2.2. Wider X-ray Surveys
Wider Chandra and XMM-Newton surveys (see Table 2) are a comparably large and important "industry" to the deep surveys. These typically involve investigation of X-ray sources in ~ 4-150 X-ray observations of moderate exposure (usually 20-60 ks, but sometimes as short as 5 ks); the observations are sometimes obtained from the public data archives. The wider surveys serve to bridge the observational "gap" between the deepest Chandra observations and the deepest observations made by previous X-ray missions (e.g., ROSAT; see Figure 2), and they effectively target the intermediate 0.5-8 keV flux levels (10-15 - 10-13 erg cm-2 s-1) which contribute most significantly to the XRB.
|Survey Name||(deg2)||Representative Reference or Note|
|ChaMP||14||D.W. Kim et al., 2004, ApJS, 150, 19|
|Clusters Serendipitous||1.1||P. Gandhi et al., 2004, MNRAS, 348, 529|
|CYDER||...||F.J. Castander et al., 2003, AN, 324, 40|
|Lockman Hole NW||0.4||A.T. Steffen et al., 2003, ApJ, 596, L23|
|MUSYC||1||PI: van Dokkum|
|NOAO DWFS||9.3||PI: Jones|
|SEXSI||2.2||F.A. Harrison et al., 2003, ApJ, 596, 944|
|SWIRE Lockman||0.6||PI: Wilkes|
|1 hr Field||0.2||PI: McHardy|
|13 hr Field||0.2||I.M. McHardy et al., 2003, MNRAS, 342, 802|
|AXIS||...||X. Barcons et al., 2002, A&A, 382, 522|
|CFRS||0.6||T.J. Waskett et al., 2003, MNRAS, 341, 1217|
|HELLAS2XMM||2.9||A. Baldi et al., 2002, ApJ, 564, 190|
|LSS||64||M. Pierre et al., 2004, astro-ph/0305191|
|Survey Science Center||...||M.G. Watson et al., 2001, A&A, 365, L51|
|2dF||1.5||A. Georgakakis et al., 2003, MNRAS, 344, 161|
The second column above lists estimated survey solid angles; survey sensitivities are not uniform but rather vary significantly across these solid angles. In some cases, survey solid angles are not well defined and thus are not listed. In these cases, the reader should consult the listed reference or note for further details.
The wider X-ray surveys provide a broad census of the X-ray source population, often generating enormous numbers of sources (1000-6000 or more; e.g., see Figure 2). They thereby allow discovery of both intrinsically rare source types as well as low-redshift examples of sources found in the deep X-ray surveys. However, complete multiwavelength follow-up often must be compromised for reasons of observational economy; thus many of the wider surveys target specific source types of interest. Often targeted are sources with unusually hard X-ray spectra, sources with unusually large X-ray-to-optical flux ratios, or sources that appear likely to be at high redshift based upon optical imaging data.
Figure 2. Number of sources predicted from the ChaMP survey (for 137 ChaMP fields from Chandra Cycle 1 and Cycle 2) compared to numbers of sources from the Chandra Deep Fields and the ROSAT surveys analyzed by T. Miyaji, G. Hasinger, & M. Schmidt, 2000, A&A, 353, 25. An impressive 6000 ChaMP sources are expected in total, and these largely lie at intermediate 0.5-2 keV flux levels of (4-60) × 10-16 erg cm-2 s-1. From D.W. Kim, R.A. Cameron, J.J. Drake, et al., 2004, ApJS, 150, 19.