Recent Talks

I will describe the major scientific motivation and outline design concept for a new 2 degree field, 1000 fibre multi-object spectroscopy facility for the WHT. WEAVE is expected to be completed by early 2017 and will be capable of addressing a wide range of Galactic and extra-Galactic goals, covering the redial velocity follow-up to the full depth of the Gaia astrometric catalogue, stellar abundances and chemical labelling in the Galactic halo, galaxy evolution from integral field studies and from the identification of the LOFAR source population, and Cosmology. The instrument is complex, but not necessarily challenging, and will provide a major resource for the whole ING community for the next decade.

Thick discs are disc-like components with a scale height larger than that of the classical discs. They are  most easily detected in close to edge-on galaxies in which they appear as a roughly exponential excess of light which appears a few thin disc scale heights above the midplane. Their origin has been considered mysterious until recently and several formation theories have been proposed. Unveiling the origin of thick discs is important for understanding galaxy evolutionary processes.
I will review the results we obtained on thick discs using data from the S4G:
1) Thick discs are ubiquitous.
2) Thick discs are much more massive than previously thought. This advocates for an in situ origin of thick discs at high redshift and for them being a reservoir of missing baryons.
3) The superposition of thin and thick discs with different scale lengths is the reason of at least half of disc antitruncations.

Massive early-type galaxies constitute an ideal test bed to probe our understanding of galaxy formation and evolution. Their high mass, spheroidal morphology and overly old stellar populations, along with their presence over a wide range of redshifts put to the test our current paradigm of formation via hierarchical growth. In this talk I will review recent work focused on the dark and bright sides of this problem. The former is tackled via gravitational lensing, comparing the dark matter and luminous components out to several effective radii, probing the efficiency of baryon collapse and ejection, and its feedback on the dark matter distribution (adiabatic compression). The bright side of early-type galaxies is approached via photo-spectroscopic analyses of the stellar populations, revealing a complex formation and assembly history with two well-defined phases of growth, and an intriguing connection with the "microphysics" of star formation.

A simple model using the balance of photodissociation assuming a one-dimensional plane-parallel model yields total hydrogen volume densities for a column of atomic hydrogen under the influence of a far-ultraviolet radiation field. This can be applied wherever atomic hydrogen can be assumed to be the product of photodissociation, or perhaps where it is being kept in its atomic state because of the local radiation field. I have previously applied this model to the nearby spiral galaxies M33, M81 and M83 in the past, but the application is mostly manual and cumbersome. In order to make this method suitable to apply to larger samples of galaxies, we developed an automated procedure that identifies candidate PDRs, calculates the balance of photodissociation at locations where PDR-produced HI can be expected and provides total hydrogen volume densities. We applied the procedure to M83 as a consistency check. It is also ready to take advantage of the latest integral field spectroscopy data (metallicity), which we did in the case of M74. In principle this procedure is most suitable to probe the diffuse interstellar medium at the edges of HII regions in other galaxies than our own. However, if detailed morphological information is already available, we can improve our understanding of the method by applying it to very specific cases, such as parts of the Taurus molecular cloud. While the results are highly sensitive to the local morphology, they can potentially be used as an independent probe of the molecular gas.

We review observations of a representative set of extrasolar planets that transit their stars, concentrating on those discovered and characterized by the XO Project. Spectra of these planets in transit and in eclipse have made significant contributions to our understanding of hot gas giant exoplanets, including 1) evidence for planet-planet scattering to transfer the planets from where they are formed to where we observe them, 2) hot stratospheres of these exoplanets, and two possible mechanisms to maintain them, and 3) water vapor detected in the near-IR spectrum of the exoplanet XO-1b in transit. For the latter case, we compare near-IR spectra obtained with two HST instruments: NICMOS and WFC3 with its new spatial scanning technique. We then present the spectrum of the super-Earth exoplanet GJ 1214b from the visible to the infrared, and focus on the definitive results obtained with HST WFC3 that show a featureless near-IR spectrum, indicative of either a large mean molecular weight in the planet's atmosphere, or obscuring haze (Berta et al. 2012). We identify similar observations that are being made with HST now, and will be made with JWST, and other telescopes in the future. We conclude by summarizing the Transiting Exoplanet Survey Satellite, TESS, which will discover the nearest, transiting rocky exoplanets, those most interesting and most suitable for follow-up characterization of the sort we have presented.

I will review some recent results about the molecular content of galaxies and its dynamics, obtained from CO lines, dense tracers (HCN,HCO+), or the dust continuum emission. New data to constrain the conversion factor XCO will be discussed. The molecular surface density is essential to determine the star formation efficiency in galaxies, and the resolved Kennicutt-Schmidt law will be presented as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.

One of the main contributions that archaeoastronomy —assisted by rigorous methodology— can bring to studies of religious practice, particularly in Greece, is to reintegrate the visible landscape and sky with ancient religious ritual. This paper is an introduction to the approach we can use in order to better understand the role of astronomical observations in the timing of ancient Greek religious festivals and cult. The paper demonstrates that, in the case of Greece, general conclusions on the predominant eastern orientation of Greek temples do not help us improve our narrative about the role of astronomy in Greek religious practice. The Greek religious system was complex, being influenced by local traditions, identity and myths. Therefore, by combining archaeology, ancient history and classics we are able to integrate the archaeoastronomical data in the context of specific cults and thus to better understand the religious experience of the people who attended and participated in these cults.

I am going to present the new massive and obscured cluster Masgomas-1. This cluster, discovered by our group formed by astronomers from the IAC and CEFCA, is the
first candidate derived from the preliminary version of our systematic search algorithm for obscured (and young) massive clusters, and part of the MASGOMAS project  (MAssive Stars in Galactic Obscured MAssive clusterS). In this talk I will present the spectrophotometric observations obtained with LIRIS at William Herschel Telescope (ORM), which allowed the physical characterization of the massive stellar population of Masgomas-1, and the confirmation of the  cluster's massive nature
(i.e. Mcl > 10^4 Msun).

Measuring distances to galaxies and determining their chemical compositions are two fundamental activities in modern extragalactic astronomy, in that they help characterizing the physical properties of their constituents and their evolutionary status. Ultimately, these measurements lead to stronger constraints on the cosmological parameters of an expanding universe and the history of cosmic chemical enrichment. Both these questions can be tackled afresh with the quantitative analysis of the absorption line spectra of individual massive and luminous, young B- and A-type supergiant stars. A spectroscopic distance determination method, the FGLR, can yield accurate distances up to several Mpc, extending to a local volume where the results can be compared with those obtained from Cepheids and other distance indicators. Moreover, and this being a unique advantage of the FGLR, reddening values and metallicities are simultaneously determined for each individual stellar target. These stellar metallicities are very accurate and can be used to constrain the formation and evolution of galaxies and to assess and overcome the systematic uncertainties of H II region strong-line abundances through a galaxy-by-galaxy comparison. Moreover, stellar spectroscopy provides fundamental complementary abundance information for star forming galaxies on additional atomic species such as iron-group elements. I will present recent results of our on-going efforts to study individual blue supergiant stars in galaxies within and beyond the Local Group based on medium and low resolution optical spectra collected with ESO VLT and the Keck telescopes. The promising perspectives of future work, based on the giant ground-based telescopes of the next generation (E-ELT, TMT) are also discussed.