Recent Talks

With the detailed measurements available for our Galaxy and the local volume, the Milky Way and its satellites are a unique laboratory for the galactic archaeology field, which is trying to reconstruct the galactic evolution history from fossil records. In this context, spectroscopy is one of the primary tools to explore the physics of the Universe. This field, encompassing a wide range of subjects from detecting exoplanets to studying the expansion of the Universe, has begun collecting massive data-sets, yielding remarkable outcomes. Among the various applications of spectroscopy, the study of stellar abundances is of primary importance. In fact, the chemical information enclosed in a stellar spectrum is extremely informative, as galactic chemical evolution tells us that elemental abundance ratios can be used to trace star formation history between stellar generations. This holds true for both our galaxy and its satellites. My talk will be about the application of stellar spectroscopy to investigate chemical evolution. I will present a spectroscopic dataset that I assembled to characterise the stellar populations of the Sagittarius dwarf spheroidal galaxy. Additionally, I’ll explore the potential (and limitations) of chemical tagging a subject I've investigated using various spectroscopic datasets. Despite their diversity, the common aim is to understand the most effective ways to use stellar spectroscopy and chemical abundance ratios for retracing the chemical evolution within distinct galactic environments. 

The intensity interferometry technique enables telescopes to achieve exceptionally high angular resolutions, on the order of hundreds of microarcseconds, in the optical range. I will explain how, in contrast to traditional phase interferometry, this technique readily accommodates blue and near UV wavelengths, and is straightforward to expand to longer telescope baselines with the potential to reach angular resolutions of a few microarcseconds for baselines of a few kilometers. In addition to its regular gamma-ray observations, we have been operating MAGIC as an optical interferometer for several years. We have recently measured the diameters of 13 early-type stars that lacked prior measurements. In addition, in 2024 we have extended the same technical solutions to the first CTA Large-Sized Telescope operating at ORM, LST-1. I will present these observations, delineate plans for the upcoming upgrades to the four LSTs currently under deployment, and describe a science cases that are within reach during the next few years, among others the study of early type stars, fast rotators, and expansion of novae.

Black Holes are for most of their life in a dormant state, and yet, just a small amount of accreted mass would be needed for them to trigger the most luminous Quasars. We find however that there is plenty of matter ready to fall into the accretion disc in most galactic nuclei, why then are most of them fainter than expected?
I will discus the ubiquity of dust and molecular gas in the central parsec of galaxies. This dust and gas often form a nuclear spiral of filaments, which may slow down inflow towards the centre. Using multiwavelength, parsec-scale and JWST data collected by our group for low activity Black Holes I will show a first evidence for a cold Quasar-like accretion disc, and that the main channel of energy release in these sources is via jets.

The Javalambre Photometric Local Survey (J-PLUS) is an ongoing 12-band photometric optical survey, observing thousands of square
degrees of the Northern hemisphere from the dedicated JAST/T80 telescope at the Observatorio Astrofísico de Javalambre.
The larger field of view (FoV), high spatial resolution, contiguous narrow band filters cover a wide wavelength (330-1100 nm)
of J-PLUS/J-PAS surveys act like a low resolution IFU, which is suitable for spatially resolved studies of galaxies. J-surveys have
large Field of view (FoV) and can offer large contiguous observing areas to understand the complete structure of all galaxies
and trace their environment without any pre-selection. In my talk, I will present the results from the spatially resolved study of Halpha 
emission line maps of nearby galaxies at z < 0.017 using JPLUS DR3. We validate our method to build the J-PLUS IFU (J-IFU) emission line maps 
with other IFUs such as CALIFA, MANGA and MUSE. I will also present spatially resolved star-forming regions, its photospectra and star formation maps 
of JPLUS galaxies.

The James Webb Space Telescope has shown us that we cannot consider exoplanet atmospheres as globally uniform objects in chemical equilibrium. On the contrary: day and night sides can have a completely different composition and disequilibrium effects such as mixing and photochemistry will affect chemical abundances, and hence, our understanding of how these planets were formed.

In this talk, I will present new chemical models that incorporate disequilibrium chemistry and three-dimensionality in hot Jupiter atmospheres. I will show that photochemistry can have a global impact and may explain some enigmatic observations on ultra-hot planets. Finally, I will discuss the important effect that photodissociation and ionization have on the atmospheric structure of exoplanets.

The conventional (blink) detection techniques require large aperture telescopes for finding the faintest Solar System objects. Nevertheless, unknown objects can be discovered from stacking short exposures across all potential trajectories. This method is called Synthetic Tracking (ST). Due to the large number of potential trajectories, ST is perceived as computationally expensive, thus most surveys still prefer the blink method.

I will present a moving object detection software called Synthetic Tracking on Umbrella (STU), which leverages GPU computation and multiple search-space optimizations for real time synthetic tracking of fast-moving NEOs, even on large, multi-CCD instruments. This software was validated using a large observational archive and multiple mini-surveys, operating in near real-time under realistic conditions. The archive, of more than 100 000 images, was obtained from various telescopes including the 0.25m T025-BD4SB from Bucharest Observatory, the 1.52 m Telescopio Carlos Sánchez, as well as the 2.54m Isaac Newton Telescope. The most active telescopes used for mini-surveys are the 1.6m KASI telescope located in Chile and the aforementioned INT.

