim$90% down to $I$ $\simeq$ 19.4 mag (or MV $\simeq$ –10.2 mag at
the distance of N2997). Our detection rate of bright DGCs in NGC 2997 is
comparable with that of the SAGA survey (Mao et al., 2021) on 36 MW-analog
galaxies. For example, in NGC 6181, a spiral galaxy with a mass similar to
that of NGC 2997, the SAGA survey spectroscopically confirmed 9 satellites
with MV $\lesssim$ –13 mag. Adopting the same satellite selection criteria of
SAGA — which are within the projected distance of $\sim$ 300 kpc and redshift
$\pm$ 275 km s-1 from the host — for the 10 DGCs with MV $\lesssim$ –13 mag in
our sample, we find that 7 of them can be confirmed as satellites. These 7
DGCs are the bright ones that were previously discovered (See Table 3). Since
we do not have spectroscopic information for the remaining three DGCs, the
number of confirmed satellites for NGC 2997 upon the same SAGA selection
criteria is in the range of 7–10 in our study, comparable to 9 for NGC 6181
from SAGA.

The number density of contaminating background galaxies in typical KMTNet
stacked images was estimated to be 1.75 $\pm$ 0.66 deg-2 from the analysis of
the KSP images of KK 196 field (Park et al., 2019), which has been observed in
very similar manner to other KSP fields like NGC 3585 or NGC 2997. The
distance to the KK 196 field, which belongs to the Centaurus A group, is only
$\sim$4 Mpc, and dwarf galaxies belong to this group should appear resolved.
Applying the same visual inspection procedures adopted for the KSP stacked
images of NGC 2784 and NGC 3585 fields, Park et al. (2019) identified 11 dwarf
galaxy candidates from the 4 deg2 KK 196 field. Out of these 11 identified
dwarf galaxy candidates, 4 of them are resolved, while the rest 7 are
unresolved. The 4 resolved candidates include 2 previously known dwarf
galaxies associated with the Centaurus group. The 7 unresolved candidates
appear to be randomly distributed in the field. Park et al. (2019) concluded
that the 4 resolved candidates are associated with the Centaurus group,
whereas the 7 unresolved candidates are unassociated with the group and,
therefore, background sources. This gives the contamination level of 1.75
$\pm$ 0.66 deg-2 for the stacked KSP images of KK 196 field. All of the 7
background sources are fainter than MV = –13.6 mag (or MV $\simeq$ –12.5 mag
at the distance of NGC 2997), and their average colors are $(B-V)_{0}$ = 0.67
$\pm$ 0.08 mag and $(V-I)_{0}$= 0.82 $\pm$ 0.10 mag. None of them are
nucleated or UDGs. These background contaminants are more likely to be
luminous late-type galaxies because background early-type ellipticals are not
expected to be identified as DGCs in a foreground field due to their steep
surface brightness profiles from the center. Assuming the same background
contamination level between the KK 196 and NGC 2997 field images that have
very similar photometric depths, we estimate 7–16 as the number of potential
background contamination sources for the 55 DGCs in the NGC 2997 group.

###  3.2 Surface Photometry and Catalog

We carry out surface photometry of the 55 DGCs by constructing their radial
isophotal profiles using the ELLIPSE fitting task from the python-based
photometry package Photutils 555https://photutils.readthedocs.io/en/stable/.
The ELLIPSE task calculates the best-fit isophotal parameters (i.e., the
central position, positional angle, and ellipticity) by fitting a galaxy based
on the initial visual estimations of those parameters under the assumption of
an elliptical geometry. The typical linear step-size of fitting is 2–3 pixels
along the semi-major axis; however, for the brighter and larger ($r_{e}$ $>$
15″) sources, we conduct the fitting in logarithmic scale for efficiency. We
mask out foreground/background objects that overlap with the DGCs when
possible. The intensity of each isophote is determined by the median value of
the isophote’s pixels, which effectively minimizes the influence of any
interfering artifacts/sources in the foreground/background; and the total
intensity of each isophote is obtained by multiplying the median value with
the total number of pixels within. The sky background level, which is
estimated using the median value of source-free pixels surrounding a DGC, is
subtracted from the isophotal intensities. The outermost isophote of a DGC is
determined when the isophotal intensity is $\simeq$ 1-$\sigma$ above the sky
background level. We then estimate the total instrumental magnitudes of the
DGCs by integrating the total intensities of their isophotal models. Figure 3
shows example results for 6 dwarf galaxy candidates where the data, masked
data, models, and residuals are shown. For the $B$\- and $V$-band images of
the DGCs, we follow the same procedure above using the isophotal models from
$I$-band images to construct their surface brightness profiles as well as
their instrumental magnitudes in $B$\- and $V$-bands. Finally, we obtain the
corrected apparent magnitudes of the DGCs as outlined in §2, including the
conversion from instrumental magnitudes to apparent magnitudes using zero-
point offsets (Table 2), $B$-band color correction and $I$-band magnitude
offset correction, as well as Galactic extinction correction.

Figure 3: Cutout images of the six example DGCs demonstrating our photometric
processes for obtaining isophotal models: DW88, DW89, DW104, DW121, DW123 and
ESO434-27 from top to bottom. The rows are for the data (or stacked images;
first row), the data with masks (second row), fitted isophotal models (third
row), and residual of the data after subtraction of the isophotal models (see
Section 3.2).
Figure 4: Difference between isophotal model magnitudes and direct aperture
magnitudes of 13 isolated DGCs for the $B$ (blue squares), $V$ (green
triangles), and $I$ (red circles) bands.

Figure 4 compares the isophotal model magnitudes of 13 relatively isolated
DGCs in our sample with their magnitudes obtained by aperture photometry. The
13 DGCs are the entirety of DGCs that appear to be free from apparently
significant interference by overlapping sources. As seen in the figure, the
magnitude differences between the two methods are small, with about 75% of
them showing differences $\;\buildrel<\over{\sim}\;$ 0.05 mag, although a few
of them reach differences of $\sim$ 0.2 mag. We note that the isophotal method
produces slightly larger (= fainter) magnitudes than the aperture photometry
method. One possible explanation for this is the contribution by faint
overlapping sources to the aperture photometry. The 7 previously-discovered
dwarf galaxies in Table 3, for which $B$-band magnitudes from previous studies
are available, do not belong to this group of 13 apparently isolated DGCs. The
average $B$-band magnitude differences between their literature values and
isophotal model magnitudes obtained in this study is 0.14 mag. We, therefore,
conclude that there exists a reasonable agreement between magnitudes obtained
by our isophotal method and aperture photometry method, as well as those
obtained in previous studies.

