The galactic HI-to-halo mass relation from isolated galaxies to cosmological hydrodynamic simulations
The relation between HI and dark matter (DM) halo masses provides key insights into gas accretion and the regulation of galaxy formation. In a previous study based on SPARC and LITTLE THINGS samples, we showed that the ratio between HI mass and DM halo mass remains approximately constant with stellar mass for nearby disc galaxies ($\log(M_{HI}/M_{200})=-1.90$ with a $1σ$ scatter of 0.37 dex). In this work, we extend that analysis by incorporating galaxies from the Analysis of the interstellar Medium in Isolated GAlaxies (AMIGA) sample and from the Gassendi HAlpha survey of SPirals (GHASP). The AMIGA sample provides the most rigorously selected sample of isolated galaxies in the local Universe, well-suited for testing whether the relation found in the previous samples holds in interaction-free galaxies. We construct mass models from high-resolution rotation curves and infrared photometry, and derive DM halo parameters. We confirm the proportionality between HI and DM halo masses and find a nearly constant HI-mass-to-halo-mass ratio of $\log(M_{HI}/M_{200})=-1.90$ over nearly five orders of magnitude in stellar mass ($7\leq\log(M_{\star}/M_\odot)\leq 11.5$), with a $1σ$ scatter of 0.36 dex. The AMIGA and GHASP samples are statistically consistent with the relation previously found for the SPARC and LITTLE THINGS samples, indicating that it is robust across galaxies spanning a broad range of isolation levels. In contrast, cosmological hydrodynamic simulations such as SIMBA, IllustrisTNG, and NIHAO predict a dependence on stellar mass, with a break at the high stellar mass end for disc galaxies ($M_{\star}>10^{10}M_{\odot}$). Our results thus further demonstrate that the HI-mass-to-halo-mass ratio is remarkably self-similar across rotationally-supported disc galaxies, hinting at mass-independent self-regulation mechanisms that are not yet understood in current theoretical models.