X-ray Sources in Two Nearby Dwarf Spheroidal Galaxies

Abstract

We observed the dwarf spheroidal (dSph) galaxy Leo I for 80,000 seconds with XMM‐Newton and detected 105 non Galactic X‐ray sources (XRS) in its field. We examined deep optical images and catalogs, and discuss the possibility that some of the sources are Low Mass X‐Ray Binaries (LMXB) intrinsic to Leo I. We also studied an archival XMM‐Newton observation of the Fornax dwarf spheroidal galaxy, and compare it with Leo I. 104 non Galactic XRS were detected in the Fornax field; one of them coincides with a blue object at the outskirt of the Fornax 4 globular cluster. In both observations about a third of the XRS are identified with extragalactic objects observed in optical and radio. We discuss the similarities between the two XRS groups and the differences, which may be due to the a small number of intrinsic LMXB in the two galaxies. Fornax is at half the distance of Leo I, and has an almost 4 times larger luminous mass, but is also much more sparse on the sky. Leo I has had at least one more recent episode ...