Figure 5 shows eight examples of surface brightness profiles obtained from our
surface photometry (full figure in appendix, Figure 15). The top panels show
the $I$-band surface brightness profiles (black crosses), reaching as faint as
28.0 mag arcsec-2, that we obtained using median values of their isophotes for
the 55 DGCs. To examine the radial distributions of light, we fit the surface
brightness profiles with the Sérsic function $\mu_{I}$ = $\mu_{o,I}$ \+ 1.0857
$(r/r_{o,I})^{1/n_{I}}$, where $\mu_{I}$, $\mu_{0,I}$, $r$, $r_{o,I}$ and
$n_{I}$ are the surface brightness, central surface brightness, radius, scale
length, and Sérsic index. During the fitting, we only use isophotes with
intensities higher than the sky background level at a confidence level of 90%
(1.6-$\sigma$), and those isophotes used in the fitting are marked by red
circles in Figure 5. The solid blue curves in the figure represent the best-
fit Sérsic profiles, and the vertical dashed lines in blue indicate the
effective radius $r_{e}$ = $(2.3026\times Bn)^{n}$ $r_{o}$, where $Bn$ = 0.868
$n$ – 0.142 (Chiboucas et al., 2009). The bottom panels show the DGCs’ color
profiles — green open circles for $(B\,-\,V)_{0}$ and black crosses for
$(V\,-\,I)_{0}$. The green and red dashed lines indicate the values for
$(B\,-\,V)_{0}$ and $(V\,-\,I)_{0}$ colors obtained using the difference in
total magnitudes, respectively. Table 4 lists the parameters of the 55 DGCs
including their names, coordinates, $I$-band total apparent magnitudes ($I$),
$(V\,-\,I)_{0}$ and $(B\,-\,V)_{0}$ colors, three best-fit Sérsic parameters
(i.e., $\mu_{0,I}$, $r_{o,I}$, $n_{I}$), effective radius in $I$-band
($r_{e,I}$), and $V$-band total absolute magnitudes (MV). The final column
(“Comments”) shows if the candidates are morphologically identified as ultra-
diffuse, or nucleated, and/or irregular galaxies (see § 3.3). All the DGCs are
brighter than 21.24 mag in $I$-band, whereas the faintest $B$-band and
$V$-band magnitudes are 23.98 and 22.41 mag, respectively. Their colors are in
the range of 0.22 – 1.17 mag for $(V\,-\,I)_{0}$, and 0.25 – 1.57 mag for
$(B\,-\,V)_{0}$ . The central surface brightnesses of all candidates are
brighter than $\mu_{0,B}$ $\simeq$ 27.9, $\mu_{0,V}$ $\simeq$ 26.7, and
$\mu_{0,I}$ $\simeq$ 25.4 mag arcsec-2. The $I$-band Sérsic scale lengths and
the curvature indices vary in the range of 2$\aas@@fstack{\prime\prime}$5
$\lesssim$ $r_{0,I}$ $\lesssim$ 57$\aas@@fstack{\prime\prime}$9 and 0.25
$\lesssim$ $n_{I}$ $\lesssim$ 1.39, respectively. The $I$-band effective radii
($r_{e,I}$) are in the range of
2$\aas@@fstack{\prime\prime}$4–50$\aas@@fstack{\prime\prime}$4, or 0.142–2.97
kpc at the distance of 12.2 Mpc. About 87% (or 48 out of 55) have effective
radii smaller than 12″ (or 0.71 kpc). The largest newly discovered DGC in our
sample is KSP-DW106, a very elongated source with an $I$-band effective radius
of 22$\aas@@fstack{\prime\prime}$9\. However, it is smaller than most of the 7
previously discovered candidates.

Figure 5: Eight examples of surface brightness profiles of the DGCs. Upper
Panels: $I$-band surface brightness profiles. The black crosses with error
bars, often encircled by a red circle, represent $\mu_{I}$ and its
uncertainty. Only those data points with a red circle are used in 1D Sérsic
fitting. The blue solid curves show the resulting best-fit Sérsic profiles.
The vertical blue dashed lines mark the estimated effective radii. Lower
Panels: $(B\,-\,V)_{0}$ and $(V\,-\,I)_{0}$ color profiles are shown in green
circles and black crosses, respectively. The green and red horizontal dashed
lines represent the mean $(B\,-\,V)_{0}$ and $(V\,-\,I)_{0}$ colors obtained
from difference in total apparent magnitudes (See § 3.2), respectively.  Table
4: Catalog of NGC 2997 Dwarf Galaxy Candidates

