arXiv subjects

Vittorio Ghirardini

Publications and source records attributed to Vittorio Ghirardini.

At least 19 recordsLinked to original sources

arXiv2026

The life of central radio galaxies in clusters: AGN-ICM studies of eRASS1 clusters in the ASKAP fields

The mechanical feedback from the central AGNs can be crucial for balancing the radiative cooling of the intracluster medium at the cluster centre. We aim to understand the relationship between the power of AGN feedback and the cooling of gas in the centres of galaxy clusters by correlating the radio properties of the brightest cluster galaxies (BCGs) with the X-ray properties of their host clusters. We used catalogues from the first SRG/eROSITA All-Sky Survey (eRASS1) along with ASKAP radio data. In total, we identified 134 radio sources associated with BCGs of the 151 eRASS1 clusters located in the PS1, PS2, and SWAG-X ASKAP fields. Non-detections were treated as upper limits. We correlated BCG radio luminosity, largest linear size (LLS), and BCG offset with the integrated X-ray luminosity of their host clusters. To characterise cool cores (CCs) and non-cool cores (NCCs), we used the concentration parameter $c_{R_{500}}$ and combined it with the BCG offset to assess cluster dynamical state. We analysed the correlation between radio mechanical power and X-ray luminosity within the CC subsample. We observe a potential positive trend between LLS and BCG offset, suggesting an environmental effect on radio-source morphology. We find a weak trend where more luminous central radio galaxies are found in clusters with higher X-ray luminosity. Within the CC subsample, there is a positive but highly scattered relationship between the mechanical luminosity of AGN jets and the X-ray cooling luminosity. This finding is supported by bootstrap resampling and flux-flux analyses. The correlation indicates that AGN feedback is ineffective in high-luminosity (high-mass) clusters. At a cooling luminosity of $L_{\mathrm{X},~r<R_\mathrm{cool}}\approx 5.50\times10^{43}$ erg/s, on average, AGN feedback appears to contribute only about 13%-22% of the energy needed to offset the radiative losses in the ICM.

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arXiv2025

The SRG/eROSITA All-Sky Survey. The Weak-Lensing Mass Calibration and the Stellar Mass-to-Halo Mass Relation from the Hyper Suprime-Cam Subaru Strategic Program

We present the weak-lensing mass calibration and constrain the BCG (brightest cluster galaxy) stellar-mass-to-halo-mass-and-redshift ($M_{\star,\mathrm{BCG}}-M-z$) relation for a sample of $124$ galaxy clusters and groups at redshift $0.1<z<0.8$ from the first Data Release of the $eROSITA$ All-Sky Survey (eRASS1), using data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The cluster survey is conducted by the $eROSITA$ X-ray telescope aboard the Spectrum-Roentgen-Gamma (SRG) space observatory. The cluster sample is X-ray-selected and optically confirmed with a negligibly low contamination rate ($\approx5%$). On a basis of individual clusters, the shear profiles of $96$ clusters are derived using the HSC Three-Year (HSC-Y3) weak-lensing data, while the BCG stellar masses of $101$ clusters are estimated using the SED template fitting to the HSC five-band ($grizY$) photometry. The observed X-ray photon count rate is used as the mass proxy, based on which individual halo masses are obtained at the given count rate in a population modelling while accounting for systematic uncertainties in the weak-lensing modelling through a simulation-calibrated weak-lensing mass-to-halo-mass relation. The count rate and BCG stellar mass relations are simultaneously constrained in a forward and population modelling. In agreement with the results based on the weak-lensing data from the DES and KiDS surveys, we obtain a count rate relation with a self-similar redshift scaling and a mass trend that is steeper than the self-similar prediction. Our results suggest that the BCG stellar mass at a fixed halo mass has remained stable with a moderate increase at a level of $\left(20\pm8\right)%$ since redshift $z\approx0.8$. This finding supports the picture of the ``rapid-then-slow'' BCG formation, where the majority of the stellar mass must have been assembled at much earlier cosmic time.

