Science Meeting 2024-2025
Ecogia Science Meetings 2024-2025
Schedule
Meetings are at 14 in the Pavillon meeting room at Ecogia and on Zoom
X-GAP is a collection of galaxy groups followed up with XMM-Newton, with the main goal of constraining AGN feedback models via gas fraction and thermodynamic profiles measurements and comparison to hydro-simulations. I will provide an update on the end-to-end mocks we are developing to forward model the X-GAP selection function, a key component for its comparison to simulations and theoretical models.
2024-10-21 00:00:00 Skipped
The new JAXA/NASA satellite XRISM has successfully conducted its commissioning and performance verification phases, and it has now moved into its normal operation phase. Results from the PV phase observations are now slowly coming in. In this context, I will present the results of two observations of the Coma cluster with XRISM, that I am co-leading. I will present the high-resolution XRISM spectra and the surprising results they seem to be leading to.
TBD
I will present one of the latest collaborative efforts of the LISA Astro Group to understand the population of massive black holes detectable by the gravitational wave antenna.
Even though discovered some 70 years ago, and exploited until 1974, Intensity Interferometry in astronomy went dormant for 50 years. The technique is making a very strong comeback since a few years, mainly due to the technological advancements that enable to go beyond what had been measured already. I'll go through an overview of the technique, the current interferometers in operation, the measurements done at the department, and the plans for the immediate and longer-term future.
Starburst (SB) galaxies are a rare population of galaxies with star formation rates (SFRs) greatly exceeding those of the majority of star-forming galaxies with similar stellar mass. It is unclear whether these bursts are the result of either especially large gas reservoirs or enhanced efficiencies in converting gas into stars. Tidal torques resulting from gas-rich galaxy mergers are known to enhance the SFR by funneling gas towards the centre. However, recent theoretical works show that mergers do not always trigger a SB and not all SB galaxies are interacting systems, raising the question of what drives a SB. We analysed a large sample of SB galaxies and a mass- and redshift-matched sample of control galaxies, drawn from the FIREbox cosmological volume at z=0-1. We found that SB galaxies have both larger molecular gas fractions and shorter molecular depletion times than control galaxies, but similar total gas masses. Control galaxies evolve towards the SB regime by gas compaction in their central regions, over timescales of 70 Myr, accompanied by an increase in the fraction of ultra-dense and molecular gas. The driving mechanism behind the SB varies depending on the mass of the galaxy. Massive (Mstar > 1e10 Msun) galaxies undergoing intense, long-lasting SBs are mostly driven by galaxy interactions. Conversely, SBs in non-interacting galaxies are often triggered by a global gravitational instability, that can result in a breathing mode in low-mass galaxies.
Beta Cephei type stars are massive (7 20 M) and known to have several pulsation modes with a period of typically a few hours. Despite a better understanding of their physics since 1993, the inner structure of these stars involves key stellar physics processes that are still uncertain. Asteroseismology offers insights into these variable stars by analyzing pulsation modes helping to probe their inner layers and understand their structure and mixing processes Therefore, building an asteroseismic model that would reliably predict an observable quantity of a Beta Cephei star would be a significant improvement, allowing us to reduce the uncertainty on their internal structure (e.g., overshooting parameter or metallicity). We provide -Ophiuchi known pulsation modes and observational to an asteroseismic model, which allows us to estimate a radius of 5.07 R. Additionally, the recent angular diameter measurements done with the MAGIC telescopes make it possible to have an experimental value on the radius of Ophiuchi. Using the parallax of Gaia, we show that the experimental result is in good agreement with the asteroseismic model, allowing other constaints to the model, hence and hence could reduce the uncertainty on the inner star structure like the overshooting parameter.
The ESA Euclid mission is a space initiative aimed at constraining dark matter and dark energy via weak gravitational lensing. A foreground gravitational potential distorts the images of background sources, and with redshift information, we can map the mass distribution, trace the evolution of cosmic structures, and interpret the properties of dark energy. Using the Early Release Observation(ERO) data, captured by the end of 2023 from Abell 2390, we conducted the first weak lensing measurements based on real observational data. In this talk, I will present the Euclid first weak lensing measurements and provide mass constraints on the Abell 2390.
X-ray surveys of AGN provide direct constraints on the properties of individual AGN, such as their accretion, reflection, and obscuration. Previous AGN population synthesis models have not addressed such constraints self-consistently. Here we use a simulation-based inference approach to constrain the geometrical and physical properties of the AGN population. We perform numerical simulations with our ray-tracing code, RefleX, which allows the self-consistent modelling of the X-ray emission of AGN with flexible circumnuclear and source geometries. We create our synthetic population by sampling the black hole mass function and Eddington ratio distribution function of local AGN and we construct a geometry based on the radiation-regulated model. Using the RefleX-simulated emission of the AGN population, we attempt to simultaneously reproduce several observed properties of Swift/BAT detected AGN, such as their differential number counts, the line-of-sight NH distribution, the number of obscured and unobscured AGN as a function of Eddington ratio, and the Compton-thick fraction. With this approach, we can test the consistency of the radiation-regulated model in the local Universe with the most comprehensive set of X-ray observables, while constraining the size and density of the dusty torus.
