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

Abstract

We present a deep search for and analysis of X-ray sources in a sample of dwarf galaxies (M${}_r$ < -15.5 mag) located within twelve galaxy clusters from the Kapteyn IAC WEAVE INT Cluster Survey (KIWICS) of photometric observations in the $\text{r}$ and $\text{g}$ using the Wide Field Camera (WFC) at the 2.5-m Isaac Newton telescope (INT). We first investigated the optical data, identified 2720 dwarf galaxies in all fields and determined their characteristics; namely, their colors, effective radii, and stellar masses. We then searched the $\text{Chandra}$ 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$\times 10^{-15}$ to 4.1$\times 10^{-14}$ erg cm${}^{-2}$ s${}^{-1}$ and X-ray luminosities varying from 2$\times 10^{39}$ to 5.4$\times 10^{41}$ 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$\times 10^4$ to 1.5$\times 10^6$ M${}_{\odot }$. 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.

Accepted for publication in MNRAS, 11 pages, 7 figures

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