The total mass of a galaxy cluster is one of its most fundamental properties. Together with the redshift, the mass links observation and theory, allowing us to use the cluster population to test ...models of structure formation and to constrain cosmological parameters. Building on the rich heritage from X-ray surveys, new results from Sunyaev-Zeldovich and optical surveys have stimulated a resurgence of interest in cluster cosmology. These studies have generally found fewer clusters than predicted by the baseline
Planck
Λ
CDM model, prompting a renewed effort on the part of the community to obtain a definitive measure of the true cluster mass scale. Here we review recent progress on this front. Our theoretical understanding continues to advance, with numerical simulations being the cornerstone of this effort. On the observational side, new, sophisticated techniques are being deployed in individual mass measurements and to account for selection biases in cluster surveys. We summarise the state of the art in cluster mass estimation methods and the systematic uncertainties and biases inherent in each approach, which are now well identified and understood, and explore how current uncertainties propagate into the cosmological parameter analysis. We discuss the prospects for improvements to the measurement of the mass scale using upcoming multi-wavelength data, and the future use of the cluster population as a cosmological probe.
Autoantibodies target the RNA binding protein Ro60 in systemic lupus erythematosus (SLE) and Sjögren's syndrome. However, it is unclear whether Ro60 and its associated RNAs contribute to disease ...pathogenesis. We catalogued the Ro60-associated RNAs in human cell lines and found that among other RNAs, Ro60 bound an RNA motif derived from endogenous Alu retroelements. Alu transcripts were induced by type I interferon and stimulated proinflammatory cytokine secretion by human peripheral blood cells. Ro60 deletion resulted in enhanced expression of Alu RNAs and interferon-regulated genes. Anti-Ro60–positive SLE immune complexes contained Alu RNAs, and Alu transcripts were up-regulated in SLE whole blood samples relative to controls. These findings establish a link among the lupus autoantigen Ro60, Alu retroelements, and type I interferon.
We examine the radial entropy distribution and its scaling using 31 nearby galaxy clusters from the representative XMM-Newton cluster structure survey (REXCESS), a sample in the temperature range ...2-9 keV selected in X-ray luminosity only, with no bias toward any particular morphological type. The entropy profiles are robustly measured at least out to R1000 in all systems and out to R500 in thirteen systems. Compared to theoretical expectations from non-radiative cosmological simulations, the observed distributions show a radial and mass-dependent excess entropy, such that the excess is greater and extends to larger radii in lower mass systems. At R500, the mass dependence and entropy excess are both negligible within the large observational and theoretical uncertainties. Mirroring this behaviour, the scaling of gas entropy is shallower than self-similar in the inner regions, but steepens with radius, becoming consistent with self-similar at R500. There is a large dispersion in scaled entropy in the inner regions, apparently linked to the presence of cool cores and dynamical activity; at larger radii the dispersion decreases by approximately a factor of two to 30 per cent, and the dichotomy between subsamples disappears. There are two peaks in the distribution of both inner slope and, after parameterising the profiles with a power law plus constant model, in central entropy K0. However, we are unable to distinguish between a bimodal or a left-skewed distribution of K0 with the present data. The distribution of outer slopes is unimodal with a median value of 0.98, and there is a clear correlation of outer slope with temperature. Renormalising the dimensionless entropy profiles by the gas mass fraction profile fgas (<R), leads to a remarkable reduction in the scatter, implying that gas mass fraction variations with radius and mass are the cause of the observed entropy structural and scaling properties. The results are consistent with the picture of a cluster population in which entropy modification is centrally concentrated and extends to larger radii at lower mass, leading to both a radial and a mass-dependence in the gas mass fraction, but which is increasingly self-similar at large radius. The observed normalisation, however, would suggest entropy modification at least up to R1000, and even beyond, in all but the most massive systems. We discuss a tentative scenario to explain the observed behaviour of the entropy and gas mass fraction in the REXCESS sample, in which a combination of extra heating and merger mixing maintains an elevated central entropy level in the majority of the population, and a smaller fraction of systems is able to develop a cool core.
