XMM-Newton study of the Draco dwarf spheroidal galaxy ⋆
Institut für Astronomie und Astrophysik, Kepler Center for Astro and
Particle Physics, Eberhard Karls Universität Tübingen,
2 ISDC Data Center for Astrophysics, Université de Genève, 16 Chemin d’Ecogia, 1290 Versoix, Switzerland
Received: 31 March 2015
Accepted: 2 October 2015
Aims. We present the results of the analysis of five XMM-Newton observations of the Draco dwarf spheroidal galaxy (dSph). The aim of the work is the study of the X-ray population in the field of the Draco dSph.
Methods. We classified the sources on the basis of spectral analysis, hardness ratios, X-ray-to-optical flux ratio, X-ray variability, and cross-correlation with available catalogues in X-ray, optical, infrared, and radio wavelengths.
Results. We detected 70 X-ray sources in the field of the Draco dSph in the energy range of 0.2 − 12 keV and classified 18 AGNs, 9 galaxies and galaxy candidates, 6 sources as foreground stars, 4 low-mass X-ray binary candidates, 1 symbiotic star, and 2 binary system candidates. We also identified 9 sources as hard X-ray sources in the field of the galaxy. We derived the X-ray luminosity function of X-ray sources in the Draco dSph in the 2 − 10 keV and 0.5 − 2 keV energy bands. Using the X-ray luminosity function in the energy range of 0.5 − 2 keV, we estimate that ~10 X-ray sources are objects in the Draco dSph. We have also estimated the dark matter halo mass that would be needed to keep the low-mass X-ray binaries gravitationally bound to the galaxy.
Key words: galaxies: individual: Draco dwarf spheroidal galaxy / X-rays: galaxies / X-rays: binaries
© ESO, 2016