Context. The environment inside and on the outskirts of galaxy clusters has a profound impact on the star formation rate and active galactic nucleus (AGN) activity in cluster galaxies. While the ...overall star formation and AGN suppression in the inner cluster regions has been thoroughly studied in the past, recent X-ray studies also indicate that conditions on the cluster outskirts may promote AGN activity. Aims. We investigate how the environment and the properties of host galaxies impact the levels of AGN activity and star formation in galaxy clusters. We aim to identify significant trends in different galaxy populations and suggest possible explanations. Methods. We studied galaxies with stellar mass log M * ( M ⊙ ) > 10.15 in galaxy clusters with mass M 500 > 10 13 M ⊙ extracted from box2b (640 comoving Mpc h −1 ) of the Magneticum Pathfinder suite of cosmological hydrodynamical simulations at redshifts 0.25 and 0.90. We examined the influence of stellar mass, distance to the nearest neighbouring galaxy, cluster-centric radius, substructure membership, and large-scale surroundings on the fraction of galaxies hosting an AGN, star formation rate, and the ratio between star-forming and quiescent galaxies. Results. We find that in low-mass galaxies, AGN activity and star formation are similarly affected by the environment and decline towards the cluster centre. In massive galaxies, the impact is different; star-formation level increases in the inner regions and peaks between 0.5 and 1 R 500 with a rapid decline in the centre, whereas AGN activity declines in the inner regions and rapidly rises below R 500 towards the centre. We suggest that this increase is a result of the larger black hole masses relative to stellar masses in the cluster centre. After disentangling the contributions of neighbouring cluster regions, we find an excess of AGN activity in massive galaxies on the cluster outskirts (∼3 R 500 ). We also find that the local density, substructure membership, and stellar mass strongly influence star formation and AGN activity but verify that they cannot fully account for the observed radial trends.
Aims.
The eROSITA Final Equatorial-Depth Survey has been carried out during the performance verification phase of the Spectrum-Roentgen-Gamma/eROSITA telescope and was completed in November 2019. ...This survey is designed to provide the first eROSITA-selected sample of clusters and groups and to test the predictions for the all-sky survey in the context of cosmological studies with clusters of galaxies.
Methods.
In the area of ~140 square degrees covered by eFEDS, 542 candidate clusters and groups of galaxies were detected as extended X-ray sources with the
eSASS
source detection algorithm. We performed imaging and spectral analysis of the 542 cluster candidates with eROSITA X-ray data and studied the properties of the sample.
Results.
We provide the catalog of candidate galaxy clusters and groups detected by eROSITA in the eFEDS field down to a flux of ~10
–14
erg s
–1
cm
–2
in the soft band (0.5
–
2 keV) within 1’. The clusters are distributed in the redshift range ɀ
=
0.01, 1.3 with a median redshift ɀ
median
= 0.35. With eROSITA X-ray data, we measured the temperature of the intracluster medium within two radii, 300 kpc and 500 kpc, and constrained the temperature with >2
σ
confidence level for ~1/5 (102 out of 542) of the sample. The average temperature of these clusters is ~2 keV. Radial profiles of flux, luminosity, electron density, and gas mass were measured from the precise modeling of the imaging data. The selection function, the purity, and the completeness of the catalog are examined and discussed in detail. The contamination fraction is ~1/5 in this sample and is dominated by misidentified point sources. The X-ray luminosity function of the clusters agrees well with the results obtained from other recent X-ray surveys. We also find 19 supercluster candidates in this field, most of which are located at redshifts between 0.1 and 0.5, including one cluster at ɀ ~ 0.36 that was presented previously.
Conclusions.
The eFEDS cluster and group catalog at the final eRASS equatorial depth provides a benchmark proof of concept for the eROSITA All-Sky Survey extended source detection and characterization. We confirm the excellent performance of eROSITA for cluster science and expect no significant deviations from our pre-launch expectations for the final all-sky survey.
A classification of the galaxy cluster’s dynamical state is crucial when dealing with large samples. The identification of the most relaxed and most disturbed objects is necessary for both ...cosmological analysis, focused on spherical and virialised systems, and astrophysical studies, centred around all those micro-physical processes that take place in disturbed clusters (such as particle acceleration or turbulence). Among the most powerful tools for the identification of the dynamical state of clusters is the analysis of their intracluster medium (ICM) distribution. In this work, we performed an analysis of the X-ray morphology of the 118 (Cluster HEritage project with
XMM-Newton
– Mass Assembly and Thermodynamics at the Endpoint of structure formation) CHEX-MATE clusters, with the aim of providing a classification of their dynamical state. To investigate the link between the X-ray appearance and the dynamical state, we considered four morphological parameters: the surface brightness concentration, the centroid shift, and the second- and third-order power ratios. These indicators result to be strongly correlated with each other, powerful in identifying the disturbed and relaxed population, characterised by a unimodal distribution, and not strongly influenced by systematic uncertainties. In order to obtain a continuous classification of the CHEX-MATE objects, we combined these four parameters in a single quantity,
M
, which represents the grade of relaxation of a system. On the basis of the
M
value, we identified the most extreme systems of the sample, finding 15 very relaxed and 27 very disturbed galaxy clusters. From a comparison with previous analysis on X-ray selected samples, we confirmed that the Sunyaev-Zeldovich (SZ) clusters tend to be more disturbed. Finally, by applying our analysis to a simulated sample, we found a general agreement between the observed and simulated results, with the only exception being the concentration. This latter behaviour is partially related to the presence of particles with a high smoothed-particle-hydrodynamics density in the central regions of the simulated clusters due to the action of the idealised isotropic thermal active galactic nucleus (AGN) feedback.
