Searching for X-ray sources in nearby late-type galaxies with low star formation rates

TL;DR

This study used XMM-Newton observations to identify X-ray sources in 11 nearby late-type galaxies, discovering ultraluminous sources, potential neutron star binaries, and a galaxy cluster, expanding knowledge of X-ray populations in low star formation environments.

Contribution

First systematic X-ray survey of nearby late-type galaxies with low star formation rates, identifying diverse X-ray sources including ultraluminous and quasi-soft sources.

Findings

18 X-ray sources detected, most point-like

One ultraluminous X-ray source found

A galaxy cluster at redshift z=0.25 identified

Abstract

Late type non-starburst galaxies have been shown to contain X-ray emitting objects, some being ultraluminous X-ray sources. We report on XMM-Newton observations of 11 nearby, late-type galaxies previously observed with the Hubble Space Telescope (HST) in order to find such objects. We found 18 X-ray sources in or near the optical extent of the galaxies, most being point-like. If associated with the corresponding galaxies, the source luminosities range from $2 \times 10^{37}$ erg s$^{-1}$ to $6 \times 10^{39}$ erg s$^{-1}$. We found one ultraluminous X-ray source, which is in the galaxy IC 5052, and one source coincident with the galaxy IC 4662 with a blackbody temperature of $0.166 \pm 0.015$ keV that could be a quasi-soft source or a quiescent neutron star X-ray binary in the Milky Way. One X-ray source, XMMU J205206.0$-$691316, is extended and coincident with a galaxy cluster visible on an HST image. The X-ray spectrum of the cluster reveals a redshift of $z = 0.25 \pm 0.02$ and a temperature of 3.6$\pm$0.4 keV. The redshift was mainly determined by a cluster of Fe XXIV lines between the observed energy range $0.8-1.0$ keV.