Recent Talks

Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive stellar deaths, usually associated with supernovae (Woosley et al. 2006). They release ultra-relativistic jets producing non-thermal emission through synchrotron radiation as they interact with the surrounding medium (Zhang et al. 2004). Here we report observations of the peculiar GRB 101225A (the "Christmas burst"). Its gamma-ray emission was exceptionally long and followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody after which an additional component, consistent with a faint supernova, emerged. We determine its distance to 1.6 Gpc by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a helium star-neutron star merger that underwent a common envelope phase expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which gets thermalized by interacting with the dense, previously ejected material and thus creating the observed black-body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy (Campana et al. 2011).

The origin of galaxy morphology has to be seen in the context of the hierarchical build up of structure and baryons expected in a CDM Universe. Star formation and structural properties of galaxies are well known to relate to their environment and stellar mass. We quantify the relation between galaxy morphology and both stellar and halo mass. In this talk, we present our sample, and the remarkably different morphological trends for the most massive ("central") and other ("satellite") galaxies in groups. We then interpret these trends both empirically and in the context of purpose-built recipes applied to two independent semi-analytic galaxies of galaxy formation, which account for the full merger history of galaxies.

I revisit the claim of Dark Energy detection after stacking CMB data on the angular position of voids and superclusters in Sloan Data. I examine the theoretically expected amplitude for the ISW-induced signal and explore its scale dependence. I next confront these predictions with results obtained from real WMAP data, and evaluate the degree of agreement and the possible presence of contaminants. In a more general context, I address the possibility of unveiling the signature of Dark Energy on the CMB by looking at isolated regions on the sky hosting high-threshold projected under/over-densities: this constitutes a novel approach since it is less sensitive to large angle systematics commonly present in large scale structure surveys.

To understand the formation and evolution of galaxies, it is important to have a full comprehension of the role played by Metallicity, Star Formation Rate (SFR), and stellar mass of galaxies. The interplay of these parameters at different redshifts will substantially affect the evolution of galaxies and, as a consequence, the evolution of these parameters provides important constraints for the galaxy evolution models. We studied the relationships and dependencies between the SFR, stellar mass, and gas metallicity of star forming galaxies from the Sloan Digital Sky Survey-Data Release 7 (SDSS DR7) and Galaxy and Mass Assembly (GAMA) surveys. We have combined both surveys finding evidence of SFR and metallicity evolution for galaxies down to redshift ~0.2. Also, we have proved the existence of a Fundamental Plane in the 3D space formed by the SFR, mass and metallicity for the SDSS and GAMA samples.