Multi-messenger gravitational lensing and the Vera Rubin Observatory

I will introduce the emerging field of multi-messenger gravitational lensing, starting from a broad outline of the science and the messengers, that include electromagnetic radiation, gravitational waves, neutrinos. I will then summarise our ongoing observing campaign with the DECam instrument on the Blanco telescope, that aims to detect the gravitationally lensed kilonova counterpart to the gravitationally lensed gravitational wave signal from a distant binary neutron star merger. Whilst we may be fortunate to make this monumental breakthrough by the end of the current gravitational wave run (summer 2025), we are more likely to succeed in the future, aided by the Vera C. Rubin Observatory. I will therefore introduce “Rubin”, including her capabilities, broad science impact (solar system to cosmology), status of on-sky commissioning observations, and how the international Rubin community continues to expand.

Physical properties and evolution of Galactic massive stars: towards a new paradigm driven by observations

The IACOB project is a long-term ambitious observational project which
aims to provide an (unprecedented) holistic empirical overview of the
main physical properties of Galactic massive O- and B-type stars. The
project pursues that the compiled information can be used as a reliable
and long-lasting anchor point for our theories of stellar atmospheres,
winds, interiors and evolution of massive stars.

Last November we celebrated the 15th anniversary of the first observing campaign of the IACOB project. The team is also working hard to wrap up the project before summer 2026. Many things have happened during these years which are slowly but surely driving us to a paradigm shift of our traditional understanding of the physical properties and evolution of (Galactic) massive stars. I will (1) highlight the main results obtained by the IACOB project in the last decade (2) explain why we now know that massive star evolution is not so simple as explained in the traditional textbooks, and (3) describe plans of the IACOB project, including data from the next-generation large-scale spectroscopic surveys WEAVE-SCIP and 4MIDABLE-LR-OB, in which the Spanish massive star community will be playing a key role.

Cosmological constraints from cluster abundances in the first SRG/eROSITA All-Sky Survey

Galaxy groups and clusters trace the distribution of the most prominent peaks in the matter density field at late time. Therefore, they provide valuable insights into the growth of structure in our Universe, the nature of dark matter, and, in general, the cosmological parameters that describe the content of our Universe and govern its formation and evolution.

The primary science goal of eROSITA, on board the SRG Mission, launched in 2019, is to perform a precision cosmology experiment through the evolution of cluster mass function. I will present the cosmological constraints from the 5263 clusters of galaxies securely detected and optically confirmed in the area of 13791 deg ² of the Western Galactic Hemisphere covered by Legacy Survey DR10-South. The overlap of 4968 deg ² containing 2348 clusters between eROSITA survey and DES, KiDS, and HSC are used to perform mass calibration using the weak gravitational lensing effect. In particular, we have tested four different cosmological models: the standard LCDM, wCDM where we fit for dark energy equation of state, nuCDM where we fit for the right-handed neutrino summed masses, and the nuwCDM where we fit for both dark energy equation of state and summed neutrino masses.
I will present the results and focus particularly on the key aspects of this analysis that allow us to perform a precision cosmological experiment using cluster number counts. Namely, contamination treatment, selection function, weak lensing mass calibration, and the whole Bayesian hierarchical forward modeling approach.

New Results from the Abundance of SPT Clusters with DES and HST Weak Lensing

The splashback radius as a probe of mass accretion history and cosmology

Splashback radius is formed at the first apocenters of infalling matter around halos, which is shown in observation as an abrupt density drop in the profile. Therefore, it defines a natural boundary of halos and is highly sensitive to the recent mass accretion histories which in turn strongly depend on cosmology. In this talk, I will present recent theoretical works on the splashback radius as a probe of mass accretion history of halos, observational studies for the detection, and potential for using it as a probe of cosmology in the near future.

Merger-Free Co-evolution of SMBH and their Host Galaxies

Galaxies and their supermassive black holes are known to co-evolve, and this is shown via a number of relations. However, the drivers of this co-evolution are not well understood. Mergers between two or more galaxies have been shown to be one pathway, thought for many years to be the dominant pathway, but recently it has been shown that most black hole growth occurs in the absence of major mergers. I will talk about my contributions to this field, first using a sample of luminous, Type 1 AGN hosted in galaxies which have not experienced any major mergers since redshift 2 to investigate merger-free black hole growth, with a particular focus on the effect of large-scale galactic bars. We find that the bar fraction in our AGN hosts is marginally higher (fbar = 59 ± 9 %) than in a well-matched sample of merger-free galaxies lacking an AGN (fbar = 44 ± 9 %). I will then move onto my work using DESI to investigate the variation AGN prominence with bar strength in disk dominated galaxies. We find that strongly barred galaxies are more likely to host AGN than weakly barred galaxies, which are in turn more likely to host AGN than unbarred galaxies at all stellar masses and colours.

