Context. Some indications for tension have long been identified between cosmological constraints obtained from galaxy clusters and primary cosmic microwave background (CMB) measurements. Typically, ...assuming the matter density and fluctuations, as parameterized with Ωm and σ8, estimated from CMB measurements, many more clusters are expected than those actually observed. This has been reinforced recently by the Planck collaboration. One possible explanation could be that certain types of galaxy groups or clusters were missed in samples constructed in previous surveys, resulting in a higher incompleteness than estimated. Aims. In this work, we aim to determine if a hypothetical class of very extended, low-surface-brightness galaxy groups or clusters have been missed in previous X-ray cluster surveys based on the ROSAT All-Sky Survey (RASS). Methods. We applied a dedicated source-detection algorithm sensitive also to more unusual group or cluster surface-brightness distributions. It includes a multiresolution filtering, a source-detection algorithm, and a maximum-likelihood fitting procedure. To optimize parameters, this algorithm is calibrated using extensive simulations before it is used to reanalyze the RASS data. In addition, the cross-correlation of the candidates with optical/infrared surveys is used for cluster identification and redshift estimation. Results. We found many known groups but also a number of new group candidates, which are not included in any previous X-ray or SZ cluster catalogs. In this paper, we present a pilot sample of 13 very extended groups discovered in the RASS at positions where no X-ray source has been detected previously and with clear optical counterparts. The X-ray fluxes of at least 5 of these are above the nominal flux-limits of previous RASS cluster catalogs (≳3 × 10−12 erg s−1 cm−2 in the 0.1 − 2.4 keV energy band). They have low mass (1013 M⊙ ≲M500 ≲ 1014 M⊙; i.e., they are galaxy groups), are at low redshift (z < 0.08), and exhibit flatter surface-brightness distributions than usual. Conclusions. We demonstrate that galaxy groups were missed in previous RASS surveys, possibly due to the flat surface-brightness distributions of this potential new population. Analysis of the full sample will show if this might have a significant effect on previous cosmological parameter constraints based on RASS cluster surveys.
ABSTRACT
We present a weak lensing analysis for galaxy clusters from the APEX-SZ survey. For 39 massive galaxy clusters that were observed via the Sunyaev–Zel’dovich effect (SZE) with the APEX ...telescope, we analyse deep optical imaging data from WFI(@2.2mMPG/ESO) and Suprime-Cam(@SUBARU) in three bands. The masses obtained in this study, including an X-ray selected sub-sample of 27 clusters, are optimized for and used in studies constraining the mass to observable scaling relations at fixed cosmology. A novel focus of our weak lensing analysis is the multicolour background selection to suppress effects of cosmic variance on the redshift distribution of source galaxies. We investigate the effects of cluster member contamination through galaxy density, shear profile, and recovered concentrations. We quantify the impact of variance in source redshift distribution on the mass estimate by studying nine sub-fields of the COSMOS survey for different cluster redshift and magnitude limits. We measure a standard deviation of ∼6 per cent on the mean angular diameter distance ratio for a cluster at z = 0.45 and shallow imaging data of R ≈ 23 mag. It falls to ∼1 per cent for deep, R = 26 mag, observations. This corresponds to 8.4 per cent and 1.4 per cent scatter in M200. Our background selection reduces this scatter by 20−40 per cent, depending on cluster redshift and imaging depth. We derived cluster masses with and without using a mass concentration relation and find consistent results, and concentrations consistent with the used mass–concentration relation.
The XXL Survey Sereno, Mauro; Ettori, Stefano; Eckert, Dominique ...
