Recent Talks

Current planet formation theories are bound to comply with the observational constraint that protoplanetary disks have lifetime of ~3 Myr. This timescale is mostly based on spectroscopic studies of objects accreting matter from a circumstellar disk around pre-main sequence stars (PMS) located in low-density, nearby (d<1-2kpc) star forming regions. These objects do not reflect the conditions in place in the massive starburst clusters where most of star formation occurs in the universe. Using a new robust method to indentify PMS objects through their photometric excess in the Halpha band, we have studied with the HST and ground based facilities the PMS population several starburst clusters, namely NGC3603 in the Milky Way and several clusters in the Carina Nebula,  30 Doradus and the surrounding regions in the Large Magellanic Cloud and NGC 346 and NGC 602 in the Small Magellanic Cloud. We found a wide spread of ages (0.5 to 20 Myr) for PMS stars, clearly showing that accretion from circumstellar disks is still going on well past 10 Myr. This finding challenges our present understanding of protoplanetary disk evolution, and can imply a new scenario for the planet formation mechanism and of star clusters formation in general. Based on these results we were recently granted 175hr with OmegaCAM at the VST to carry out a deep optical wide field survey of nearby (<3kpc) star forming regions. These observations will provide physical parameters (including mass accretion rates) for over 10000 PMS stars and will establish whether the long timescales of circumstellar discs are common.

Talk to update on progress of IAC scientists with SDSS-IV data.

X-ray observations performed during the last few decades have provided a rich data base on accreting black holes and neutron stars in X-ray binaries. A strong coupling between the properties of the accretion flow and the presence of outflows, such as radio-jets and X-ray winds, has been found to be a fundamental characteristic of black hole systems; a feature which might be shared by super-massive black holes in active galactic nuclei.
I will present some novel results corresponding to the 2015 outburst of the prototypical black hole transient V404 Cyg (Muñoz-Darias et al. 2016, Nature). During this event, arguably the most interesting of its kind in decades, we have discovered a sustained outer accretion disc wind, which is simultaneous to the radio jet.  Our GTC-10.4m spectra show  that the outflowing wind is neutral, has a large covering factor, expands at 1% of the speed of light and triggers a nebular phase once accretion sharply drops and the ejecta become optically thin. I will discuss the implications of these results in the context of black hole accretion.

Elliptical and lenticular galaxies are often thought of as ‘red and dead’. However, hierarchical mergers are likely to leave traces of the process of galaxy evolution. We have investigated this question using a complete sample of galaxies. I will introduce the survey data that we are using and present results for the largest sample of early-type-galaxies in the local Universe. We have made a complete assessment of their dust characteristics covering all galaxies in the survey areas down to r-band absolute magnitudes of Mr > -17.4 (similar to the SMC), and as a function of environment. The unexpected results found will be presented and contrasted with what is going on in the nearby Virgo cluster, for early-type galaxies.

The ARCADE-2 CMB balloon experiment detected an unexplained low frequency component which was postulated to be a previously unknown population of extragalactic sources. We conducted a deep 2-4 GHz survey with the recently upgraded EVLA to search for this population and to measure the faint radio source counts. Faint source counts constrain the cosmic evolution of the populations represented including sources powered by star formation. Previous attempts at measuring faint source counts produced more scatter in results than are easily accounted for and may reflect the variety of techniques used to correct for various effects. I will describe a deep confusion limited analysis using the "P of D" technique to derive the source counts at, and below the confusion which avoids many of the difficult to correct effects. Results are in excellent agreement with theoretical expectations effectively ruling out the ARCADE-2 anomaly being due to discrete sources. I will also summarize ongoing observations to determine the size distribution of the microJy population.

A discussion of the first observation ever of gravitational waves. Present detectors, future detectors, and the perspectives for gravitational wave astronomy.

Solar surface convection displays highly localized sinks where cold plasma returns to the solar interior. On its way to being engulfed by a downdraft the plasma can also advect and intensify magnetic fields up to kG field strengths. Such theoretical predictions strengthen the idea that localized downdrafts are places where the concentration of magnetic fields is favored. The observational discovery of convectively driven sinks is rather recent, however, and its role in the formation and evolution of quiet-Sun magnetic features is still poorly characterized. In our work, we provide both quantitative and qualitative bases for the association between sinks and magnetic fields using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board Sunrise. We find 3.1 x 10-3 sinks Mm-2 minute-1 located at mesogranular vertices. These sinks are associated to (1) horizontal velocity flows converging to a central point and (2) long-lived downdrafts.  The spatial distribution of magnetic fields in the quiet Sun is also examined. The strongest magnetic fields are preferentially located at sinks. We find that 40% of the pixels with longitudinal component of the magnetic field higher than 500 G are located in the close neighborhood of sinks.  The study of individual examples reveal that sinks can play an important role in the evolution of quiet-Sun magnetic features.

We study the connection of star formation to atomic (HI) and molecular hydrogen (H2) in isolated, low metallicity dwarf galaxies with high-resolution SPH simulations. The model includes self-gravity, non-equilibrium cooling, shielding from an interstellar radiation field, the chemistry of H2 formation, H2-independent star formation, supernova feedback and metal enrichment. We find that the H2 mass fraction is sensitive to the adopted dust-to-gas ratio and the strength of the interstellar radiation field, while the star formation rate is not. Star formation is regulated by stellar feedback, keeping the gas out of thermal equilibrium for densities n < 1 cm-3. Because of the long chemical timescales, the H2 mass remains out of chemical equilibrium throughout the simulation. Star formation is well-correlated with cold gas, but this dense and cold gas - the reservoir for star formation - is dominated by HI, not H2. In addition, a significant fraction of H2 resides in a diffuse, warm phase, which is not star-forming. The cold gas fraction is regulated by feedback at small radii and by the assumed radiation field at large radii. The decreasing cold gas fractions result in a rapid increase in depletion time (up to 100 Gyr) for total gas surface densities, in agreement with observations of dwarf galaxies in the Kennicutt-Schmidt plane.