Recent Talks

This is the first talk of a series of four aimed to discuss about Cosmology. Here, I will review the basic concepts of the standard cosmological model, which will be further discussed in the following talks, as well as the observational evidence in support of the Lambda-CDM model. As the subject is very broad, I will focus the discussion on topics related with inflation, dark matter and dark energy. Moreover, I will mainly discuss large scale structure probes.

It has been thirty years since the seminal work of Alan Dressler on the density-morphology relation, which established environment as a driving mechanism for galaxy formation and evolution. In the following three decades, we have learned that both the intrinsic processes (nature) and environment (nurture) contribute towards shaping the galaxy populations, and the connection between these two still remains an open question. I will summarize recent results on the interplay between environment and galaxy evolution, obtained from the SDSS DR4 galaxy groups catalogue (Yang et al. 2007) by comparing the properties of central and satellite galaxies as a function of their stellar mass and the dark matter mass of their
host halos.

In this talk I consider two questions. First, I investigate the formation of molecular clouds from diffuse interstellar gas. It has been argued that the midplane pressure controls the fraction of molecular hydrogen present, and thus the star formation rate. Alternatively, I and others have suggested that the gravitational instability of the disk controls both. I present numerical results demonstrating that the observed correlations between midplane pressure, molecular hydrogen fraction, and star formation rate can be explained within the gravitational instability picture. Second, I discuss how ionization affects the formation of massive stars. Although most distinctive observables of massive stars can be traced back to their ionizing radiation, it does not appear to have a strong effect on their actual formation. Rather, I present simulations suggesting that stars only ionize large volumes after their accretion has already been throttled by gravitational fragmentation in the accretion flow. At the same time these models can explain many aspects of the observations of ultracompact H II regions.

The massive black holes found at the centers of most nearby galaxies including our own, are believed to be the ashes of the fuel that powered quasars early in the history of the universe. I will briefly review the astronomical evidence for these objects and then describe some of the exotic dynamical phenomena that originate in their vicinity, including hypervelocity stars, resonant relaxation, and warped and lopsided stellar disks.

At the end of 2008, on ideas of teams from the Observatoire de la Côte d’Azur (OCA) and IAC, the CoRoT satellite observed the star HD 46375, known to host a non-transiting Saturn-mass exoplanet with a 3.023 day period. HD 46375 is the brightest star with a known close-in planet in the CoRoT accessible field of view. As such, it was targeted by the CoRoT additional program and observed in a CCD normally dedicated to the asteroseismology program, to obtain an ultra-precise photometric lightcurve and detect or place upper limits on the brightness of the planet. In addition, a ground-based support was simultaneously performed with the high-resolution NARVAL spectro-polarimeter to constrain the stellar atmospheric and magnetic properties. In this seminar, I will present the main results, in particular the stellar constrain we obtained thanks to the detection of the oscillation mode signature and the plausible detection of the planetary signal, which, if confirmed with future observations, would be the first detection of phase changes in the visible for a non-transiting planet.

The proper characterization of the least massive population of the young Sigma Orionis star cluster is required to understand the form of the cluster mass function and its impact on our comprehension of the substellar formation processes. SOri70 (T5.5±1) and SOri73, two T-type cluster member candidates, would have likely masses between 3 and 7 MJup if their age is 3 Myr. SOri73 awaits confirmation of its methane atmosphere. Here I present the results of a search of T-type objects in an area of ~120 arcmin^2 in the Sigma Orionis cluster, the confirmation of the presence of methane absorption in SOri73 and the study of SOri70 and 73 cluster membership via photometric colors and accurate proper motion analysis. This results would have a dramatic impact in the cluster mass function, in one of the scenarios explored, they suggest a decrease in cluster members with planetary masses in the interval 3.5-6 Mjup.

We present the K band FP of the ETGs members of the clusters observed by the WINGS survey. The data confirm a different tilt of the FP with respect to the V solution and the presence of a substantial tilt in the K band. This led us to further investigate the hypothesis that ETG non-homology greatly contribute to the tilt of the FP.

The WINGS data show that there are now several evidence of both structural and dynamical non-homology for the class of ETGs. Among these we will discuss in detail the tight relation between the mass of the ETGs, their stellar mass-to-light ratio M/L, and the Sersic index n describing the shape of their light profiles. We guess through a series of mock simulations that this relation acts as a fine-tuning that keeps small the scatter around the FP. We therefore conclude that ETG non-homology is closely connected either with the problem of the tilt and with the small scatter around the FP.

ExPo is an imaging polarimeter that has been built in Utrecht University. ExPo works in the visible, and it combines the dual-beam technique, together with very short exposure times and a high polarization sensitivity. After four successful campaigns at the William Herschel Telescope, we have obtained polarization images of circumstellar environments around T Tau's and Herbig Ae's stars, evolved (post-AGB) stars and planets like Venus and Saturn. Our results prove the utility of imaging polarimetry to characterize faint structures around very different objects. In this talk I will go through the instrument details, and I will show some of our science results.

VIMOS is visible multi-object spectrometer operating on the VLT.  The high multiplex of the VLT visible imager and multi object/integral-field spectrometer, VIMOS, makes it a powerful instrument for large-scale spectroscopic surveys of faint sources. Following community input and recommendations by ESO's Science and Technology Committee, it was decided to upgrade the instrument in phases. The first phase of the upgrade is described and included changing the shutters, installing an active flexure compensation system, replacing the detectors with CCDs with a far better red sensitivity and less fringing, and improving the data reduction pipeline.

With imaging at 3.6 and 4.5 microns where the light in nearby galaxies is dominated by old stars, the Spitzer Survey of Nearby Galaxies (S4G) stands poised for an optimal view of stellar mass and structure in the local Universe.  I will describe an effort to construct accurate 2D stellar mass maps from S4G images, starting with a correction for non-stellar (e.g. PAH and hot dust) contaminant emission using only the two S4G images as inputs; contaminant emission is isolated from the old stellar light using an Independent Component Analysis (ICA) technique designed to separate statistically independent source distributions.  An inventory of recovered contaminants is established via comparison to the non-stellar emission in archival 8 micron images.  Once these contaminants are removed, maps of the underlying distribution of old stars are revealed that retain a high degree of structural information and exhibit [3.6]-[4.5] colors consistent with those of K and M giants.  Contaminant-free S4G maps constructed with this approach should be ideally suited for tracing the stellar mass in galaxies spanning a range of morphological properties, dust contents and star formation histories.