A Minisurvey of X‐Ray Point Sources in Starburst and Nonstarburst Galaxies

Abstract

We present a comparison of X-ray point-source luminosity functions of three starburst galaxies (the Antennae, M82, and NGC 253) and four nonstarburst spiral galaxies (NGC 3184, NGC 1291, M83, and IC 5332). We find that the luminosity functions of the starbursts are flatter than those of the spiral galaxies; the starbursts have relatively more sources at high luminosities. This trend extends to early-type galaxies that have steeper luminosity functions than spirals. We show that the luminosity function slope is correlated with 60 μm luminosity, a measure of star formation. We suggest that the difference in luminosity functions is related to the age of the X-ray binary populations, and we present a simple model that highlights how the shape of the luminosity distribution is affected by the age of the underlying X-ray binary population.