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arXiv2025

The SRG/eROSITA All-Sky Survey : Subaru/HSC-SSP weak-lensing mass measurements for the eRASS1 Galaxy Clusters

We performed individual weak-lensing (WL) mass measurements for 78 eROSITA's first All-Sky Survey (eRASS1) clusters in the footprint of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) S19A. We did not adopt priors on the eRASS1 X-ray quantities or assumption of the mass and concentration relation. In the sample, we found three clusters are misassociated with optical counterparts and 12 clusters are poorly fitted with an NFW profile. The average mass for the 12 poor-fit clusters changes from $\sim 10^{14}h_{70}^{-1}M_\odot$ to $\sim 2\times 10^{13}h_{70}^{-1}M_\odot$ when lensing contamination from surrounding mass structures is taken into account. The scaling relations between the true mass and cluster richness and X-ray count-rate agree well with the results of the eRASS1 western Galactic hemisphere region based on count-rate-inferred masses, which were calibrated with the HSC-SSP, DES, and KiDS surveys. We developed a Bayesian framework for inferring the mass-concentration relation of the cluster sample, explicitly incorporating the effects of weak-lensing mass calibration in the mass-concentration parameter space. The redshift-dependent mass and concentration relation is in excellent agreement with predictions of dark-matter-only numerical simulations and previous studies using X-ray-selected clusters. Based on the two-dimensional (2D) WL analysis, the offsets between the WL-determined centers and the X-ray centroids for 36 eRASS1 clusters with high WL S/N can be described by two Gaussian components. We find that the miscentering effect with X-ray centroids is smaller than that involving peaks in the galaxy maps. Stacked mass maps support a small miscentering effect, even for clusters with a low WL S/N. The projected halo ellipticity is $\langle \varepsilon \rangle=0.45$ at $M_{200}\sim 4\times10^{14}h_{70}^{-1}M_\odot$.

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arXiv2025

The SRG/eROSITA All-Sky Survey: Large-scale view of the Centaurus cluster

Methods. We utilized the combined five SRG/eROSITA All-Sky Survey data (eRASS:5) to perform X-ray imaging and spectral analyses of the Centaurus cluster in various directions to large radii. Surface brightness (SB) profiles out to $2R_{200}$ were constructed. We acquired gas temperature, metallicity, and normalization per area profiles out to $R_{200}$. We compared our results with previous Centaurus studies, cluster outskirts measurements, and simulations. Comprehensive sky background analysis was done across the FoV, in particular, to assess the variation of the eROSITA Bubble emission that partially contaminates the field. Results. The processed X-ray images show the known sloshing-induced structures in the core. The core ($r\leq11~\mathrm{kpc}$) is better described with a 2T model than a 1T model. Here, we measured lower T from the cooler component (~1.0 keV) and higher Z ($\sim\!1.6Z_\odot$), signifying an iron bias. In the intermediate radial range, we observed prominent SB and normalization per area excesses in the eastern sector (Cen 45 location), reaching out to $R_{500}$. Temperature enhancements near the location of Cen 45 imply that the gas is shock-heated due to the interaction with Cen 30, the significant excess behind Cen 45 center might be the tail/ram-pressure-stripped gas. We found good agreement between the outskirt temperatures with the profile from simulations and fit from Suzaku outskirts measurements. We detected significant SB emission to the sky background level out to $R_{200}$ with a $3.5σ$ and followed by $2.9σ$ at $1.1R_{200}$. The metallicity at $R_{500}-R_{200}$ is low but within the ranges of other outskirts studies. Conclusions. We present the first measurement of ICM morphology and properties of Centaurus cluster sampling the whole azimuth beyond $30'$, increasing the probed volume by a factor of almost 30.

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arXiv2024

Gas thermodynamics meets galaxy kinematics: Joint mass measurements for eROSITA galaxy clusters

The mass of galaxy clusters is a critical quantity for probing cluster cosmology and testing theories of gravity, but its measurement could be biased given assumptions are inevitable. In this paper, we employ and compare two mass proxies for galaxy clusters: thermodynamics of the intracluster medium and kinematics of member galaxies. We select 22 galaxy clusters from the cluster catalog in the first SRG/eROSITA All-Sky Survey (eRASS1) that have sufficient optical and near-infrared observations. We generate multi-band images in the energy range of (0.3, 7) keV for each cluster, and derive their temperature profiles, gas mass profiles and hydrostatic mass profiles using a parametric approach that does not assume dark matter halo models. With spectroscopically confirmed member galaxies collected from multiple surveys, we numerically solve the spherical Jeans equation for their dynamical mass profiles. Our results quantify the correlation between dynamical mass and line-of-sight velocity dispersion with an rms scatter of 0.14 dex. We find the two mass proxies lead to roughly the same total mass, with no observed systematic bias. As such, the $σ_8$ tension is not specific to hydrostatic mass or weak lensing shears, but also appears with galaxy kinematics. We also compare our hydrostatic masses with the latest weak lensing masses inferred with scaling relations. The comparison shows the weak lensing mass is significantly higher than our hydrostatic mass by $\sim$110%. This might explain the significantly larger value of $σ_8$ from the latest measurement using eRASS1 clusters than almost all previous estimates in the literature. Finally, we test the radial acceleration relation (RAR) established in disk galaxies. We confirm the missing baryon problem in the inner region of galaxy clusters using three independent mass proxies for the first time.

