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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 We use a sample of 73 simulated satellite and central dwarf galaxies spanning a stellar mass range of 10^5.3–10^9.1M_⊙to investigate the origin of their stellar age gradients. We find that dwarf galaxies often form their stars “inside-out,” i.e., the stars form at successively larger radii over time. However, the oldest stars get reshuffled beyond the star-forming radius by fluctuations in the gravitational potential well caused by stellar feedback (the same mechanisms that cause dwarfs to form dark matter cores). The result is that many dwarfs appear to have an “outside-in” age gradient atz= 0, with younger stellar populations more centrally concentrated. However, for the reshuffled galaxies with the most extended star formation, young stars can form out to the large radii to which the old stars have been reshuffled, erasing the age gradient. We find that major mergers do not play a significant role in setting the age gradients of dwarfs. We find similar age gradient trends in satellites and field dwarfs, suggesting that environment plays only a minor role, if any. Finally, we find that the age gradient trends are imprinted on the galaxies at later times, suggesting that the stellar reshuffling dominates after the galaxies have formed 50% of their stellar mass. The later reshuffling is at odds with results from thefire-2simulations. Hence, age gradients offer a test of current star formation and feedback models that can be probed via observations of resolved stellar populations.