The STU detection rate depends on the quality of the input images. For example, on the TCS frames without pre-processing issues no object was missed. Similarly, an analysis on the WFC dataset has shown an 82% detection rate, with most false negatives again coming from pre-processing issues. From the real-time mini-surveys, key examples are 2023 DZ2, a NEO and former Virtual Impactor, discovered by our group in February 2023, and 2024 CW2, a fast-moving NEA (9.5 arcsec/min), reported by us the same day the data was acquired. Even at this apparent motion, the scanning phase of the synthetic tracking operation finished faster (15 min) than the data acquisition (20 min).

Through our work, we have shown that Synthetic Tracking is not as expensive as was once thought and now it can be done at survey speed. For this reason, we expect that Synthetic Tracking will become a foundational method of asteroid discovery and will thus completely displace the blink method and single-image trail detection approaches.

At present, our understanding of the formation history of the MW is limited due to the complexity of observing the imprints of accretion events and of reproducing them in numerical simulations. Moreover, though being the only galaxy, in which the Galactic potential can be probed in detail, the distribution of mass in the MW, and hence of the dark matter, is poorly constraint, especially at large distances. In addition, the MW is not isolated, and it has recently been suggested that the infall of the LMC can induce a perturbation in the stellar and dark matter distribution of the MW. As a consequence, the details of the formation history of our Galaxy are still unknown, such as the number of accretion events, the mass of the accreted galaxies, and the epoch of these events. Yet, this information is crucial to understand our environment and to constrain the theoretical models and simulations that try to reproduce it. In this talk I will present recent works that have been conducted to better characterized our Galaxy and its history thanks to new large scale surveys that provide detailed dynamical and chemical information. I will also present the major improvement that will bring the new generation of large, multi-aspect surveys, to study both our Galactic history, as well as the fundamental nature of the dark matter.

Primitive asteroids are small bodies that have evolved relatively little since their formation. Their study is essential to understand the chemical composition of the early solar system and its evolution over the past 4.57 billion years. The understanding of the evolutionary processes of primitive asteroids is all the more important as these objects could have brought water and organic matter into the inner solar system.

In the 2010s, two space missions, OSIRIS-Rex (NASA) and Hayabusa2 (JAXA), embarked on a journey to two primitive asteroids in order to collect samples from their surface. The carbonaceous-type asteroid (162173) Ryugu was the target of the Hayabusa2 mission. The spacecraft performed two samplings, collecting surface and subsurface materials excavated by an artificial impactor, because the subsurface is more likely preserved from the alteration by space weathering processes. In December 2020, the sealed capsule containing 5.4 of precious samples returned to Earth. The capsule was opened in the Curation Facility (Sagamihara, Japan), a complex of clean chambers, in order to carry out a first analysis of the grains without exposing them to the terrestrial atmosphere.

A non-destructive spectral analysis of the whole collection was conducted in the Curation Facility. Then, some of the grains, up to several mm in size, were extracted from the Facility and analysed with other techniques, by international teams, in order to precisely characterise their mineralogy and their chemical composition. These analyses revealed that the samples are mainly composed of minerals formed by the aqueous alteration at low temperature (~40°C) of Ryugu’s parent body. The detection of rare anhydrous minerals reveals that some regions in the parent body were preserved from extensive aqueous alteration. Moreover, the analyses of the samples show that space weathering modified the physical and chemical properties of the particles exposed to space environment at the surface of the asteroid. The closest meteoritical analogs of Ryugu samples are CI chondrites, a class of meteorites probably originating from carbonaceous asteroids. However, some of the spectral and compositional differences between them suggest that CI chondrites could have been partly contaminated by terrestrial contamination. Thus, the asteroid samples are the most pristine primitive materials in our collections.

The capsule of the OSIRIS-REx spacecraft, containing the samples from (101955) Bennu, landed in the Utah desert in September 2023, and was then transferred to the Johnson Space Center at Houston. Analysis of Bennu samples is underway, and initial results suggest that Bennu, like Ryugu, contains hydrated minerals and organic matter. The laboratory characterization of these two asteroids will represent a major advancement in understanding the composition of our primitive solar system and its evolution.

Galaxy surveys of the next decade will observe hundreds of millions of galaxies over unprecedented cosmic volumes. They will produce detailed 3D maps of the Universe that we can use to precisely measure the growth and expansion histories of the Universe. They will also observe photometry and spectroscopy of each galaxy that encode its physical properties. In my talk, I will present how we will extract this cosmological information from the major galaxy surveys that I am leading: the Dark Energy Spectroscopic Instrument (DESI) and the Prime Focus Spectrograph (PFS). Furthermore, I will demonstrate how my work, ranging from survey design to the cutting-edge machine learning methods I have pioneered, will maximize the scientific impact of these surveys. In particular, I will show how I will test the standard "Lambda-CDM" cosmological model in new regimes and with unmatched precision to probe the nature of dark energy. I will also show how I will extract detailed galaxy properties, such as star formation or chemical enrichment histories, of millions of galaxies across 12 billion years of cosmic history to constrain the physical processes that drive galaxy evolution.