XMM-Newton XMM-LSS  

Index - ... - Simulations (3/3) - The Optical Follow-up - The Radio Follow-up - ...

5. The Optical Follow-up

5.1 - Imaging

The 8 x 8 deg2 area will be imaged both by MegaCam at CFHT as part of the Canada-France-Hawaii Legacy Survey. Observations will be done in the u, g' ,r' ,i' ,z' bands at a depth of i' ~25.5 with the aim of performing extensive weak lensing analysis, thus ensuring deep high quality images. Observations of the XMM-LSS, as priority target, will start by mid-2002; before then, we use the CFH12K/CFHT. Data pipelines and processing have been developed by the TERAPIX consortium which provides object catalogues and astrometric positions for the entire surveyed region.

Special care will be devoted to the obtention in a large set of bands, in order to derive photometric reshifts.
Typical 5 3" AB limiting magnitudes will be:

exposure time
u*25.56000 s
g'25.62500 s
r'25.72000 s
i'25.54300 s
z'24.07200 s

The proposed i' magnitude limit will enable us to measure galaxy moments down to this limiting magnitude and achieve the number density of 50 galaxies/sq.arcmin. needed for measuring a weak lensing signal from a massive cosmic filament located at z ~ 0.5.

5.2 - The spectroscopic follow-up

5.2.1 - Main Strategy

The number of clusters of galaxies candidates present in the XMM-LSS catalogue will be a challenge for a complete spectroscopic follow-up to be carried out in a reasonable amount of time. Moreover, we expect that only a small fraction of the cluster will have a known redshifts from the literature. From the expected redshift distribution (Fig. 2) estimated for the X-ray flux limit of about 5 x 10-15 ergs.s-1.cm-2 (0.5-2 keV) reached in 10 ks exposure time, we will have about 900 candidates within the covered area of 64 deg2 within 0 < z < 1, with about half of them below z < 0.7 .
To fulfill our LSS goals, we need to measure redshifts for all z < 1 clusters. This will be done in Multi-Object-Spectroscopy mode, using NTT/EMI and VLT/VIMOS. We plan to take 1 mask per cluster, randomly sampling the AGN population at the same time, the underlying filamentary galaxy distribution connecting clusters, radio sources from our VLA survey as well as, possibly, a representative sample of the SWIRE sources. This mapping around the 0 < z < 1 clusters will have an enormous scientific potential for studies of galaxy environments and bias. We shall subsequently undertake programmes of advanced spectroscopy (TNG, Las Campanas, CFHT, AAT, WHT, 2xGemini, Magellan, LBT, VLT) that will focus on individual objects, and include high resolution spectroscopy, the measurement of cluster velocity dispersions, QSO absorption line surveys, as well as NIR spectroscopy of our z > 1 cluster candidates.

We will plan the observational schedule using two telescope classes: the 4 meter class for the lower redshift bin (0 < z < 0.5) and the 8 meter class for the higher redshift bin (0.5 < z). In both cases we compute a mean progress rate of 5-7 clusters per night, all observed spectroscopically in multi-object mode (MOS).

5.2.2 - Manpower

We can give here a rough estimate of the manpower needed for the spectroscopic follow-up. The two Co-Is involved at the OABr will be in charge of the sub-project management, observing and data reduction procedure definitions, as well as careful book- and schedule- keeping and data archive. On the basis of the table reported below, we estimate that a dozen observing runs are foreseen each year. Observing and data reduction tasks will need a team of 6 people with at least 50% of working time allocated to the project: such a number of PhD/post-doc positions should be raised by the participating Institutes.

Index - ... - Simulations (3/3) - The Optical Follow-up - The Radio Follow-up - ...
Web Pages : Alain Detal, Oct 2001.