The H i gas disc thickness of the ultra-diffuse galaxy AGC 242019

Abstract

Ultra-diffuse galaxies (UDGs) are as faint as dwarf galaxies but whose sizes are similar to those of spiral galaxies. A variety of formation mechanisms have been proposed, some of which could result in different disc thicknesses. In this study, we measure the radial profile of the H i scale height (hg) and flaring angle (hg/R) of AGC 242019 through the joint Poisson-Boltzmann equation based on its well spatially-resolved H i gas maps. The mean H i scale height of AGC 242019 is langle h g 537.15 ± 89.4 pc, and the mean flaring angle is hg/R 0.19 ± 0.03. As a comparison, we also derive the disc thickness for a sample of 14 dwarf irregulars. It is found that the H i disc of AGC 242019 has comparable thickness to dwarfs. This suggests that AGC 242019 is unlikely to experience much stronger stellar feedback than dwarf galaxies, which otherwise leads to a thicker disc for this galaxy.