List of all the talks in the archive, sorted by date.
I will address the question of the formation of the first generations of stars in the Local Group dwarf spheroidal galaxies as well as in the Milky Way halo. I will outline our latest news on the observational front focussing on the dispersion (or not) in abundance ratios, discuss LTE and NLTE treatments of the elemental abundances, and present how high resolution numerical simulations can help us understand the onset of the galaxy star formation histories.
Models of the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) stellar evolutionary phase play a critical role across astrophysics, from the chemical composition of meteorites in the pre-solar nebula up to galaxy evolution in the high-redshift Universe. In spite of its importance, the modelling of TP-AGB is still affected by large uncertainties which propagate into the field of extragalactic astronomy, impinging on the predicting power of current population synthesis models of galaxies in terms of their basic properties such as ages, masses and chemical enrichment. In this context I will review recent advances and ongoing efforts toward a physically-sound TP-AGB calibration that, moving beyond the classical use of the Magellanic Cloud clusters, combines increasingly refined TP-AGB stellar models with exceptionally high-quality data for resolved TP-AGB stars in nearby galaxies.
The lack of detection of elementary particles that could explain dark matter and the recent detection of gravitational waves by the LIGO experiment have renewed interest in the hypothesis that dark matter can be made of Primordial Massive Black Holes (PMBH). We review very briefly the outcomes and limits of the classical MACHO experiment, used to probe the dark matter in the halo of the Milky Way from galactic microlensing, and introduce the more universal scenario of quasar microlensing. Quasar microlensing is sensitive to any population of compact objects in the lens galaxy, to their abundance and to their mass. Using microlensing data from 24 lensed quasars, we conclude that the fraction of mass in any type of MACHO is negligible outside of the 0.05 MSun<M<0.45 MSun mass range. This excludes any significant population of intermediate mass PBH. We estimate a fraction of halo mass in microlenses of 20%. The range of masses and abundances are in agreement with those expected for the stellar component. Using the mean mass estimate and some limits derived from multiwavelength microlensing observations we speculate about the stellar Present Day Mass Function.
We present Hubble Space Telescope (HST) F606W-band imaging observations of 21 galaxy-Lyα emitter lens candidates in the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for GALaxy-Lyα EmitteR sYstems (BELLS GALLERY) survey. 17 systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately 0.55, while the lensed sources are Lyα emitters (LAEs) at redshifts from 2 to 3. The HST imaging data are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field. The Einstein radii of the BELLS GALLERY lenses are on average 60% larger than those of the BELLS lenses because of the much higher source redshifts which will allow a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average ∼ 13× lensing magnification, the LAEs are resolved to comprise individual star-forming knots of a wide range of properties with characteristic sizes from less than 100 pc to several kpc, rest-frame far UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.
The discovery of Quantum Physics gave rise to one of the most important scientific and technological revolutions experienced by mankind. It triggered, for instance, the discovery of lasers, semiconductors, or nuclear power. In the last few years we are experiencing a second "Quantum Revolution", where the most exotic features of Quantum Physics can not only be confirmed, but also have major technological consequences. In particular, new cryptographic and computational opportunities are emerging, which will be impossible to reach with any other technology. Nowadays, there exists an extensive international effort to build quantum computers, cryptographic systems, as well as other devices. In this talk I will explain the basics of all those devices, their potential applications, as well as the status of that international effort and its prospects of giving rise to powerful technologies.
Helioseismology is about 40 years old, still a young science. It has been a tremendous success providing many more results than initially expected, including those coming from Izana of course. Now we really know a lot of the solar internal structure and rotation.
However, one important parameter has still resisted to this investigation, the solar core rotation, which is not accessible to acoustic modes of oscillation, and helioseismlogy successes have all been obtained from acoustic modes. The reason is simple: the second type of seismic oscillations, called g modes (g for gravity, as the waves on the sea) are confined in the deepest layers of the Sun, while the observers are staying outside. These g modes that contain the information on all properties of the solar core have never been convincingly detected despite many efforts and attempts during the last forty years.
We have used a differential parameter of the acoustic modes, carefully selecteded to have a maximum sensitivity to the deepest layers and a minimum sensitivity to the surface layers, to look for its possible modulation produced by periodic motions in the solar core. The frequencies possibly accessible are very low, they correspond to periods between about half a day and two days. The advantage is that in this very low frequency range, if g modes exist, they must follow an asymptotic behaviour that makes possible a collective detection. Using a long data set (16.5 years) from the GOLF instrument onboard the SOHO space mission, the result is the success of this search, and I will present you these asymptotic parameters, including the measurement of the core rotation within less than 1 percent uncertainty.
How far can we see galaxies in the distant Universe? When are the first metals and the first dust formed?
We have now the first results on these topics (Laporte et al. 2017, ApJL, 837, 21L) based on the detailed analysis of
a gravitationally lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field
cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate the proximate
detection of a significant 1 mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric
redshift of z~8. Deep X-SHOOTER spectra confirms the high-redshift identity of A2744_YD4 via the detection of Lyα emission
at a redshift z =8.38. The association with the ALMA detection is confirmed by the presence of [O III] 88 μm emission at the
same redshift. Although both emission features are only significant at the 4-sigma level, we argue their joint detection and
the positional coincidence with a high-redshift dropout in the Hubble Space Telescope images confirms the physical association.
Analysis of the available photometric data and the modest gravitational lensing magnification indicates A2744_YD4
has a stellar mass of ∼2 × 10^9 solar mass, a star formation rate of ∼20 solar mass_yr^‑1 and a dust mass of ∼6 × 10^6 solar mass.
We discuss the implications of the formation of such a dust mass only ≃ 200 Myr after the onset of cosmic reionization.
While there may be some possibilities of detecting biological signatures (“biomarkers”) outside the Solar System from the ground, most authorities
believe that major installations in space are required to do so.
In this talk we present the background, a brief summary of possible biomarkers, of possible targets and of the ways and means to observe them.
I will present results from the "Local Volume HI Survey'' (LVHIS), including a multi-wavelength atlas of 82 nearby galaxies. The LVHIS project targets all nearby, gas-rich galaxies with vLG < 550 km/s or D < 10 Mpc that are detected in the "HI Parkes All-Sky Survey" (HIPASS). A declination limit of DEC < -30 degrees was chosen for observations with the Australia Telescope Compact Array (ATCA). The majority of LVHIS galaxies are dwarf galaxies, but we also mapped the disks and outskirts of several very large galaxies (eg M83).
I will also introduce the Australian Square Kilometre Array Pathfinder (ASKAP) which consists of 36 x 12-m dishes, each equipped with Phased-Array Feeds, operating from 0.7 to 1.8 GHz. With a field-of-view of 30 square degr ASKAP is a fast 21-cm survey machine. Early Science with 12 antennas has started and I will present first results on our target field: nearby groups and clusters.
I've heard many times about the Virtual Observatory, but what really is VO? Is it just for IT people?, for data centres?, for astronomers?, for everybody? Who is behind VO? Is the Virtual Observatory sustainable in the medium-term? Was it just a nice idea or is it really having an impact on the way astronomers make science with archive data?
In this talk I'll try to answer all these questions by describing the Spanish Virtual Observatory, an initiative that began in 2004 with the aim of coordinating at national level the VO-related activities in four different fields.
Special focus will be given to usage examples of VO tools for real VO-science projects.
- MOSAIC: Making the MOSt of the ELTDr. Ruben SanchezMonday October 16, 2017 - 12:30
- 3D Spectroscopy of resolved stellar populations in NGC300, observed with MUSE at the VLTDr. Martin RothTuesday October 31, 2017 - 12:30