XMM-Newton XMM-LSS  

Index - Consortium - The survey characteristics - Scientific Goals - ...

2. The Survey Characteristics

2.1 - The survey sensitivity

We perform a 8 x 8 deg2 survey at high galactic latitude to reach a sensitivity of ~ 5 10-15 erg.cm-2.s-1 in the [0.5-2] keV band.
The survey consist of 24 x 24 10 ks XMM/EPIC pointings separated by 20 arcmin offsets.

Current pointings.

2.2 - The survey location ** Modified Location Oct 2003; new center: 2h 18m 00s, -7° 00' 00" (J2000)**

New center (J2000):
2h 18m 00s
-7° 00' 00"
XMDS & VVDS deep

VVDS wide

XMM Subaru Deep Survey


NOAO Deep Survey


nh_2.pdf (37144 bytes)

Figure 1: Large white square indicating the location of the XMM-LSS survey is overlaid on a map of NH  (1.4 1020 < NH < 3.5 1020 for the XMM-LSS field). The survey area surrounds two deep XMM surveys based on guaranteed time: the XMM_SSC/Subaru Deep Survey (80 ks exposures in 1 deg2) and the XMM Medium Deep Survey (XMDS; 20 ks exposures in 2 deg2) also corresponding to the VIRMOS-DESCART Deep Survey [deep], the latter being a collaboration between several instrumental teams: XMM-OM (Liège), XMM-EPIC (IASF-MILANO), XMM-SSC (Saclay), CFHTLS (Saclay, IAP) and VIRMOS (LAM, IASF-MILANO, OAB). The area overlap will greatly assist in quantifying the completeness of the survey. Also indicated are the positions of the associated DESCART-VIRMOS Deep Survey [wide], the SWIRE SIRTF Legacy Survey, the Galex survey and the NOAO deep survey; the 8.75 deg2 UKIDSS survey is centered on the Subaru Deep Survey and the CTIO R-z' imaging covers a region corresponding to the VVDS [wide] and [deep] surveys.

(The center of the whole XMM-LSS survey has been shifted by 2 degrees southward from its initial position because of the presence of the variable type M7 star Mira Ceti (02 19 20.8, -02 58 39) which can reach I=1, and cause difficulties with optical mapping.)

2.3 - The expected numbers of objects

2.3.1 - Clusters of galaxies

Figure 2: Predicted redshift distribution for cluster selected in the X-ray with the XMM-LSS (kT > 2 keV and F[0.5-2.0] keV > 10-15 erg/s/cm2)
The X-ray cluster counts are shown both for a LCDM model (with w = -1.0) and for a QCDM model (with w = -0.8). We also show the predicted cluster counts expected for the weak lensing analysis.

Current favoured values have been assumed here for CDM. For this model, the entire cluster/group population will be detected out to z = 0.5 and the total number of clusters will be of the order of 900 between 0 < z < 1. The XMM-LSS will also be ideal to probe the behaviour of the bright end of the XLF beyond z > 1 : a new exciting territory.

Note: these numbers are quite sensitive to the adopted values for the cosmological parameters as well as to the the uncertainties in the M-L-T relationships at high redshifts. By the time the XMM-LSS is completed, better insights will be gained thanks to deep pointed cluster observations. Indeed, physical processes, such as feedback from early star formation and reionization, can modify these relationships and therefore yield detectable changes in the cluster counts and correlation function . Another important issue is the existence of high redshift cooling flows which may affect the detectability of distant clusters and their L-T relationship.

There will be about 50 clusters with useful X-ray spectroscopic information over the entire area (1000 photons collected within R1 in the [0.4-4] keV band). They will be located below z < 0.5.

2.3.2 - AGN and QSO... and stars

For a 10 ks XMM exposure, it will be possible to detect with the PN + MOS instruments (5 detections) point-like sources brighter than typically 3 10-15 erg.cm-2.s-1 in the [0.5-2] keV band. At such low flux, we expect to detect approximately 300 X-ray sources per square degree, among which typically (cf. Lehmann et al. 2001): 15-20 will be clusters of galaxies, about 200 AGNs and QSOs and the remainder stars and nearby galaxies.

Thus, in total, 100 QSO/AGN per deg2 with z < 1. The surface density of QSOs/AGN (~ 200 objects per square degree) in the proposed XMM-LSS survey is almost an order of magnitude larger than those expected in the forthcoming (color biased, z < 2.5, ...) optical surveys carried out over large sky areas (SDSS, 2dF, etc.). Furthermore, compared to optical surveys, the completeness of X-ray selected QSOs/AGN is known to be much better defined.

Index - Consortium - The survey characteristics - Scientific Goals - ...
Web Pages : Alain Detal, Nov 2003.