Orateur
Dr
Edmond Giraud
(LPTA Universite Montpellier 2 CNRS/IN2P3)
Description
We study spectral evolution of galaxies in a magnitude limited sample in a pencil beam of ~10' x 10' from z = 1 down to 0.3. We concentrate on the large structures along the line of sight, and we bin our individual
galaxy spectra to obtain representative high S/N spectra of each structure. We divide the resulting average spectra in three groups to facilitate the analysis: galaxies with pure absorption line spectra, galaxies with emission lines and blue continua, and galaxies with emission lines and red continua. We restrict the analysis to the range
0.3 < z < 1.0, for which the statistical properties of the sample are well understood down to R=23.
We estimate the downsizing in emission-line galaxies between z = 0.9 and z = 0.45 in our pencil-beam and find the following results: (1) strong star formation in emission line galaxies, (2) aging in emission line galaxies,
(3) aging in absorption systems, are shifting from bright to faint systems as cosmological time increases. Each redshift bin is repopulated in new starbursts.
Therefore at redshifts z <1 galaxy formation is downsizing both in luminosity and number density. Cold
Dark Matter (CDM) models are hierarchical in the sense that large halos are built from the merging of small
halos. Our observations indicate that at z < 1 star formation and halo assemblage are no more in phase.
Author
Dr
Edmond Giraud
(LPTA Universite Montpellier 2 CNRS/IN2P3)
Co-auteurs
Fernando Selman
(ESO Santiago, Chile)
Hernan Quintana
(P. Universidad Pontifica Santiago, Chile)
Jorge Melnick
(ESO Santiago, Chile)
Qiusheng Gu
(Nanjing University, P. R. China)
