the neutral IGM in filaments with the SKA
---

cosmology: theory – diffuse radiation – intergalactic medium – large scale structure of universe

Introduction {#sec:intro}
============

In the standard picture, the structure in the Universe forms through non-linear gravitational collapse. This creates an intricate pattern of galaxies, filaments and voids, collectively known as the cosmic web. Such structures are clearly seen in simulations based on the $\Lambda$-Cold Dark Matter ($\Lambda$CDM) cosmological model. Simulations can provide information on both the dark matter and the baryonic gas particles, whereas, on the observational side, the main probe of the large-scale structure has been through the three-dimensional distribution of the observed galaxies, such as in the Sloan Digital Sky Survey [SDSS, @art:sdss1; @art:sdss8], the 6-degree Field (6dF) Galaxy Redshift Survey [@art:6df1; @art:6df3] and the Two Micron All-Sky Redshift Survey [2MRS, @art:2mrs]. Specifically, a significant effort has been made in inferring and characterizing large-scale filaments from galaxy surveys and they seem to match the predictions made by the $\Lambda$CDM model [e.g., @art:sousbie08; @art:jasche10; @art:smith12; @art:tempel14]. Unfortunately however, the positions of galaxies only provide a biased tracer of the underlying density field and give little information on the gas content in the filaments themselves.\
Recent observations 