arXiv subjects

M. Bolzonella

Publications and source records attributed to M. Bolzonella.

274 records · Page 16Linked to original sources

arXiv2002

The lensing system towards the doubly imaged quasar SBS 1520+530

The gravitational potential responsible for the lensing effect in SBS 1520+530 is studied over length scales from a few arc-seconds to a few arc-minutes. For this purpose, we use sharply deconvolved Hubble Space Telescope images in the optical and near-IR, in combination with ground based optical data obtained over a wider field-of-view. In particular, we have carried out a multi-color analysis in order to identify groups or clusters of galaxies along the line of sight. Photometric redshifts are measured for 139 galaxies unveiling significant excesses of galaxies 1.0 arcmin, NW and 1.7 arcmin, SW of the main lensing galaxy. The photometric redshift inferred both for the main lensing galaxy and for the galaxy concentrations is z=0.9^{+0.10}_{-0.25}. This is in rough agreement with the measured spectroscopic redshift of the main lensing galaxy, z=0.71 (Burud et al. 2002), suggesting that it is part of a larger group or cluster. We investigate the impact of including the galaxy cluster, first on the modelling of the lensing system, and second on the expected time--delay between the two quasar images.

astro-ph↗

arXiv2000

Interpreting the optical data of the Hubble Deep Field South: colors, morphological number counts and photometric redshifts

We present an analysis of the optical data of the Hubble Deep Field South. We derive F300W(AB), F450W(AB), F606W(AB) and F814W(AB) number counts for galaxies in all four bands. The slope is steeper at shortest wavelengths: we estimated gamma(F300W(AB))=0.47, gamma(F450W(AB))=0.35, gamma(F606W(AB))=0.28 and gamma(F814W(AB))=0.28. Morphological number counts are actually dominated by late type galaxies, while early type galaxies show a decreasing slope at faint magnitudes. Combining this information with photometric redshifts, we notice that galaxies contributing with a steep slope to morphological number counts (i.e. spiral and irregular galaxies) have z>1, suggesting a moderate merging. However we emphasize that any cut in apparent magnitude at optical wavelengths results in samples biased against elliptical galaxies, affecting as a consequence the redshift distributions and the implications on the evolution of galaxies along the Hubble sequence.

astro-ph↗

arXiv2000

Photometric Redshifts and Gravitational Telescopes

We review the use of photometric redshifts in the particular context of Gravitational Telescopes. We discuss on the possible application of such a technique to the study of both the faint population of distant sources and the properties of cluster lenses. Photometric reshifts could be used to derive the redshift distribution and properties of a very faint subsample of high-z lensed galaxies, otherwise out of reach. Concerning the mass distribution in lensing clusters, photometric reshifts are strongly needed to scale the mass in weak lensing analysis, and to characterize the lensing structure.

astro-ph↗

arXiv1999

Properties of high-z galaxies as seen through lensing clusters

We discuss the first results obtained on the study of a sample of high-z galaxies (2 < z < 7), using the gravitational amplification effect in the core of lensing clusters. Sources are located close to the critical lines in clusters with well constrained mass distributions, and selected through photometric redshifts, computed on a large wavelength domain, and lens inversion techniques.

astro-ph↗