ID | RA | DEC | $I$ | $(V\,-\,I)_{0}$ | $(B\,-\,V)_{0}$ | $\mu_{0,I}$ | $r_{o,I}$ | $n_{I}$ | $r_{e,I}$ |  MV |  Comments$\dagger$
---|---|---|---|---|---|---|---|---|---|---|---
| (hh:mm:ss) | (dd:mm:ss) | (mag) | (mag) | (mag) |  (mag arcsec-2) | (arcsec) |  | (arcsec) | (mag) |
KSP-DW78 | 9:45:14.2 | -30:10:01.2 | 18.44 | 0.60 | 0.45 |  23.13$\pm$0.07 |  4.92$\pm$0.42 |  0.73$\pm$0.14 | 5.42 | -11.39 |
KSP-DW79 | 9:46:12.8 | -30:27:51.2 | 17.98 | 0.72 | 0.53 |  22.39$\pm$0.04 |  5.07$\pm$0.27 |  0.71$\pm$0.07 | 5.36 | -11.72 | dIr
KSP-DW80 | 9:45:42.8 | -30:28:42.9 | 17.82 | 0.73 | 0.69 |  22.54$\pm$0.04 |  4.43$\pm$0.21 |  0.75$\pm$0.06 | 4.98 | -11.88 |
KSP-DW81 | 9:46:15.7 | -30:14:29.6 | 19.25 | 0.83 | 0.45 |  24.12$\pm$0.11 |  6.37$\pm$0.62 |  0.44$\pm$0.16 | 4.91 | -10.36 | dIr
LEDA 718707 | 9:45:34.9 | -30:18:51.3 | 15.90 | 0.62 | 0.50 |  20.92$\pm$0.01 |  7.05$\pm$0.06 |  0.71$\pm$0.01 | 7.54 | -13.91 | dIr
KSP-DW82 | 9:44:25.2 | -30:12:38.3 | 18.92 | 0.58 | 0.51 |  23.15$\pm$0.05 |  4.45$\pm$0.24 |  0.56$\pm$0.07 | 3.93 | -10.93 |
ESO 434-39 | 9:47:04.2 | -30:23:12.5 | 14.17 | 0.68 | 0.53 |  20.66$\pm$0.00 |  12.22$\pm$0.05 |  0.86$\pm$0.01 | 16.30 | -15.58 | dIr
ESO 434-34 | 9:45:29.3 | -30:20:35.5 | 13.22 | 0.60 | 0.42 |  21.31$\pm$0.00 |  57.87$\pm$0.36 |  0.55$\pm$0.01 | 50.40 | -16.61 | dIr
KSP-DW83 | 9:41:05.6 | -30:18:45.3 | 17.23 | 0.71 | 0.68 |  21.61$\pm$0.02 |  3.33$\pm$0.11 |  1.15$\pm$0.05 | 6.73 | -12.49 | dIr
KSP-DW84 | 9:40:16.3 | -30:17:22.7 | 17.94 | 0.48 | 0.45 |  23.86$\pm$0.08 |  10.31$\pm$0.97 |  0.46$\pm$0.17 | 8.13 | -12.00 | dIr
KSP-DW85 | 9:40:52.1 | -30:00:17.5 | 19.10 | 0.87 | 1.10 |  23.48$\pm$0.08 |  4.49$\pm$0.35 |  0.49$\pm$0.14 | 3.65 | -10.46 |
KSP-DW86 | 9:48:04.3 | -31:52:07.1 | 17.06 | 0.71 | 0.29 |  22.58$\pm$0.05 |  7.13$\pm$0.44 |  0.82$\pm$0.09 | 8.92 | -12.66 | dIr
KSP-DW87 | 9:47:15.7 | -31:47:34.7 | 19.90 | 0.83 | 0.26 |  23.60$\pm$0.09 |  3.81$\pm$0.35 |  0.54$\pm$0.15 | 3.26 | -9.71 |
KSP-DW88 | 9:48:27.9 | -31:47:56.3 | 18.86 | 0.85 | 0.68 |  22.61$\pm$0.04 |  3.12$\pm$0.13 |  0.69$\pm$0.06 | 3.21 | -10.69 |
KSP-DW89 | 9:44:38.9 | -31:35:28.2 | 18.30 | 0.59 | 0.25 |  24.47$\pm$0.11 |  11.48$\pm$1.12 |  0.36$\pm$0.17 | 8.21 | -11.54 |
IC 2507 | 9:44:34.0 | -31:47:22.4 | 11.82 | 0.78 | 0.33 |  19.55$\pm$0.00 |  23.98$\pm$0.13 |  0.66$\pm$0.01 | 23.71 | -17.83 | dIr
KSP-DW90 | 9:44:47.2 | -31:28:14.5 | 19.70 | 0.84 | 0.65 |  23.32$\pm$0.06 |  3.67$\pm$0.21 |  0.48$\pm$0.09 | 2.94 | -9.89 |
KSP-DW91 | 9:45:28.3 | -31:22:47.4 | 17.88 | 0.87 | 0.67 |  22.25$\pm$0.03 |  2.76$\pm$0.19 |  1.39$\pm$0.12 | 9.65 | -11.68 | N
KSP-DW92 | 9:46:21.7 | -31:17:03.4 | 18.56 | 0.85 | 0.71 |  24.10$\pm$0.21 |  9.71$\pm$2.90 |  0.70$\pm$0.58 | 10.19 | -11.02 |
KSP-DW93 | 9:46:46.9 | -31:05:20.2 | 20.62 | 1.08 | 0.60 |  24.51$\pm$0.16 |  4.56$\pm$0.74 |  0.52$\pm$0.27 | 3.83 | -8.74 |
KSP-DW94 | 9:46:51.8 | -31:02:02.0 | 21.24 | 1.17 | 1.57 |  25.14$\pm$0.33 |  5.69$\pm$2.77 |  0.65$\pm$0.89 | 5.61 | -8.02 |
KSP-DW95 | 9:47:51.8 | -30:55:44.2 | 20.00 | 0.99 | 0.55 |  23.44$\pm$0.07 |  2.54$\pm$0.25 |  0.78$\pm$0.15 | 3.00 | -9.44 |
KSP-DW96 | 9:47:27.1 | -30:56:40.4 | 16.85 | 0.89 | 0.58 |  21.87$\pm$0.03 |  5.24$\pm$0.17 |  0.64$\pm$0.04 | 5.05 | -12.69 |
ESO 434-41 | 9:47:46.4 | -31:30:27.6 | 13.57 | 0.68 | 0.34 |  21.86$\pm$0.00 |  33.60$\pm$0.45 |  0.82$\pm$0.02 | 41.86 | -16.18 | dIr
KSP-DW97 | 9:40:12.9 | -31:50:42.3 | 17.72 | 0.58 | 0.52 |  22.27$\pm$0.03 |  3.76$\pm$0.17 |  0.78$\pm$0.06 | 4.44 | -12.13 |
KSP-DW98 | 9:41:07.5 | -31:45:45.1 | 19.51 | 0.64 | 0.65 |  24.22$\pm$0.16 |  5.60$\pm$0.85 |  0.41$\pm$0.22 | 4.18 | -10.29 |
KSP-DW99 | 9:41:32.8 | -31:29:04.6 | 19.98 | 0.51 | 0.42 |  23.27$\pm$0.06 |  3.15$\pm$0.23 |  0.69$\pm$0.10 | 3.26 | -9.94 | dIr
KSP-DW100 | 9:41:29.6 | -31:30:43.3 | 16.91 | 0.89 | 0.75 |  21.54$\pm$0.01 |  3.80$\pm$0.08 |  0.96$\pm$0.03 | 5.90 | -12.63 |
KSP-DW101 | 9:42:56.4 | -31:29:46.9 | 20.83 | 0.47 | 0.83 |  24.71$\pm$0.29 |  3.73$\pm$1.20 |  0.46$\pm$0.58 | 2.93 | -9.14 |
KSP-DW102 | 9:39:40.8 | -31:08:57.6 | 20.83 | 1.06 | 1.38 |  23.77$\pm$0.10 |  3.39$\pm$0.37 |  0.59$\pm$0.18 | 3.09 | -8.54 |
KSP-DW103 | 9:42:45.7 | -30:57:42.3 | 18.64 | 0.77 | 0.51 |  22.31$\pm$0.03 |  2.63$\pm$0.10 |  0.87$\pm$0.05 | 3.57 | -11.03 |
KSP-DW104 | 9:51:17.2 | -31:23:59.5 | 18.91 | 0.74 | 0.41 |  22.48$\pm$0.03 |  2.73$\pm$0.13 |  0.88$\pm$0.06 | 3.72 | -10.78 |
KSP-DW105 | 9:51:13.1 | -31:07:44.3 | 17.37 | 0.82 | 0.49 |  21.33$\pm$0.01 |  2.71$\pm$0.06 |  1.10$\pm$0.03 | 5.38 | -12.25 | dIr
KSP-DW106 | 9:48:24.8 | -30:44:47.3 | 17.68 | 0.63 | 0.57 |  24.59$\pm$0.11 |  25.40$\pm$2.60 |  0.58$\pm$0.18 | 22.86 | -12.12 | U
KSP-DW107 | 9:43:44.8 | -31:33:43.0 | 18.56 | 0.39 | 0.85 |  25.36$\pm$0.20 |  16.53$\pm$2.58 |  0.25$\pm$0.25 | 10.65 | -11.48 |
KSP-DW108 | 9:44:43.4 | -31:26:40.4 | 16.45 | 0.69 | 0.61 |  21.22$\pm$0.01 |  3.41$\pm$0.07 |  1.19$\pm$0.02 | 8.04 | -13.29 | dIr
KSP-DW109 | 9:50:50.4 | -32:40:48.0 | 19.07 | 0.91 | 0.47 |  23.68$\pm$0.08 |  5.39$\pm$0.47 |  0.61$\pm$0.14 | 5.03 | -10.45 |
KSP-DW110 | 9:48:19.6 | -32:40:33.9 | 17.87 | 0.82 | 0.49 |  23.23$\pm$0.04 |  7.13$\pm$0.31 |  0.52$\pm$0.07 | 5.98 | -11.73 |
KSP-DW111 | 9:49:21.7 | -32:29:56.1 | 19.25 | 0.89 | 0.62 |  23.49$\pm$0.07 |  4.75$\pm$0.35 |  0.66$\pm$0.11 | 4.70 | -10.29 |
KSP-DW112 | 9:49:29.2 | -32:36:38.8 | 19.10 | 0.90 | 0.82 |  23.34$\pm$0.06 |  4.50$\pm$0.29 |  0.63$\pm$0.09 | 4.32 | -10.44 |
KSP-DW113 | 9:50:39.9 | -32:37:03.2 | 19.77 | 0.93 | 0.47 |  23.49$\pm$0.06 |  3.62$\pm$0.24 |  0.53$\pm$0.11 | 3.08 | -9.73 |
KSP-DW114 | 9:48:03.9 | -32:17:44.1 | 19.30 | 0.72 | 0.42 |  23.58$\pm$0.06 |  5.05$\pm$0.29 |  0.55$\pm$0.09 | 4.37 | -10.41 |
KSP-DW115 | 9:49:07.5 | -31:53:39.3 | 19.90 | 0.61 | 0.37 |  23.52$\pm$0.07 |  3.22$\pm$0.27 |  0.61$\pm$0.12 | 3.01 | -9.92 |
KSP-DW116 | 9:49:49.3 | -32:26:55.5 | 15.86 | 0.96 | 0.64 |  21.78$\pm$0.02 |  8.04$\pm$0.18 |  0.86$\pm$0.03 | 10.75 | -13.61 |
KSP-DW117 | 9:45:34.7 | -32:21:37.1 | 19.03 | 0.85 | 0.58 |  23.48$\pm$0.06 |  4.85$\pm$0.33 |  0.53$\pm$0.09 | 4.10 | -10.55 |
KSP-DW118 | 9:47:33.0 | -32:24:00.6 | 20.28 | 0.89 | 0.71 |  23.42$\pm$0.09 |  2.61$\pm$0.27 |  0.59$\pm$0.15 | 2.39 | -9.25 |
KSP-DW119 | 9:45:40.3 | -32:00:30.7 | 17.90 | 0.92 | 0.45 |  22.93$\pm$0.03 |  8.80$\pm$0.28 |  0.45$\pm$0.05 | 6.87 | -11.61 | dIr
KSP-DW120 | 9:44:06.2 | -31:59:11.5 | 19.54 | 0.80 | 0.82 |  22.97$\pm$0.04 |  2.59$\pm$0.15 |  0.75$\pm$0.07 | 2.91 | -10.09 |
KSP-DW121 | 9:43:31.9 | -32:00:59.2 | 19.80 | 0.88 | 0.79 |  24.01$\pm$0.12 |  4.67$\pm$0.63 |  0.67$\pm$0.19 | 4.69 | -9.75 |
KSP-DW122 | 9:45:46.7 | -32:10:44.0 | 19.18 | 0.73 | 0.64 |  22.79$\pm$0.04 |  3.68$\pm$0.21 |  0.81$\pm$0.08 | 4.49 | -10.53 | dIr
KSP-DW123 | 9:47:13.9 | -32:02:07.7 | 16.26 | 0.84 | 0.61 |  21.98$\pm$0.02 |  7.84$\pm$0.17 |  0.72$\pm$0.03 | 8.47 | -13.33 |
KSP-DW124 | 9:46:44.0 | -32:35:41.6 | 17.24 | 0.82 | 0.66 |  22.52$\pm$0.03 |  7.18$\pm$0.31 |  0.86$\pm$0.06 | 9.55 | -12.38 |
ESO 434-33 | 9:44:47.6 | -31:49:32.0 | 12.08 | 0.66 | 0.35 |  21.52$\pm$0.01 |  49.43$\pm$0.54 |  0.41$\pm$0.01 | 36.99 | -17.69 | dIr
ESO 434-27 | 9:44:05.2 | -32:09:54.3 | 13.87 | 0.73 | 0.56 |  22.05$\pm$0.01 |  24.99$\pm$0.43 |  0.89$\pm$0.02 | 34.85 | -15.83 | dIr
KSP-DW125 | 9:42:51.9 | -31:58:46.2 | 19.82 | 0.73 | 0.81 |  23.17$\pm$0.06 |  2.65$\pm$0.22 |  0.79$\pm$0.12 | 3.19 | -9.88 |