2024-12-23 00:00:00 Holidays
2024-12-30 00:00:00 Holidays
2025-01-06 00:00:00 Holidays
Recent measurements of cosmological parameters highlight possible tensions between values determined by CMB measurements and late-epoch observations, particularly for the clumpiness parameter 8 and the matter density parameter m. To investigate this, we developed a forward cosmological modeling pipeline using simulation-based inference, allowing us to determine these parameters from galaxy cluster counts. The implemented pipeline generates samples of galaxy clusters from the halo mass function, incorporates all observational effects, and applies exact survey selection functions. We test our method on mock samples through various validation steps before applying it to the XXL survey data. One of the key strengths of simulation-based inference is its potential to integrate multiple datasets into a single model, enabling joint analyses across observables such as clustering, cluster counts, and BAO for more robust and consistent cosmological inferences.
The Cosmic X-ray Background (CXB) represents a critical measure of the cumulative energy released through black hole accretion across the Universe, primarily from supermassive black holes, such as Active Galactic Nuclei (AGN). The Cosmic X-ray Background Explorer (CXBe) aims to measure the CXB spectrum with an unprecedented ~1% accuracy (the current data is at ~15-20%). This improvement will refine synthesis models of the CXB and deepen our understanding of the AGN population, including their obscuration and X-ray reflection. The CXBe project has been endorsed for deployment on the China Space Station (CSS) and recently secured funding from NASO for Phase A/B1 studies. In this talk, I will introduce the preliminary profile of the CXBe project and discuss its prospects for this decade.
In the Gaia processing pipelines we compute a lot of different models to fit our data to identify different 'variability' signals. These models often contain common blocks of linear and non-linear parameters. When performing model comparison (e.g. using the Bayesian information criterion) we often pit models from low to high complexity against each other, in which we usually have a high level of replication of such common model (parameter) blocks. In this talk I will explain how the introduction of the parameterisation of such model blocks is starting to be be used in Gaia processing to define and compute many (new) models with extreme ease, thereby enhancing the identification of specific (calibration) signals in the data.
In the project Quasar we need to establish very precise time synchronization over several kilometers. As probably you will hear a lot about time synchronization in the following years I will explain some basic concepts about how time synchronization is achieved.
I will show that current mm-to-X-ray polarization trends, observed during recent IXPE campaigns for HBLs, and the ROBOPOL trend for Fermi blazars, relating the fractional polarization to the peak frequency of the synchrotron emission, can be successfully reproduced by a multi-zone scenario without the need for an energy-stratified scenario. I will also discuss some implications for the statistical properties of the polarization angle and for the underlying acceleration processes.
With the establishment of the CTAO European Research Infrastructure Consortium (ERIC), the observatory has entered a new phase of development and construction. In my talk, I will provide an overview of the progress at the CTAO Northern site, with a particular focus on the status of the Large-Sized Telescope prototype (LST-1) located there. The LST-1 is designed to detect gamma rays in the energy range of 20 GeV to 3 TeV and will operate in stereo mode as part of a four-telescope mini-array increasing overall sensitivity. Although still in its commissioning phase, the LST-1 is already conducting regular scientific observations, participates in multi-wavelength campaigns and perform transients observations. I will discuss some of the recent scientific results related to PeVatron candidates, the Crab Nebula observations, and GRBs follow-ups, as well as outline future research goals.
It has long been known from simulations and observed behaviours that the dark matter component that governs galaxy clusters does not always follow a spherically symmetric geometry, but more that of a concentric triaxial density profile. However, analytic models such as the standard NFW and Einasto profiles tend to work under the spherical symmetry assumption. In this talk I will discuss the models and mock observables developed for my MSc thesis. I will introduce my method and the mock observable computations, and discuss the implications of analysing these systems as a spherical distribution. I will also briefly touch on the continuation to the work that Iam currently performing.
