Recent Talks

The discovery of relic galaxies in our nearby Universe allow us to explore the physical conditions that took place at the early stages of galaxy formation (z>2) with unprecedented detail. In this talk, we will describe how these objects have been found, what is the physical motivation to explore them and what are the most relevant results we have learnt so far. In particular, in this seminar, we will focus on our recent publication in the journal Nature, where we study the globular cluster population of the massive compact relic galaxy NGC1277 using the Hubble Space Telescope. The analysis of its globular cluster population has confirmed the extraordinary nature of this object. This galaxy underwent  an early collapse phase but failed to evolve and accrete smaller satellite galaxies. The study of the globular cluster of this system (which has no similar counterpart in the near Universe) gives unique insights into the formation and evolutionary processes of the most massive galaxies.

The kinematic characterization of different galaxy populations is a key
observational input to distinguish between different galaxy evolutionary
scenarios, since it helps to determine the number ratio of rotating disks
to mergers at different cosmic epochs. Local luminous and ultra-luminous
infrared galaxies [(U)LIRGs] offer a unique opportunity to study at high
linear resolution and S/N extreme star forming events and compare them
with those observed at high z.
We obtained Very Large Telescope (VLT) VIMOS optical integral field
spectroscopy (IFS) data of a sample of 38 local (z < 0.1) (U)LIRGs (50
individual objects). Our goal is to analyze in detail the kinematics of
the
H\alpha ionized gas applying kinematic criteria able to characterize the
evolutionary status of these systems. In particular, the unweighted and
weighted kinemetry-based methods are used to kinematically classify our
galaxies in disk and merger. We also simulate our systems at z=3 to
evaluate how a loss of angular resolution affects our results.
From the kinemetry-based analysis we are able classify our local (U)LIRGs
in three distinct kinematic groups according to their total kinematic
asymmetry values (Ktot) as derived when using the weighted (unweighted)
method: 1) 25 out of 50 galaxies are kinematically classified as disk; 2)
9 out of 50 galaxies are kinematically classified as merger; 3) 16 out of 50
galaxies lie in the transition region, in which disks and mergers coexist.
When we apply our criteria to the high-z simulated systems, a lower total
kinematic asymmetry frontier value is derived with respect to that found
locally. The loss of angular resolution smears out the kinematic features,
thus making objects to appear more kinematically regular than actually they
are.

KIC 8462852, also known as the Boyajian's star, was observed by the Kepler mission during 4 years. During that time, this star underwent several events of strong brightness variations that are unlike that of any other known astronomical object. Since 2017, an intense ground-based observing campaign has been under way to closely survey this target for further brightness variations. The coverage of several minor such variations from both multicolor photometry and spectrophotometry showed that these events have a color-signature. This observation is compatible with the hypothesis by Neslu?an & Budaj of a pool of dusty planetesimals that may occasionally pass close to the star. Their  optically thin dust shroud might then generate the observed colors. However, while current observations support this scenario, they do not prove it. Alternative explanations for the star’s behavior will be revised, and in particular, variations in the temperature of the stellar surface will be evaluated for their compatibility with the observations. Furthermore, an update on the observing campaign of Boyajian’s star will be given, possibly with input from new data acquired in the first half of 2018.

This paper puts forward a possible new indicator for the presence of moderately advanced civilizations on transiting exoplanets. The idea is to examine the region of space around a planet where potential geostationary or geosynchronous satellites would orbit (herafter, the Clarke exobelt). Civilizations with a high density of devices and/or space junk in that region, but otherwise similar to ours in terms of space technology (our working definition of “moderately advanced”), may leave a noticeable imprint on the light curve of the parent star. The main contribution to such signature comes from the exobelt edge, where its opacity is maximum due to geometrical projection. Numerical simulations have been conducted for a variety of possible scenarios. In some cases, a Clarke exobelt with a fraction alface-on opacity of ∼10^{-4} would be easily observable with existing instrumentation. Simulations of Clarke exobelts and natural rings are used to quantify how they can be distinguished by their light curve.

To appear in ApJ.

En esta charla hablaremos sobre el proceso de actualización
del telescopio IAC80 en los últimos años, con el objetivo de llevar a cabo
observaciones muy exigentes en cuanto a número de imágenes, precisión temporal y astrométrica.
Se presentará la nueva cámara de gran campo CAMELOT-2
y su interfaz inteligente de usuario, que permite una observación cuasi-robótica por medio de macros
automáticas. Por último, se presentará el diseño del nuevo sistema de control, base de una futura robotización.

In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this talk I will first give an overview of some of the main properties of the Milky Way stellar halo based on literature studies. I will then present results concerning the chemical properties of the outer regions of the Milky Way stellar halo, based on the elemental abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, -3.1 ≲ [Fe/H] ≲-0.6. We show that the ratio of α-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H] ≳-1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples. 

Galaxy groups and clusters are believed to influence galaxy evolution. It has been shown that the groups with early formation epoch, also known as fossil groups, differ in halo and IGM properties, compared to the general population of galaxy groups. However, there is a controversy over the properties of the brightest group galaxies which may have been affected by the group's dynamical state. I will focus on two properties of the brightest group galaxies, the AGN activity and the stellar population. The groups with early formation epoch, or dynamically old, host under luminous AGNs in radio relative to those hosted by dynamically young groups. There is no evidence that such a distinction exists in the stellar population of these galaxies, leaving the debate open whether this is an observational limitation. 

Molecular hydrogen (H2) is a fundamental component of galaxies, being the most abundant element in molecular clouds, where stars form, and an important source of radiative cooling at low temperature. With the advent of the ALMA telescope, a large amount of data about the distribution of H2 in galaxies has become available. However, the large majority of numerical simulations on galactic and cosmological scales still lacks the ability to directly follow the formation and dissociation of H2, and must rely on pre-calibrated sub-grid models to compare the results with observations. I will present a new model to self-consistently track the evolution of H2, including gas and dust shielding, H2 self-shielding, star formation (SF), supernova feedback, and extragalactic and local stellar radiation. I will discuss the results of a suite of hydrodynamic simulations of an isolated gas-rich galaxy at z=3, showing that the model can naturally reproduce the observed correlation between SF and H2 surface densities, without assuming any a priori dependence of SF on the H2 abundance. I will also present a study of the kinematics and dynamics of molecular gas in high-redshift quasars (z=6), where we investigate whether a central accreting black hole (BH) can significantly affect the H2 distribution in the host galaxy and generate molecular outflows.

Lecture 3 by George