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ABSTRACT The baryonic Tully–Fisher relation (bTFR) provides an empirical connection between baryonic mass and dynamical mass (measured by the maximum rotation velocity) for galaxies. Due to the impact of baryonic feedback in the shallower potential wells of dwarf galaxies, the bTFR is predicted to turn down at low masses from the extrapolated power-law relation at high masses. The low-mass end of the bTFR is poorly constrained due to small samples and difficulty in connecting the galaxy’s gas kinematics to its dark matter halo. Simulations can help us understand this connection and interpret observations. We measure the bTFR with 75 dwarf galaxies from the Marvel-ous and Marvelous Massive Dwarfs hydrodynamic simulations. Our sample has M$$_\star = 10^6-10^9$$ M$$_\odot$$, and is mostly gas dominated. We compare five velocity methods: V$$_\text{out,circ}$$ (spatially resolved mass-enclosed), V$$_\text{out,mid}$$ (spatially resolved mid-plane gravitational potential), and unresolved H i linewidths at different percentages of the peak flux (W$$_\text{10}$$, W$$_\text{20}$$, and W$$_\text{50}$$). We find an intrinsic turndown in the bTFR for maximum halo speeds $$\lesssim 50$$ km s$$^{-1}$$, or total baryonic mass M$$_\text{bary}\lesssim 10^{8.5}$$ M$$_\odot$$. We find that observing H i in lower-mass galaxies to the conventional surface density limit of 1 M$$_\odot$$ pc$$^{-2}$$ is not enough to detect a turndown in the bTFR; none of the H i velocity methods, spatially resolved or unresolved, recover the turndown, and we find bTFR slopes consistent with observations of higher-mass galaxies. However, we predict that the turndown can be recovered by resolved rotation curves if the H i limit is $$\lesssim 0.08$$ M$$_\odot$$ pc$$^{-2}$$, which is within the sensitivity of current H i surveys like FEASTS and MHONGOOSE. 

ABSTRACT Understanding what shapes the cold gas component of galaxies, which both provides the fuel for star formation and is strongly affected by the subsequent stellar feedback, is a crucial step towards a better understanding of galaxy evolution. Here, we analyse the H i properties of a sample of 46 Milky Way halo-mass galaxies, drawn from cosmological simulations (EMP-Pathfinder and Firebox). This set of simulations comprises galaxies evolved self-consistently across cosmic time with different baryonic sub-grid physics: three different star formation models [constant star formation efficiency (SFE) with different star formation eligibility criteria, and an environmentally dependent, turbulence-based SFE] and two different feedback prescriptions, where only one sub-sample includes early stellar feedback. We use these simulations to assess the impact of different baryonic physics on the H i content of galaxies. We find that the galaxy-wide H i properties agree with each other and with observations. However, differences appear for small-scale properties. The thin H i discs observed in the local universe are only reproduced with a turbulence-dependent SFE and/or early stellar feedback. Furthermore, we find that the morphology of H i discs is particularly sensitive to the different physics models: galaxies simulated with a turbulence-based SFE have discs that are smoother and more rotationally symmetric, compared to those simulated with a constant SFE; galaxies simulated with early stellar feedback have more regular discs than supernova-feedback-only galaxies. We find that the rotational asymmetry of the H i discs depends most strongly on the underlying physics model, making this a promising observable for understanding the physics responsible for shaping the interstellar medium of galaxies.