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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 ltapprox 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 gtapprox 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.

Table 1. Some Deep X-ray Surveys with Chandra and XMM-Newton

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 approx 50 ks). Only the first approx 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 approx (2.5-5) × 10-17 erg cm-2 s-1, corresponding to count rates of ltapprox 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 gtapprox 10. The CDF-N and CDF-S are clearly "pencil-beam" surveys, each covering approx 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 approx 580 and approx 370 sources, respectively.

Figure 1

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 approx 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.

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