Recent Talks

Current scientific cosmology hosts a plurality of scenarios that articulate in different ways the precision astronomy's observations. However, this palette of alternatives is not taken as the true scientific production. There is a monist tendency to think that scientific results should be represented by a single scenario. The present work seeks to undermine the attempts to justify that tendency and to show that even if a single and final stage is waiting, methodological pluralism also would be the best option to achieve it.

Our Universe is filled with a mind-blowing diversity and different types and appearances of galaxies. Finding out about how they formed and evolved is one of the most challenging tasks in astronomy. When looking about 10 billion years back, to an epoch about 3 billion years after the big bang, we can see galaxies at earlier stages of their lives. In this talk, studies of different kinds of galaxies in the early universe will be presented. Two examples of the very intriguing population of massive quiescent z~2 galaxies were analyzed in terms of their stellar populations and morphologies. As the spectroscopic sample is still small, especially for galaxies at the faint end of the luminosity function, we make use of the biggest available "telescopes" in the universe: We search for red z~2 galaxies whose apparent brightnesses have been boosted by the Gravitational Lensing effect of intermediate redshift galaxy clusters with available mass models. Our findings indicate older ages for these galaxies than expected. Also, their remarkable compactness was corroborated. Furthermore, I'm going to present a study of a special case of so-called Damped Lyman-alpha Absorbers (DLAs), with two intervening galaxies in the line of sight of a higher-redshift QSO, which is also one example of only about a dozen known galaxy counterparts of a DLA. It fits into the emerging paradigm that galaxies which are responsible for higher metallicity DLAs are more massive and luminous than typical DLA galaxies. Motivated by that particular discovery, during the past few years we have undertaken a survey targeting candidate dust-reddened quasars missing in the sample from Sloan Digital Sky Survey. Spectroscopic follow-up with the NOT and the NTT has demonstrated a very high success rate of our selection (>90%). The main motivation is to search for quasars reddened by foreground dusty galaxies and we have found several such examples. We have also serendipitously found quasars with abnormal, very UV-steep extinction curves as well as a large number of broad absorption line quasars (BALs). The latter allow us to study the dependence of the BAL QSO population on redshift, reddening and luminosity. The results show a strong evolution of the BAL QSO fraction with cosmic time, with a peak at z~2.5 where several quantities in the Universe are also found to peak or vary. In addition,the dependence of this fraction with reddening and luminosity provides new constraints on the models for broad absorption origin in quasars. We are currently carrying out a pilot study of a search for even redder quasars selected from a combination of SDSS, UKIDSS and WISE photometry with the aim of selecting very dust-obscurred quasars or high-redshift BALs at z>2. Preliminary results from the first run et the NOT in March 2015 of the brightest candidates show very promising results which will also be briefly shown in the talk.

Recent works show that the restframe colours of X-ray selected AGN host galaxies at z~1 are no different from those of inactive galaxies once stellar mass selection effects are taken into account. However, there is a clear deficit of AGN among quiescent galaxies, and the average star formation rates of AGN hosts are comparable or higher than those of inactive star-forming galaxies. These apparently contradictory findings could be a consequence of higher extinction in star-forming AGN hosts compensating for their younger stellar populations in observed colours. In this talk I will present a new method of extinction correction that breaks the degeneracy with stellar age and metallicity by comparing the restframe U-V colour with measurements of the Dn(4000) index on intermediate band photospectra from SHARDS. I'll show that the distribution of extinction corrected U-V colours and Dn(4000) for AGN hosts at z<1 is significantly different from that of comparison samples of inactive galaxies, with a clear deficit of AGN in intrinsic red galaxies and a higher prevalence among those with intermediate age stellar populations.