astro-ph.CO↗

arXiv2024

The SRG/eROSITA All-Sky Survey: Weak-Lensing of eRASS1 Galaxy Clusters in KiDS-1000 and Consistency Checks with DES Y3 & HSC-Y3

We aim to participate in the calibration of the X-ray photon count rate to halo mass scaling relation of galaxy clusters selected in the first eROSITA All-Sky Survey on the Western Galactic Hemisphere (eRASS1) using KiDS-1000 weak-lensing (WL) data. We measure the radial shear profiles around eRASS1 galaxy clusters using background galaxies in KiDS-1000, as well as the cluster member contamination. Furthermore we provide consistency checks with the other stage-III WL surveys who take part in the eRASS1 mass calibration, DES Y3 and HSC-Y3. We determine the cluster member contamination of eRASS1 clusters present in KiDS-1000 based on source number density profiles, where we account for the obscuration caused by cluster galaxies. The extracted shear profiles, together with the contamination model and the lens sample selection, are then analysed through a Bayesian population model. We calibrate the WL mass bias parameter by analysing realistic synthetic shear profiles from mock cluster catalogues. Our consistency checks between KiDS-1000 and DES Y3 & HSC-Y3 include the comparison of contamination-corrected density contrast profiles employing the union of background sources around common clusters, as well as the individual scaling relation results. We present a global contamination model for eRASS1 clusters in KiDS-1000 and the calibration results of the X-ray photon count rate to halo mass relation. The results of the WL mass bias parameter show that the uncertainty of the multiplicative shear bias dominates the systematic error budget at low clusters redshifts while the uncertainty of our contamination model does at high ones. The cross-checks between the three WL surveys show that they are statistically consistent with each other. This enables for the first time cosmological constraints from clusters calibrated by three state-of-the-art WL surveys. (abridged)

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arXiv2023

The eROSITA view of the Abell 3391/95 field: Cluster Outskirts and Filaments

Aims. We aim to characterize the gas properties in the cluster outskirts ($R_{500} R_{200}$) of the A3391/95 system and to compare them to predictions. Methods. We performed X-ray image and spectral analyses using the eROSITA PV data to assess the gas morphology and properties in the outskirts and the filaments in the directions of the previously detected Northern and Southern Filament of the A3391/95 system. We took particular care of the foreground. Results. In the filament-facing outskirts of A3391 and the Northern Clump, we find higher temperatures than typical cluster outskirts profiles, with a significance of $1.6-2.8σ$, suggesting heating due to their connections with the filaments. We confirm SB excess in the profiles of the Northern, Eastern, and Southern Filaments. From spectral analysis, we detect hot gas of ~1 keV for the Northern and Southern Filaments. The filament metallicities are below 10% solar metallicity and the $n_e$ range between 2.6 and $6.3\times10^{-5}~\mathrm{cm^{-3}}$. The characteristic properties of the Little Southern Clump (~1.5$R_{200}$ from A3395S in the Southern Filament) suggest that it is a small galaxy group. Excluding the LSC from the analysis of the Southern Filament decreases the gas density by 30%. This shows the importance of taking into account any clumps to avoid overestimation of the gas measurement in the outskirts and filament regions. Conclusions. The $n_e$ of the filaments are consistent with the WHIM properties as predicted by cosmological simulations, but the temperatures are higher, close to the upper WHIM temperature limit. As both filaments are short and located in a denser environment, stronger gravitational heating may be responsible for this temperature enhancement. The metallicities are low, but still within the expected range from the simulations.

