The nature of red dwarf galaxies

TL;DR

This study reveals that a significant fraction of faint dwarf galaxies are red, especially those associated with larger halos, challenging standard galaxy formation models and highlighting environmental effects on galaxy color.

Contribution

It provides new insights into the environmental influences on dwarf galaxy colors and their distribution relative to massive halos, using SDSS data and mock catalogs.

Findings

Approximately 25% of central dwarf galaxies are red, contrary to expectations.

About 45% of red dwarf galaxies are satellites in massive halos.

Over 30% of red dwarf galaxies are isolated, with unknown origins.

Abstract

Using dark matter halos traced by galaxy groups selected from the Sloan Digital Sky Survey Data Release 4, we find that about 1/4 of the faint galaxies ($\rmag >-17.05$, hereafter dwarfs) that are the central galaxies in their own halo are not blue and star forming, as expected in standard models of galaxy formation, but are red. In contrast, this fraction is about 1/2 for dwarf satellite galaxies. Many red dwarf galaxies are physically associated with more massive halos. In total, about $\sim 45$% of red dwarf galaxies reside in massive halos as satellites, while another $\sim 25$% have a spatial distribution that is much more concentrated towards their nearest massive haloes than other dwarf galaxies. We use mock catalogs to show that the reddest population of non-satellite dwarf galaxies are distributed within about 3 times the virial radii of their nearest massive halos. We suggest that this population of dwarf galaxies are hosted by low-mass halos that have passed through their massive neighbors, and that the same environmental effects that cause satellite galaxies to become red are also responsible for the red colors of this population of galaxies. We do not find any significant radial dependence of the population of dwarf galaxies with the highest concentrations, suggesting that the mechanisms operating on these galaxies affect color more than structure. However, over 30% of dwarf galaxies are red and isolated and their origin remains unknown.