Project Title: Deep X-ray Observations of Local Group Galaxies using Chandra and XMM

Project Advisor: Dr. Andrea H. Prestwich

Background: Recent X-ray observations of galaxies have revealed some very exciting results. The overall X-ray flux is composed of discrete sources and diffuse emission, but it is the discrete sources that dominate the flux. These point sources are all X-ray binaries -- a compact object (such as a black hole, neutron star or white dwarf) accreting material from a "normal" star companion (the donor star). In star forming galaxies, these X-ray galaxies tend to be "High Mass X-ray Binaries" -- systems in which the donor star is a high mass (hence short lived) star. In ellipticals and galaxies where there is an old stellar population "Low Mass X-ray Binaries" are also seen. These binaries have a low (approximately solar) mass donor. Studies of X-ray binary populations have the potential to tell us a lot about the current star formation and star formation history of a galaxy. For example, high mass binaries in starbursts might be used to probe the initial mass function of stars in the burst, and can be another indicator of burst age. Low mass binaries form a "fossil record" of previous episodes of star formation. While this field is full of potential, it is still in it's infancy and much pioneering work needs to be done.

Scientific Questions: This project involves in-depth analysis of two deep X-ray images of Local Group Galaxies. The goal of this study is to detect the faintest (low luminosity) X-ray binaries. The scientific goals of this study are very basic. How many low luminosity binaries are detected? Do they have optical counterparts? What can we say about the stellar environments of these sources? Are these numbers consistent with theoretical models of X-ray binary formation?

The first dataset is a deep (100ks) XMM exposure of the Fornax Dwarf Spheroidal. This galaxy has very little evidence for current star formation; all X-ray binaries in this system are likely to be Low Mass. The second dataset is a deep Chandra image of IC 10. In contrast IC 10 has a vigorous star burst and we will likely detect High Mass sources. The two datasets are complementary.

Characterizing the lowest luminosity X-ray binaries is best done in local group galaxies because X-ray binaries in the Milky Way are frequently absorbed by gas and dust in the galactic plane. Furthermore, the distances to binaries in our galaxy are very uncertain; local group galaxies provide a nice population of sources all at the same distance!

Scientific Methodology: This project involves very detailed analysis of both the Chandra and XMM datasets. In oder to remove background quasars and foreground stars from our sample of X-ray sources and to study the stellar environments of X-ray sources it will be necessary to analyze both optical and infrared images of these fields. We plan to do follow-up optical spectroscopy of binary sources in IC 10. Last (but definitely not least!) we will compare our results with theoretical models of binary formation in collaboration with Prof. V Kalogara of North Western University.

Other links related to this project

• Dr. Andrea Prestwich
• Prof. Vicky Kalogara