To learn about AGN physics and evolution in a complete manner, both "deep" and "wider" X-ray surveys are required; the trade-off between the two, of course, is between sensitivity and solid-angle coverage on the sky. None of the Chandra and XMM-Newton surveys discussed in this paper is truly wide-field, in that the widest still only cover 1% of the sky. (4) Both deep and wider X-ray surveys are reviewed briefly below.
2.1. Deep X-ray Surveys
Table 1 makes it clear that deep Chandra and XMM-Newton surveys are a major "industry". The 21 surveys listed there have a total exposure exceeding 70 days, and 50 scientists have invested substantial effort on the analysis and interpretation of these data. Comparable effort has also been expended on multiwavelength follow-up studies of these surveys; due to the small solid angles under investigation, superb multiwavelength coverage can be obtained relatively economically.
|Survey Name||Exposure||Representative Reference or Note|
|Chandra Deep Field-North||1950 ks||D.M. Alexander et al., 2003, AJ, 126, 539|
|Chandra Deep Field-South||940 ks||R. Giacconi et al., 2002, ApJS, 139, 369|
|HRC Lockman Hole||300 ks||PI: Murray|
|Extended CDF-S||250 ks||PI: Brandt|
|Groth-Westphal||200 ks||PI: Nandra|
|Lynx||185 ks||D. Stern et al., 2002, AJ, 123, 2223|
|LALA Cetus||177 ks||PI: Malhotra|
|LALA Boötes||172 ks||J.X. Wang et al., 2004, AJ, 127, 213|
|SSA13||101 ks||A.J. Barger et al., 2001, AJ, 121, 662|
|3C295||100 ks||V. D'Elia et al., 2004, astro-ph/0403401|
|Abell 370||94 ks||A.J. Barger et al., 2001, AJ, 122, 2177|
|SSA22 "protocluster"||78 ks||L.L. Cowie et al., 2002, ApJ, 566, L5|
|ELAIS||75 ks||J.C. Manners et al., 2003, MNRAS, 343, 293|
|WHDF||75 ks||PI: Shanks|
|Lockman Hole||766 ks||G. Hasinger et al., 2001, A&A, 365, L45|
|Chandra Deep Field-South||317 ks||A. Streblyanska et al., 2004, astro-ph/0309089|
|13 hr Field||200 ks||M.J. Page et al., 2003, AN, 324, 101|
|Chandra Deep Field-North||180 ks||T. Miyaji et al., 2003, AN, 324, 24|
|Subaru Deep||100 ks||PI: Watson|
|ELAIS S1||100 ks||PI: Fiore|
|Groth-Westphal||80 ks||T. Miyaji et al., 2004, astro-ph/0402617|
The Extended Chandra Deep Field-South is comprised of four fields (each 250 ks), the XMM-Newton ELAIS S1 survey is comprised of four fields (each 100 ks), and the Chandra ELAIS survey is comprised of two fields (each 75 ks). The XMM-Newton Subaru Deep survey also has seven flanking fields (each 50 ks). Only the first 100 ks of the XMM-Newton Lockman Hole data have been published at present.
The two most sensitive surveys in Table 1, by a significant factor, are the 2 Ms Chandra Deep Field-North (CDF-N; see Figure 1) and 1 Ms Chandra Deep Field-South (CDF-S). Both are situated in intensively studied regions of sky with little Galactic foreground X-ray absorption. They reach 0.5-2 keV fluxes of (2.5-5) × 10-17 erg cm-2 s-1, corresponding to count rates of 1 count every 2-4 days. At these flux levels, even moderate-luminosity AGN (similar to Seyfert galaxies in the local universe) can be detected to z 10. The CDF-N and CDF-S are clearly "pencil-beam" surveys, each covering 400 arcmin2; for reference, this is ~ 1/2 the solid angle of the full Moon and ~ 75 times the solid angle of the original Hubble Deep Field-North (HDF-N; see Figure 1). Public X-ray source catalogs are available for both the CDF-N and CDF-S (see the references in Table 1); these contain 580 and 370 sources, respectively.
Figure 1. Adaptively smoothed image of the 2 Ms CDF-N, constructed from data in the 0.5-2 keV (red), 2-4 keV (green), and 4-8 keV (blue) bands. Nearly 600 sources are detected in the 448 arcmin2 field. The regions covered by the HDF-N and GOODS-N surveys are denoted. Adapted from D.M. Alexander, F.E. Bauer, W.N. Brandt, et al., 2003, AJ, 126, 539.
The other deep X-ray surveys in Table 1 have generally been performed in regions of sky where (1) extensive coverage already exists at one-to-several wavelengths, and/or (2) some interesting astronomical object is present (e.g., 3C295, Abell 370, or the SSA22 "protocluster"). They are all sensitive enough to detect moderate-luminosity AGN to z ~ 3-5, and in total the surveys in Table 1 cover a solid angle of ~ 3.5 deg2 (~ 16 Moons).
4 For this reason, we denote these surveys as "wider" (relative to the deep Chandra and XMM-Newton surveys) rather than "wide-field." Back.