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arXiv2022

The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray Properties and Scaling Relations of Galaxy Clusters and Groups

We investigate the scaling relations between X-ray observables of the clusters detected in the eFEDS field using Spectrum-Roentgen-Gamma/eROSITA observations taking into account the selection effects and the distributions of observables with cosmic time. We extract X-ray observables (Lx, Lbol, T, Mgas, Yx) within R500 for the sample of 542 clusters in the eFEDS field. By applying detection and extent likelihoods, we construct a subsample of 265 clusters with a contamination level of <10% (including AGNs and spurious fluctuations) to be utilized in the scaling relation analysis. The selection function based on the state-of-the-art simulations of the eROSITA sky is fully accounted for in our work. We provide the X-ray observables in the core-included 3sigma confidence level however, our results are in good agreement with the simulations including non-gravitational physics and the recent results that take into account selection effects. Strong deviations we find from the self-similar scenario indicate that the non-gravitational effects play an important role in shaping the observed physical state of clusters. This work extends the scaling relations to low mass, low luminosity galaxy cluster and group regime using eFEDS observations, demonstrating eROSITA's ability to measure ICM emission out to R500 with survey-depth exposures and constrain the scaling relations in a wide mass-luminosity-redshift range.

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arXiv2022

The eROSITA Final Equatorial-Depth Survey (eFEDS): Galaxy Clusters and Groups in Disguise

The eROSITA Final Equatorial-Depth Survey (eFEDS), executed during the performance verification phase of the Spectrum-Roentgen-Gamma (SRG)/eROSITA telescope, was completed in Nov. 2019. One of the science goals of this survey is to demonstrate the ability of eROSITA to detect samples of clusters and groups at the final depth of the eROSITA all-sky survey. Because of the sizeable point-spread function of eROSITA, high-redshift clusters of galaxies or compact nearby groups hosting bright active galactic nuclei (AGN) can be misclassified as point sources by the source detection algorithms. A total of 346 galaxy clusters and groups in the redshift range of 0.1<z<1.3 were identified based on their red sequence in the point source catalog. We examine the multiwavelength properties of these clusters and groups to understand the potential biases in our selection process and the completeness of the extent-selected sample. The majority of the clusters and groups in the point source sample are indeed underluminous and compact compared to the extent-selected sample. Their faint X-ray emission, well below the flux limit of the extent-selected eFEDS clusters, and their compact X-ray emission are likely to be the main reason for this misclassification. In the sample, we confirm that 10% of the sources host AGN in their brightest cluster galaxies (BCGs) through optical spectroscopy and visual inspection. By studying their X-ray, optical, infrared, and radio properties, we establish a method for identifying clusters and groups that host AGN in their BCGs. We successfully test this method on the current point source catalog through the Sloan Digital Sky Survey optical spectroscopy and find eight clusters and groups with active radio-loud AGN that are particularly bright in the infrared. They include eFEDSJ091437.8+024558, eFEDSJ083520.1+012516, and eFEDSJ092227.1+043339 at redshifts 0.3-0.4. [ABRIDGED]

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arXiv2022

Establishing the X-ray Source Detection Strategy for eROSITA with Simulations

The eROSITA X-ray telescope on board the Spectrum-Roentgen-Gamma (SRG) satellite has started to detect new X-ray sources over the full sky at an unprecedented rate. Understanding the performance and selection function of the source detection is important for the subsequent scientific analysis of the eROSITA catalogs. Through simulations, we test and optimize the eROSITA source detection procedures, and we characterize the detected catalog quantitatively. Taking the eROSITA Final Equatorial-Depth Survey (eFEDS) as an example, we ran extensive photon-event simulations based on our best knowledge of the instrument characteristics, the background spectrum, and the population of astronomical X-ray sources. We introduce a method of analyzing source detection completeness, purity, and efficiency based on the origin of each photon. According to the source detection efficiency measured in the simulation, we chose a two-pronged strategy to build eROSITA X-ray catalogs, creating a main catalog using only the most sensitive band (0.2-2.3 keV) and an independent hard-band-selected catalog using multiband detection in a range up to 5 keV. Because our mock data are highly representative of the real eFEDS data, we used the mock catalogs to measure the completeness and purity of the eFEDS catalogs as a function of multiple parameters, such as detection likelihood, flux, and luminosity. These measurements provide a basis for choosing the eFEDS catalog selection thresholds. The mock catalogs (available with this paper) can be used to construct the selection function of active galactic nuclei and galaxy clusters. A direct comparison of the output and input mock catalogs also gives rise to a correction curve that converts the raw point-source flux distribution into the intrinsic number counts distribution.

