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E. Bulbul

Publications and source records attributed to E. Bulbul.

At least 55 records · Page 3Linked to original sources
arXiv2024

The SRG/eROSITA All-Sky Survey: First catalog of superclusters in the western Galactic hemisphere

Superclusters of galaxies mark the large-scale overdense regions in the Universe. Superclusters provide an ideal environment to study structure formation and to search for the emission of the intergalactic medium such as cosmic filaments and WHIM. In this work, we present the largest-to-date catalog of X-ray-selected superclusters identified in the first SRG/eROSITA All-Sky Survey (eRASS1). By applying the Friends-of-Friends method on the galaxy clusters detected in eRASS1, we identified 1338 supercluster systems in the western Galactic hemisphere up to redshift 0.8, including 818 cluster pairs and 520 rich superclusters with $\ge 3$ members. The most massive and richest supercluster system is the Shapley supercluster at redshift 0.05 with 45 members and a total mass of $2.58\pm0.51 \times10^{16} M_{\odot}$. The most extensive system has a projected length of 127~Mpc. The sizes of the superclusters we identified in this work are comparable to the structures found with galaxy survey data. We also found a good association between the eRASS1 superclusters and the large-scale structures formed by optical galaxies. 3948 clusters, corresponding to $45\%$ of the cluster sample, were identified as supercluster members. The reliability of each supercluster was estimated by considering the uncertainties in cluster redshifts and peculiar velocities. 63\% of the systems have a reliability larger than 0.7. The eRASS1 supercluster catalog provided in this work represents the most extensive sample of superclusters selected in the X-ray band in terms of the unprecedented sample volume, sky coverage, redshift range, the availability of X-ray properties, and the well-understood selection function of the parent cluster sample, which enables direct comparisons with numerical simulations. This legacy catalog will greatly advance our understanding of superclusters and the cosmic large-scale structure.

astro-ph.CO↗
arXiv2024

The SRG/eROSITA All-Sky Survey: Dark Energy Survey Year 3 Weak Gravitational Lensing by eRASS1 selected Galaxy Clusters

Number counts of galaxy clusters across redshift are a powerful cosmological probe, if a precise and accurate reconstruction of the underlying mass distribution is performed -- a challenge called mass calibration. With the advent of wide and deep photometric surveys, weak gravitational lensing by clusters has become the method of choice to perform this measurement. We measure and validate the weak gravitational lensing (WL) signature in the shape of galaxies observed in the first 3 years of the DES Y3 caused by galaxy clusters selected in the first all-sky survey performed by SRG/eROSITA. These data are then used to determine the scaling between X-ray photon count rate of the clusters and their halo mass and redshift. We empirically determine the degree of cluster member contamination in our background source sample. The individual cluster shear profiles are then analysed with a Bayesian population model that self-consistently accounts for the lens sample selection and contamination, and includes marginalization over a host of instrumental and astrophysical systematics. To quantify the accuracy of the mass extraction of that model, we perform mass measurements on mock cluster catalogs with realistic synthetic shear profiles. This allows us to establish that hydro-dynamical modelling uncertainties at low lens redshifts ($z<0.6$) are the dominant systematic limitation. At high lens redshift the uncertainties of the sources' photometric redshift calibration dominate. With regard to the X-ray count rate to halo mass relation, we constrain all its parameters. This work sets the stage for a joint analysis with the number counts of eRASS1 clusters to constrain a host of cosmological parameters. We demonstrate that WL mass calibration of galaxy clusters can be performed successfully with source galaxies whose calibration was performed primarily for cosmic shear experiments.

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arXiv2024

The SRG/eROSITA All-Sky Survey: Tracing the Large-Scale Structure with a clustering study of galaxy clusters

