N. Chamba | Searcharxiv

arXiv2026

The Bright Future of the Dark and Dim Universe

This chapter investigates the low-mass frontier of galaxy formation through two complementary populations: the starless Reionization-Limited HI Clouds (RELHICs) that trace the ``dark'' Universe, and the faint, gas-rich galaxies that define the ``dim'' Universe. RELHICs offer pristine laboratories for probing the distribution of DM on sub-galactic scales, providing a direct test of the Lambda Cold Dark Matter ($\Lambda$CDM) model predictions. The dim Universe provides statistical constraints on cosmology, galaxy formation and evolution, as well as baryoninc physics through key observables including the low-mass end of the neutral-hydrogen mass function (HIMF), the neutral-hydrogen velocity function (HIVF), and the low-mass end of the baryonic Tully-Fisher relation (bTFR). This chapter outlines core science questions that can be tackled leveraging radio observations of both the dark and dim Universe. Additionally, it outlines strategies to identify RELHICs amid tidal or pressure-confined contaminants, while providing observational predictions for the dim Universe. The Square Kilometre Array (SKA) in its mid-frequency Array Assembly 4 (AA4) configuration will, for the first time, resolve the internal gas structure of nearby RELHICs and build deep, wide-area datasets that definitively constrain the HIMF, HIVF, and bTFR down to masses of $10^{6}~\msol$ -- offering a complete observational framework to test the $\Lambda$CDM paradigm and the baryonic processes that shape the faint end of galaxy formation.

astro-ph.GA↗

arXiv2022

The edges of galaxies: Tracing the limits of star formation

The outskirts of galaxies have been studied from multiple perspectives for the past few decades. However, it is still unknown if all galaxies have clear-cut edges like everyday objects. We address this question by developing physically motivated criteria to define the edges of galaxies. Based on the gas density threshold required for star formation, we define the edge of a galaxy as the outermost radial location associated with a significant drop in either past or ongoing in-situ star formation. We explore $\sim$1000 low-inclination galaxies with a wide range in morphology (dwarfs to ellipticals) and stellar mass ($10^7 M_{\odot} < M_{\star} < 10^{12}M_{\odot}$). The location of the edges of these galaxies ($R_{\rm edge}$) are visually identified as the outermost cut-off or truncation in their radial profiles using deep multi-band optical imaging from the IAC Stripe82 Legacy Project. We find this characteristic feature at the following mean stellar mass density which varies with galaxy morphology: $2.9\pm0.10\,M_{\odot}$/pc$^2$ for ellipticals, $1.1\pm0.04\,M_{\odot}/$pc$^2$ for spirals and $0.6\pm0.03\,M_{\odot}/$pc$^2$ for present-day star forming dwarfs. Additionally, we find that $R_{\rm edge}$ depends on its age (colour) where bluer galaxies have larger $R_{\rm edge}$ at a fixed stellar mass. The resulting stellar mass--size plane using $R_{\rm edge}$ as a physically motivated galaxy size measure has a very narrow intrinsic scatter ($\lesssim 0.06$ dex). These results highlight the importance of new deep imaging surveys to explore the growth of galaxies and trace the limits of star formation in their outskirts.

astro-ph.GA↗