astro-ph.IM↗

arXiv2022

The eROSITA view of the Abell 3391/95 field: The Northern Clump. The largest infalling structure in the longest known gas filament observed with eROSITA, XMM-Newton, and Chandra

SRG/eROSITA PV observations revealed the A3391/95 cluster system and the Northern Clump (MCXC J0621.7-5242 galaxy cluster) are aligning along a cosmic filament in soft X-rays, similarly to what has been seen in simulations before. We aim to understand the dynamical state of the Northern Clump as it enters the atmosphere ($3\times R_{200}$) of A3391. We analyzed joint eROSITA, XMM-Newton, and Chandra observations to probe the morphological, thermal, and chemical properties of the Northern Clump from its center out to a radius of 988 kpc ($R_{200}$). We utilized the ASKAP/EMU radio data, DECam optical image, and Planck y-map to study the influence of the WAT radio source on the Northern Clump central ICM. From the Magneticum simulation, we identified an analog of the A3391/95 system along with an infalling group resembling the Northern Clump. The Northern Clump is a WCC cluster centered on a WAT radio galaxy. The gas temperature over $0.2-0.5R_{500}$ is $k_BT_{500}=1.99\pm0.04$ keV. We employed the $M-T$ scaling relation and obtained a mass estimate of $M_{500}=(7.68\pm0.43)\times10^{13}M_{\odot}$ and $R_{500}=(636\pm12)$ kpc. Its atmosphere has a boxy shape and deviates from spherical symmetry. We identify a southern surface brightness edge, likely caused by subsonic motion relative to the filament gas. At $\sim\! R_{500}$, the southern atmosphere appears to be 42% hotter than its northern atmosphere. We detect a downstream tail pointing toward the north with a projected length of $\sim318$ kpc, plausibly the result of ram pressure stripping. The analog group in the Magneticum simulation is experiencing changes in its gas properties and a shift between the position of the halo center and that of the bound gas while approaching the main cluster pair.

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arXiv2021

The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray Observable-to-Mass-and-Redshift Relations of Galaxy Clusters and Groups with Weak-Lensing Mass Calibration from the Hyper Suprime-Cam Subaru Strategic Program Survey

We present the first weak-lensing mass calibration and X-ray scaling relations of galaxy clusters and groups selected in the $eROSITA$ Final Equatorial Depth Survey (eFEDS) observed by Spectrum Roentgen Gamma/$eROSITA$ over a contiguous footprint with an area of $\approx140$ deg$^2$, using the three-year (S19A) weak-lensing data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. In this work, a sample of $434$ optically confirmed galaxy clusters (and groups) at redshift $0.01\lesssim z \lesssim1.3$ with a median of $0.35$ is studied, of which $313$ systems are uniformly covered by the HSC survey to enable the extraction of the weak-lensing shear observable. In a Bayesian population modelling, we perform a blind analysis for the weak-lensing mass calibration by simultaneously modelling the observed count rate $η$ and the shear profile $g$ of individual clusters through the count rate-to-mass-and-redshift ($η$--$M_{500}$--$z$) and weak-lensing mass-to-mass-and-redshift ($M_{\mathrm{WL}}$--$M_{500}$--$z$) relations, respectively, while accounting for the bias in these observables using simulation-based calibrations. As a result, the count rate-inferred and lensing-calibrated cluster mass is obtained from the joint modelling of the scaling relations, as the ensemble mass spanning a range of $10^{13}h^{-1}M_{\odot}\lesssim M_{500}\lesssim10^{15} h^{-1}M_{\odot}$ with a median of $\approx10^{14} h^{-1}M_{\odot}$ for the eFEDS sample. With the mass calibration, we further model the X-ray observable-to-mass-and-redshift relations, including the rest-frame soft-band and bolometric luminosity ($L_{\mathrm{X}}$ and $L_{\mathrm{b}}$), the emission-weighted temperature $T_{\mathrm{X}}$, the mass of intra-cluster medium $M_{\mathrm{g}}$, and the mass proxy $Y_{\mathrm{X}}$, which is the product of $T_{\mathrm{X}}$ and $M_{\mathrm{g}}$. (abridged)

astro-ph.CO↗

arXiv2021

The eROSITA view of the Abell 3391/95 field: a case study from the Magneticum cosmological simulation

