XMM-Newton observation of a sample of four close dSph galaxies

TL;DR

This study analyzes deep X-ray observations of four dwarf spheroidal galaxies to characterize their X-ray source populations and investigate the presence of central intermediate-mass black holes, finding no definitive evidence for such black holes.

Contribution

It provides a comprehensive X-ray source catalog for four dSph galaxies and constrains the properties and existence of central black holes using archival XMM-Newton data.

Findings

96 sources in Draco with no central black hole evidence

116 sources in Leo I with no black hole detection

54 sources in Ursa Minor with a possible central source

Abstract

We present the results of the analysis of deep archival \sat\ observations towards the dwarf spheroidal galaxies Draco, Leo I, Ursa Major II and Ursa Minor in the Milky Way neighbourhood. The X-ray source population is characterized and cross-correlated with available databases with the aim to infer their nature. We also investigate if intermediate-mass black holes are hosted in the center of these galaxies. In the case of Draco, we detect 96 high-energy sources, two of them being possibly local stars, while no evidence for any X-ray emitting central compact object is found. Towards the Leo I and UMa II field of view we reveal 116 and 49 X-ray sources, respectively. None of them correlates with the putative central black holes and only one is likely associated with a UMa II local source. The study of the UMi dwarf galaxy shows 54 high-energy sources and a possible association {with a source at the dSph center}. We put an upper limit to the central compact object luminosity of 4.02$\times$10$^{33}$ erg/s. Furthermore, via the correlation with a radio source near the galactic center, we get that the putative black hole should have a mass of $\left(2.76^{+32.00}_{-2.54}\right)\times10^6 M_{\odot}$ and be radiatively inefficient. This confirms a previous result obtained by using Chandra data alone.