  * •

$\dagger$ Candidates identified as UDG (U), Nucleated (N), or irregularly
shaped (dIr).

  * •

$I$ and MV are apparent $I$-band magnitude and absolute $V$-band magnitude,
respectively, estimated using the fitted parameters of the Sérsic function.
$\mu_{0,I}$, $r_{o,I}$, and $n_{I}$ are the central surface brightness, scale
length, and the Sérsic index from the fitting of $I$-band images,
respectively. $r_{e,I}$ is the effective radius obtained from $r_{o,I}$ and
$n_{I}$. $(V\,-\,I)_{0}$ and $(B\,-\,V)_{0}$ are the observed mean colors
after correction of the reddening in the Milky Way.

###  3.3 Morphological Classifications: Nucleated, Ultra-Diffuse, and
Irregular Dwarf Galaxies

Dwarf galaxies with distinctively bright and compact cores have been
morphologically classified as nucleated dwarf galaxies (e.g., Côté et al.,
2006; Trentham & Tully, 2009; Park et al., 2019; Zaritsky et al., 2021). We
identify KSP-DW91 to be the only nucleated dwarf galaxy out of the 55 DGCs in
NGC 2997 based on the presence of a clearly distinguishable central point-
source core with color similar to the rest of the galaxy (Figure 14), although
0.22 mag arcsec-2 difference of the core in the $V$-band from the Sérsic-fit
expected brightness is a bit smaller than those found in nucleated dwarf
galaxies in other groups (e.g., Park et al., 2019). The lack of nucleated
dwarf galaxies in NGC 2997 is in stark contrast with the range of 10–30 % of
the incidence rate of previous studies (e.g., Trentham & Tully, 2009; Park et
al., 2017, 2019).

Dwarf galaxies with extremely diffuse morphological features have been
classified as ultra-diffuse galaxies (UDGs; e.g., van Dokkum et al., 2015;
Müller et al., 2018; Park et al., 2019). For example, van Dokkum et al. (2015)
applies the following criteria to identify UDGs: $\mu_{o,V}$ $\gtrsim$ 23.7
mag arcsec-2 and $r_{e,V}$ $\gtrsim$ 1.5 kpc. The two DGCs with the most
extreme diffuse distribution of surface brightness in our sample are KSP-DW106
($r_{e,V}$ = 1.38 $\pm$ 0.4 kpc, $\mu_{o,V}$ = 25.23 $\pm$ 0.11 mag arcsec-2)
and KSP-DW107 ($r_{e,V}$ = 0.66 $\pm$ 0.48 kpc, $\mu_{o,V}$ = 25.78 $\pm$ 0.17
mag arcsec-2). If we apply the same criteria above, KSP-DW106 can be
classified as a potential UDG, given its effective radius uncertainty.

Finally, we identify 17 DGCs irregularly-shaped dwarf galaxies in our sample
based on the presence of clearly non-elliptical morphology, faint but still
identifiable structures, or the peak emission being off the geometrical
center. Their average values of the effective radius ($I$-band), absolute
magnitudes ($V$-band), and $(B\,-\,V)_{0}$ color are
16$\aas@@fstack{\prime\prime}$07 (or 0.95 kpc), –13.56 mag, and 0.47 mag,
respectively. These irregularly-shaped dwarf galaxies, which include all the 7
previously discovered dwarf galaxies (Table 4), appear to be significantly
larger, brighter, and bluer than re,I $\simeq$ 8$\aas@@fstack{\prime\prime}$80
(or 0.52 kpc), MV $\simeq$ –11.61 mag, and $(B\,-\,V)_{0}$ $\simeq$ 0.60 mag,
which are the average values for the entire DGC population. We note that it is
easier to select large DGCs as irregularly-shaped than smaller ones based on
our selection criteria, and there could be a group of small irregularly-shaped
DGCs that was not selected. The real difference in size, brightness and color
between the irregularly-shaped DGCs and the entire DGC population of NGC 2997,
therefore, could be smaller.

##  4 Properties of Dwarf Galaxy Candidates in the NGC 2997 group

###  4.1 Radial Distribution of Number Density and Color

Figure 6 shows how the projected radial number density distribution (filled
circles) of DGCs in the NGC 2997 group decreases with radial distance after
subtracting the expected background contamination, 1.75 DGCs deg-2 (see §3.1).
We adopt both linear and logarithmic radial distance binnings in panel a) and
b), as was done in previous studies (Park et al., 2017, 2019). We fit the
exponential function $\Sigma$ = $e^{\alpha\rm R+\beta}$, where R is the
projected distance, to the number density distribution, and we obtain the
best-fit parameters $\alpha$ = –1.03 $\pm$ 0.40 and $\beta$ = 2.75 $\pm$ 0.37,
shown as the dashed line in panel a). In the fitting, we exclude the last data
point from the outermost bin at R = 1.9° to minimize the effects of the
unexpected concentration of DGCs in the south-eastern corner of the field (see
§3.1). The dashed line in panel b) represents the best-fit power-law function
$\Sigma$ = ${\alpha\rm R^{\beta}}$, with $\alpha$ = 5.23 $\pm$ 1.03 and
$\beta$ = –0.57 $\pm$ 0.33.

Figure 6: Radial number density profiles of the 55 DGCs in the NGC 2997 group
in linear (left) and logarithmic (right) scale in x-axis. The dashed line in
panel a) shows the best-fit exponential function for R $\lesssim$ 1.6 ° (see
§4.1) obtained by fitting the first five data points, excluding the last one.
The dashed line in panel b) shows the best-fit power-law function obtained
using all the six data points in the panel.

Figure 7 compare the radial distributions of the binned number density (top
panel) and mean $(B\,-\,V)_{0}$ color (bottom panel) between bright and faint
groups of DGCs in the NGC 2997 group divided by their median brightness of MV
= –11.02 mag. The radial number density distributions of both groups — filled
squares for the bright group and filled triangles for the faint group (top
panel), are largely similar to each other, resulting in a relatively flat
radial distribution of the fraction of bright galaxies (filled circles). The
best-fit parameters of the exponential function ($\Sigma$ = $e^{\alpha\rm
R+\beta}$) for the radial number density distribution are $\alpha$ = –0.83
$\pm$ 0.54 and $\beta$ = 2.02 $\pm$ 0.51 (bright group) and $\alpha$ = –0.86
$\pm$ 0.52 and $\beta$ = 1.96 $\pm$ 0.52 (faint group). All the DGCs located
at $\rm R$ $>$ 1.6° belong to the faint group, and the outermost data point is
excluded from the fitting as above.

