Galaxy evolution with large-scale galaxy redshift surveys

Resum

The currently favored LCDM model of cosmology describes an accelerated expanding universe containing 70% of dark energy, 25% of collisionless cold dark matter and only 5% of ordinary baryonic matter. Within this framework, the formation of large-scale structure by the hierarchical merging of dark matter halos is relatively well understood. Unfortunately, the complex physics involved in the cooling, in-fall and condensation of baryons and the formation of stars within the potential wells of dark matter halos is still severely under-constrained. Only recently, with the advent of large-scale galaxy redshift surveys and with the help of N-body numerical simulations, have we commenced to identify some of the processes that drive the evolution of galaxies and their interaction with the environment, from an entangled web of observed correlations between galaxy properties. In the last years, the formation and evolution of galaxies has become one of the most active and rapidly expanding fields in Astrophysics. During my PhD, I had the opportunity to approach the galaxy formation and evolution picture from different but complementary angles. In this sense, my thesis work was motivated by the challenge of providing more accurate observational constraints to current theories. For the sake of clarity, I have divided this dissertation, which is a compendium of different but related projects, into three parts. In the first part, I present and discuss in detail the luminosity function of galaxies in the nearby universe, which I have measured with unprecedented accuracy in the SDSS. The second part is devoted to galaxy evolution from z~1. In particular, in this part I analyze some fundamental statistical properties of the low-redshift galaxy population and describe a method for obtaining stellar masses in the ALHAMBRA photometric survey. In addition, I provide a measurement of the the AGN - density relation at z~1 in the DEEP2 GRS, and discuss its evolution down to z~0 using the SDSS. Finally, constraining galaxy formation and evolution theories in the near future requires the development of new survey spectrographs and the optimization of galaxy survey techniques. In the last part of this dissertation, I contribute to this goal by discussing survey optimizations for next-generation fiber-fed spectrographs such as the SIDE instrument, which was proposed for the 10-meter Gran Telescopio Canarias, or BigBOSS, for the 4-meter Mayall Telescope. At low redshift, the characterization of the galaxy population has benefitted extensively from the development of large-scale galaxy redshift surveys. In particular, the SDSS provides photometric and spectroscopic information for ~ 1 million galaxies, allowing for a detailed study of the main statistical properties of the galaxy population. The luminosity function of galaxies is one of the most fundamental of these properties. In this dissertation, I take advantage of the huge increase in galaxy statistics provided by the Sixth Data Release of the SDSS to present the most accurate estimation of the low-redshift luminosity function of galaxies to date. Interestingly, I find several remarkable deviations as compared to the previous SDSS work of Blanton et al. (2003). Namely, I obtain steeper faint end slopes in all bands (alpha = -1.26 in the 0.1r band) and a remarkable bright-end excess with respect to the Schechter fit in the bluer bands (of ~1.7 dex at 0.1Mu~20.5). Such an excess, that I call bright-end bump, seems to be associated with AGN and star-forming galaxies. A preliminary comparison with semi-analytic models of galaxy formation and evolution is also provided. This comparison has been performed in collaboration with Carlton Baugh and his team at the ICC and Durham University. During the last years, I have been involved in the Advance Large Homogeneous-Area Medium-Band Redshift Astronomical Survey, which is lead by the Instituto de Astrofísica de Andalucía. ALHAMBRA is a photometric survey specifically designed for the study of galaxy evolution, that uses 20 narrow-band filters covering the entire optical range plus the near-infrared JHK bands, and reaches down to magnitude I(AB)~25. In this dissertation, I provide a preliminary low-redshift analysis that will facilitate the scientific exploitation of the survey. The main statistical properties of the low-z ALHAMBRA galaxy population, including galaxy number counts, color and magnitude distributions and luminosity functions have been obtained and compared with other surveys, especially with the SDSS. In addition, I have carried out a stellar population synthesis analysis, using the Flexible Stellar Population Synthesis code, which has allowed me to compute photometric stellar masses in ALHAMBRA. Our results on the main statistical properties of the ALHAMBRA low- redshift galaxy population are in good agreement with other surveys and confirm its potential to shed light into the evolution of galaxies. At high redshift, providing observational constraints to galaxy formation and evolution models is remarkably hindered by telescope time requirements and strong selection effects. In these models, both active galactic nuclei (AGN) and environment are assumed to play key roles. Nuclear activity could be responsible for the suppression of cooling flows in massive galaxies and the consequent quenching of star formation. The influence of environment on galaxies is supported by undisputed observational evidence (i.e. color-density relation, morphology-density relation). I have measured the dependence of the AGN fraction on local environment at z~1, using spectroscopic data taken from the DEEP2 Galaxy Redshift Survey, and Chandra X-ray data from the All-Wavelength Extended Groth Strip International Survey (AEGIS). I provide evidence that high redshift LINERs in DEEP2 tend to favour higher density environments relative to the red population from which they were drawn. In contrast, Seyferts and X-ray selected AGN at z~1 show little (or no) environmental dependencies within the same underlying population. I compare these results with a sample of local AGN drawn from the SDSS. Contrary to the high redshift behaviour, I find that both LINERs and Seyferts in the SDSS show a slowly declining red sequence AGN fraction towards high density environments. Interestingly, at z~1 red sequence Seyferts and LINERs are approximately equally abundant. By z~0, however, the red Seyfert population has declined relative to the LINER population by over a factor of ~4.5. This work was created during a research visit at the University of California at Berkeley, in collaboration with Marc Davis, Darren Croton and the rest of the DEEP2 team. Progress in the galaxy formation and evolution field in the next decades will depend upon our capacity to collect deeper, larger and less biased galaxy samples. High-redshift spectroscopic surveys are needed to disentangle correlations between galaxy properties and link different galaxy populations at different redshifts. In the last part of this dissertation, I discuss survey optimizations for next-generation wide-field fiber-fed spectrographs. In particular, I present an optimized algorithm for assigning fibers to targets that ensures that the maximum number of targets in a given target field is observed in the first few tiles (spectrograph exposures). Using randomly distributed targets and mock galaxy catalogs, I have estimated that the gain provided by our algorithm as compared to a random assignment can be as much as 2% for the first tiles. This would imply for a next-generation survey like BigBOSS saving for observation several hundred thousand objects or, alternatively, reducing the covered area in ~ 350 sq deg. Additional optimizations of the fiber positioning process are also discussed. In particular, I show that allowing for rotation of the focal plane can improve the efficiency of the process in ~ 3.5 - 4.5 \% even if only small adjustments are permitted (up to 2 deg). For instruments that allow large rotations of the focal plane the expected gain increases to ~ 5 - 6 %. These results, therefore, strongly support focal plane rotation in future spectrographs, as far as the efficiency of the fiber positioning process is concerned. This work was primarily conceived for the Super Ifu Deployable Experiment (SIDE), a fiber-fed multi-object spectrograph proposed for the GTC.