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1.2. Current Deep Surveys with Chandra and XMM-Newton

The superb Wolter telescopes and charge-coupled device (CCD) detectors on Chandra and XMM-Newton provide deep-survey researchers with

  1. Sensitive imaging spectroscopy from approx 0.5-10 keV, with up to 50-250 times (depending upon the energy band considered) the sensitivity of previous X-ray missions.

  2. X-ray source positions with accuracies of approx 0.3-1" (Chandra) and approx 1-3" (XMM-Newton). These high-quality positions are essential for matching to faint multiwavelength counterparts in deep surveys, thereby allowing efficient follow-up studies.

  3. Large source samples (100-600 sources or more, per survey) allowing reliable statistical inferences to be drawn about faint extragalactic X-ray source populations.

The deep-survey capabilities of Chandra and XMM-Newton are complementary in several important respects. Due to its sub-arcsecond imaging which provides a small source detection cell, Chandra can achieve the highest possible approx 0.5-8 keV sensitivity with long exposures; the faintest Chandra sources detected have count rates of approx 1 count every 2-4 days. Even the deepest Chandra observations performed to date do not suffer from significant source confusion (Alexander et al. 2003b), in contrast to the case for XMM-Newton, where confusion becomes significant for gtapprox 100-200 ks exposures. XMM-Newton has a substantially larger photon collecting area than Chandra, allowing efficient X-ray spectroscopy at fluxes above its confusion limit. The field of view for XMM-Newton is also approx 2.5 times that of Chandra.

Table 1 lists the current deep Chandra and XMM-Newton surveys; these 21 surveys have a total exposure exceeding 80 days. The most sensitive surveys performed by Chandra and XMM-Newton, the 2.0 Ms Chandra Deep Field-North (CDF-N) and the 770 ks XMM-Newton Lockman Hole field, are shown in Figure 2. The surveys in Table 1 have generally been performed in regions of sky where (1) the extensive requisite multiwavelength supporting data already exist and/or some interesting astronomical object is present (e.g., Abell 370, 3C 295, or the SSA22 "protocluster"), and (2) there is little Galactic foreground X-ray absorption (e.g., Lockman 2004). At the flux levels probed by these surveys, even moderate-luminosity AGN, similar to Seyfert 1 galaxies in the local universe, can be detected to zgtapprox 4. The surveys in Table 1 span a significant range of solid angle coverage; however, they are all "pencil-beam" surveys in that even the widest cover only approx 5 × 10-5 of the sky (about nine times the solid angle of the full Moon).

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

Survey Max. Eff. Solid Angle Representative
Name Exp. (ks) (arcmin2) Reference or Note


Chandra Deep Field-North 1950 448 Alexander et al. (2003b)
Chandra Deep Field-South 940 391 Giacconi et al. (2002)
HRC Lockman Hole 300 900 PI: S.S. Murray
Extended CDF-S 250 900 PI: W.N. Brandt
Extended Groth Strip 200 1800 Nandra et al. (2005)
Lynx 185 286 Stern et al. (2002a)
LALA Cetus 174 428 Wang et al. (2004b)
LALA Boötes 172 346 Wang et al. (2004a)
SSA13 101 357 Barger et al. (2001a)
Abell 370 94 357 Barger et al. (2001b)
3C 295 92 274 D'Elia et al. (2004)
SSA22 "protocluster" 78 428 Cowie et al. (2002)
ELAIS N1+N2 75 586 Manners et al. (2003)


Lockman Hole 770 1556 Hasinger (2004)
Chandra Deep Field-South 370 802 Streblyanska et al. (2004)
Chandra Deep Field-North 180 752 Miyaji et al. (2003)
13 hr Field 130 665 Page et al. (2003)
Subaru XMM-Newton Deep 100 4104 PI: M.G. Watson
ELAIS S1 100 1620 PI: F. Fiore
Groth-Westphal 81 727 Miyaji et al. (2004)
Marano Field 79 2140 Lamer et al. (2003)
COSMOS 75 7200 PI: G. Hasinger

The solid angles quoted above represent the total sky coverage at bright X-ray flux limits. These surveys have wide ranges of sensitivity across their respective solid angles due to instrumental effects and differing satellite pointing strategies. Furthermore, follow-up studies of detected X-ray sources have only been done for subregions of some of these surveys. Please consult the cited papers for details.

Figure 2

Figure 2. (a) The 2.0 Ms Chandra Deep Field-North, the deepest Chandra observation to date. This image has been constructed from 0.5-2 keV (red), 2-4 keV (green), and 4-8 keV (blue) adaptively smoothed images. The two most prominent red diffuse patches are galaxy groups/clusters (Bauer et al. 2002a). The regions covered by the HDF-N (Ferguson, Dickinson & Williams 2000) and GOODS-N (Giavalisco et al. 2004) surveys with HST are outlined and labeled. This field subtends approx 448 arcmin2 (approx 60% the solid angle of the full Moon), and approx 580 sources are detected. Adapted from Alexander et al. (2003b). (b) The 770 ks XMM-Newton Lockman Hole field, the deepest XMM-Newton observation to date. This image has been constructed from 0.5-2 keV (red), 2-4.5 keV (green), and 4.5-10 keV (blue) images. This field subtends approx 1556 arcmin2, and approx 550 sources are detected. Adapted from Hasinger (2004).

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