Results from the Serendipitous Extragalactic X-ray Source Identification (SEXSI) Program

F. A. Harrison(Caltech) D. J. Helfand (Columbia University) P. H. Mao (Caltech) D. Stern (JPL) J. Chakan (Caltech) S. G. Djorgovski (Caltech) E. Laird (Columbia University)


The raison d'etre for the Chandra Observatory when it was proposed 25 years ago was to resolve the X-ray background. It is not clear whether this goal will literally be achieved by Chandra, but it is already apparent from the first moderately deep pointings that new contributing populations are being discovered. To date, extensive optical followup has been concentrated in a few of the deepest fields. It is now clear that the limited survey area covered by these deep exposures is insufficient to answer many interesting questions related to the evolution of high energy source populations.

The SEXSI survey is extending deep optical and infrared followup of hard X-ray (2 - 10 keV) selected sources in a sky area increased more than an order of magnitude compared to the Chandra deep fields. We have accumulated over two dozen extragalacted Chandra fields with X-ray exposures ranging from 50 - 200 ksec. These contain more than 700 hard-band-selected sources in an area of $\sim 1.25$deg2. We have completed deep imaging on most of these fields using the Palomar 60 $\prime\prime$ and 200 $\prime\prime$ and the MDM 2.4 m telescopes, and spectroscopy on more than 150 sources using Keck/LRIS. In this paper we present results from the survey to-date, including the optical properties, classification, and redshift distribution of more than 100 extragalactic spanning a wide range of X-ray luminosities.



Himel Ghosh