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
Sensitive imaging spectroscopy from 0.5-10 keV, with up to 50-250 times (depending upon the energy band considered) the sensitivity of previous X-ray missions.
X-ray source positions with accuracies of 0.3-1" (Chandra) and 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.
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 0.5-8 keV sensitivity with long exposures; the faintest Chandra sources detected have count rates of 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 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 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 z 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 5 × 10-5 of the sky (about nine times the solid angle of the full Moon).
Survey | Max. Eff. | Solid Angle | Representative |
Name | Exp. (ks) | (arcmin2) | Reference or Note |
Chandra | |||
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) |
XMM-Newton | |||
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. (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 448 arcmin2 ( 60% the solid angle of the full Moon), and 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 1556 arcmin2, and 550 sources are detected. Adapted from Hasinger (2004). |