A multiwavelength study of near- and mid-infrared selected galaxies at
  high redshift: ERGs, AGN-identification and the contribution from dust
  The main focus of this thesis is the IR spectral regime, which since the 70's
and 80's has revolutionised our understanding of the Universe. A
multi-wavelength analysis on Extremely Red Galaxy populations is first
presented in one of the most intensively observed patch of the sky, the Chandra
Deep Field South. By adopting a purely statistical methodology, we consider all
the photometric and spectroscopic information available on large samples of
Extremely Red Objects (EROs, 553 sources), IRAC EROs (IEROs, 259 sources), and
Distant Red Galaxies (DRGs, 289 sources). We derive general properties:
redshift distributions, AGN host fraction, star-formation rate densities, dust
content, morphology, mass functions and mass densities. The results point to
the fact that EROs, IEROs, and DRGs all belong to the same population, yet seen
at different phases of galaxy evolution. The second part of this thesis is
dedicated to the AGN selection in the IR, with particular relevance to the
James Webb Space Telescope, to be launched in 2018. We develop an improved IR
criterion (using K and IRAC bands) as an alternative to existing IR AGN
criteria for the z<2.5 regime, and develop another IR criterion which reliably
selects AGN hosts at 0<z<7 (using K, Spitzer-IRAC, and Spitzer-MIPS24um bands,
KIM). The ability to track AGN activity since the end of reionization holds
great advantages for the study of galaxy evolution. The thesis then focus on
the importance of dust. Based on deep IR data on the Cosmological Survey, we
derive rest-frame 1.6, 3.3, and 6.2um luminosity functions and their dependency
on redshift. We estimate the dust contribution to those wavelengths and show
that the hot dust luminosity density evolves since z=1-2 with a much steeper
drop than the star-formation history of the Universe. Future prospects are
finally discussed in the last chapter.