Astronomy and astrophysics (Berlin),
12/2019, Volume:
632
Journal Article
Peer reviewed
Open access
Context. Scaling relations between cluster properties embody the formation and evolution of cosmic structure. Intrinsic scatters and correlations between X-ray properties are determined from merger ...history, baryonic processes, and dynamical state. Aims. We look for an unbiased measurement of the scatter covariance matrix among the three main X-ray observable quantities attainable in large X-ray surveys: temperature, luminosity, and gas mass. This also gives us the cluster property with the lowest conditional intrinsic scatter at fixed mass. Methods. Intrinsic scatters and correlations can be measured under the assumption that the observable properties of the intra-cluster medium hosted in clusters are log-normally distributed around power-law scaling relations. The proposed method is self-consistent, based on minimal assumptions, and requires neither external calibration by weak lensing, or dynamical or hydrostatic masses, nor the knowledge of the mass completeness. Results. We analysed the 100 brightest clusters detected in the XXL Survey and their X-ray properties measured within a fixed radius of 300 kpc. The gas mass is the less scattered proxy (∼8%). The temperature (∼20%) is intrinsically less scattered than the luminosity (∼30%), but it is measured with a larger observational uncertainty. We found some evidence that gas mass, temperature, and luminosity are positively correlated. Time evolutions are in agreement with the self-similar scenario, but the luminosity–temperature and the gas mass–temperature relations are steeper. Conclusion. Positive correlations between X-ray properties can be determined by the dynamical state and the merger history of the halos. The slopes of the scaling relations are affected by radiative processes.
We present a joint weak lensing and X-ray analysis of 4 deg2 from the CFHTLS and XMM-LSS surveys. Our weak lensing analysis is the first analysis of a real survey using shapelets, a new generation ...weak lensing analysis method. We create projected mass maps of the images, and extract six weak-lensing-detected clusters of galaxies. We show that their counts can be used to constrain the power-spectrum normalization σ8= 0.92+0.26−0.30 for Ωm= 0.24. We show that despite the large scatter generally observed in the mass–temperature (M–T) relation derived from lensing masses, tight constraints on both its slope and normalization M* can be obtained with a moderate number of sources provided that the covered mass range is large enough. Adding clusters given by Bardeau et al. to our sample, we measure M*= 2.71+0.79−0.61× 1014h−1M⊙. Although they are dominated by shot noise and sample variance, our measurements are consistent with currently favoured values, and set the stage for future surveys. We thus investigate the dependence of those estimates on survey size, depth and integration time, for joint weak lensing and X-ray surveys. We show that deep surveys should be dedicated to the study of the physics of clusters and groups of galaxies. For a given exposure time, wide surveys provide a larger number of detected clusters and are therefore preferred for the measurement of cosmological parameters, such as σ8 and M*. We show that a wide survey of a few hundred square degrees is needed to improve upon current measurements of these parameters. More ambitious surveys covering 7000 deg2 will provide the 1 per cent accuracy in the estimation of the power-spectrum and the M–T relation normalizations.
Context. Cosmological studies have now entered Stage IV according to the Dark Energy Task Force (DETF) prescription. New missions ( Euclid , Rubin Observatory, SRG/eROSITA) will cover very large ...fractions of the sky with unprecedented depth. These are expected to provide the required ultimate accuracy in the dark energy (DE) equation of state (EoS), which is required for the elucidation of the origin of the acceleration of cosmic expansion. However, none of these projects have the power to systematically unveil the galaxy cluster population in the 1 < z < 2 range. There therefore remains the need for an Athena -like mission to run independent cosmological investigations and scrutinise the consistency between the results from the 0 < z < 1 and 1 < z < 2 epochs. Aims. We study the constraints on the DE EoS and on primordial non-gaussanities for typical X-ray cluster surveys executed by a generic Athena -like Wide Field Imager. We focus on the impact of cluster number counts in the 1 < z < 2 range. Methods. We consider two survey designs: 50 deg 2 at 80 ks (survey A) and 200 deg 2 at 20 ks (survey B). We analytically derive cluster number counts and predict the cosmological potential of the corresponding samples, A and B, by means of a Fisher analysis. We adopt an approach that forward models the observed properties of the cluster population in the redshift–count rate–hardness ratio parameter space. Results. The achieved depth allows us to unveil the halo mass function down to the group scale out to z = 2. We predict the detection of thousands of clusters down to a few 10 13 h −1 M ⊙ , in particular 940 and 1400 clusters for surveys A and B, respectively, at z > 1. Such samples will allow a detailed modelling of the evolution of cluster physics along with a standalone cosmological analysis. Our results suggest that survey B has the optimal design as it provides greater statistics. Remarkably, high-redshift clusters represent 15% or less of the full samples but contribute at a much higher level to the cosmological accuracy: by alleviating various degeneracies, these objects allow a significant reduction of the uncertainty on the cosmological parameters: Δ w a is reduced by a factor of ∼2.3 and Δ f NL loc by a factor of ∼3. Conclusions. Inventorying the deep high- z X-ray cluster population can play a crucial role in ensuring overall cosmological consistency. This will be the major aim of future new-generation Athena -like missions.
