Abstract
We analytically derive the observed size–mass relation of galaxies’ atomic hydrogen (H I), including limits on its scatter, based on simple assumptions about the structure of H I discs. We trial three generic profiles for H I surface density as a function of radius. First, we assert that H I surface densities saturate at a variable threshold, and otherwise fall off exponentially with radius or, secondly, radius squared. Our third model assumes the total gas surface density is exponential, with the H I fraction at each radius depending on local pressure. These are tested against a compilation of 110 galaxies from the THINGS, LITTLE THINGS, LVHIS, and Bluedisk surveys, whose H I surface density profiles are well resolved. All models fit the observations well and predict consistent size–mass relations. Using an analytical argument, we explain why processes that cause gas disc truncation – such as ram-pressure stripping – scarcely affect the H I size–mass relation. This is tested with the IllustrisTNG(100) cosmological, hydrodynamic simulation and the DARK SAGE semi-analytic model of galaxy formation, both of which capture radially resolved disc structure. For galaxies with m∗ ≥ 109 M and mH I ≥ 108 M, both simulations predict H I size–mass relations that align with observations, show no difference between central and satellite galaxies, and show only a minor, second-order dependence on host halo mass for satellites. Ultimately, the universally tight H I size–mass relation is mathematically inevitable and robust. Only by completely disrupting the structure of H I discs, e.g. through overly powerful feedback, could a simulation predict the relation poorly.
Original language | English |
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Pages (from-to) | 96-113 |
Number of pages | 18 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 490 |
Issue number | 1 |
DOIs | |
Publication status | Published - 21 Nov 2019 |
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Data from: Origin of the galaxy H I size-mass relation
Stevens, A. (Creator), Diemer, B. (Creator), Lagos Urbina, C. (Creator), Nelson, D. (Creator), Obreschkow, D. (Creator), Wang, J. (Creator) & Marinacci, F. (Creator), SAO/NASA Astrophysics Data System (ADS), Nov 2019
https://ui.adsabs.harvard.edu/abs/2019MNRAS.490...96S/abstract and one more link, https://ui.adsabs.harvard.edu/link_gateway/2019MNRAS.490...96S/SIMBAD (show fewer)
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