Using a sample of ten nearby (z QQQ ? 0.15), relaxed galaxy clusters in the temperature range 2-9 keV, we have investigated the scaling relation between the mass at various density contrasts (d = ...2500, 1000, 500, 200) and the cluster temperature. The masses are derived from NFW-type model fits to mass profiles, obtained under the hydrostatic assumption using precise measurements, with XMM-Newton, at least down to d = 1000. The logarithmic slope of the M-T relation is well constrained and is the same at all d, reflecting the self-similarity of the mass profiles. At d = 500, the slope of the relation for the sub-sample of hot clusters (kT > 3.5 keV) is consistent with the standard self-similar expectation: a = 1.49 c 0.15. The relation steepens when the whole sample is considered: a = 1.71 c 0.09. The normalisation of the relation is discrepant (by 630 per cent), at all density contrasts, with the prediction from purely gravitation based models. Models that take into account radiative cooling and galaxy feedback are generally in better agreement with our data. We argue that remaining discrepancies, in particular at low d, are more likely due to problems with models of the ICM thermal structure rather than to an incorrect estimate of the mass from X-ray data.
Many galaxy clusters host megaparsec-scale radio halos, generated by ultrarelativistic electrons in the magnetized intracluster medium. The X-ray luminosity and redshift-limited Extended GMRT Radio ...Halo Survey provides a rich and unique dataset for statistical studies of the halos. We uniformly analyze the radio and X-ray data for the GMRT cluster sample, and use the new Planck Sunyaev-Zel'dovich (SZ) catalog to revisit the correlations between the power of radio halos and the thermal properties of galaxy clusters. Our bigger and more homogenous sample confirms that the X-ray luminous (L sub(500) > 5 x 10 super(44) erg s super(-1)) clusters branch into two populations-radio halos lie on the correlation, while clusters without radio halos have their radio upper limits well below that correlation. Bimodality of both correlations can be traced to clusters dynamics, with radio halos found exclusively in merging clusters. These results confirm the key role of mergers for the origin of giant radio halos, suggesting that they trigger the relativistic particle acceleration.
We present a detailed study of the integrated total hydrostatic mass profiles of the five most massive M500SZ < 5 × 1014 M⊙ ( M 500 SZ > 5 × 10 14 M ⊙ ) $\left( {M_{500}^{{\rm{SZ}}} > 5 \times ...{{10}^{14}}\,{M_ \odot }} \right)$ galaxy clusters selected at z ∼ 1 via the Sunyaev–Zel’dovich effect. These objects represent an ideal laboratory to test structure formation models where the primary driver is gravity. Optimally exploiting spatially-resolved spectroscopic information from XMM-Newton and Chandra observations, we used both parametric (forward, backward) and non-parametric methods to recover the mass profiles, finding that the results are extremely robust when density and temperature measurements are both available. Our X-ray masses at R500 are higher than the weak lensing masses obtained from the Hubble Space Telescope (HST), with a mean ratio of 1.39−0.35+0.47 1.39 − 0.35 + 0.47 $1.39^{+0.47}_{-0.35}$ . This offset goes in the opposite direction to that expected in a scenario where the hydrostatic method yields a biased, underestimated, mass. We investigated halo shape parameters such as sparsity and concentration, and compared to local X-ray selected clusters, finding hints for evolution in the central regions (or for selection effects). The total baryonic content is in agreement with the cosmic value at R500. Comparison with numerical simulations shows that the mass distribution and concentration are in line with expectations. These results illustrate the power of X-ray observations to probe the statistical properties of the gas and total mass profiles in this high mass, high-redshift regime.
We present the results of the radio halo survey of 16 REXCESS southern clusters up to a redshift of 0.2 with the Australia Telescope Compact Array (ATCA) at 1.4 and 2.1 GHz. This cluster sample ...called the ATCA REXCESS Diffuse Emission Survey (ARDES) includes clusters in a wide range of X-ray luminosities and is morphologically unbiased. We find two diffuse radio sources in the clusters RXCJ2234.5-3744 (Abell 3888) and RXCJ0225.1-2928. The diffuse radio emission in RXCJ2234.5-3744 is a giant radio halo and the diffuse emission in RXCJ0225.1-2928 is a peculiar radio relic candidate. The radio halo has a spectral index of ... = -1.48 plus or minus 0.14 and the K-corrected P sub( 1.4) is 1.9 plus or minus 0.2 x 10 super( 24) W Hz super( -1). The properties of the detected halo are consistent with both the current P sub( 1.4)-L sub( X) and P sub( 1.4)-Y sub( SZ) correlations. The putative radio relic is located approximately 1 Mpc from the cluster in a filament and has a physical extent of 346 plus or minus 20 kpc and a power of P sub( 1.4) = 3.3 plus or minus 0.8 x 10 super( 23) W Hz super( -1), which places it in the lower power region of currently known relics. (ProQuest: ... denotes formulae/symbols omitted.)
