H I observations of baryon-dominated dwarf galaxy candidates

Abstract

We present resolved H i observations of six dwarf galaxies drawn from a sample of baryon-dominated dwarf galaxy (BDDG) candidates previously identified using global H i spectra from ALFALFA and optical inclinations from SDSS, both of which suffer from systematic uncertainties in irregular dwarf galaxies. Using uGMRT interferometric observations, we obtain high-resolution H i cubes that enable more reliable determination of their geometry, circular velocity, and dynamical mass. We find that optical axial ratios systematically underestimate true disc thickness, inflating inclinations and underestimating rotation velocities in earlier work. Our H i-derived axial ratios and kinematic position angles yield larger inclination corrections and hence larger dynamical masses. Four of these galaxies, UGC 6438, UGC 7983, AGC 191707, and AGC 733302, appear dark-matter deficient. The latter three of these four exhibit baryon enhancement efficiency factor (ratio of baryonic mass accumulated by a halo to the maximum expected value for its halo mass) exceeding 50 per cent, with AGC 191707 appearing formally superefficient. Only UGC 9500 and AGC 220901 are consistent with being dark-matter dominated. Two of these high-efficiency galaxies lie in relatively isolated environments, showing no clear signatures of tidal disturbance or stripping, making their dark matter deficiency difficult to reconcile with standard CDM expectations for low-mass halos. Our results underscore the importance of resolved H i kinematics in confirming genuine BDDGs and suggest that more such systems may exist. Identifying a larger sample is essential for assessing their implications for baryon–halo coupling and structure formation within the CDM paradigm.