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. The ability of eROSITA onboard Spectrum-Roentgen-Gamma (SRG) to discover galaxy clusters allows probing the association of extended X-ray emission to dark matter haloes. We aim to measure the projected two-point correlation function to study the occupation of dark matter halos by clusters and groups detected by the first eROSITA all-sky survey (eRASS1). We create five volume-limited samples probing clusters with different redshift and X-ray luminosity. We interpret the correlation function with halo occupation distribution (HOD) and halo abundance matching (HAM) models. We simultaneously fit cosmological parameters and halo bias of a flux-limited sample of 6493 clusters with purity > 96%. Results. We obtain a detailed view of the halo occupation for eRASS1 clusters. The fainter population at low redshift (S0: LX = 4.63E43 erg/s, 0.1 < z < 0.2) is the least biased compared to dark matter, with b = 2.95 $\pm$ 0.21. The brightest clusters up to higher redshift (S4: LX = 1.77E44 erg/s , 0.1 < z < 0.6) exhibit a higher bias b = 4.34 $\pm$ 0.62. Satellite groups are rare, with a satellite fraction < 14.9% (8.1) for the S0 (S4) sample. We combine the HOD prediction with a HAM procedure to constrain the scaling relation between LX and mass in a new way and find a scatter of 0.36. We obtain cosmological constraints for the physical cold dark matter density 0.12+0.03-0.02 and an average halo bias b = 3.63+1.02-0.85. We model the clustering of galaxy clusters with a HOD approach for the first time, paving the way for future studies combining eROSITA with 4MOST, SDSS, Euclid, Rubin, and DESI to unravel the cluster distribution in the Universe.

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arXiv2024

The SRG/eROSITA All-Sky Survey: X-ray selection function models for the eRASS1 galaxy cluster cosmology

Characterising galaxy cluster populations from catalog of sources selected in astronomical surveys requires knowledge of sample incompleteness, known as selection function. The first All-Sky Survey (eRASS1) by eROSITA onboard Spectrum Roentgen Gamma (SRG) has enabled the collection of large samples of galaxy clusters detected in the soft X-ray band over the Western Galactic hemisphere. The driving goal consists in constraining cosmological parameters, which puts stringent requirements on accuracy, flexibility and explainability of the selection function models. We use a large set of mock observations of the eRASS1 survey and we process simulated data identically to the real eRASS1 events. We match detected sources to simulated clusters and we associate detections to intrinsic cluster properties. We train a series of models to build selection functions depending only on observable surface brightness data. We develop a second series of models relying on global cluster characteristics such as X-ray luminosity, flux, and expected instrumental count-rate as well as on morphological properties. We validate our models using our simulations and we rank them according to selected performance metrics. We validate the models with datasets of clusters detected in X-rays and via the Sunyaev-Zeldovich effect. We present the complete Bayesian population modelling framework developed for this purpose. Our results reveal the surface brightness characteristics most relevant to cluster selection in the eRASS1 sample, in particular the ambiguous role of central surface brightness at the scale of the instrument resolution. We have produced a series of user-friendly selection function models and demonstrated their validity and their limitations. Our selection function for bright sources reproduces well the catalog matches with external datasets. (abridged)

astro-ph.CO↗
arXiv2024

The SRG-eROSITA All-Sky Survey : Constraints on f(R) Gravity from Cluster Abundance

The evolution of the cluster mass function traces the growth of the linear density perturbations and can be utilized for constraining the parameters of cosmological and alternative gravity models. In this context, we present new constraints on potential deviations from general relativity by investigating the Hu-Sawicki parametrization of the f(R) gravity with the first SRG-eROSITA All-Sky Survey (eRASS1) cluster catalog in the Western Galactic Hemisphere in combination with the overlapping Dark Energy Survey Year 3, KiloDegree Survey and Hyper Supreme Camera data for weak lensing mass calibration. For the first time, we present constraints obtained from cluster abundances only. When we consider massless neutrinos, we find a strict upper limit of log |fR0| < -4.31 at 95% confidence level. Massive neutrinos suppress structure growth at small scales, and thus have the opposite effect of f(R) gravity. We consequently investigate the joint fit of the mass of the neutrinos with the modified gravity parameter. We obtain log |fR0| < -4.12 jointly with \sum m_ν< 0.44 e.V. at 95% confidence level, tighter than the limits in the literature utilizing cluster counts only. At log |fR0|= - 6, the number of clusters is not significantly changed by the theory. Consequently, we do not find any statistical deviation from general relativity from the study of eRASS1 cluster abundance. Deeper surveys with eROSITA, increasing the number of detected clusters, will further improve constraints on log |fR0| and investigate alternative gravity theories.