Context.
The characterization of the dynamical state of galaxy clusters is key to studying their evolution, evaluating their selection, and using them as a cosmological probe. In this context, the ...offsets between different definitions of the center have been used to estimate the cluster disturbance.
Aims.
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 clusters detected by the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spectrum-Roentgen-Gamma (SRG) observatory. We aim to connect observations to predictions by hydrodynamical simulations and
N
-body models. We assess the astrophysical effects affecting the displacements.
Methods.
We measured the offset for clusters observed in the eROSITA Final Equatorial-Depth Survey (eFEDS) and the first eROSITA all-sky survey (eRASS1). We focus on a subsample of 87 massive eFEDS clusters at low redshift, with
M
500c
> 1×10
14
M
⊙
and 0.15 <
z
< 0.4. We compared the displacements in such sample to those predicted by the TNG and the Magneticum simulations. We additionally link the observations to the offset parameter
X
off
measured for dark matter halos in
N
-body simulations, using the hydrodynamical simulations as a bridge.
Results.
We find that, on average, the eFEDS clusters show a smaller offset compared to eRASS1 because the latter contains a larger fraction of massive and disturbed structures. We measured an average offset of Δ
X−O
= 76.3
−27.1
+30.1
kpc, when focusing on the subsample of 87 eFEDS clusters. This is in agreement with the predictions from TNG and Magneticum, and the distribution of
X
off
from dark matter only (DMO) simulations. However, the tails of the distributions are different. Using Δ
X − O
to classify relaxed and disturbed clusters, we measured a relaxed fraction of 31% in the eFEDS subsample. Finally, we found a correlation between the offset measured on hydrodynamical simulations and
X
off
measured on their parent dark-matter-only run and we calibrated the relation between them.
Conclusions.
We conclude that there is good agreement between the offsets measured in eROSITA data and the predictions from simulations. Baryonic effects cause a decrement (increment) in the low (high) offset regime compared to the
X
off
distribution from dark matter-only simulations. The offset–
X
off
relation provides an accurate prediction of the true
X
off
distribution in Magneticum and TNG. It allows for the offsets to be introduced in a cosmological context with a new method in order to marginalize over selection effects related to the cluster dynamical state.
The Abell 3391/95 galaxy cluster system Reiprich, T. H.; Veronica, A.; Pacaud, F. ...
Astronomy and astrophysics (Berlin),
03/2021, Letnik:
647
Journal Article
Recenzirano
Odprti dostop
Context.
Inferences about dark matter, dark energy, and the missing baryons all depend on the accuracy of our model of large-scale structure evolution. In particular, with cosmological simulations in ...our model of the Universe, we trace the growth of structure, and visualize the build-up of bigger structures from smaller ones and of gaseous filaments connecting galaxy clusters.
Aims.
Here we aim to reveal the complexity of the large-scale structure assembly process in great detail and on scales from tens of kiloparsecs up to more than 10 Mpc with new sensitive large-scale observations from the latest generation of instruments. We also aim to compare our findings with expectations from our cosmological model.
Methods.
We used dedicated SRG/eROSITA performance verification (PV) X-ray, ASKAP/EMU Early Science radio, and DECam optical observations of a ~15 deg
2
region around the nearby interacting galaxy cluster system A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the surrounding large-scale structure and its formation process, the morphological complexity in the inner parts of the clusters, and the (re-)acceleration of plasma. We also used complementary Sunyaev-Zeldovich (SZ) effect data from the
Planck
survey and custom-made Galactic total (neutral plus molecular) hydrogen column density maps based on the HI4PI and IRAS surveys. We relate the observations to expectations from cosmological hydrodynamic simulations from the Magneticum suite.
Results.