The binned mean $(B\,-\,V)_{0}$ color distributions of both groups — blue
curve for the bright group and red curve for the faint group (bottom panel) —
largely appear to be constant along the radial distance without any
significant difference between them, resulting in a flat distribution of the
mean $(B\,-\,V)_{0}$ color for the 55 DGCs (filled black circles). The filled
blue and red circles represent colors of all individual DGCs: blue for the
DGCs of the bright group and red for the faint group. The three DGCs (KSP-
DW85, KSP-DW94, and KSP-DW102) with exceptionally red colors $(B\,-\,V)_{0}$
$\gtrsim$ 1.10 mag (empty circles; Table 4) are very faint, i.e., MV $\gtrsim$
$-$10.35 mag, and apparently separated from the rest. They are excluded from
the 3-sigma clipping process during the calculation of mean colors to minimize
the effects of potential outliers.

Figure 7: Upper Panel: Radial number density distributions of faint
(triangles) and bright (squares) groups of the DGCs in the NGC 2997 group
divided by MV = –11.02 mag. The circles show the distribution of the bright-
to-faint ratio. Lower Panel: Radial color distribution of the DGCs. The small
circles show the radial distances and the $(B\,-\,V)_{0}$ colors of the entire
55 DGCs population. Those encased by red and blue circles are the faint and
bright members, respectively. (Three out of fifty-five are open circles, while
the rest are filled). The black solid circle, red and blue dashed lines are
the mean color distributions of the entire sample, faint sample, and bright
sample, respectively. The three small unfilled circles are excluded in the
mean color calculations in order to avoid potential contributions from
outliers.

###  4.2 Color and Structure Parameters

Figure 8 presents the color-magnitude diagrams, i.e., $(B\,-\,V)_{0}$ vs. MV
(top panel) and $(V\,-\,I)_{0}$ vs. MV (bottom panel), for all the DGCs from
the four groups: NGC 2784 (open squares; Park et al., 2017), NGC 3585 (open
triangles; Park et al., 2019), NGC 2997 (filled red circles), and M83 (open
diamonds; Müller et al., 2015). The mean values of the $(B\,-\,V)_{0}$ and
$(V\,-\,I)_{0}$ colors are respectively 0.66 $\pm$ 0.16 and 0.84 $\pm$ 0.18
mag for NGC 2784, 0.69 $\pm$ 0.18 and 0.87 $\pm$ 0.14 mag for NGC 3585, and
0.56 $\pm$ 0.15 and 0.77 $\pm$ 0.16 mag for NGC 2997, while the
$(B\,-\,V)_{0}$ color of M83 is 0.82 $\pm$ 0.25 mag. The dashed blue lines in
Figure 8 represent the color-magnitude relation (CMR) for the DGCs brighter
than MV = –11 mag in the NGC 2784 and NGC 3585 groups (Park et al., 2019),
with slopes of –0.012 and –0.013 for $(B\,-\,V)_{0}$ and $(V\,-\,I)_{0}$
colors, respectively. These slopes change to $\simeq$ 0 when we also include
the DGCs from the NGC 2997 group (solid red lines), indicating that the DGCs
in the NGC 2997 group have opposite CMRs to those of NGC 2784 and NGC 3585.

We examine the correlation between the two parameters (i.e., color vs.
absolute magnitude) of the CMR of each group as follows. For the
$(B\,-\,V)_{0}$ color (Figure 9), the best-fit CMR slopes and the linear
correlation coefficients are –0.01 $\pm$ 0.02 and –0.12 (NGC 2784), –0.01
$\pm$ 0.02 and –0.06 (NGC 3585), 0.03 $\pm$ 0.01 and 0.41 (NGC 2997), 0.04
$\pm$ 0.02 and 0.33 (M83). These results show a clear distinction that the
brighter DGCs appear bluer in the two groups with a late-type spiral host
(i.e., NGC 2997 and M83), while they show an opposite pattern in the other two
groups with an early-type elliptical host (i.e., NGC 2784 and NGC 3585). The
correlation between the color and magnitude is much stronger in NGC 2997 and
M83. For the $(V\,-\,I)_{0}$ color (Figure 10), the best-fit CMR slopes and
the linear correlation coefficients are 0.003 $\pm$ 0.02 and 0.03 (NGC 2784),
–0.007 $\pm$ 0.01 and –0.08 (NGC 3585), 0.004 $\pm$ 0.01 and 0.05 (NGC 2997).
We find that correlations in general are much weaker for the $(V\,-\,I)_{0}$
colors, and the slopes are essentially flat.

Recent large surveys on MW-like system satellites have estimated structural
properties of satellites of a large number of MW-like systems (e.g. SAGA and
ELVES, Mao et al., 2021; Carlsten et al., 2021b, 2022). In Figure 11, we show
the distributions of structural parameters — the central surface brightness
$\mu_{0,V}$ (top panel), the effective radius $r_{e}$ (middle panel), and the
Sérsic curvature index $n$ (bottom panel) — for DGCs of NGC 2784, NGC 3585,
NGC 2997 and M83 from our studies together with those of the 444 satellites
around MW-like systems from the ELVES survey (Carlsten et al., 2022) as a
function of their $V$-band absolute magnitudes. (Note that individual data
values of the Sérsic curvature indices of the ELVES satellites are unavailable
other than a median value of 0.72 (Carlsten et al., 2021b); thus, they are
excluded from the bottom panel.) For the two structural parameters of
$\mu_{0,V}$ and $r_{e}$, as expected, we can first identify that almost all
DGCs and satellites in the collected sample reside within the completeness
boundary curve (gray dashed curves; see Ferguson & Sandage, 1988; Müller et
al., 2015, for equations) calculated using the selection criteria on our DGCs:
(1) the limiting surface brightness of $\mu_{0,V}$ $\simeq$ 28 mag arcsec-2
that we estimate by analyzing their surface brightness profiles; and (2) the
limiting size of $r_{e}$ $\simeq$ 4$\aas@@fstack{\prime\prime}$ (Section 3.1).
This confirms that the distributions of the structure parameters of NGC 2997
DGCs from our study conform to the predictions on detection limits by Ferguson
& Sandage (1988). The one DGC located outside the boundary curve is DW94 from
NGC 2997, and it is very faint (See Figure 14). Both the two structure
parameters, i.e., $\mu_{0,V}$ and $r_{e}$, of DGCs from our studies and
satellites from ELVES survey in Figure 11 appear to increase as the $V$-band
luminosity increases. The median value of the Sérsic curvature index of the
DGCs from NGC 2997 is 0.68, largely consistent with 0.8 for NGC 2784 and NGC
3584, as well as 0.72 for the satellites from the ELVES survey (Carlsten et
al., 2021b). It’s a bit smaller than 1.1 for M83, but still not significantly
different. This similarity and consistency of the structure parameters from
our studies and the ELVES survey for the dwarf galaxies of MW-like systems is
encouraging and may indicate the presence of common patterns in their
properties. Future investigation of their distributions and properties using
more statistically significant samples can lead to advanced understanding of
their origin and evolution and provide important information for our
understanding of challenges that the current $\Lambda$CDM model faces (e.g.,
Weinberg et al., 2015).