astro-ph.CO↗
arXiv2024

The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere

The eROSITA telescope array aboard the Spektrum Roentgen Gamma (SRG) satellite began surveying the sky in December 2019, with the aim of producing all-sky X-ray source lists and sky maps of an unprecedented depth. Here we present catalogues of both point-like and extended sources using the data acquired in the first six months of survey operations (eRASS1; completed June 2020) over the half sky whose proprietary data rights lie with the German eROSITA Consortium. We describe the observation process, the data analysis pipelines, and the characteristics of the X-ray sources. With nearly 930000 entries detected in the most sensitive 0.2-2.3 keV energy range, the eRASS1 main catalogue presented here increases the number of known X-ray sources in the published literature by more than 60%, and provides a comprehensive inventory of all classes of X-ray celestial objects, covering a wide range of physical processes. A smaller catalogue of 5466 sources detected in the less sensitive but harder 2.3-5 keV band is the result of the first true imaging survey of the entire sky above 2 keV. We show that the number counts of X-ray sources in eRASS1 are consistent with those derived over narrower fields by past X-ray surveys of a similar depth, and we explore the number counts variation as a function of the location in the sky. Adopting a uniform all-sky flux limit (at 50% completeness) of F_{0.5-2 keV} > 5 \times 10^{-14}$ erg\,s$^{-1}$\,cm$^{-2}$, we estimate that the eROSITA all-sky survey resolves into individual sources about 20% of the cosmic X-ray background in the 1-2 keV range. The catalogues presented here form part of the first data release (DR1) of the SRG/eROSITA all-sky survey. Beyond the X-ray catalogues, DR1 contains all detected and calibrated event files, source products (light curves and spectra), and all-sky maps. Illustrative examples of these are provided.

astro-ph.HE↗
arXiv2023

The X-ray invisible Universe. A look into the halos undetected by eROSITA

The paper presents the analysis of optically selected GAMA groups and clusters in the SRG/eROSITA X-ray map of eFEDS (eROSITA Final Equatorial Depth Survey), in the halo mass range $10^{13}-5{\times}10^{14}$ $M_{\odot}$ and at $z < 0.2$. All X-ray detections have a clear GAMA counterpart, but most of the GAMA groups in the halo mass range $10^{13}-10^{14}$ $M_{\odot}$ remain undetected. We compare the X-ray surface brightness profiles of the eROSITA detected groups with the mean stacked profile of the undetected low-mass halos at fixed halo mass. Overall, we find that the undetected groups exhibit less concentrated X-ray surface brightness, dark matter, and galaxy distributions with respect to the X-ray detected halos. The mean gas mass fraction profiles are consistent in the two samples within 1.5$σ$, indicating that the gas follows the dark matter profile. The low mass concentration and the magnitude gap indicate that these systems are young. They reside with a higher probability in filaments while X-ray detected groups favor the nodes of the Cosmic Web. Because of the lower central emission, the undetected systems tend to be X-ray under-luminous at fixed halo mass and to lie below the $L_X-M_{halo}$ relation. Interestingly, the X-ray detected systems inhabiting the nodes scatter the less around the relation, while those in filaments tend to lie below it. We do not observe any strong relationship between the system X-ray appearance and the AGN activity. We cannot exclude the role of the past AGN feedback in affecting the gas distribution over the halo lifetime. However, the data suggests that the observed differences might be related to the halo assembly bias.

astro-ph.CO↗
arXiv2023

SPT-SZ MCMF: An extension of the SPT-SZ catalog over the DES region

We present an extension to a Sunyaev-Zel'dovich Effect (SZE) selected cluster catalog based on observations from the South Pole Telescope (SPT); this catalog extends to lower signal-to-noise than the previous SPT-SZ catalog and therefore includes lower mass clusters. Optically derived redshifts, centers, richnesses and morphological parameters together with catalog contamination and completeness statistics are extracted using the multi-component matched filter algorithm (MCMF) applied to the S/N>4 SPT-SZ candidate list and the Dark Energy Survey (DES) photometric galaxy catalog. The main catalog contains 811 sources above S/N=4, has 91% purity and is 95% complete with respect to the original SZE selection. It contains 50% more total clusters and twice as many clusters above z=0.8 in comparison to the original SPT-SZ sample. The MCMF algorithm allows us to define subsamples of the desired purity with traceable impact on catalog completeness. As an example, we provide two subsamples with S/N>4.25 and S/N>4.5 for which the sample contamination and cleaning-induced incompleteness are both as low as the expected Poisson noise for samples of their size. The subsample with S/N>4.5 has 98% purity and 96% completeness, and will be included in a combined SPT cluster and DES weak-lensing cosmological analysis. We measure the number of false detections in the SPT-SZ candidate list as function of S/N, finding that it follows that expected from assuming Gaussian noise, but with a lower amplitude compared to previous estimates from simulations.