2025-03-03 00:00:00 Skipped
Massive black holes (BHs) are ubiquitous in galaxies across a wide mass range, from dwarf to massive galaxies. When these BHs actively accrete matter, they emit immense energy, making them detectable even in the early Universe 13 billion years ago. However, despite the evidence of their existence, the mechanisms underlying their formation and coevolution with host galaxies remain poorly understood. In this talk, I will present black holes' current observation and simulation state. Recent JWST findings suggest that massive black holes and AGN exist beyond the pre-JWST quasar frontier. These populations are more numerous than predicted by some theoretical models. Some of these BH candidates are more massive at high redshift than previously thought. They require a high initial BH mass or efficient BH accretion. How could BH grow so fast so early? In the previous decade, large-scale simulations such as EAGLE, TNG, or SIMBA were calibrated to reproduce the local universe BH populations. I will show that these simulations do not reproduce the observed JWST BH candidates. To make the comparison with observations more meaningful, I am designing a novel BH formation model in star clusters in large-scale simulations.
2025-03-17 00:00:00 Skipped
Galaxy clusters are the most massive virialised structures in the Universe, and they trace the highest density peaks in the Large Scale Structure of the Universe, which makes them key cosmological probes, but also perfect laboratories to study the (g)astrophysics of the intracluster medium. The CHEX-MATE project is a program to follow up 118 galaxy clusters with XMM-Newton, with the goal of studying the end point of structure formation, combining X-ray, SZ, lensing, and optical data. The scientific exploration of CHEX-MATE relies on our ability to analyze the data without introducing any bias. We are working on verifying the precision and accuracy of our observational techniques with simulations. In this talk, I will introduce the CHEX-MATE galaxy cluster sample, explain the strategy, the processing, and the analysis of our realistic simulations. I will show our current results in the comparison between input and recovered properties. Finally, I will discuss some open questions, whose answer will be a key step in the interpretation of CHEX-MATE cluster properties.
Supermassive black hole feedback is the currently favoured mechanism to regulate the star formation rate of galaxies and prevent the formation of ultra-massive galaxies (M_star > 1e12 Msun). However, the mechanism through which the outflowing energy is transferred to the surrounding medium strongly varies from one galaxy evolution model to another, such that a unified model for AGN feedback does not currently exist. The hot atmospheres of galaxy groups are highly sensitive laboratories of the feedback process, as the injected black hole energy is comparable to the binding energy of halo gas particles. The integrated AGN energy input can be estimated by comparing the observed group entropy with the expectations of adiabatic models including gravitational collapse only, since in regions where gas cooling is negligible the entropy can only increase. In this respect, I will present multi-wavelength observations of the fossil galaxy group SDSSTG 4436. This galaxy group features an unexpectedly elevated level of entropy, which implies that non-gravitational energy input in the past has heated up the gas to the point where it can no longer condense and form a classical cooling core. I will then discuss the implications of this discovery for our understanding of the feedback phenomenon in galaxy groups and massive galaxies.
Red quasars constitute an important but elusive phase in the evolution of supermassive black holes, where dust obscuration can significantly alter their observed properties. Using the Euclid Q1 dataset, we developed a selection method based on machine learning and multidimensional colour analysis, identifying over 150,000 candidate red quasars. Compared to VISTA+DECAm based colour selection criteria, Euclids superior depth, resolution, and optical-to-NIR coverage improves the identification of the reddest, most obscured sources. To refine our selection function, our approach combines probabilistic Random Forest classification with UMAP visualization, achieving 98% completeness and 88% purity. Notably, Euclid's exquisite resolution in the VIS filter unveils the presence of a candidate dual quasar system, highlighting the potential for Euclid to contribute to future studies on the population of dual AGN systems. In this talk, I will give an overview of the latest Euclid Q1 data release. I will also discuss how this analysis provides a first census of candidate red quasars in Euclid Q1 and sets the groundwork for future studies in the Euclid Wide Survey (EWS), including spectral and host morphology analyses.
Since recent progress on single photon detectors reaching accuracies under 10ps, various stellar intensity interferometry projects are starting and show great potential in astronomy. Despite the working principle being demonstrated in 1956 by Hanbury Brown and Twiss, it was only in 1963 that R.J. Glauber provided a complete quantum explanation of optical coherence, for which he received the Nobel Prize in 2005. The optical coherence of light has a great potential in astrophysics: Probing the second order coherence over km range baselines leads to angular resolution of the order of microarcsecond. Understanding the underlying effect requires some quantum context, specifically the fundamental difference, between the classical and the quantum explanation. In this presentation, I'll review the main ideas behind the quantum optical coherence developed by Glauber by providing a comprehensive explanation. I will also show the great potential that single photon detectors offer for astrophysics with recent results obtained in the lab using different types of sources.
2025-04-21 00:00:00 Holidays
2025-04-28 00:00:00 Skipped
Our oriject of systematically censing energy-dependent pulse profiles in accreting X-ray binaries with cyclotron resonance scattering features impressed on their spectrum revealed common trends and drastically different behaviors. We extract systematically maps of phase vs energy and optimize the signal to noise, then we use reduced quantities as the pulsed fraction to track differences. I will present three different cases and a preliminary attempt to model the results that potentially brings to some constraints in the model parameter space.