We trace the irregular morphology of warm and hot gas of the main clusters from their centers out to well beyond their characteristic radii,
r
200
. Between the two main cluster systems, we observe an emission bridge on large scale and with good spatial resolution. This bridge includes a known galaxy group but this can only partially explain the emission. Most gas in the bridge appears hot, but thanks to eROSITA’s unique soft response and large field of view, we discover some tantalizing hints for warm, truly primordial filamentary gas connecting the clusters. Several matter clumps physically surrounding the system are detected. For the “Northern Clump,” we provide evidence that it is falling towards A3391 from the X-ray hot gas morphology and radio lobe structure of its central AGN. Moreover, the shapes of these X-ray and radio structures appear to be formed by gas well beyond the virial radius,
r
100
, of A3391, thereby providing an indirect way of probing the gas in this elusive environment. Many of the extended sources in the field detected by eROSITA are also known clusters or new clusters in the background, including a known SZ cluster at redshift
z
= 1. We find roughly an order of magnitude more cluster candidates than the SPT and ACT surveys together in the same area. We discover an emission filament north of the virial radius of A3391 connecting to the Northern Clump. Furthermore, the absorption-corrected eROSITA surface brightness map shows that this emission filament extends south of A3395 and beyond an extended X-ray-emitting object (the “Little Southern Clump”) towards another galaxy cluster, all at the same redshift. The total projected length of this continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees across the entire eROSITA PV observation field. The Northern and Southern Filament are each detected at >4
σ
. The
Planck
SZ map additionally appears to support the presence of both new filaments. Furthermore, the DECam galaxy density map shows galaxy overdensities in the same regions. Overall, the new datasets provide impressive confirmation of the theoretically expected structure formation processes on the individual system level, including the surrounding warm-hot intergalactic medium distribution; the similarities of features found in a similar system in the Magneticum simulation are striking. Our spatially resolved findings show that baryons indeed reside in large-scale warm-hot gas filaments with a clumpy structure.
Abell 3266 is one of the X-ray brightest galaxy clusters in the sky and is a well-known merging system. Using the ability of the eROSITA telescope onboard
SRG
(
Spectrum Röntgen Gamma
) to observe a ...wide field with a single pointing, we analysed a new observation of the cluster out to a radius of
R
200
. The X-ray images highlight sub-structures present in the cluster, including the north-east-south-west merger seen in previous ASCA,
Chandra
, and
XMM-Newton
data, a merging group towards the north-west, and filamentary structures between the core and one or more groups towards the west. We compute spatially resolved spectroscopic maps of the thermodynamic properties of the cluster, including the metallicity. The merging subclusters are seen as low entropy material within the cluster. The filamentary structures could be the rims of a powerful outburst of an active galactic nucleus, or most likely material stripped from the western group(s) as they passed through the cluster core. Seen in two directions is a pressure jump at a radius of 1.1 Mpc, which is consistent with a shock with a Mach number of ~1.5–1.7. The eROSITA data confirm that the cluster is not a simple merging system, but it is made up of several subclusters which are merging or will shortly merge. We computed a hydrostatic mass from the eROSITA data, finding good agreement with a previous
XMM-Newton
result. With this pointing we detect several extended sources, where we find secure associations between
z
= 0.36–1.0 for seven of them, that is background galaxy groups and clusters, highlighting the power of eROSITA to find such systems.
Context.
Galaxy clusters are the most massive bound objects in the recent history of the universe; 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 scaling relations between mass and observables.
Aims.
X-ray observables can be biased by a number of effects, including 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 an overdensity radius such as
r
500c
. Using simulated galaxy clusters from a realistic cosmological simulation, our aim is to determine the importance of these biases in the context of Spectrum-Roentgen-Gamma/eROSITA observations of clusters.
Methods.
We extracted clusters from the
Box2_hr
simulation from the Magneticum suite, and simulated synthetic eROSITA observations of these clusters using
PHOX
to generate the photons and the end-to-end simulator
SIXTE
to trace them through the optics and simulate the detection process. We fitted the spectra from these observations and compared the fitted temperatures and luminosities to the quantities derived from the simulations. We fitted an intrinsically scattered
L
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.
Results.
The largest biases on the estimated temperature and luminosities of the clusters come from the inadequacy of single-temperature model fits to represent emission from multiphase gas, and from 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 comparatively small. We find eROSITA-like measurements of Magneticum clusters following a
L
X
−
T
scaling relation that has a broadly consistent but slightly shallower slope compared to the literature values. We also find that the intrinsic scatter of
L
X
at given
T
is lower compared to the recent observational results where the selection effects are fully considered.
We studied the imprints that feedback from Active Galactic Nuclei (AGN) leaves on the intracluster plasma during the assembly history of galaxy clusters. To this purpose we used state-of-the-art ...cosmological hydrodynamical simulations based on an updated version of the Tree-PM SPH GADGET-3 code, comparing three sets of simulations with different prescriptions for the physics of baryons (including AGN and/or stellar feedback). We explore the effect of these different physics, in particular AGN feedback, on IntraCluster medium (ICM) properties observed via Sunyaev-Zel’dovich (SZ) effect using an extended set of galaxy clusters (~100 clusters with M
500 masses above 5 × 1013
M
⊙/h). Some of the main findings are that the scaling relation between the integrated SZ flux and the galaxy cluster total mass is in good accordance with several observed samples, especially for massive clusters, and does not show any clear redshift evolution, with the slope of the relation close to the theoretical one in the AGN feedback case. As for the scatter of this relation, we obtain a mild dependence on the cluster dynamical state.
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