X-rays From Nearby Galaxies

One of the outstanding legacies of the Chandra X-ray Observatory stems from its unique capacity to view nearby galaxies at unprecedented spatial resolution. Chandra observations of galaxies such as the grand design spiral M81 and the Local Group dwarf galaxy NGC 6822 have revolutionized our understanding of the dynamics and evolution of these objects through analysis of their X-ray source populations. These sources are predominantly X-ray binaries, compact neutron stars or black holes accreting matter from a companion star, which provide important information about how and where these systems form in their host galaxies and the role these endpoints of stellar evolution play in galaxy studies.

In addition to point-like sources, many nearby galaxies emit X-rays from diffuse hot gas. Chandra is the only observatory that is able to isolate the point sources from this diffuse emission thereby enabling studies of this important component. The hot gas arises from stellar winds and shocks from supernovae and from outflows from central supermassive black holes. The hot gas ablates cold gas from molecular clouds and can regulate future star formation. Thus, diffuse hot gas represents one aspect of feedback which is critical to our understanding of the star-formation cycle.

The X-ray astronomy group at MSFC has made significant contributions to the study of nearby galaxies beginning with our early analysis of the X-ray source population in M81, our study of super-soft sources in M81, and a complete catalog of the X-ray emission from M81 including analysis of SN 1993J, the ultraluminous X-ray source (ULX) X6 and the low-luminosity AGN at its center. There is also a paper on a bright transient in M81.

Other papers on nearby galaxies include a study of the X-ray properties of NGC 6822, the discovery of a transient X-ray source in the compact stellar nucleus of NGC 2403, circumnuclear star formation in NGC 3351, and a multiwavelength study of the X-ray sources in NGC 5018.

At somewhat longer distances, where central compact objects dominate the X-ray emission from galaxies, our contributions to the literature on galaxies and AGN include a study of the largest ring galaxy, UGC 7069, the discovery of Soft X-Ray-loud Broad Absorption Line Quasars, the physics of Polar Broad Absorption Line Quasars, the peculiar X-ray object in RBS 1032, a study of the Narrow-Line Seyfert 1 Galaxy RX J0136.9-3510, and detection of X-ray emission from galaxies inside the Bootes Void.