The Euclid Quick Release 1 (Q1) dataset provides a unique opportunity to study galaxy evolution through a large area. By measuring galaxy clustering across a wide area and high number density, we can trace the growth of cosmic structure over time. Euclids high resolution visible imager and deep infrared bands allow classification by morphology and colour, enabling analysis of clustering for different galaxy types (e.g., spirals, ellipticals, red, blue). This facilitates detailed studies of environmental effects and galaxy formation processes. Additionally, galaxy clustering halo occupation distribution fitting opens the path to constraining the stellar-to-halo mass relation, a key probe of galaxyhalo co-evolution. In this talk, I will share preliminary results from clustering analyses using Euclid Q1 data.
The growth of galaxies is closely tied to the growth of their dark matter haloes, which funnel in gas that cools, forms stars, or is expelled by feedback processes. In massive haloes, however, gas remains hot and strips star-forming material from galaxies, halting star formation. Identifying when and where this transition occurs is key to understanding galaxy evolution. To determine halo masses for galaxies of a given stellar mass, we rely on structure formation. Dark matter haloes cluster in patterns that reflect their mass and redshift. By measuring galaxy clustering, we infer halo masses using halo occupation distribution (HOD) modeling. My thesis investigates the evolution in the clustering of different galaxy populations across redshift ranges up to z =1 in four of the Dark Energy Survey (DES) Deep fields. Using the angular correlation function, we measure galaxy bias and infer the connection between galaxies and dark matter haloes. By analyzing multiple independent fields, we aim to mitigate cosmic variance effects and improve constraints on the clustering properties of galaxies.
The formation and growth of Supermassive Black Holes (BHs) of mass MBH = 10^(6 - 10) Msol, have always challenged our understanding of modern astronomy. Indeed, some of these objects were already in place at very early cosmic times, which makes us wonder how they assembled so quickly, and what happens once they reach such high masses that early in the history of the Universe. The focus of this talk is the BH - galaxy assembly in the most massive galaxies. We chose to explore the Botes field, making use of multi-wavelength data to target efficiently both Active Galactic Nuclei (AGN) in the X-ray with Chandra, and the host galaxy with optical/IR photometry to build their Spectral Energy Distribution (SED). By doing so, we assess how often massive galaxies host a growing BH, and how growth is governed in these extreme objects. Is it still on-going ? If so, how many of these objects are still growing and at which rate ? What are the properties of the galaxies hosting these extreme active BHs ? We found that, while AGN seem preferentially located in moderately massive galaxies of log(Mstar) > 10 Msol, we do not find a strong stellar mass dependence in AGN fraction or accretion rate distribution above this mass threshold. Our BH-galaxy growth tracks reveal that while most BH mass has been accumulated since z=4 for lower mass BHs, the assembly of the most massive BHs is more complex, with little to no mass gain since this epoch, and that the bulk of their mass was already in place very early on. This implies that we cannot account for most of BH growth through accretion between z=0-4, and that rapid and intense growth episodes over the first billion year of the Universe, were necessary to form these massive BHs.
The abundance of galaxy clusters across cosmic time offers a sensitive probe of cosmology. Designed as a discovery machine for galaxy clusters, the eROSITA soft X-ray telescope observes the hot intracluster gas that emits brightly in the X-ray band. In January 2024, the eROSITA collaboration released its first public data and results from the eRASS1 all-sky survey. As the collaboration moves toward the next major data release, significant efforts are underway to develop the tools required for robust cosmological analyses efforts to which I actively contribute. In this talk, I will present the scientific goals of the eROSITA mission and highlight key findings from the first data release (DR1). I will then discuss the role of simulations in modeling the detection of the cluster population, characterizing systematics, and refining the cluster selection function, critical steps toward unbiased cluster cosmology. I will introduce new simulations currently under development, share some early results, and outline how they feed into upcoming efforts to calibrate X-ray observablemass scaling relations for galaxy clusters.
2025-06-09 00:00:00 Holidays
The Cosmic X-ray Background Explorer (CXBe) is designed to measure the Cosmic X-ray Background (CXB) spectrum with unprecedented ~1% uncertainty, an order of magnitude better than existing measurements. This leap in accuracy will significantly enhance CXB synthesis modelling, particularly for understanding the Compton-thick black hole population. Supported by NASO, the project is currently in Phase A/B1, with preliminary design work and prototype development underway. A PRODEX proposal has recently been submitted to support the Flight Model development, with the goal of launching CXBe by 2029. In this talk, I will present recent progress and ongoing activities within the CXBe project.
2025-06-23 00:00:00 Dimitra Gerolymatou ** TBD
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2025-06-30 00:00:00 Nicolas Produit ** TBD
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Science Meeting Presentations
