VIRMOS deep survey

People involved: Bardelli, Cappi, Origlia, Pozzetti, Zamorani, Zucca.

The Bologna Astronomical Observatory is part of the Consortium for the ESO-VLT Instruments VIRMOS (Visual Infra-Red Multi-Object Spectrographs).

The visual spectrograph VIMOS³ has been shipped to Chile in December 2001 and has been mounted at VLT-Melipal. It saw its first light successfully on February 26, 2002. Additional commissioning and testing will start at the end of May and VIMOS will soon be offered to the ESO community.

The huge multiplex capabilities of VIMOS will allow to assemble redshifts of large samples of faint galaxies. The Consortium guaranteed time will be used to perform a deep redshift survey of more than $10^5$ galaxies selected from both visual ($B$ and $I$) and infrared ($K$) defined samples. Given the large number of expected redshift measurements [about 100,000 galaxies from the wide survey (16 sq.deg.) and about 50,000 galaxies from the deep survey (1 sq.deg.)] and the expected redshift coverage (up to z $\lower.5ex\hbox{$\; \buildrel > \over \sim \;$}$ 2, with a median redshift in the interval 0.6 - 0.9), this survey will allow to determine with excellent statistics the evolution with redshift of the luminosity functions in different bands for each galaxy type.
Just a few of the crucial issues which will therefore be possible to address from these data are:
$\bullet$ detailed tests of the predictions of various models of galaxy evolution (e.g. hierarchical versus monolithic models);
$\bullet$ precise estimates, on the basis of a single sample with well understood selection criteria, of the star formation history up to at least z $\sim$ 2;
$\bullet$ studies of the still uncertain nature of the extremely red galaxies (EROS), determining which fraction of them is actually associated to old elliptical galaxies at high redshift and which fraction is associated with dusty starburst galaxies.

As a by-product, since no morphological selection will be applied to the objects to be observed, this survey, with its expected $\sim$ 1000 AGNs down to I $\sim$ 24.0, will allow the study of the optical luminosity function and evolution of the faint (e.g. Seyfert-like) AGNs in a magnitude range where the selection of the AGN candidates with the standard color and morphological criteria is very difficult and, possibly, largely incomplete.

The survey, which is expected to start at the end of 2002, has already required a lot of scientific preparation. In particular, during the year 2001 we worked on the following topics:
$\bullet$ We collaborated to the production of the photometric multiband ($BVRI + K$) catalogues which will be the starting point of the spectroscopic survey. In particular we applied various tests to these catalogues in order to verify the quality of the data.
We have also explored the effects due to the detection limits, i.e. surface brightness limit and minimum area, and to the photometric measurements in the optical survey CFDF ($I<24$ and $\mu_I \sim 28$ mag/arcsec$^2$). Most of the objects have surface brightness well above the nominal limit. We have compared the data with the tracks expected for normal galaxies, and we found that surface brightness selection effects are negligible for $L<10 L^*$ galaxies.
$\bullet$ We are working to the development of tools for the scientific analysis of the survey: in particular, we concentrated on the luminosity function analysis, implementing different estimators and testing their statistical robustness on simulated samples with different completeness.
$\bullet$ We compared the results of different cluster finding methods, applying the various algorithms on simulated samples.
$\bullet$ We are working on the preparation of the tools which will be used in the statistical analysis of the galaxy distribution, in particular on the correlation function and high-order statistics; we are presently testing the best methods to correct for incompleteness and observational biases, and the tools for data reduction.
$\bullet$ Moreover we are studying how to discriminate between cosmological models from redshift surveys; we have studied the Alcock-Paczynski geometrical test and the statistics of gravitational lensing, with a focus on ``quintessence" and also more exotic models.