Figure 8: Color-magnitude diagrams. Color-magnitude diagram of the DGCs in NGC
2997 (red filled circles) compared with those of the NGC 2784 (squares, Park
et al., 2017), NGC 3585 (triangles, Park et al., 2019), and M83 (diamonds,
Müller et al., 2015). The blue dashed line represents the best-fit linear
relation obtained in Park et al. (2019) using the DGCs from both NGC 2784 and
NGC 3585 groups. The red solid line represents the best-fit linear relation
that we obtain from the DGCs of NGC 2997, NGC 2784, and NGC 3585 together.
Figure 9: $(B\,-\,V)_{0}$ vs. MV color-magnitude diagrams of the DGCs in NGC
2784 (Park et al., 2017), NGC 3585 (Park et al., 2019), NGC 2997 (this work),
and M83 (Müller et al., 2015) shown in circles. The blue solid lines represent
the best-fit linear relation with 3-$\sigma$ clipping that we obtain between
the two parameters. In panel c), the red circles mark the 7 previously
discovered dwarf galaxies (Table 3). The circles with a green diamond are
those morphologically identified as irregular, while the rest are elliptical.
Figure 10: Same as Figure 9, but for $(V\,-\,I)_{0}$ vs. MV for NGC 2784, NGC
3585, and NGC 2997. The red solid lines are the best-fit linear relations that
we obtain between the parameters.  Figure 11: Distributions of the apparent
central surface brightness ($\mu_{0,V}$; top panel), effective radii ($r_{e}$;
middle panel), and Sérsic indices ($n$; bottom panel) along the $V$-band
absolute magnitudes (MV) of the DGCs in NGC 2784 (squares), NGC 3585
(triangles), NGC 2997 (filled circles), M83 (diamonds). The gray dashed lines
in the top and middle panels are the completeness boundaries. The red error
bars in the left-hand part of each diagram represents the mean uncertainties
of the parameters for the candidates in NGC 2997.

###  4.3 Luminosity Function

In Figure 12 (top panel), we show a cumulative LF of the NGC 2997 group
constructed with 53 DGCs that we used for the radial number density
distribution analysis (Figure 6), excluding three DGCs in the last radial bin,
together with MV $\simeq$ –20.65 mag for NGC 2997 itself (de Vaucouleurs &
Longo, 1988). The 53 DGCs are at projected distances $\lesssim$ 400 kpc, which
is the virial radius of the group, and include all of the previously-
discovered members. The dashed line in the top panel of Figure 12 represents
the best-fit Schechter function with a faint-end slope of $\alpha$ = –1.43
$\pm$ 0.02 obtained by fitting the LF where MV $\leq$ –10 mag, as was done in
our previous studies, using the non-linear least-square fitting method. The
shaded region shows the area for MV $\;\buildrel>\over{\sim}\;$ –10.2 mag,
which is the 90% completeness magnitude limit of our detection (Section 3.1).
It is noteworthy that the slope of the LF for the faint dwarf galaxy
candidates in this area becomes more flattened as the luminosity decreases,
indicating that the flattening is at least partially attributed by the
incompleteness of our detection for $M_{V}$ $\;\buildrel>\over{\sim}\;$ –10.2
mag. The bottom panel of Figure 12 compares the cumulative LF of NGC 2997 with
those of NGC 2784 (Park et al., 2017), NGC 3585 (Park et al., 2019), and M83
(Müller et al., 2015). Applying the same fitting method, we obtain their best-
fit LF faint-end slopes to be –1.22 $\pm$ 0.03 (NGC 2784), –1.33 $\pm$ 0.03
(NGC 3585), and –1.40 $\pm$ 0.04 (M83). The faint-end slope of NGC 2997 is
very similar to that of M83, while it is a bit steeper than those of NGC 2784
and NGC 3585. Compared to the range of –1.9 $\lesssim$ $\alpha$ $\lesssim$
–1.6 typically predicted by $\Lambda$CDM models (e.g., Klypin et al., 1999;
Trentham & Tully, 2002; Springel et al., 2008; Han et al., 2016; Li et al.,
2019), the faint-end LF slopes of these galaxies appear to be consistently
flatter. However, we note that recent $\Lambda$CDM simulations based on
different types of stellar-to-halo mass relation, which is still poorly
constrained for low-mass dwarf galaxies, have shown that there exists a great
uncertainty in the predicted LFs (e.g., Carlsten et al., 2021a). It is,
therefore, uncertain whether the slope that we measure for the NGC 2997 group
is in an agreement or disagreement with $\Lambda$CDM model prediction.

Figure 13 shows the distributions of the LFs for bright ($M_{V}$
$\;\buildrel<\over{\sim}\;$ –12.1 mag) satellites around 11 MW-like galaxies:
four (NGC 6181, 6278, 5297, and 7366; shown in blue-hued circles and lines)
from the SAGA survey, four (NGC 3627, 3379, 1808, and 1291; purple-hued
circles and lines) from the ELVES survey, and three (NGC 2784, 3585, and 2997;
red-hued circles and lines) from the KSP (including this study). The SAGA
groups consist of the 4 most populated groups from the survey in terms of the
number of confirmed satellites, while the 4 galaxies in the ELVES group are
selected because they have distances similar to that of NGC 2997 with a
satellite survey size comparable to that of the SAGA survey, i.e., R
$\;\buildrel<\over{\sim}\;$ 300 kpc. We can identify in the figure that the
LFs of the three KSP group members, which are similar to each other, lie
between those of the ELVES groups for faint regime of MV
$\;\buildrel>\over{\sim}\;$ –14 mag with more rapid increase of number of
satellites as they become fainter. The LF slopes of the KSP and the two ELVES
groups appear to be much steeper than that of the SAGA survey in this faint
regime. According to (Carlsten et al., 2022), this might have been caused by
incompleteness beyond what is accounted for in the SAGA survey, especially in
the low-mass regime (see the reference for the details). As we explained in
Section 3.1, the detection rate of bright satellites from our work on NGC 2997
is similar to that of the SAGA survey, which we can confirm in their LFs in
Figure 13. Two galaxy groups, which are NGC 3379 and NGC 3627, from the ELVES
survey have brightest ($<$ –20 mag) satellites as well as the largest number
of faint ones, confirming that groups with brighter satellites tend to have a
larger number of satellites, as have been found in recent studies (Mao et al.,
2021; Carlsten et al., 2022).

We identify a magnitude gap of $\simeq$ 2 mag around MV = –15 mag in the LF of
NGC 2997 group, with no DGCs found within the gap and steeper increase of
slopes around it. In the SAGA survey of small galaxy groups (Geha et al.,
2017), the majority of the groups show similar magnitude gaps in the range of
2.2–3.6 mag, which is consistent with the prediction by numerical simulations
presented in the same work, while a small number of faint (i.e., MK
$\;\buildrel>\over{\sim}\;$ –23.75 mag for the host galaxy luminosity) groups
have gaps greater than 5 mag. Considering that NGC 2997 is a MW-analog system
with MK $\simeq$ –24.02 mag (§1), similar to the systems studied in the SAGA
survey, the 2.2 mag gap in the LF of NGC 2997 appears to be consistent with
the SAGA survey results (see also Bennet et al., 2019). We estimate the
significance of the gap in the NGC 2997 LF to be only about 60 % in our
examination of 100000 cases of randomly sampled 55 dwarf galaxies from a
Schechter function constructed by using LF parameters of the NGC 2997 group,
while no confidence level of the LF gaps identified in the SAGA survey is
available. If the presence of such luminosity gaps is indeed common in small
group systems, it is suggestive that small galaxy groups, due to their low
velocity dispersion, are more susceptible to merging process which is known to
be the main mechanism responsible for the creation of magnitude gaps in LFs
(e.g., Miles et al., 2004; Lee et al., 2016). More future samples showing the
presence of similar luminosity gaps with a higher statistical significance are
required to further validate this possibility.

Figure 12: (Top) The cumulative LF (red filled circles) of the NGC 2997 group.
The dotted line represents the best-fit Schechter function with the faint-end
slope $\alpha$ $\simeq$ –1.43. The shaded area indicates the magnitude region
below our work’s 90% completeness magnitude limit ($M_{V}$
$\;\buildrel>\over{\sim}\;$ –10.2 mag). (Bottom) The cumulative LFs of NGC
2997 compared with those of NGC 2784 (squares; Park et al., 2017), NGC 3585
(triangles; Park et al., 2019), and and M83 (diamonds; Müller et al., 2015).
The black dotted line is the case of $\alpha$ = –1.8 predicted by the
$\Lambda$CDM model (Trentham & Tully, 2002).  Figure 13: Luminosity function
of NGC 2997 compared with those of sample galaxies from the ELVES and SAGA
surveys as well as from our previous studies (see Section 4.3).

