Recent Talks

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.

Current state-of-the-art imaging surveys deliver images with limiting surface brightness of 26.5 mag/arcsec^2. This depth is around 100 times fainter than the brightness of the sky in professional observatories. This view of the Universe is the basis of most of our visual understanding of the closest (galactic and extragalactic) objects. However, going deeper is absolutely mandatory if we want to understand a plethora of astrophysical phenomena that manifest themselves at lower surface brightness limits. To understand from the smallest scales of our local Galactic cirrus to the huge extensions of the intra-cluster light of massive galaxy clusters I will present in this talk two important steps forward conducted here at the IAC.  The first one is The IAC Stripe82 Legacy Project: a public survey for the astronomical community which includes 275 square degrees in 5 optical bands reaching 28.5 mag/arcsec^2 depth. The second one is the deepest ever imaging of the nearby Universe: 8h of GTC time on the near UGC00180 galaxy reaching a limiting surface brightness of 31.5 mag/arcsec^2 (100 times deeper than traditional surveys). A large amount of unexpected discoveries emerge in these unprecedented set of images.

In mid nineteens, it was discovered that the Sun had a dipolar global magnetic field, whose temporal evolution followed the Solar Cycle. Polar regions, as well as sunspots that appear in the activity belts, changed their polarity every 11 years: sunspots during each activity minima, and the poles in activity maxima. This fact, made people think that the poles reversal was related to the arrival of opposite polarity magnetic flux dragged from active regions by a meridional flow. Such new flux reduced the dominant polarity at the poles by cancellation, and built the opposite one until next minimum of activity. In our study, we have used the high quality full disc magnetograms, recorded by the HMI instrument onboard the SDO satellite since the beginning of the mission, in april 2010. We perform a deep study of the evolution with time of the line of sight component of the magnetic field at the solar poles. In our data, we see many aspects of the solar cycle as the decay of the dominant polarity of both poles while we approach to the activity maximum. But the main result is the detection of a monthly oscillatory pattern of the pole's magnetic field. Such oscillation, related to solar rotation is a clear evidence of a non-axisymmetric component of the magnetic field. One of the possible explanations is that the global field is tilted with respect to the rotation axis. This rather usual finding in other stars, here represents a breach of modern solar dynamo theories for the generation and maintenance of the Sun's magnetic field.

Planck satellite provides for the first time the possibility to detect galaxy clusters using their Sunyaev-Zeldovich (SZ) effect signature covering the full sky (Planck Col XXIX, 2013). Planck SZ catalogs I and II include more than 1900 sources, of which 700 remain unknown. The study of the purity of these samples and the characterization of SZ sources is essential to perform cosmology with cluster counts. With this aim in mind, the IAC-Planck group is performing the optical validation and characterization of these samples through two long-term observing programs at Canary Island observatories, the ITP 13B15A and the large-term 15B-17A. In this talk we will present intermediate results of this validation program. Using photometric and spectroscopic information (mainly multi-object techniques) we estimate redshifts and dynamical masses in order to minimize the errors in the Msz-Mdyn scaling relation and the SZ clusters mass function which allow a better determination of cosmological parameters (mainly Omega_m, sigma_8 and neutrino mass) from Planck SZ survey.