The nature of the X-ray sources in dwarf galaxies in nearby clusters from the KIWICS

Abstract

ABSTRACT We present a deep search for and analysis of X-ray sources in a sample of dwarf galaxies (Mr < −15.5 mag) located within twelve galaxy clusters from the Kapteyn IAC WHT Enhanced Area Velocity Explores Isaac Newton Telescope Cluster Survey of photometric observations in the r and g using the Wide Field Camera at the 2.5-m Isaac Newton telescope. We first investigated the optical data, identified 2720 dwarf galaxies in all fields and determined their characteristics; namely, their colours, effective radii, and stellar masses. We then searched the Chandra data archive for X-ray counterparts of optically detected dwarf galaxies. We found a total of 20 X-ray emitting dwarf galaxies, with X-ray flux ranging from 1.7 × 10−15 to 4.1 × 10−14 erg cm−2 s−1 and X-ray luminosities varying from 2 × 1039 to 5.4 × 1041 erg s−1. Our results indicate that the X-ray luminosity of the sources in our sample is larger than the Eddington luminosity limit for a typical neutron star, even at the lowest observed levels. This leads us to conclude that the sources emitting X-rays in our sample are likely black holes. Additionally, we have employed a scaling relation between black hole and stellar mass to estimate the masses of the black holes in our sample, and have determined a range of black hole masses from 4.6 × 104 to 1.5 × 106 M⊙. Finally, we find a trend between X-ray to optical flux ratio and X-ray flux. We discuss the implications of our findings and highlight the importance of X-ray observations in studying the properties of dwarf galaxies.