Found 93 talks archived in Cosmology

Luminous high-redshift radio galaxies (HzRGs) are associated with the most massive known galaxies in the early Universe. These galaxies have the properties expected of the progenitors of dominant galaxies in rich clusters.
I shall describe the properties of HzRGs and demonstrate how they can be used to study the formation and evolution of galaxies and clusters. I shall also show how LOFAR, the new European radio telescope, can be used to extend these probes into the epoch of reionisation.

In this work we have tried to verify what types of bulges are the descendants and the precursors of the bulges with blue colors observed at intermediate z. These may be the result of intense star formation in the central regions of the disks, related to the phenomenon of pseudo-bulges in the local universe or, alternatively, they may result from rejuvenation processes of old and red classical bulges, formed at high z, perhaps through secular evolution produced by internal or external agents. We can identify and distinguish between these processes analyzing the central surface brightness of the galaxies, μ₀. For the general bulge population in the local universe, color is strongly correlated with surface density, in the sense that redder bulges are denser. Classical bulges and pseudo-bulges occupy different regions in a color-μ₀ diagram. We have studied the redshift evolution of the relation between the colors and the central surface brightness for samples of spiral galaxy bulges selected from HST/ACS GOODS-N survey, and have analysed the ability of color-μ₀ diagram to segregate different types of bulges at z ~ 1. The results show that, up to z ~ 0.8, galaxy nuclear and global colors are strongly correlated with the central surface brightness and, therefore, with the central surface density, in the sense that denser bulges are redder. This suggests that these formed the bulk of their stars at earlier epochs than less dense bulges. For z > 0.8, we find an important fraction of galaxies with high central surface brightness and nuclear colors much bluer than the rest of the galaxy, which probably corresponds to episodes of strong nuclear star formation that may result in the growth of the bulges inside the disks. From simple evolution models we can infer that these nuclei with star formation evolve towards the formation/growth of moderate central surface brightness, intermediate color z ~ 0 pseudobulges rather than classical bulges. These models also argue against rejuvenation processes for z ~ 1 dense and old bulges.

I will review the status of our understanding of galaxy formation in the prevailing cold dark matter paradigm. After reviewing the successes and failures of the most natural predictions of this scenario I will focus on the consequences of two of its main predictions: the presence of large numbers of low-mass dark matter halos and the prevalence of accretion events during the formation of normal galaxies. In particular, I will discuss the interpretation of the recent discovery of a population of ultra-faint galaxies in the Local Group, and its relation to the profuse cold dark matter substructure expected in the Galactic halo. I will also discuss the importance that accretion events might have had in shaping not only the stellar halo but also the disk component(s) of the Milky Way.