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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 Stellar streams in the Milky Way are promising detectors of low-mass dark matter (DM) subhalos predicted by ΛCDM. Passing subhalos induce perturbations in streams that indicate the presence of the subhalos. Understanding how known DM-dominated satellites impact streams is a crucial step toward using stream perturbations to constrain the properties of dark perturbers. Here, we cross-match a Gaia Early Data Release 3 and SEGUE member catalog of the Cetus-Palca stream (CPS) with H3 for additional radial velocity measurements and fit the orbit of the CPS using this six-dimensional (6D) data. We demonstrate for the first time that the ultra-faint dwarf Segue 2 had a recent (77 ± 5 Myr ago) close flyby (within the stream's 2σwidth) with the CPS. This interaction enables constraints on Segue 2’s mass and density profile at larger radii ( $O\left(1\right)$kpc) than are probed by its stars ( $O\left(10\right)$pc). While Segue 2 is not expected to strongly affect the portion of the stream covered by our 6D data, we predict that if Segue 2’s mass within ∼ 6 kpc is 5 × 10⁹M_⊙, the CPS's velocity dispersion will be ∼ 40 km s⁻¹larger atϕ₁ > 20° than atϕ₁ < 0°. If no such heating is detected, Segue 2’s mass cannot exceed 10⁹M_⊙within ∼ 6 kpc. The proper motion distribution of the CPS near the impact site is mildly sensitive to the shape of Segue 2’s density profile. This study presents a critical test for frameworks designed to constrain properties of dark subhalos from stream perturbations. 

Abstract We present the first comprehensive census of the satellite population around a Large Magellanic Cloud stellar-mass galaxy, as part of the Magellanic Analog Dwarf Companions and Stellar Halos (MADCASH) survey. We have surveyed NGC 2403 (D= 3.0 Mpc) with the Subaru/Hyper Suprime-Cam imager out to a projected radius of 90 kpc (with partial coverage extending out to ∼110 kpc, or ∼80% of the virial radius of NGC 2403), resolving stars in the uppermost ∼2.5 mag of its red giant branch. By looking for stellar overdensities in the red giant branch spatial density map, we identify 149 satellite candidates, of which only the previously discovered MADCASH J074238+65201-dw is a bona fide dwarf, together with the more massive and disrupting satellite DDO 44. We carefully assess the completeness of our search via injection of artificial dwarf galaxies into the images, finding that we are reliably sensitive to candidates down toM_V∼ −7.5 mag (and somewhat sensitive to even fainter satellites). A comparison of the satellite luminosity function of NGC 2403 down to this magnitude limit to theoretical expectations shows overall good agreement. This is the first of a full sample of 11 Magellanic Cloud–mass host galaxies we will analyze, creating a statistical sample that will provide the first quantitative constraints on hierarchical models of galaxy formation around low-mass hosts.