We investigated the origin and gas properties of a simulated galaxy cluster pair, to connect simulation predictions to the SRG/eROSITA X-ray observations of the Abell 3391/95 field. The simulated system has been extracted from the (352 cMpc/h)^3 volume of the Magneticum Pathfinder cosmological simulations at z=0.07. We tracked back in time the main progenitors of the pair clusters and surrounding groups to study the assembly history of the system and its evolution. Similarly to the observed A3391/95 system, the simulated pair is embedded in a complex network of gas filaments, with structures aligned over more than 20 projected Mpc and the whole region collapsing towards the central overdense node. The spheres of influence (3*R200) of the two main clusters already overlap at z=0.07, but their virial boundaries are still physically separated. The diffuse gas located in the interconnecting bridge closely reflects the WHIM, with typical temperature of ~1 keV and overdensity $\sim 100$, with respect to the mean baryon density of the Universe, and lower enrichment level compared to the ICM in clusters. We find that most of the bridge gas collapsed from directions roughly orthogonal to the intra-cluster gas accretion directions, and its origin is mostly unrelated to the two cluster progenitors. We find clear signatures in the surrounding groups of infall motion towards the pair, such as significant radial velocities and slowdown of gas compared to dark matter. These findings further support the picture of the Northern Clump (MCXC J0621.7-5242) cluster infalling along a cosmic gas filament towards Abell 3391, possibly merging with it. We conclude that, in such a configuration, the pair clusters of the A3391/95-like system are in a pre-merger phase, and did not interact yet. The diffuse gas in the interconnecting bridge is mostly warm filament gas, rather than tidally-stripped cluster gas.

astro-ph.CO↗

arXiv2020

Full-sky photon simulation of clusters and active galactic nuclei in the soft X-rays for eROSITA

The eROSITA X-ray telescope on board the Spectrum-Roentgen-Gamma (SRG) mission will measure the position and properties of about 100,000 clusters of galaxies and 3 million active galactic nuclei over the full sky. To study the statistical properties of this ongoing survey, it is key to estimate the selection function accurately. We create a set of full sky light-cones using the MultiDark and UNIT dark matter only N-body simulations. We present a novel method to predict the X-ray emission of galaxy clusters. Given a set of dark matter halo properties (mass, redshift, ellipticity, offset parameter), we construct an X-ray emissivity profile and image for each halo in the light-cone. We follow the eROSITA scanning strategy to produce a list of X-ray photons on the full sky. We predict scaling relations for the model clusters, which are in good agreement with the literature. The predicted number density of clusters as a function of flux also agrees with previous measurements. Finally, we obtain a scatter of 0.21 (0.07, 0.25) for the X-ray luminosity -- mass (temperature -- mass, luminosity -- temperature) model scaling relations. We provide catalogues with the model photons emitted by clusters and active galactic nuclei. These catalogues will aid the eROSITA end to end simulation flow analysis and in particular the source detection process and cataloguing methods.

astro-ph.CO↗

arXiv2020

Low-scatter galaxy cluster mass proxies for the eROSITA all-sky survey

The on-going X-ray all-sky survey with the eROSITA instrument will yield large galaxy cluster samples, which will bring strong constraints on cosmological parameters. In particular, the survey holds great promise to investigate the tension between CMB and low-redshift measurements. The current bottleneck preventing the full exploitation of the survey data is the systematics associated with the relation between survey observable and halo mass. Numerous recent studies have shown that gas mass and core-excised X-ray luminosity exhibit very low scatter at fixed mass. We propose a new method to reconstruct these quantities from low photon count data and validate the method using extensive eROSITA-like simulations. We find that even near the detection threshold of ~50 counts the core-excised luminosity and the gas mass can be recovered with 20-30% precision, which is substantially less than the scatter of the full integrated X-ray luminosity at fixed mass. When combined with an accurate calibration of the absolute mass scale (e.g. through weak gravitational lensing), our technique reduces the systematics on cosmological parameters induced by the mass calibration.

astro-ph.CO↗

arXiv2020

The distribution of dark matter and gas spanning six megaparsecs around the post-merger galaxy cluster MS0451-03