We present the integrated mass profiles for a sample of ten nearby (z less than or approximate to 0.15), relaxed galaxy clusters, covering a temperature range of keV, observed with XMM-Newton. The ...mass profiles were derived from the observed gas density and temperature profiles under the hypothesis of spherical symmetry and hydrostatic equilibrium. All ten mass profiles are well described by an NFW-type profile over the radial range from 0.01 to 0.5 R sub(200), where R sub(200) is the radius corresponding to a density contrast of 200 with respect to the critical density at the cluster redshift. A King model is inconsistent with these data. The derived concentration parameters and total masses are in the range c sub(200) = 4-6 and M sub(200) = 1.2 x 10 super(14)-1.2 x 10 super(15) M direct sum , respectively. Our qualitative and quantitative study of the mass profile shape shows, for the first time, direct and clear observational evidence for the universality of the total mass distribution in clusters. The mass profiles scaled in units of R sub(200) and M sub(200) nearly coincide, with a dispersion of less than 15% at 0.1 R sub(200). The c sub(200)-M sub(200) relation is consistent with the predictions of numerical simulations for a Lambda CDM cosmology, taking into account the measurement errors and expected intrinsic scatter. Our results provide further strong evidence in favour of the Cold Dark Matter cosmological scenario and show that dark matter collapse is well understood, at least down to the cluster scale.
ABSTRACT
We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters ...persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ⩽
z
⩽ 1 are selected from the COSMOS 2 deg
2
survey, based only on their X-ray luminosity and extent. This sample is complemented by 27 nearby clusters with a robust, analogous determination of the total and stellar mass inside
R
500
. The total sample of 118 groups and clusters with
z
⩽ 1 spans a range in
M
500
of ∼10
13
–10
15
M
☉
. We find that the stellar mass fraction associated with galaxies at
R
500
decreases with increasing total mass as
M
−0.37 ± 0.04
500
, independent of redshift. Estimating the total gas mass fraction from a recently derived, high-quality scaling relation, the total baryon mass fraction (
f
stars+gas
500
=
f
stars
500
+
f
gas
500
) is found to increase by ∼25%, when
M
500
increases from 〈
M
〉 = 5 × 10
13
M
☉
to 〈
M
〉 = 7 × 10
14
M
☉
. After consideration of a plausible contribution due to intracluster light (11%–22% of the total stellar mass) and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.3σ for groups of 〈
M
〉 = 5 × 10
13
M
☉
. The discrepancy decreases toward higher total masses, such that it is 1σ at 〈
M
〉 = 7 × 10
14
M
☉
. We discuss this result in terms of nongravitational processes such as feedback and filamentary heating.
We present the first cluster catalog extracted from combined space-based (
Planck
) and ground-based (South Pole Telescope; SPT-SZ) millimeter data. We developed and applied a matched multi-filter ...(MMF) capable of dealing with the different transfer functions and resolutions of the two datasets. We verified that it produces results consistent with publications from
Planck
and SPT collaborations when applied on the datasets individually. We also verified that
Planck
and SPT-SZ cluster fluxes are consistent with each other. When applied blindly to the combined dataset, the MMF generated a catalog of 419 detections (
S
/
N
> 5), of which 323 are already part of the SPT-SZ or PSZ2 catalogs; 54 are new SZ detections, which have been identified in other catalogs or surveys; and 42 are new unidentified candidates. The MMF takes advantage of the complementarity of the two datasets,
Planck
being particularly useful for detecting clusters at a low redshift (
z
< 0.3), while SPT is efficient at finding higher redshift (
z
> 0.3) sources. This work represents a proof of concept that blind cluster extraction can be performed on combined, inhomogeneous millimeter datasets acquired from space and ground. This result is of prime importance for planned ground-based cosmic microwave background (CMB) experiments (e.g., Simons Observatory, CMB-S4) and envisaged CMB space missions (e.g., PICO, Backlight) that will detect hundreds of thousands of clusters in the low mass regime (
M
500
≤ 10
14
M
⊙
), for which the various sources of intra-cluster emission (gas, dust, synchrotron) will be of the same order of magnitude and hence require broad ground and space frequency coverage with a comparable spatial resolution for adequate separation.
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