Our nearest star-forming galaxy, the Large Magellanic Cloud (LMC), has been largely neglected in X-ray binary (XRB) populations studies targeting quiescent luminosities. In Chandra Cycle 24, we were awarded a Very Large Program (1 Ms) to perform a comprehensive survey of sources brighter than ~2 x 10^{32} erg/s in 10 LMC fields dominated by young (10 - 100 Myr) stellar populations of different...
Astrophysical black holes are surprisingly simple physical objects. Their gravitational field can be fully described by two parameters: mass and spin. We cannot directly observe black holes as no light escapes from the event horizon. However, we can detect the light from accreting gas, which forms a dense disk around the black hole, known as an accretion disk. The accretion of material by a...
Accreting supermassive black holes, or active galactic nuclei (AGN), are known to grow behind clouds of gas and dust, obscuring their view.
In orientation unification models, unobscured ($20<\log(N_{\rm H}/{\rm cm}^{-2}<22$) and obscured ($22< \log(N_{\rm H}/{\rm cm}^{-2}<24$) AGN differ only by their viewing angle, while evolutionary models suggest that obscuration correspond to a specific...
Theoretical models and hydrodynamical simulations of AGN feedback predict that outflows developing in AGN host galaxies have a multiphase and multiscale nature and that some physical mechanisms must link the inner regions where the SMBH gravitational field dominates, to the larger scales, where its direct influence is negligible. This paradigm has been unambiguously confirmed by a plethora of...
Blazars are highly variable radio-loud AGN, with jets closely aligned with the line-of-sight. These sources can be observed over the entire electromagnetic spectrum and are well monitored at, e.g., radio or gamma-ray wavelengths. The eROSITA telescope with its all-sky survey presents a unique opportunity to obtain an unbiased view of the blazar population in the X-ray band. By matching the...
The eRASS is expected to include tens of thousands of blazars. We present the initial results of an extensive search for blazars in both the eRASS1 and EFEDS surveys, primarily conducted at the Brera Observatory using the tools from the Firmamento online platform. We estimate the statistical properties of blazars, distinguishing between low and high energy peaked objects, as well as between...
Through its all-sky surveys, SRG/eROSITA has uncovered a large sample of X-ray transients associated with the nuclei of galaxies that show no signatures of prior AGN activity. A particular subclass is represented by tidal disruption events (TDEs), in which a flare of radiation is emitted as a star is ripped apart by wandering too close to a massive or supermassive black hole. Here, I will...
Period-bounce cataclysmic variables (CVs) are systems where a white dwarf accretes from a brown dwarf donor, having reached a point where the degeneracy of the donor reverses the orbit period evolution. A large portion of the CV population, between 40$\%$ and 70$\%$, is predicted to be made up of period-bouncers. However, due to their intrinsic faintness, only on the order of a dozen such...
The formation and growth of Supermassive Black Holes (BHs) of mass MBH = 10^(6 - 10) Msun, 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...
We report the detection of three simultaneous quasi-periodic oscillations (QPOs) at ∼ 40 Hz, ∼ 800 Hz, and ∼ 1100 Hz, along with a broad feature at ∼ 150 Hz from the AstroSat-LAXPC observation of NS-LMXB 4U 1728-34. For the very first time, we obtain thirteen sets of QPO triplets in time-resolved power density spectra for a particular observation. These QPO triplet frequencies are found to...
A direct approach to studying the galaxy-halo connection is the analysis of observed groups and clusters of galaxies that trace the underlying dark matter halos, making identifying galaxy clusters and their associated brightest cluster galaxies (BCGs) crucial. We test and propose a robust density-based clustering algorithm that outperforms the traditional Friends-of-Friends (FoF) algorithm in...
Despite many studies, superclusters, the largest structures in the cosmic web containing galaxy clusters on scales of tens to hundreds of megaparsecs (Mpc), remain enigmatic in their evolutionary processes. To shed light on this, we present a catalogue of 662 superclusters identified using a modified Friends-of-Friends algorithm applied to the WHL cluster catalogue within a redshift range of...
Active Galactic Nuclei (AGN) are powered by accretion of gas onto supermassive black holes. Persistently accreting AGNs, alongside inherent stochastic variability, sometimes display extreme flux and spectral changes (X-ray and/or optical fluxes), usually linked to significant variations in the global accretion rate. These drastic changes in the continuum flux are sometimes accompanied by...