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arXiv2023

Central radio galaxies in galaxy clusters: Joint surveys by eROSITA and ASKAP

The extended ROentgen Survey with an Imaging Telescope Array (eROSITA) telescope onboard the Spectrum-Roentgen-Gamma (SRG) mission has finished the first eROSITA All-Sky Survey (eRASS:1), and detected 10$^4$ galaxy clusters in the western Galactic hemisphere. In the radio band, the Australian Square Kilometre Array Pathfinder (ASKAP) telescope finished its pilot 1 phase of the project 'Evolutionary Map of the Universe' (EMU) with 220.000 sources in a 270 deg$^2$ field overlapping with eRASS:1. These two surveys are used to study radio-mode Active Galactic Nuclei (AGN) in clusters. In order to understand the efficiency of radio-mode feedback at the centers of galaxy clusters, we relate the radio properties of brightest cluster galaxies (BCG) to the X-ray properties of the host clusters. We identify the central radio sources in eRASS:1 clusters or calculate corresponding upper limits on the radio luminosity. Then, we derive relations between the X-ray properties of the clusters and the radio properties of the corresponding central radio source. We also apply a mid-infrared color criterion using WISE colors to identify AGN. In total we investigate a sample of 75 clusters. We find a statistically significant correlation between the X-ray luminosity of the cluster and the 944 MHz radio luminosity of the corresponding central radio galaxy. There is also a positive trend between the radio power and the largest linear size (LLS) of the radio source. The density and the LLS do not show any correlation. We find that in high luminosity clusters with L_X > $10^{43}$ erg s$^{-1}$ the kinetic luminosity of the radio jets is not longer correlated with the X-ray luminosity and discuss various reasons. We find an anti-correlation between the central cooling time t_cool and the radio luminosity L_R indicating a need for more powerful AGN in clusters with short central cooling times.

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arXiv2023

ViCTORIA project: The LOFAR HBA Virgo Cluster Survey

The Virgo cluster is the nearest massive galaxy cluster and thus a prime target to study astrophysical processes in dense large-scale environments. In the radio band, we can probe the non-thermal components of the inter-stellar medium (ISM), intracluster medium (ICM) and of active galactic nuclei (AGN). With the ViCTORIA (Virgo Cluster multi-Telescope Observations in Radio of Interacting galaxies and AGN) project, we are carrying out multiple wide-field surveys of the Virgo cluster at different frequencies. We aim to investigate the impact of the environment on the evolution of galaxies and the contribution of AGN to the ICM-heating, from the inner cluster regions out to beyond the virial radius. We present a survey of the cluster at 120-168 MHz using LOFAR. We image a 132 deg$^2$ region of the cluster, reaching an order of magnitude greater sensitivity than existing wide-field radio surveys of this field at three times higher spatial resolution compared to other low-frequency observations. We developed a tailored data processing strategy to subtract the bright central radio galaxy M87 from the data. This allowed us to correct for the systematic effects due to ionospheric variation as a function of time and direction. In the final mosaic with a resolution of 9"x5", we reach a median noise level of 140 $μ$Jy/beam inside the virial radius and 280 $μ$Jy/beam for the full area. We detect 112 Virgo member galaxies and 114 background galaxies. In at least 18 cases, the radio morphology of the cluster member galaxies shows clear signs of ram-pressure stripping. This includes three previously unreported candidates. In addition, we reveal for the first time 150 kpc long tails from a previous epoch of AGN activity for NGC 4472 (M 49). While no cluster-scale diffuse radio sources are discovered, we find the presence of an extended radio signature of the W$'$-group.

