HI Observations of Baryon-Dominated Dwarf Galaxy Candidates

TL;DR

This study uses high-resolution HI observations to identify baryon-dominated dwarf galaxies, revealing some are dark-matter deficient and challenging standard cosmological models.

Contribution

First resolved HI kinematic analysis of baryon-dominated dwarf galaxy candidates, highlighting the importance of accurate inclination corrections and revealing potential dark-matter deficiencies.

Findings

Four galaxies appear dark-matter deficient.

High baryon enhancement factors exceeding 50% in three galaxies.

Two high-efficiency galaxies are in isolated environments, challenging standard models.

Abstract

We present resolved HI observations of six dwarf galaxies drawn from a sample of baryon-dominated dwarf galaxy (BDDG) candidates previously identified using global HI 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 HI 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 HI-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 high baryon enhancement efficiency factor (ratio of baryon mass accumulated by a halo to the maximum expected value for its halo mass) exceeding 50%, with AGC 191707 appearing formally super-efficient. Only UGC 9500 and AGC 220901 are consistent with being dark-matter dominated. Two of these high-efficiency dwarf 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 $\Lambda CDM$ expectations for low-mass halos. Our results underscore the importance of resolved HI 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 $\Lambda CDM$ paradigm.