Analysis of galaxies at the extremes: A survey of stellar populations in ultra-diffuse galaxies

Ultra-diffuse galaxies (UDGs) have been in the spotlight since their (re)discovery in 2015. These galaxies challenge our understanding of the field of galaxy formation and evolution as they have the sizes of giants, but luminosities of dwarfs. Although UDGs have been heavily studied in the past few years, most works have relied on spectroscopy to understand their stellar population properties, which is extremely challenging for such faint sources, requiring unrealistically large amounts of time on the world’s largest telescopes.
In this work, we alternatively employ spectral energy distribution fitting techniques on photometric data to recover the stellar populations of ~90 UDGs distributed across environments. We find evidence of a stellar population dependence on the environment and globular cluster (GC)-richness of UDGs: (1) Field UDGs are systematically younger than their cluster counterparts; (2) The GC-poor UDGs are consistently more metal-rich than GC-rich ones. As a consequence, GC-poor UDGs are consistent with the mass-metallicity relation (MZR) for dwarf galaxies, suggesting that they may be puffed-up dwarfs. However, GC-rich UDGs lie well below the MZR, in the region where failed galaxy scenarios might be expected.

The Assembly History of the Milky Way using Globular Clusters

CMB, Large-Scale Structures and the distance ladder: Precision cosmology or Cosmic discordance?

Euclid Mission and Legacy Science

ESA’s Euclid space telescope, designed to map the geometry of the Universe and scheduled for launch this year, will observe billions of galaxies with the goal of providing new insights into the nature of dark matter and dark energy. In this talk, I will give an overview of the instruments and the current status of the Euclid mission. I will then focus on the legacy science that will be achieved with Euclid and describe some of the challenges and approaches we are taking in order to enhance the scientific return and discovery power of Euclid.

Investigating the structure and evolution of the Universe with weak gravitational lensing

The cosmological standard model, which describes the accelerated expansion of the Universe, is well established. However, several lingering issues remain, including the nature of Dark Energy and tensions between measurements in the early and local Universe. One tool to address these questions is the weak gravitational lensing effect, which describes the distortion of observed galaxy shapes by the matter distribution of the Universe.

In this talk, I will give an overview of weak lensing is used to determine cosmological parameters, as well as some of the challenges of these analyses. The power of weak lensing analyses can be considerably improved by using new types of statistics called higher-order statistics (HOS). I will introduce one particular HOS, the third-order shear statistic, which is a promising method for better understanding the structure of the Universe. Finally, I will present the next step for weak lensing analyses - the Euclid telescope, which will be launched later this year.

A High-Resolution Near-IR Spectroscopic Atlas of the F5 IV-V Standard Star Procyon (extraordinary meeting, Thesis Defense)

TBD

Staff Meeting

The imprint of star formation on stellar pulsations

In the earliest phases of their evolution, stars gain mass through the acquisition of matter from their birth clouds. The widely accepted classical concept of early stellar evolution neglects the details of this accretion phase and assumes the formation of stars with large initial radii that contract gravitationally. In this picture, the common idea is that once the stars begin their fusion processes, they have forgotten their past. By analysing stellar oscillations in recently born stars, we show that the accretion history leaves a potentially detectable imprint on the stars’ interior structures. Currently available data from space would allow discriminating between these more realistic accretion scenarios and the classical early stellar evolution models. This opens a window to investigate the interior structures of young pulsating stars that will also be of relevance for related fields, such as stellar oscillations in general and exoplanet studies.

Constraining the Intergalactic Magnetic Field by Means of Gamma Ray Observation (Thesis Defense)

Star forming regions as hadronic cosmic ray accelerators (Thesis Defense)

Towards robust cluster cosmological inference

Number counts of galaxy clusters are a well established cosmological probe, which infers the cosmological model by measuring the abundance of clusters as a function of their mass and cosmic age. We review first the key ingredients for cluster cosmological inference, identifying two main regions of systematic uncertainty: cluster mass measurements and cluster selection modelling. Based on recent work for the South Pole Telescope and the Dark Energy survey cluster cosmological analyses, we present how to tackle these issues via a combination of Bayesian population modelling, cosmological volume hydrodynamical simulations and multi-wavelength observations. Finally, we outline how these new methods will lead to robust cluster cosmological inference in the age of the next generations surveys like eROSITA, Rubin, Euclid, and CMB-Stage IV.

A multi-messenger view on the TeV transient gamma-ray sky

Investigating Artificial Neural Networks and Their Possible Applications in Astrophysical Fluid Simulations (Msc Thesis Defensio)

Institutsversammlung

Discovery of a large sample of free-floating planets

The first free-floating planets were discovered at the turn of the century, but the lack of large samples prevents us from better understanding their origin and properties. Are they born orphans of planetary systems, or are they expelled from their place of birth in their childhood? I will present the largest homogeneous sample of free-floating planets to date and discuss how it can be used to shed light on their origin. The lack of precise ages is one of the main difficulties in knowing the mass of these objects. I will present a methodology based on kinematics to determine the ages of young stellar associations.

PhD Thesis Defensio

Diffuse gamma-ray emission models: ISRF, geometry and resolution improvements (PhD Thesis Defensio)

Boron abundances in O- and B-type stars (Master Thesis Defensio)