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X-ray studies of nearby galaxies

Final Report Summary - X-RAY-GAL (X-ray studies of nearby galaxies)

One of the fundamental questions in astrophysics is how stars and galaxies form and evolve. Although the basic mechanisms are known, some the still open questions are the properties of the endpoints of stellar evolution (white dwarfs, neutron stars, black-holes), the chemical enrichment and evolution of the interstellar medium (through supernova explosions and stellar winds) and their relation to star-formation. X-ray observations provide a unique tool to address those questions since both compact objects and hot gas emit primarily in the X-ray band. Moreover, observations of other galaxies allow us to study those questions in different environments and study the evolution of star-formation and galaxies in cosmological timescales.

X-ray observations of nearby galaxies allow us to study: (a) the properties of their hot gas produced by the interaction between the stellar winds and supernova remnants with their surrounding interstellar gas; and (b) the discrete X-ray sources which are related to the end-points of the stellar evolution (e.g. supernova remnants and X-ray binaries).

The subject of this effort is to study the X-ray binaries in a small sample of nearby galaxies. X-ray binaries are systems consisting of a compact objects (white dwarf, neutron star, or black hole) accreting matter from a donor star. Depending on the nature of the donor star we can have high-mass X-ray binaries (HMXBs) or low mass X-ray binaries (LMXBs) if it is a massive (early-type) star or a low mass (<1 solar mass; late-type) star. Therefore, both signals to noise radio (SNRs) and X-ray binaries, provide important information on stellar evolution, particularly its end-points, and their populations reflect the star-formation history of a galaxy.

As part of this project we have analysed X-ray (Chandra) and supporting space (Hubble space telescope; HST) and ground based optical data for a set of nearby galaxies including our two nearest irregular galaxies (the small and large magellanic clouds) and one elliptical galaxy (NGC4261). For these galaxies we studied the properties of their X-ray sources, and we calculated their X-ray luminosity functions (including corrections for observational biases), and we compared them with a library of simulations in order to constrain parameters in their formation and evolution.