Deep X-ray Observations of Normal Galaxies from $z\approx0.1$-1

A. E. Hornschemeier(Penn State), CDF-N Team

[Contributed talk, 15min.]


Extremely deep ($\approx 1$ Ms) Chandra observations are detecting optically ``normal" galaxies in increasing numbers. These ``normal" galaxies are objects which do not show the obvious signatures of actively accreting supermassive black holes, and likely have X-ray emission dominated by X-ray binaries, supernova remnants and diffuse ISM. In some cases these objects also have contribution from a low-luminosity AGN. In even deeper (> 1 Ms) Chandra surveys, these normal galaxies are expected to arise as perhaps the most numerous class of X-ray emitters.

The Chandra Deep Field-North (CDF-N) survey has reached 1 Ms of ACIS coverage of the Hubble Deep Field-North and its environs. This superb X-ray coverage maintains this region of extragalactic sky as the most comprehensively studied at all wavelengths, which also makes it an excellent choice for a comprehensive X-ray study of normal galaxies at higher redshifts (z > 0.1). We are thus now able to place X-ray constraints on galaxy evolution over cosmologically interesting timescales.

Of the 370 X-ray sources detected in the CDF-N area, approximately 70 have the low X-ray to optical flux ratios typical of normal galaxies. The CDF-N team is following up these 70 objects with optical spectroscopy using the Hobby-Eberly and Keck Telescopes. For well-characterized galaxies (those with redshift and morphological information) not individually detected in the X-ray, we find statistical detections using stacking analyses. Both of these approaches and their impact on our understanding of the evolution of galaxies will be discussed.



Himel Ghosh