Due to its high sensitivity in the soft X-ray band, eROSITA provides the perfect opportunity to study the diffuse X-ray emission of nearby galaxies. A Catalog of Neighboring Galaxies, presented by Karachentsev et al. (2013), was used to establish a sample of 72 nearby galaxies with distances $d \lesssim 17\,\mathrm{Mpc}$. For the 10 most luminous galaxies, the distribution and spectra were...
Thanks to their rapid rotation, millisecond pulsars are one of the most important sources to search for signatures of r-mode oscillations, which may be used to constrain the composition of neutron stars. This requires measurements or bounds on the surface temperatures of these faint objects. e-ROSITA, onboard Spektrum-Roentgen-Gamma satellite, recently completed the most detailed X-ray survey...
We present the preliminary results of our cross-correlation function (CCFs) measurements between eROSITA Final Equatorial-Depth Survey (eFEDS) AGNs and galaxies in the Galaxy And Mass Assembly (GAMA). The overlapped field covers ~60 deg$^2$, about half of the full eFEDS field. The X-ray sample is from our previous work (Comparat et al. 2023). The CCF enables us to measure the clustering...
An accurate mass calibration of galaxy clusters is a crucial step towards precise constraints on the cosmological parameters σ8 and Ωm from clusters. In the millimeter, via the Sunyaev-Zel’dovich (SZ) effect, and X-rays domains, cluster masses can be estimated assuming hydrostatic equilibrium, but several physical and observational effects can alter this calculation. One of those are...
In our project, we analyze the positions of X-ray selected AGNs on the
Baldwin-Phillips-Terlevich (BPT) diagram using eROSITA data. Previous
results from a sample of 1347 galaxies (z < 0.35) in SDSS DR17 revealed
a significant dependence of galaxy positions on the BPT diagram on the
X-ray/Hα flux ratio. Higher log(X-ray/Hα) values are associated with
Seyfert and LINER...
Nova explosions are thermonuclear events on top of an accreting white dwarf in a cataclysmic variable (CV) or a symbiotic system. The nova event results in the increase of the optical luminosity by 7-8 orders of magnitude. That makes the nova outburst detectable at any distance in the Galaxy, in the Local Group and even beyond the Local Group. However, due to the resulting distance...
Mapping the distribution of baryonic mass in our Universe down to the group-sized halo masses it is essential to clarify how much baryonic matter is locked up in halos and in filaments. Non-gravitational processes affect the thermodynamical conditions of the hot gas and baryonic content of groups and clusters of galaxies, causing deviations from the theoretical self-similar expectations....
We study the angular distribution of the exponent $(\rm x)$ of the differential number counts $\rm n(S) = \big(\frac{\rm d^{2}N}{\rm dSd\Omega}\big)\propto \rm S^{-1-x}$, i.e., number of quasars per unit solid angle per unit flux density $(\rm S)$, employing the CatWISES2020 catalog. We find the dipole anisotropy in this parameter with dipole amplitude $0.005\pm0.002$ and direction points...
The eROSITA telescope is revolutionizing X-ray astronomy with its ability to produce large all-sky surveys. eROSITA will catalog the hot intracluster medium (ICM) of thousands of galaxy clusters. This unprecedented sample of galaxy clusters is crucial for updating our theoretical understanding of the physics shaping the gaseous cores of clusters.
Inspired as a theoretical counterpart to...
Context. Cosmological simulations indicate that half of the baryons in the nearby universe exist as warm-hot intergalactic medium (WHIM), and half of this WHIM gas resides in cosmic filaments that connect galaxy clusters. Accurate prescription of the filament gas is therefore essential for understanding the gravitational and baryonic processes that affect the assembly of the cosmic...
Classical novae are known to demonstrate a supersoft X-ray source (SSS) state following outbursts. This state is associated with residual thermonuclear burning on the white dwarf (WD) surface. We performed a spectral analysis of the supersoft X-ray phase of the classical nova AT 2018bej, which was observed in X-rays by the eROSITA and XMM-Newton telescopes. To describe the spectrum we...
When measuring photon counts from incoming sky fluxes, X-ray observatories imprint nuisance effects on the data that must be accurately removed. Some detector effects can be easily inverted, while others are not trivially invertible such as the point spread function and shot noise. Using information field theory and Bayes' theorem, we infer the posterior mean and uncertainty for the sky flux....
The first eROSITA All-Sky Survey (eRASS-1) yielded a wealth of galaxy clusters across the sky. With the public release of this data in February 2024, the need for tools to automate and streamline large sample analysis became imperative. We present a sample of approximately 150 galaxy clusters detected by the Dark Energy Survey’s (DES) redMaPPer algorithm, eROSITA source detection, and in XMM...
