The Ursa Major Association of Galaxies. VI: A relative dearth of gas-rich dwarf galaxies

TL;DR

This study measures the HI mass function of galaxies in the Ursa Major group, revealing a shallower slope and fewer low-mass, gas-rich dwarf galaxies compared to larger surveys, indicating environmental effects on galaxy gas content.

Contribution

It provides the first detailed HI mass function for the Ursa Major association, highlighting environmental dependence of galaxy gas richness and dwarf galaxy abundance.

Findings

Shallower HI mass function slope than larger surveys

Fewer low HI mass galaxies in Ursa Major

Environmental factors influence galaxy gas content

Abstract

We determined the HI mass function of galaxies in the Ursa Major association of galaxies using a blind 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_{\odot}) = 9.8+/-0.8 and {\alpha} = -0.92+/-0.16. The high-mass end is determined by a complementary, targeted WSRT survey, the low-mass end is determined by the blind VLA survey. The slope is significantly shallower than the slopes of the HIPASS ({\alpha} = -1.37+/-0.03+/-0.05) and ALFALFA ({\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 HI mass galaxies in the Ursa Major region. This difference in the slope strongly hints at an environmental dependence of the HI mass function slope.