Do Ultraluminous X-Ray Sources Exist in Dwarf Galaxies?

TL;DR

This study investigates the presence of ultraluminous X-ray sources in dwarf galaxies, finding a decreasing occurrence rate with increasing galaxy mass and discussing implications for ULX origins.

Contribution

It provides the first systematic search for ULXs in dwarf galaxies and analyzes their frequency relative to galaxy mass.

Findings

ULX frequency decreases with galaxy mass above 10^8.5 solar masses

No ULXs detected in galaxies below this mass threshold

Discussion on differences between dwarf and giant galaxies regarding ULXs

Abstract

A thorough search for Ultraluminous X-ray source candidates within the Local Volume is made. The search spatially matches potential ULXs detected in X-ray images or cataloged in the literature with galaxies tabulated in the Catalog of Neighboring Galaxies compiled by Karachentsev et al. (2004). The specific ULX frequency (occurrence rate per unit galaxy mass) is found to be a decreasing function of host galaxy mass for host masses above $\sim10^{8.5}$ solar mass. There is too little mass in galaxies below this point to determine if this trend continues to lower galaxy mass. No ULXs have yet been detected in lower-mass galaxies. Systematic differences between dwarf and giant galaxies that may explain an abundance of ULXs in dwarf galaxies and what they may imply about the nature of ULXs are discussed.