Although flux variability is one of the fundamental properties of accretion flows onto supermassive black holes, its dependence on physical parameters such as the mass of the compact object and the Eddington ratio are still debated. In this contribution I will present new observational constraints on the Power Spectral Density (PSD) of the X-ray variability of Active Galactic Nuclei as a...
An open question in extragalactic astronomy is the extent to which Active Galactic Nuclei (AGN) affect the evolution of their host galaxies. Host galaxy properties of AGN, such as Star Formation Rate and Stellar Mass, are key parameters for studying the role of AGN in galaxy evolution.
However, disentangling the emission of AGN and star-forming components is a challenging task that...
The interstellar medium (ISM) is heated and ionized by radiation, by stellar winds, and finally, by supernova explosions. Since these processes are often correlated in space and time, they can form large interstellar structures called superbubbles, which are filled with hot thin plasma. If superbubbles expand and break, the hot plasma will escape into the galactic disk and also out of the...
Context. The spatial distribution of galaxy clusters provides a reliable tracer of the large-scale distribution of matter in the Universe.
The clustering signal depends on intrinsic cluster properties and cosmological parameters.
Aims. The ability of eROSITA on board Spectrum-Roentgen-Gamma (SRG) to discover galaxy clusters allows the association of
extended X-ray emission with dark matter...
The soft X-ray telescope eROSITA aboard the Spectrum-Roentgen-Gamma (SRG) mission is the first located in a halo orbit around the Sun-Earth L2 Lagrangian Point. With its main scientific goal to find 100000 clusters of galaxies for cosmological studies detailed knowledge of the background is crucial to be able to distiniguish faint extended objects from point-like sources and to determine...
In this work we will scrutinize the universality of the well-known non-linear relation between the UV and X-ray luminosity of AGNs. The LX-LUV correlation provides insights on the energy generating mechanisms and structural characteristics of AGNs, but it has also been proposed as a cosmological probe, under the assumption that it is redshift independent. However, recent works on the subject...
The formation and evolution of the first supermassive black holes have been put in the spotlight after the discovery of few hundreds extremely massive quasars at high redshift. An interesting twist in our understanding of the matter was introduced by the discovery of an unusual number of jetted sources: X-ray observations of blazars (i.e. AGN with jets aligned to our LoS) at z>4 prove that the...
Accreting compact binaries (ACB) are among the most luminous X-ray sources within the Galaxy. By incorporating machine learning techniques, we have identified roughly 11,000 potential ACB candidates in the eROSITA data sample. Optical spectroscopic observations are, however, now required to determine whether these candidates are true ACBs. For this project we are, therefore, conducting...
Evolutionary scenarios predict that obscured quasars play a key role in the evolution of galaxies; however, this role has not yet been fully understood since quasar samples are typically biased against obscured systems. We select and constrain the AGN and host galaxy properties of a complete and unbiased sample of ~600 infrared (IR) quasars ($L_{\rm AGN,IR}>10^{45} \rm \:erg\: s^{-1}$) at...
Active Galactic Nuclei (AGNs), found at the centers of galaxies, harbor supermassive black holes that emit immense energy across the electromagnetic spectrum. Traditionally, AGNs are classified based on factors like orientation (Type 1 vs. Type 2), radio emission (Radio-Loud vs. Radio-Quiet), or the presence of jets (Jetted vs. non-Jetted). However, these classifications may not fully capture...
We review recent advancements in the measurement of the weak gravitational lensing (WL) signature induced by the potentials of galaxy clusters onto the shapes of background galaxies. In the context of wide photometric surveys, we discuss how this poses unique challenges and opportunities and how we addressed and leveraged them. After discussing the recent advancements in the measurement of WL,...
AGN feedback is a key process in the evolution of massive systems in the Universe, and one for which new observational information is crucial for better implementation of numerical models. An image-manipulation technique capable of providing such information, X-arithmetic, is applied here to a sample of 15 galaxy clusters and groups deeply observed with Chandra. This technique decomposes...
Galaxy clusters, the largest gravitationally bound structures in the universe, provide astronomers with insights into the formation and evolution of large-scale structures through the study of their mergers. X-ray observations allow for direct analysis of the intracluster gas, revealing vital information such as temperature and entropy distribution, which aids in understanding the merging...
In magnetic cataclysmic variables, X-ray emission is emitted from optically thin shock-heated plasma at the poles of the white dwarf. The X-ray emitting plasma has a continuous temperature distribution that can be reflected and/or reprocessing in the system before reaching the observer. The X-ray photons are reflected by the surface of the white dwarf, leading to a fluorescent iron K-alpha...