astro-ph.GA↗
arXiv2023

A search for inter-cluster filaments with LOFAR and eROSITA

Cosmological simulations predict the presence of warm hot thermal gas in the cosmic filaments that connect galaxy clusters. This gas is thought to constitute an important part of the missing baryons in the Universe. In addition to the thermal gas, cosmic filaments could contain a population of relativistic particles and magnetic fields. A detection of magnetic fields in filaments can constrain early magnetogenesis in the cosmos. So far, the resulting diffuse synchrotron emission has only been indirectly detected. We present our search for thermal and non-thermal diffuse emission from inter-cluster regions of 106 paired galaxy clusters by stacking the $0.6-2.3$~keV X-ray and 144~MHz radio data obtained with the eROSITA telescope on board the Spectrum-Roentgen-Gamma (SRG) observatory and LOw Frequency ARray (LOFAR), respectively. The stacked data do not show the presence of X-ray and radio diffuse emission in the inter-cluster regions. This could be due to the sensitivity of the data sets and/or the limited number of cluster pairs used in this study. Assuming a constant radio emissivity in the filaments, we find that the mean radio emissivity is not higher than $1.2\times10^{-44}\,{\rm erg \, s^{-1} \, cm^{-3} \, Hz^{-1}}$. Under equipartition conditions, our upper limit on the mean emissivity translates to an upper limit of $\sim75\,{\rm nG}$ for the mean magnetic field strength in the filaments, depending on the spectral index and the minimum energy cutoff. We discuss the constraint for the magnetic field strength in the context of the models for the formation of magnetic fields in cosmic filaments.

astro-ph.HE↗
arXiv2023

Effects of Multiphase Gas and Projection on X-ray Observables in Simulated Galaxy Clusters as Seen by eROSITA

The number density of galaxy clusters as a function of mass and redshift is a sensitive function of the cosmological parameters. To use clusters for cosmological parameter studies, it is necessary to determine their masses as accurately as possible, which is typically done via mass-observable scaling relations. X-ray observables can be biased by multiphase gas and projection effects, especially in the case where cluster temperatures and luminosities are estimated from single-model fits to all of the emission with a given radius. Using simulated galaxy clusters from a realistic cosmological simulation, we seek to determine the importance of these biases in the context of Spectrum-Roentgen-Gamma/eROSITA observations of clusters. We extract clusters from the Magneticum suite, and simulate eROSITA observations of these clusters using PHOX and SIXTE. We compare the fitted observables from these observations to those derived from the simulations. We fitted an intrinsically scattered $L_{\rm X}-T$ scaling relation to these measurements following a Bayesian approach with which we fully took into account the selection effects and the mass function. The largest biases on the cluster observables come from the inadequacy of single-temperature model fits to represent emission from multiphase gas, as well as a bias arising from cluster emission within the projected $r_{500c}$ along the line of sight but outside of the spherical $r_{500c}$. We find that the biases on temperature and luminosity due to the projection of emission from other clusters within $r_{500c}$ is small. We find that our simulated clusters follow a $L_{\rm X}-T$ scaling relation that has a broadly consistent but slightly shallower slope compared to the literature, and that the intrinsic scatter of $L_{\rm X}$ at given T is lower compared to the recent observational results where the selection effects are fully considered.

astro-ph.CO↗
arXiv2023

Discovery of the lensed quasar eRASS1 J050129.5-073309 with $\textit{SRG}/$eROSITA and ${\it Gaia}$

We report the discovery and spectroscopic identification of the bright doubly lensed quasar eRASS1 J050129.5-073309 at redshift $z=2.47$, selected from the first all-sky survey of the ${\it Spectrum\; Roentgen\; Gamma\; (SRG)}$ eROSITA telescope and the ${\it Gaia}$ EDR3 catalog. We systematically search for extragalactic sources with eROSITA X-ray positions having multiple ${\it Gaia}$ counterparts and have started spectroscopic follow-up of the most promising candidates using long-slit spectroscopy with NTT/EFOSC2 to confirm the lens nature. The two images are separated by $2.7''$ and their average ${\it Gaia}$ ${\it g}$-band magnitudes are 16.95 and 17.33. Legacy Survey DR10 imaging and image modeling reveal both the lensing galaxy and tentatively the lensed image of the quasar host galaxy. Archival optical light curves show evidence of a variability time delay with the fainter component lagging the brighter by about 100 days. The fainter image has also decreased its brightness by about 1 magnitude since 2019. This dimming was still obvious at the time of the spectroscopic observations and is probably caused by microlensing. The optical spectroscopic follow-up obtained from NTT/EFOSC2 and the evidence provided by the imaging and timing analysis allow us to confirm the lensed nature of eRASS1 J050129.5-073309.

astro-ph.GA↗
arXiv2022

Offset between X-ray and optical centers in clusters of galaxies: connecting eROSITA data and simulations

