The Ursa Major association of galaxies – VI: a relative dearth of gas-rich dwarf galaxies

Abstract

ABSTRACT We determined the H i mass function of galaxies in the Ursa Major association of galaxies using a blind Very Large Array (VLA) D-array survey, consisting of 54 pointings in a cross-pattern, covering the centre as well as the outskirts of the Ursa Major volume. The calculated H i mass function has best-fitting Schechter parameters θ* = 0.19 ± 0.11 Mpc−3, log $\mbox{$M^*_{\rm H\,{\small I}}$}\ /\mathrm{ M}_{\odot } = 9.8 \pm 0.8$, and α = −0.92 ± 0.16. The high-mass end is determined by a complementary, targeted Westerbork Synthesis Radio Telescope (WSRT) survey, and the low-mass end is determined by the blind VLA survey. The slope is significantly shallower than the slopes of the H i Parkes All Sky Survey (α = −1.37 ± 0.03 ± 0.05) and Arecibo Legacy Fast Arecibo L-band Feed Array (α = −1.33 ± 0.02) H i mass functions, which are measured over much larger volumes and cover a wider range of cosmic environments: There is a relative lack of low-H i mass galaxies in the Ursa Major region. This difference in the slope strongly hints at an environmental dependence of the H i mass function slope.