The ``dark flow'' dipole is a statistically significant dipole found at the position of galaxy clusters in filtered maps of Cosmic Microwave Background (CMB) temperature anisotropies. The dipole measured in WMAP 3, 5 and 7 yr data releases was roughly aligned with the all-sky CMB dipole and correlated with cluster X-ray luminosity. We analyzed the final WMAP 9 yr and the first Planck data releases using a catalog of 980 clusters outside the Kp0 mask to test our earlier findings. The dipoles measured on these new data sets are fully compatible with our earlier estimates, being similar in amplitude and direction to our previous results and in disagreement with the results of an earlier study by the Planck Collaboration. Further, in Planck data dipoles are independent of frequency, ruling out the Thermal Sunyaev-Zeldovich as the source of the effect. The signal is dominated by the most massive clusters, with a statistical significance better than 99%, slightly larger than in WMAP. Since both data sets differ in foreground contributions, instrumental noise and other systematics, the agreement between WMAP and Planck dipoles argues against them being due to systematic effects in either of the experiments.

Direct imaging of wide planetary mass companions provide a unique opportunity to fully characterize their spectroscopic and photometric properties. They share similar physical properties to gas giant exoplanets found by radial velocity and transit techniques, with overlapping temperatures in the range of ~1000–1500K and masses from a few to a dozen Jupiter masses. We have recently identified a young L-type companion at ~100 AU of a previously unrecognized M dwarf. We determined the parallactic distance of the system of 12.7 ± 1.0 pc. By comparison with evolutionary models we derived a mass of 73 (+20, -15) MJup for the primary, at around the substellar mass limit and 11.2 (+9.7, -1.8) MJup for the secondary, near the deuterium burning mass limit. In this talk I will present the properties of the two components of this new pair and discuss the possibilities for future thorough characterization.

Divulgation Lecture to Celebrate the International Year of Light and 150th Anniversary of Maxwell´s great paper on Electromagnetism of 1865.

Evidence is mounting for the presence of complex low surface brightness structures in the outer regions of galaxies. While the most spectacular examples are provided by systems hosting coherent debris streams, the most common examples may be extremely diffuse stellar envelopes. Wide-field imagers on large telescopes are allowing us to quantitatively explore the resolved stellar populations in these components within and well beyond the Local Group. I will highlight some recent  results from our work and discuss the insight these outer structures provide on understanding massive  galaxy assembly.  I will also discuss how we are using deep HST studies of M31's outer regions to probe its evolutionary history in unprecedented detail.

( * Please bring your laptop or your smartphone with you * )

Astronomers are not only skilled computer users, but also experienced Internet users. Their work could benefit from latest improvement in the world of the web. In particular, new client-side, server-side, and database technologies can be used to set up:

1) extremely performing data mining applications;

2) multi-thread CPU/GPU simulation or reduction software;

3) efficient ways to communicate results or to exchange data;

4) modern web-based tools for astronomic research and outreach.

After a quick introduction and a basic history of the evolution of web technologies during these last 15 years, we will present interactive examples of the above-mentioned technologies, focusing on client-side innovations.

Progress in our understanding of the Solar corona and its underlying heating and acceleration processes, depends critically on our ability to measure fundamental plasma parameters, such as magnetic field, density, temperature and composition. In this talk, I will introduce my main research topics which concern measurement of fundamental plasma parameters in the Solar corona and the development of new plasma diagnostic tools, in order to provide constraints for the various proposed physical mechanisms.

Coronal observations are always integrated along a line of sight (LOS). Because there may be multiple emitting sources, this considerably complicates the interpretation of the observations. To avoid this ambiguity there are several tools, including the widely used Differential Emission Measure (DEM) analysis and the tomography reconstruction technique. However, both the derivation and the interpretation of the DEM from observations are difficult mainly due to the inverse nature of the problem. I will present a new strategy to evaluate the robustness of the DEM inversion problem. An application of the DEM formalism will be presented, allowing us to measure the relative abundances in both interplumes and plumes using Hinode/Extreme Ultraviolet Imaging Spectrometer (EIS) data. Finally, I will present the inversion code I developed, able to perform the coupling of the DEM formalism and the tomography, providing a three dimensional diagnostic in temperature and density of the solar corona.