The characterization of the dynamical state of clusters is key to study their evolution, their selection, and use them as a cosmological probe. The offsets between different definitions of the center have been used to estimate the cluster disturbance. Our goal is to study the distribution of the offset between the X-ray and optical centers in clusters of galaxies. We study the offset for eROSITA clusters. We aim to connect observations to hydrodynamical simulations and N-body models. We assess the astrophysical effects affecting the displacements. We measure the offset for clusters observed in eFEDS and eRASS1. We focus on a subsample of 87 massive eFEDS clusters at low redshift. We link the observations to the offset parameter Xoff measured on dark matter halos in N-body simulations, using the hydrodynamical simulations as a bridge. eFEDS clusters show a smaller offset compared to eRASS1, because the latter contains a larger fraction of massive and disturbed structures. We measure an average offset of 76.3+30.1-27.1 kpc on the subsample of 87 eFEDS clusters. This is in agreement with the predictions from TNG and Magneticum, and the distribution of Xoff from DMO simulations. The tails of the distributions are different. Using the offset to classify relaxed and disturbed clusters, we measure a relaxed fraction of 31% in the eFEDS subsample. Finally, we find a correlation between the offset in hydrodynamical simulations and Xoff measured on their parent DMO run and calibrate a relation between them. There is good agreement between eROSITA data and simulations. Baryons cause a decrement (increment) in the low (high) offset regime compared to the Xoff distribution. The offset-Xoff relation provides an accurate prediction of the true Xoff distribution in Magneticum and TNG. It allows introducing the offsets in cosmology, marginalizing on dynamical selection effects.

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arXiv2022

X-ray analysis of JWST's first galaxy cluster lens SMACS J0723.3-7327

SMACS~J0723.3-7327 is the first galaxy cluster lens observed by JWST. Based on the ERO data from JWST, several groups have reported the results on strong lensing analysis and mass distribution of this cluster. However, limited by the angular coverage of the JWST data, the strong lensing models only cover the central region. X-ray analysis on the hot ICM is necessary to obtain a more complete constraint on the mass distribution in this very massive cluster. In this work, we aim to perform a comprehensive X-ray analysis of J0723 to obtain accurate ICM hydrostatic mass measurements, using the X-ray data from SRG/eROSITA and Chandra X-ray observatories. By comparing the hydrostatic mass profile with the strong lensing model, we aim to provide the most reliable constraint on the distribution of mass up to R500. Thanks to the eROSITA all-sky survey and Chandra data, which provide high S/N and high angular resolution respectively, we are able to constrain the ICM gas density profile and temperature profile with good accuracy both in the core and to the outskirts. With the density and temperature profiles, we compute the hydrostatic mass profile, which is then projected along the line of sight to compare with the mass distribution obtained from the recent strong lensing analysis based on JWST data. We also deproject the strong lensing mass distribution using the hydrostatic mass profile we obtained in this work. The X-ray results obtained from eROSITA and Chandra agree very well with each other. The hydrostatic mass profiles we measured in this work, both projected and deprojected, are in good agreement with recent strong lensing results based on JWST data, at all radii. We also find that the radial acceleration relation in J0723 is inconsistent with the RAR for spiral galaxies, implying that the latter is not a universal property of gravity across all mass scales.

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arXiv2022

The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray properties of Subaru optically-selected clusters

We present the results of a systematic X-ray analysis of optically rich galaxy clusters detected by the Subaru HSC survey in the eROSITA eFEDS field. Through a joint analysis of SRG/eROSITA and Subaru/HSC surveys, we aim to study the dynamical status of the optically selected clusters and derive the cluster scaling relations. The sample consists of 43 optically selected galaxy clusters with a richness $>40$ in $0.16<z<0.89$. We systematically analyzed the X-ray images and spectra using the eROSITA data. We identified the BCG using the optical and far-infrared databases. We evaluated the cluster's dynamical status by measuring the offset between the X-ray peak and BCG position, the gas concentration, and the number of galaxy-density peaks. We studied the luminosity-temperature and mass-luminosity relations based on eROSITA X-ray spectra and HSC weak-lensing data analyses. Based on the these measurements, the fraction of relaxed clusters is $2(<39)$%, which is smaller than that of the X-ray-selected cluster samples. After correcting for a selection bias due to the richness cut, we obtained a shallow $L-T$ slope of $2.1\pm0.5$, which is consistent with the predictions of the self-similar model and the baseline model incorporating a mass-concentration relation. The $L-M$ slope of $1.5\pm0.3$ agrees with the above theoretical models and that of the shear-selected clusters in the eFEDs field. Our analysis of high-richness optical clusters yields a small fraction of relaxed clusters and a shallow slope for the luminosity-temperature relation. This suggests that the average X-ray properties of the optical clusters are likely to be different from those observed in the X-ray samples. Thus, the joint eROSITA and HSC observations are a powerful tool in extending the analysis to a larger sample and understanding the selection effect with a view to establish cluster scaling relations.