##  5 Evolutionary stage of the NGC 2997 group

The DGCs that we identify in the field of NGC 2997 show several notable
characteristics diagnostic of their evolutionary stage as we discuss below.

###  5.1 Color-Magnitude Relation, Star Formation Activities, and Galactic
Conformity

The CMR of the DGCs in NGC 2997 indicates that the group is populationally
young with ongoing star formation activities. Their $(B\,-\,V)_{0}$ colors
show a positive correlation with MV (Figure 9; §4.2) with brighter members
being bluer, and this suggests the presence of younger stellar populations in
the brighter and more massive members, indicating that the star-formation
activities in less massive members are more quenched than their counterparts.
Since most of our candidates are within the virial radius ($\simeq$ 400kpc) of
NGC 2997, it is highly likely that their quenching is caused by environmental
mechanisms, such as ram-pressure and tidal stripping from the massive host,
which are known to be more dominant at z $\lesssim$ 1 (Peng et al., 2010)
where NGC 2997 belongs. This interpretation is further supported by various
observational results showing a clear contrast in quenching between field and
satellite dwarf galaxies: the former have shown an extreme lack of quenching
(e.g. Weisz et al., 2011; Geha et al., 2012), whereas the latter have shown
much stronger quenching (e.g., see Fillingham et al., 2018, and references
therein). Given that the timescale of environmental quenching is much shorter
for lower mass satellites (e.g., Samuel et al., 2022), it is conceivable that
only the low-mass members of the group have had enough time for the
environmental quenching to develop, causing them to appear redder than the
massive members.

It is known that colors of shorter wavebands (e.g., $B\,-\,V$) are more
affected by star formation activities (or stellar age variations) than those
in longer wavebands (e.g., $V\,-\,I$, see Chang et al., 2006; Janz & Lisker,
2009, for example). The $(V\,-\,I)_{0}$ colors of DGCs in the NGC 2997 group
show a much weaker correlation with their brightness than $(B\,-\,V)_{0}$
color does (§4.2), supporting the interpretation that the CMR of NGC 2997
could be primarily driven by star formation activities, and hence stellar age
variations. Similar relations between the color and magnitudes of satellite
galaxies to those of NGC 2997 have been found in many recent observational and
simulation studies. More massive satellites found in the ELVES survey on
satellites around MW-like hosts appear systematically bluer than the less
massive members (Carlsten et al., 2022), consistent with the measurements made
by H$\alpha$ showing that the quenched fraction decreases as the mass of
satellites increases. Recent FIRE-II simulation of cosmological galaxy
formation (e.g. Samuel et al., 2022) has also found that massive satellites
around MW-like galaxies have significantly lower quenched fractions compared
to less massive members. The results from these observational and simulation
studies are in line with our interpretation that the more massive DGCs of
NGC2997 have experienced less quenching. Additionally, there also exists a
higher fraction of irregular morphologies among the brighter DGCs in NGC 2997
(§3.3 and §5.3), further supporting this interpretation since irregular
galaxies in general appear to have more persistent star formation activities
(Chiboucas et al., 2009; Kormendy & Bender, 2012; Kirby et al., 2013; Lassen
et al., 2021; Carlsten et al., 2021c). These observed properties of the DGCs
in NGC 2997 suggest that the brighter dwarf galaxies in NGC 2997 are more
dominated by star-forming late-type galaxies with younger stellar age.

The average $(g-r)_{0}$ color of the 127 satellite galaxies identified in the
SAGA survey around 36 MW-analog hosts with the detection limit of Mr
$\;\buildrel<\over{\sim}\;$ –12.3 mag is 0.39 $\pm$ 0.13 mag (Mao et al.,
2021), which converts to $B\,-\,V$ $\simeq$ 0.61 $\pm$ 0.13 mag when adopting
the conversion relation between $g-r$ and $B\,-\,V$ colors (Jester et al.,
2005). (Note that, according to (Jester et al., 2005), the rms conversion
uncertainty between these two colors is small at the level of 0.04 mag.) In
our study, the average $(B\,-\,V)_{0}$ color of the 18 brightest DGCs of NGC
2997 with MV $\;\buildrel<\over{\sim}\;$ –12 mag, which is equivalent to the
SAGA detection limit above, is 0.52 $\pm$ 0.13 mag. The bright DGCs in NGC
2997 have comparable $(B\,-\,V)_{0}$ colors to those of the SAGA satellites.
Considering that most of the SAGA satellites have apparent star formation
activities, this indicates that the bright DGCs in NGC 2997 have active star
formation activities, consistent with our interpretation that they are mostly
star-forming late-type galaxies.

The CMR pattern of NGC 2997 from our study appears to be different from those
of NGC 2784 and NGC 3585 from our previous studies in that the $(B\,-\,V)_{0}$
colors and brightness of the DGCs of the two early-type hosted groups show
weak, negative correlations (Park et al., 2017, 2019). We note, however, that
the DGCs of the M83 group, which has a late-type host like NGC 2997, show a
strong, positive correlation between $(B\,-\,V)_{0}$ and brightness, similar
to NGC 2997 (Figure 9), indicating more active star-formation activities in
more massive members. It appears, therefore, that the DGCs in the groups of
NGC 2784, NGC 3585, and NGC 2997 as well as M83 show star-formation activities
that are overall similar to those of their hosts, compatible with “galactic
conformity” wherein satellite galaxies tend to show similar star-formation
activities and colors to their hosts (Weinmann et al., 2006; Bray et al.,
2016; Treyer et al., 2018).

###  5.2 Radial Distribution and Dynamical State

The radial distributions of the NGC 2997 DGC number density and color in
Figure 7 appear to be indicative that the group is dynamically young. First,
there is no sign of significant mass segregation in the radial number density
distribution in NGC 2997 (top panel), whereas, in the case of mass
segregation, massive satellites are expected to dominate the central area near
the host due to higher dynamical frictions (Chandrasekhar, 1943; De Lucia et
al., 2012; Kim et al., 2020). Assuming a uniform light-to-mass ratio, we
estimate the dynamical friction time-scale for brighter (MV
$\;\buildrel<\over{\sim}\;$ –15 mag) and fainter members of the NGC 2997 group
to be about 7 Gyrs in average and longer than the Hubble time, respectively,
following the method in Jiang et al. (2008). The lack of apparent mass
segregation in NGC 2997, therefore, is consistent with the interpretation that
the group is dynamically young if the light-to-mass ratio is uniform. In
Figure 7 (bottom panel), we can also identify the absence of any apparent
radial color dependency: the $(B\,-\,V)_{0}$ color distribution along the
radial distance is overall shallow. This is in contrast to what can be
expected for an evolved system where earlier and stronger quenching of star
formation driven by stronger tidal forces and also by more effective
interactions with the intracluster medium (Wetzel et al., 2013; Park et al.,
2017) would cause central satellite galaxies to be redder than those at larger
distances (e.g., Presotto et al., 2012; Lisker et al., 2013; Lee et al.,
2016). For example, according to the study by De Lucia et al. (2012) based on
the Millennium Simulation, a much steeper radial color distribution is
plausible for dwarf galaxies that have been satellites for over at least 5–8
Gyrs. The lack of apparent color gradient is, therefore, supportive of our
interpretation that the NGC 2997 group is dynamically young. Another possible
explanation for the origin of the observed shallow color gradient of NGC 2997
is less efficient quenching for a late-type system like NGC 2997 (Weinmann et
al., 2006; Bray et al., 2016; Treyer et al., 2018) in that the shallow color
gradient of NGC 2997 may simply result from similar star formation activities
between the host and satellites (known as “galactic conformity"). Overall, the
absence of mass-segregation and steep color gradient in NGC 2997 appears to be
compatible with the scenario that the system is dynamically young, although
different interpretations for the latter cannot be ruled out.