Using the largest mosaic of Hubble Space Telescope images around a galaxy cluster, we map the distribution of dark matter throughout a $\sim$$6\times6$ Mpc$^2$ area centred on the cluster MS 0451-03 ($z=0.54$, $M_{200}=1.65\times10^{15} \rm{M}_\odot$). Our joint strong- and weak-lensing analysis shows three possible filaments extending from the cluster, encompassing six group-scale substructures. The dark-matter distribution in the cluster core is elongated, consists of two distinct components, and is characterized by a concentration parameter of $c_{200}=3.79\pm0.36$. By contrast, XMM-Newton observations show the gas distribution to be more spherical, with excess entropy near the core, and a lower concentration of $c_{200}=2.35^{+0.89}_{-0.70}$ (assuming hydrostatic equilibrium). Such a configuration is predicted in simulations of major mergers 2-7Gyr after the first core passage, when the two dark-matter halos approach second turnaround, and before their gas has relaxed. This post-merger scenario finds further support in optical spectroscopy of the cluster's member galaxies, which shows that star formation was abruptly quenched 5 Gyr ago. MS 0451-03 will be an ideal target for future studies of the growth of structure along filaments, star-formation processes after a major merger, and the late-stage evolution of cluster collisions.

astro-ph.CO↗

arXiv2020

Iron in X-COP: tracing enrichment in cluster outskirts with high accuracy abundance profiles

We present the first metal abundance profiles for a representative sample of massive clusters. Our measures extend to $R_{500}$ and are corrected for a systematic error plaguing previous outskirt estimates. Our profiles flatten out at large radii, admittedly not a new result, however the radial range and representative nature of our sample extends its import well beyond previous findings. We find no evidence of segregation between cool-core and non-cool-core systems beyond $\sim 0.3 R_{500}$, implying that, as was found for thermodynamic properties (Ghirardini et al, 2019), the physical state of the core does not affect global cluster properties. Our mean abundance within $R_{500}$ shows a very modest scatter, $< $15%, suggesting the enrichment process must be quite similar in all these massive systems. This is a new finding and has significant implications on feedback processes. Together with results from thermodynamic properties presented in a previous X-COP paper, it affords a coherent picture where feedback effects do not vary significantly from one system to another. By combing ICM with stellar measurements we have found the amount of Fe diffused in the ICM to be about ten times higher than that locked in stars. Although our estimates suggest, with some strength, that the measured iron mass in clusters is well in excess of the predicted one, systematic errors prevent us from making a definitive statement. Further advancements will only be possible when systematic uncertainties, principally those associated to stellar masses, both within and beyond $R_{500}$, can be reduced.

astro-ph.CO↗

arXiv2020

EAGLE and Illustris-TNG predictions for resolved eROSITA X-ray observations of the circumgalactic medium around normal galaxies

We simulate stacked observations of nearby hot X-ray coronae associated with galaxies in the EAGLE and Illustris-TNG hydrodynamic simulations. A forward modeling pipeline is developed to predict 4-year eROSITA observations and stacked image analysis, including the effects of instrumental and astrophysical backgrounds. We propose an experiment to stack z~0.01 galaxies separated by specific star-formation rate (sSFR) to examine how the hot (T>=10^6 K) circumgalactic medium (CGM) differs for high- and low-sSFR galaxies. The simulations indicate that the hot CGM of low-mass (M_*~10^{10.5} Msol), high-sSFR (defined as the top one-third ranked by sSFR) central galaxies will be detectable to a galactocentric radius r~30-50 kpc. Both simulations predict lower luminosities at fixed stellar mass for the low-sSFR galaxies (the lower third of sSFR) with Illustris-TNG predicting 3x brighter coronae around high-sSFR galaxies than EAGLE. Both simulations predict detectable emission out to r~150-200 kpc for stacks centered on high-mass (M_*~10^{11.0} Msol) galaxies, with EAGLE predicting brighter X-ray halos. The extended soft X-ray luminosity correlates strongly and positively with the mass of circumgalactic gas within the virial radius (f_{CGM}). Prior analyses of both simulations have established that f_{CGM} is reduced by expulsive feedback driven mainly by black hole growth, which quenches galaxy growth by inhibiting replenishment of the ISM. Both simulations predict that eROSITA stacks should not only conclusively detect and resolve the hot CGM around L^* galaxies for the first time, but provide a powerful probe of how the baryon cycle operates, for which there remains an absence of consensus between state-of-the-art simulations.

astro-ph.GA↗