astro-ph.CO↗
arXiv2022

Detecting clusters of galaxies and active galactic nuclei in an eROSITA all-sky survey digital twin

The extended ROentgen Survey with an Imaging Telescope Array (eROSITA) onboard the Spectrum-Roentgen-Gamma (SRG) observatory is revolutionizing X-ray astronomy. It provides large samples of active galactic nuclei (AGN) and clusters of galaxies, with the potential of studying X-ray sources and measuring cosmological parameters using X-ray-selected samples with higher precision than ever before. We aim to study the detection, and the selection of AGN and clusters in the first eROSITA all-sky survey (eRASS1), and to characterize the properties of the source catalog. We produced a half-sky eRASS1 simulation, by combining models that truthfully represent the clusters and AGN. In total, we simulated 1 116 758 clusters and 225 583 320 AGN. We ran the standard eROSITA detection algorithm. We matched the input and source catalogs with a photon-based algorithm. We perfectly recovered the bright sources. We detected half of the AGN brighter than 2e-14 erg/s/cm2 as point sources and half of the clusters brighter than 3e-13 erg/s/cm2 as extended in the 0.5-2.0 keV band. We quantified the detection performance in terms of completeness, false detection rate, and contamination. We studied the source catalog according to multiple cuts of detection and extension likelihood. We find that the detection of clusters is mainly driven by flux and exposure. It depends on secondary effects, such as the size of the clusters and their dynamical state. The cool core bias mostly affects faint clusters classified as point sources, while its impact on the extent-selected sample is small. The measured X-ray luminosity of the detected clusters is compatible with the simulated values. We discuss how to best build samples of galaxy clusters for cosmological purposes, accounting for the nonuniform depth of eROSITA. This simulation provides a digital twin of the real eRASS1.

astro-ph.CO↗
arXiv2022

X-Ray Studies of the Abell 3158 Galaxy Cluster with eROSITA

The most nearby clusters are the best places to study physical and enrichment effects in the faint cluster outskirts. A3158 located at z=0.059 is quite extended with a characteristic radius r$_{200}$=23.95 arcmin. In 2019, A3158 was observed as a calibration target in a pointed observation with the eROSITA telescope onboard the SRG mission. We determined 1d temperature, abundance and normalisation profiles from eROSITA and XMM-Newton and Chandra data as well as 2d maps of temperature distribution from eROSITA data. The velocity dispersion was determined and the cluster mass was calculated. The overall temperature was measured to be 4.725$\pm$ 0.035 keV. The profiles of eROSITA all agree on a ~10% level with those determined with XMM-Newton and Chandra data. From the temperature map we see that the cluster lacks a cool core, as noted before. The presence of a previously detected off-centre cool clump West of the central cluster region is observed. Furthermore there is a bow shaped edge near the location of the cool gas clump West of the cluster centre. An extension of gas is detected for the first time further out in the West. The velocity dispersion of the cluster was measured to be 1058$\pm$41 km s$^{-1}$. The total mass was determined as $M_{200}$=1.38$\pm$ 0.25x10$^{15}$ $M_{\odot}$. The mass estimate from the M-T relation is significantly lower at M$_{200}$=5.09$\pm$ 0.59x10$^{14}M_{\odot}$. An extended X-ray source located South of the cluster also coincides with a galaxy overdensity with redshifts in the range 0.05<z<0.07. These are indications that the cluster may be undergoing merger activity. Another extended source located North of the cluster is detected in X-rays and coincides with an overdensity of galaxies with redshifts in the range of 0.070<z<0.077. This is likely a background cluster not related to A3158. Additionally a known SPT cluster at z=0.53 was detected.

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