We measure the luminosity function of QSOs in the redshift range 3.5 < z <
5.2 for the absolute magnitude interval -21 < M_{145} < -28. Suitable criteria
are defined to select faint QSOs in the GOODS ...fields, checking their
effectiveness and completeness in detail. The confirmed sample of faint QSOs is
compared with a brighter one derived from the SDSS. Using a Monte-Carlo
technique we estimate the properties of the luminosity function. Our results
show that models based on pure density evolution show better agreement with
observation than models based on pure luminosity evolution, even if a different
break magnitude with respect to z ~ 2.1 is required at 3.5 < z < 5.2. According
to our modeling a faint-end slope steeper than low-redshift observations is
required to reproduce the data, moreover models with a steep bright-end slope
score a higher probability than models with a bright-end flattening.
Determining the faint-end of the luminosity function at these redshifts
provides important constraints on models of the joint evolution of galaxies and
AGNs.
We investigate the correlation of star formation quenching with internal galaxy properties and large scale environment (halo mass) in empirical data and theoretical models. We make use of the ...halo-based Group Catalog of Yang and collaborators, which is based on the Sloan Digital Sky Survey. Data from the Galaxy Evolution Explorer (GALEX) are also used to extract the recent star formation rate. In order to investigate the environmental effects, we examine the properties of "central" and "satellite" galaxies separately. For central galaxies, we are unable to conclude whether star formation quenching is primarily connected with halo mass or stellar mass, because these two quantities are themselves strongly correlated. For satellite galaxies, a nearly equally strong dependence on halo mass and stellar mass is seen. We make the same comparison for five different semi-analytic models based on three independently developed codes. We find that the models with AGN feedback reproduce reasonably well the dependence of the fraction of central red and passive galaxies on halo mass and stellar mass. However, for satellite galaxies, the same models badly overproduce the fraction of red/passive galaxies and do not reproduce the empirical trends with stellar mass or halo mass. This {\em satellite overquenching problem} is caused by the too-rapid stripping of the satellites' hot gas halos, which leads to rapid strangulation of star formation.
We measure the luminosity function of QSOs in the redshift range 3.5 < z < 5.2 for the absolute magnitude interval -21 < M_{145} < -28. Suitable criteria are defined to select faint QSOs in the GOODS ...fields, checking their effectiveness and completeness in detail. The confirmed sample of faint QSOs is compared with a brighter one derived from the SDSS. Using a Monte-Carlo technique we estimate the properties of the luminosity function. Our results show that models based on pure density evolution show better agreement with observation than models based on pure luminosity evolution, even if a different break magnitude with respect to z ~ 2.1 is required at 3.5 < z < 5.2. According to our modeling a faint-end slope steeper than low-redshift observations is required to reproduce the data, moreover models with a steep bright-end slope score a higher probability than models with a bright-end flattening. Determining the faint-end of the luminosity function at these redshifts provides important constraints on models of the joint evolution of galaxies and AGNs.