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 ≈140 deg
2
, using the three-year (S19A) weak-lensing data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. In this work, we study a sample of 434 optically confirmed galaxy clusters (and groups) at redshift 0.01 ≲
z ≲
1.3 with a median of 0.35, 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 modeling, we perform a blind analysis for the weak-lensing mass calibration by simultaneously modeling 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) relation and the weak-lensing-mass-to-mass-and-redshift (
M
WL
-
M
500
-z) relation, 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 modeling of the scaling relations, as the ensemble mass spanning a range of 10
13
h
-1
M
⊙
≲
M
500
≲ 10
15
h
-1
M
⊙
with a median of ≈10
14
h
-1
M
⊙
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
X
and
L
b
), the emission-weighted temperature
T
X
, the mass of intra-cluster medium
M
g
, and the mass proxy
Y
X
, which is the product of
T
X
and
M
g
. Except for
L
X
with a steeper dependence on the cluster mass at a statistically significant level, we find that the other X-ray scaling relations all show a mass trend that is statistically consistent with the self-similar prediction at a level of ≲1.7σ. Meanwhile, all these scaling relations show no significant deviation from the self-similarity in their redshift scaling. Moreover, no significant redshift-dependent mass trend is present. This work demonstrates the synergy between the eROSITA and HSC surveys in preparation for the forthcoming first-year eROSITA cluster cosmology.
Radio haloes are diffuse synchrotron sources on scales of ∼1 Mpc that are found in merging clusters of galaxies, and are believed to be powered by electrons re-accelerated by merger-driven ...turbulence. We present measurements of extended radio emission on similarly large scales in two clusters of galaxies hosting cool cores: Abell 2390 and Abell 2261. The analysis is based on interferometric imaging with the Karl G. Jansky Very Large Array, Very Large Array and Giant Metrewave Radio Telescope. We present detailed radio images of the targets, subtract the compact emission components and measure the spectral indices for the diffuse components. The radio emission in A2390 extends beyond a known sloshing-like brightness discontinuity, and has a very steep in-band spectral slope at 1.5 GHz that is similar to some known ultrasteep spectrum radio haloes. The diffuse signal in A2261 is more extended than in A2390 but has lower luminosity. X-ray morphological indicators, derived from XMM–Newton X-ray data, place these clusters in the category of relaxed or regular systems, although some asymmetric features that can indicate past minor mergers are seen in the X-ray brightness images. If these two Mpc-scale radio sources are categorized as giant radio haloes, they question the common assumption of radio haloes occurring exclusively in clusters undergoing violent merging activity, in addition to commonly used criteria for distinguishing between radio haloes and minihaloes.
The XXL Survey Mantz, A. B.; Abdulla, Z.; Allen, S. W. ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
We present results from a 100 ks
XMM
-
Newton
observation of galaxy cluster XLSSC 122, the first massive cluster discovered through its X-ray emission at
z
≈ 2. The data provide the first precise ...constraints on the bulk thermodynamic properties of such a distant cluster, as well as an X-ray spectroscopic confirmation of its redshift. We measure an average temperature of
kT
= 5.0 ± 0.7 keV; a metallicity with respect to solar of
Z
/
Z
⊙
= 0.33
−0.17
+0.19
, consistent with lower-redshift clusters; and a redshift of
z
= 1.99
+0.07
-0.06
, consistent with the earlier photo-
z
estimate. The measured gas density profile leads to a mass estimate at
r
500
of
M
500
= (6.3 ± 1.5) × 10
13
M
⊙
. From CARMA 30 GHz data, we measure the spherically integrated Compton parameter within
r
500
to be
Y
500
= (3.6 ± 0.4) × 10
−12
. We compare the measured properties of XLSSC 122 to lower-redshift cluster samples, and find good agreement when assuming the simplest (self-similar) form for the evolution of cluster scaling relations. While a single cluster provides limited information, this result suggests that the evolution of the intracluster medium in the most massive, well-developed clusters is remarkably simple, even out to the highest redshifts where they have been found. At the same time, our data reaffirm the previously reported spatial offset between the centres of the X-ray and SZ signals for XLSSC 122, suggesting a disturbed configuration. Higher spatial resolution data could thus provide greater insights into the internal dynamics of this system.
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