###  5.3 Morphologies

Another notable characteristic of the DGCs of NGC 2997 group is their
morphology. While we identify only one UDG and one nucleated dwarf galaxies
(see §3.3) in the NGC 2997 group, ten and four of the DGCs in NGC 3585 are
nucleated and UDGs, respectively (Park et al., 2019). In addition, as shown in
§3.1 and Figure 9, NGC 2997 appears to have a higher ratio of morphologically
irregular dwarf galaxies (dIs) — the fraction of dIs is 31% $\pm$ 9% in NGC
2997, while it is 18% $\pm$ 8% and 11% $\pm$ 7% in NGC 2784 and NGC 3585 when
adopting the same selection criteria (See § 3.3), respectively. These
potential differences in the morphology of the DGCs between the NGC 2997
system and the other two appear to be consistent with our interpretation that
the system is populationally and dynamically young. First, the relative
paucity of the nucleated dwarf galaxies can be understood in populationally
young satellite galaxies where there has not been enough time for globular
clusters to infall to form nucleus (Oh & Lin, 2000; Fahrion et al., 2021;
Poulain et al., 2021). Secondly, it might be difficult to develop UDGs in a
dynamically young group via tidal stripping of gas in dwarf galaxies and/or
their size expansion through tidal heating (Tremmel et al., 2020; Jones et
al., 2021). Thirdly, the higher fraction of dIrrs among the DGCs in NGC 2997
is compatible with a young system where there has not been enough time for dIs
to evolved into more early-type morphologies (Pasetto et al., 2003; Dunn,
2010; Chattopadhyay et al., 2015; Carlsten et al., 2021c).

##  6 Summary and Conclusion

In the work presented in this paper, we conduct photometric analysis of 55
DGCs that we have identified in the field of the giant spiral galaxy NGC 2997
using the deep stacked images obtained from the KMTNet Supernova Program. Out
of 55, 48 are newly discovered in this work while the rest seven are already
identified candidates from previous studies. Table 5 compares the parameters
of the DGCs in the NGC 2997 group that we identify in this study to those of
the NGC 2784 and NGC 3585 groups. We summarize our main results below, along
with our conclusions about the evolutionary stage of the NGC 2997 group based
on our results.

  * •

The 55 candidates show a broad range of photometric and structural parameters
that are overall compatible with those found from the dwarf galaxies in other
galaxy groups. Their $I$-band effective radii, $I$-band Sérsic index, and the
$V$-band total absolute magnitudes range from 0.14 to 2.97 kpc, from 0.25 to
1.39, and from –8.02 to –17.69 mag, respectively. The faint-end slope of their
luminosity function is $\alpha$ = –1.43 $\pm$ 0.02, which is shallower than
predictions based on $\Lambda$CDM models, but largely comparable to previously
measured values.

  * •

Compared to our previous studies of DGCs in the field of NGC 2784 and NGC 3585
using similar KMTNet data, the DGCs of NGC 2997 show a lack of more
morphologically developed candidates — out of the 55 candidates, we are able
to identify only 1 ultra-diffuse dwarf galaxy, and 1 nucleated candidates. In
contrast, there exists a significantly increased fraction of irregularly
shaped candidates (17 in total) in our sample of NGC 2997, and they are
significantly more luminous and bluer. These morphological distributions of
the DGCs indicate that the NGC 2997 group is a younger system.

  * •

The DGCs of the NGC 2997 group are bluer than those of the NGC 2784 and NGC
3585, with its brighter members being systematically bluer than the fainter
ones. The inferred higher star-formation activities in the more massive
members of the NGC 2997 group could result from their longer environmental
quenching processes.

  * •

The projected number density of the DGCs in NGC 2997 group decreases along the
distance from the center of NGC 2997, and there is no difference in this
radial number density distribution between the bright (MV $\lesssim$ –11.02
mag) and faint members of the group. The average color of them appears to be
invariant as a function of the radial distance. These again suggest that the
NGC 2997 group is dynamically young, prior to developing mass segregation
and/or radial dependency of colors identified in more evolved systems.

  * •

For the brighter DGCs in NGC 2997, we find their detection rate and the
inferred star formation activities are largely comparable to those found in
the SAGA survey, whose detection limit is MV = –12.1 mag, of MW-analog groups
in the distance range 25–42 Mpc. Similar to the results from the SAGA and also
to the ELVES survey, the faint DGCs in NGC 2997 appear to be substantially
more quenched than bright ones. Identification of whether this trend of
quenched star formation activities among faint DGCs in NGC 2997 is a general
property of faint satellites around MW-analog hosts requires more samples.

## Acknowledgments

We are very grateful to the anonymous referee for the thorough and valuable
comments that helped improve this paper significantly. This research has made
use of the KMTNet system operated by the Korea Astronomy and Space Science
Institute (KASI) at three host sites of CTIO in Chile, SAAO in South Africa,
and SSO in Australia. Data transfer from the host site to KASI was supported
by the Korea Research Environment Open NETwork (KREONET). We acknowledge with
thanks the variable star observations from the AAVSO International Database
contributed by observers worldwide and used in this research. DSM was
supported in part by a Leading Edge Fund from the Canadian Foundation for
Innovation (project No. 30951) and a Discovery Grant (RGPIN-2019-06524) from
the Natural Sciences and Engineering Research Council (NSERC) of Canada. HSP
was supported in part by the National Research Foundation of Korea (NRF) grant
funded by the Korea government (MSIT, Ministry of Science and ICT; No.
NRF-2019R1F1A1058228). Y.D.L. acknowledges support from Basic Science Research
Program through the National Research Foundation of Korea (NRF) funded by the
Ministry of Education (2020R1A6A3A01099777). This research was supported by
the Korea Astronomy and Space Science Institute under the R&D program (Project
No. 2022-1-868-04) supervised by the Ministry of Science and ICT.

## Data Availability

The data underlying this article will be publicly available online once it is
accepted for publication.

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##  Appendix A Large Figures and Tables

Figure 14: RGB cutout images of the 55 DGCs in Table 4. North is up and east
is to the left. The blue horizontal bar at the bottom of each image
corresponds to the angular size of 0$\aas@@fstack{\prime}$5 (= 1.77 kpc at the
distance of 12.2 Mpc).

Fig. 14. — Continued

Fig. 14. — Continued

Fig. 14. — Continued

Figure 15: Upper Panels: $I$-band surface brightness profiles of the DGCs. The
black crosses with error bars, often encircled by a red circle, represent
$\mu_{I}$ and its uncertainty. Only those data points with a red circle are
used in Sérsic fitting. The blue solid curves show the resulting best-fit
Sérsic profiles. The vertical blue dashed lines mark the estimated effective
radii. Lower Panels: $(B\,-\,V)_{0}$ and $(V\,-\,I)_{0}$ color profiles are
shown in green circles and black crosses, respectively. The green and red
horizontal dashed lines represent the mean $(B\,-\,V)_{0}$ and $(V\,-\,I)_{0}$
colors obtained from difference in total apparent magnitudes (See § 3.2),
respectively.

Fig. 15. — Continued

Fig. 15. — Continued

Fig. 15. — Continued

[b]

Table 5: KMTNet Dwarf Galaxy Discovery Summary Table

Host Name | Host Type | Distance |  MB |  # of DGCsa | $\langle(B\,-\,V)_{0}\rangle$ |  Cb | LF Slope
---|---|---|---|---|---|---|---
|  | (Mpc) | (mag) |  | (mag) |  |
NGC 2784 | SA(s) | 9.8 | –19.0 | 38 | 0.66 | –0.12 | –1.33
NGC 3585 | E7/S0 | 20.4 | –21.0 | 50 | 0.69 | –0.06 | –1.39
NGC 2997 | SAB(rs)c | 12.2 | –20.5 | 55 | 0.56 | 0.40 | –1.43

  * •

aThe # of DGCs includes previously discovered dwarf galaxies.

  * •

bC is the linear correlation coefficient, see §4.2.

  * •

Host type and MB information are obtained from Simbad, while the rest are from
Park et al., 2017 or Park et al., 2019.