Ultra-Low Iron Abundances in Distant Hot Gas in Galaxy Groups

Abstract

A new XMM observation of the outer regions of the galaxy group NGC 5044 indicates hot gas iron abundances of only ~0.15 solar between r=0.2 - 0.4 r_vir. While the total baryon mass within the virial radius may be close to the cosmic mean value observed in rich clusters, the ratio of total iron mass to optical light in NGC 5044 is about 3 times lower than that in rich clusters. The remarkably low iron abundance over a large volume of the intergroup gas in the outer regions of NGC 5044 cannot be easily understood in terms of the outflow of enriched gas in a group wind during its early history or by the long term enrichment by the group member galaxies that currently occupy this region. It is possible that the stars in NGC 5044 did not produce iron with the same efficiency as in clusters, or the iron resides in non-luminous clouds or stars, or the entropy of the iron-enriched gas created in early galactic starburst winds was too high to penetrate the group gas of lower entropy.