JOINT Institute Seminar

Room: SR 8/18

Multi-Messenger Lensing and the Vera Rubin Observatory

Room: SR 8/18

Perseus' Intracluster Light & Intracluster Globular Clusters with Euclid

Room: SR 8/18

MSc Thesis Defensio (extraordinary date)

Room: SR1 (ICT building)

Room: SR 8/18

MSc Defensio - Pulsating Exoplanet Host Stars

Room: SR 8/18

MSc Defensio - Bayesian Inference of Stellar Parameters in Pre-Main Sequence delta Scuti Stars assisted by Neural Network Emulation

Room: Seminarraum 12 (Architecture Building)

Room: SR 8/18

Room: HS E

Cosmology with clustering of galaxy clusters

Room: SR 8/18

Room: SR 8/18

PhD Thesis Defense

Room: SR 8/18

Room: SR 8/18

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 whichaims to provide an (unprecedented) holistic empirical overview of themain physical properties of Galactic massive O- and B-type stars. Theproject pursues that the compiled information can be used as a reliableand 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.

Room: SR 8/18

Room: SR 8/18

MSc Defense

Room: SR 8/18

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.

Room: SR 8/18

MSc Defense

Room: SR 8/18

New Results from the Abundance of SPT Clusters with DES and HST Weak Lensing The abundance of massive halos (and of the galaxy clusters they host) has long been recognized as an extremely promising probe of the large-scale structure of the universe. Over the past decade, tremendous progress was made, notably thanks to the availability of high-resolution surveys of the Cosmic Microwave Background (CMB), of high-quality measurements of gravitational lensing, and of advanced numerical simulations. The sample of galaxy clusters selected by the South Pole Telescope (SPT) in the CMB now exceeds a thousand objects. The Dark Energy Survey (DES) allows for measurements of gravitational lensing for almost 700 sample clusters with exquisit control over systematic uncertainties. We supplement this dataset with 39 lensing measurements of high-redshift clusters with the Hubble Space Telescope (HST). The joint analysis of the cluster abundance and weak-lensing mass calibration provides tight cosmological constraints that are competitive with other major probes. In my talk, I will review the SPT cluster cosmology and mass calibration program. I will focus on the latest SPT + DES Y3 + HST analysis and present new cosmological constraints.

Room: SR 8/18

Room: SR 8/18

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.

Room: SR 8/18

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.

Room: SR 8/18

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.

Room: SR 8/18

The Assembly History of the Milky Way using Globular Clusters Using globular clusters I will reverse engineer the merger history of our Milky Way galaxy, and describe the 5 disrupted satellite galaxies that have contributed around half of the MW's globular clusters. Also from new JWST data of an `infant MW' at a look back time of 9 Gyr, I discuss its globular cluster and similarities with the MW's system today.

Room: SR 8/18

Thesis Defensio

Room: SR 8/18

Thesis Defensio

Room: HS C

CMB, Large-Scale Structures and the distance ladder: Precision cosmology or Cosmic discordance? With the latest results from Planck, we have entered a new era of “precision cosmology”. However, some predictions of the canonical cosmological model namely Lambda-Cold-Dark-Matter (LCDM), calibrated on data from the early universe, are being challenged by high-accuracy measurements with probes of the late-universe. In this talk, I will review the status of two “tensions” that have attracted a lot of attention over the last few years. On the one hand, the Hubble Tension is a mismatch between measurements of the Hubble parameter with a variety of late-universe probes (the cepheid-calibrated  distance ladder in particular) and its prediction from the Planck/LCDM model. On the other hand,  a "S8 tension" has emerged between measurements of the large-scale clustering amplitude  measured via galaxy weak-lensing surveys and that predicted by the Planck/LCDM cosmology. After a brief review of the measurements and (some) possible systematic errors that could affect these measurements,  I will discuss new physics scenarios that have been suggested and what new  “concordance cosmology” may emerge from these tensions.

Room: SR 8/18

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.

Room: SR 8/18

A Multicoarsening Multigrid Approach for the Cosmic Transport Equation (extraordinary seminar, Thesis Defense)

Room: HSB 9

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.

Room: SR 8/18

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

Room: SR 8/18

TBD

Room: SR 8/18

Room: SR 8/18

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.

Room: SR 8/18

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

Room: SR 8/18

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

Room: SR 8/18

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.

Room: SR 8/18

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

Room: SR 8/18

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

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)