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 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. (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).