Clustering at high redshift

The addition of deep near infrared images to the database provided by the HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline and address a number of key issues including the total stellar content of baryonic mass, the effects of dust extinction, the dependence of morphology on the rest frame wavelength, the photometric redshifts, the detection and nature of extremely red objects (EROs). For these reasons deep near infrared images were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the HDF-S has been produced. Photometric redshifts have been generated both fitting templates to the observed SEDs and with neural network techniques. Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the galaxies brighter than I_AB< 27.5 have been used to study the evolution of galaxy clustering in the interval 0<z<4.5.Comment: 2 pages Latex, To appear in the proceedings of "The mass of galaxies at low and high redshift", Venice, Oct 24-26, 2001,eds. R. Bender and A. Renzini (ESO Astrophysics Symposia, Springer-Verlag

Comparing the Evolution of the Galaxy Disk Sizes with CDM Models: The Hubble Deep Field

The intrinsic sizes of the field galaxies with I<26 in the Hubble and ESO-NTT Deep Fields are shown as a function of their redshifts and absolute magnitudes using photometric redshifts derived from the multicolor catalogs and are compared with the CDM predictions. Extending to lower luminosities and to higher z our previous analysis performed on the NTT field alone, we find that the distribution of the galaxy disk sizes at different cosmic epochs is within the range predicted by typical CDM models. However, the observed size distribution of faint (M_B>-19) galaxies is skewed with respect to the CDM predictions and an excess of small-size disks (R_d<2 kpc) is already present at z~ 0.5. The excess persists up to z~3 and involves brighter galaxies . Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physical mechanisms governing the star formation history in CDM models.Comment: 9 pages, 3 figures, ApJ Letters in pres

Studying the Evolution of Multi-Wavelength Emissivities with the Vimos VLT Deep Survey

The VIMOS VLT Deep Survey is a unique I-selected spectroscopic sample to study galaxies all the way from z=5 to z=0. We recapitulate the first results about the evolution of the galaxy populations as a function of type, morphology, environment and luminosity.Comment: 9 pages, 11 figures. To appear in the proceedings of the XLIst Rencontres de Moriond, XXVIth Astrophysics Moriond Meeting: "From dark halos to light", Eds. L.Tresse, S. Maurogordato and J. Tran Thanh Van (Editions Frontieres

The ESO-Sculptor Faint Galaxy Redshift Survey: The Photometric Sample

We present the photometric sample of a faint galaxy survey carried out in the southern hemisphere, using CCDs on the 3.60m and NTT-3.5m telescopes at La Silla (ESO). The survey area is a continuous strip of 0.2 deg x 1.53 deg located at high galactic latitude (-83 deg) in the Sculptor constellation. The photometric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-colour photometric catalog at this depth. This photometric survey also provides the entry catalog for a fully-sampled redshift survey of ~ 700 galaxies with R < 20.5 (Bellanger et al. 1995). In this paper, we describe the photometric observations and the steps used in the data reduction. The analysis of objects and the star-galaxy separation with a neural network are performed using SExtractor, a new photometric software developed by E. Bertin (1996). The photometric accuracy of the resulting catalog is ~ 0.05 mag for R < 22. The differential galaxy number counts in B, V, R are in good agreement with previously published CCD studies and confirm the evidence for significant evolution at faint magnitudes as compared to a standard non evolving model (by factors 3.6, 2.6, 2.1). The galaxy colour distributions B-R, B-V of our sample show a blueing trend of ~ 0.5 mag between 21 < R < 23.5 in contrast to the V-R colour distribution where no significant evolution is observed.Comment: LATEX, 18 Postscript figures, 20 pages. To appear July 1997. Modified version of article. Abstract corrected for missing lin

The Evolution of the Luminosity Function in Deep Fields: A Comparison with CDM Models

The galaxy Luminosity Function (LF) has been estimated in the rest frame B luminosity at 0<z<1.25 and at 1700 {\AA} for 2.5<z<4.5 from deep multicolor surveys in the HDF-N, HDF-S, NTT-DF. The results have been compared with a recent version of galaxy formation models in the framework of hierarchical clustering in a flat Cold Dark Matter Universe with cosmological constant. The results show a general agreement for z<= 1, although the model LF has a steeper average slope at the faint end; at z~3 such feature results in an overprediction of the number of faint (I_{AB}~ 27) galaxies, while the agreement at the bright end becomes critically sensitive to the details of dust absorption at such redshifts. The discrepancies at the faint end show that a refined treatement of the physical processes involving smaller galaxies is to be pursued in the models, in terms of aggregation processes and/or stellar feedback heavily affecting the luminosity of the low luminosity objects. The implications of our results on the evolution of the cosmological star formation rate are discussed.Comment: Revised version; corrected magnitudes at 1700 Angstrom in figure 2; ApJ

Photometry in UV astronomical images of extended sources in crowded field using deblended images in optical visible bands as Bayesian priors

Photometry of astrophysical sources, galaxies and stars, in crowded field images, if an old problem, is still a challenging goal, as new space survey missions are launched, releasing new data with increased sensibility, resolution and field of view. The GALEX mission, observes in two UV bands and produces deep sky images of millions of galaxies or stars mixed together. These UV observations are of lower resolution than same field observed in visible bands, and with a very faint signal, at the level of the photon noise for a substantial fraction of objects. Our purpose is to use the better known optical counterparts as prior information in a Bayesian approach to deduce the UV flux. Photometry of extended sources has been addressed several times using various techniques: background determination via sigma clipping, adaptative-aperture, point-spread-function photometry, isophotal photometry, to lists some. The Bayesian approach of using optical priors for solving the UV photometry has already been applied by our team in a previous work. Here we describe the improvement of using the extended shape inferred by deblending the high resolution optical images and not only the position of the optical sources. The resulting photometric accuracy has been tested with simulation of crowded UV fields added on top of real UV images. Finally, this helps to converge to smaller and flat residual and increase the faint source detection threshold. It thus gives the opportunity to work on 2nd order effects, like improving the knowledge of the background or point-spread function by iterating on them