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

We determined the HI 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 HI mass function has best-fitting Schechter parameters theta* = 0.19 +/- 0.11 Mpc(-3), log M-HI/M-circle dot* = 9.8 +/- 0.8, and alpha = -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 HI Parkes All Sky Survey (alpha= -1.37 +/- 0.03 +/- 0.05) and Arecibo Legacy Fast Arecibo L-band Feed Array (alpha = -1.33 +/- 0.02) HI 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 HI mass function slope.

Automated summary

The study determined the HI mass function of galaxies in the Ursa Major association using VLA and WSRT surveys, revealing a relative lack of low-HI mass galaxies in the region. The slope of the HI mass function in Ursa Major hints at an environmental dependence, which differs from other surveys covering larger volumes and cosmic environments.