Alessandro Baldi

CLASH-X: A comparison of lensing and X-ray techniques for measuring the mass profiles of galaxy clusters

We present profiles of temperature, gas mass, and hydrostatic mass estimated from new and archival X-ray observations of CLASH clusters. We compare measurements derived from XMM and Chandra observations with one another and compare both to gravitational lensing mass profiles derived with CLASH Hubble Space Telescope and Subaru Telescope lensing data. Radial profiles of Chandra and XMM measurements of electron density and enclosed gas mass are nearly identical, indicating that differences in hydrostatic masses inferred from X-ray observations arise from differences in gas-temperature measurements. Encouragingly, gas temperatures measured in clusters by XMM and Chandra are consistent with one another at ~100–200 kpc radii, but XMM temperatures systematically decline relative to Chandra temperatures at larger radii. The angular dependence of the discrepancy suggests that additional investigation on systematics such as the XMM point-spread function correction, vignetting, and off-axis responses is yet required. We present the CLASH-X mass-profile comparisons in the form of cosmology-independent and redshift-independent circular-velocity profiles. We argue that comparisons of circular-velocity profiles are the most robust way to assess mass bias. Ratios of Chandra hydrostatic equilibrium (HSE) mass profiles to CLASH lensing profiles show no obvious radial dependence in the 0.3–0.8 Mpc range. However, the mean mass biases inferred from the weak-lensing (WL) and SaWLens data are different. As an example, the weighted-mean value at 0.5 Mpc is 〈b〉 = 0.12 for the WL comparison and 〈b〉 = −0.11 for the SaWLens comparison. The ratios of XMM HSE mass profiles to CLASH lensing profiles show a pronounced radial dependence in the 0.3–1.0 Mpc range, with a weighted mean mass bias value rising to 〈b〉 gsim 0.3 at ~1 Mpc for the WL comparison and 〈b〉 ≈ 0.25 for the SaWLens comparison. The enclosed gas mass profiles from both Chandra and XMM rise to a value ≈1/8 times the total-mass profiles inferred from lensing at ≈0.5 Mpc and remain constant outside of that radius, suggesting that M_gas × 8 profiles may be an excellent proxy for total-mass profiles at ≳ 0.5 Mpc in massive galaxy clusters.

An XMM-Newton spatially-resolved study of metal abundance evolution in distant galaxy clusters

Context. We present an XMM-Newton analysis of the X-ray spectra of 39 clusters of galaxies at 0.4 2�) abundance evolution with redshift. The most significant de viation from no evolution (at a 90% confidence level) is observed by consid ering the emission from the whole cluster (r < 0.6r500), which can be parametrized as Z ∝ (1 + z) −0.8±0.5 . Dividing the emission into three radial bins, no significan t evidence of abundance evolution is observed when fitting the data with a power law. We find close agreement with measurements presented in previous studies. Computing the error-weighted mean of the spatially resolved abundances into three redshift bins, we find that it is consi stent with being constant with redshift. Although the large error bars in the measurement of the weighted-mean abundance prevent us from claiming any statistically significant spatially resolved evolution, the trend with z in the 0.15-0.4r500 radial bin complements nicely the measures of Maughan et al., and broadly agrees with theoretical predictions. We also find that the data points derived from the spatially resolved analysis are well-fitted by the relation Z(r, z) = Z0(1 + (r/0.15r500) 2 ) −a ((1 + z)/1.6) − , where Z0 = 0.36± 0.03, a = 0.32± 0.07, and = 0.25± 0.57, which represents a significant negative trend of Z with radius and no significant evolution with redshift. Conclusions. We present the first attempt to determine the evolution of abu ndance at different positions in the clusters and with redshift. However, the sample size and the low-quality data statistics associated with most of the clusters studied pre vents us from drawing any statistically significant conclusion about the different evolutionary path that the different regions of t he clusters may have traversed.

A study of the core of the Shapley Concentration — V. The A3528 complex: a young merger event?

We present the results of a redshift survey of galaxies in the A3528 complex, a chain of interacting clusters in the core of the Shapley Concentration. This complex is characterized in the X-ray band by two pairs of roughly similar interacting clumps: one pair has been resolved as two optical Abell clusters (A3530 and A3532), while the two components of the other pair are both associated to A3528. The optical data show that the distance between the centers of A3530 and A3532 is smaller than their Abell radii, an indication of the existence at least of tidal interactions, and that the contours of galaxies in A3528 appear to be elongated in the North-South direction, pointing towards the A3530-A3532 pair. From our survey we obtained ~600 new radial velocity determinations: using this sample, we studied the dynamics of the four Abell clusters in this region (A3528, A3530, A3532 and A3535) and derived their mean velocities and velocity dispersions. Moreover we performed a substructure analysis, both bi-dimensional and three-dimensional, of the whole complex. All the characteristics of this structure seem to point toward a merging scenario in an early stage, whose effects on the galaxy population and on the cluster dynamics are not yet evident, contrary to what happens in the nearby A3558 complex, where the merging events are in a rather advanced stage and were already able to induce modifications in the galaxy population.

Shape and orientation of the gas distribution in A1689

ABSTRACT Knowledge of intrinsic shape and orientation of galaxy clusters is crucial to understand theirformation and evolution. We propose a novel model which uses Bayesian inference to deter-mine the intrinsic form of the hot intracluster medium of galaxy clusters. The method exploitsX-ray spectroscopic and photometric data plus measurements of the Sunyaev-Zel’dovich ef-fect (SZe). The gas distribution is modelled with an ellipsoidal parametric profile who can fitobserved X-ray surface-brightness and temperature. Comparison with the SZ amplitude fixesthe elongation along the line of sight. Finally, Bayesian inference allows us to deproject themeasured elongation and the projected ellipticity and constrain the intrinsic shape and orien-tation of the cluster. We apply the method to the rich cluster Abell 1689, which was targetedby the Chandra and XMM satellites as well as by several SZe observatories. Observationscover in detail a region < ∼ 1Mpc. Our analysis favours a mildly triaxial cluster with a mi-nor to major axis ratio of 0.70±0.15, preferentially elongated along the line of sight, asexpected for massive lensing clusters. The triaxial structure together with the orientation biascan reconcile X-ray with lensing analyses and supports the view of A1689 as a just slightlyover-concentrated massive cluster not so far from hydrostatic equilibrium.Key words: galaxies: clusters: general – cosmology: observations – me thods: statistical –galaxies: clusters: individual: Abell 1689

The evolution of the spatially resolved metal abundance in galaxy clusters up to z = 1.4

Context. We present the combined analysis of the metal content of 83 objects in the redshift range 0.09‐1.39, and spatially-resolved in the 3 bins (0-0:15;0:15-0:4;> 0:4)R500, as obtained with similar analysis using XMM-Newton data in Leccardi & Molendi (2008) and Baldi et al. (2012). Aims. By combining these two large datasets, we investigate the relations between abundance, temperature, radial position and redshift holding in the Intra-Cluster Medium. Methods. We fit functional forms to the combination of the different physical quantities of interest, i.e. ICM metal abundance, radius, and redshift. We use the pseudo-entropy ratio to separate the Cool-Core (CC) cluster population, where the central gas density tends to be relatively higher, cooler and more metal rich, from the Non-Cool-Core systems. Results. The average, redshift-independent, metal abundance measured in the 3 radial bins decrease moving outwards, with a mean metallicity in the core that is even 3 (two) times higher than the value of 0.16 times the solar abundance in Anders & Grevesse (1989) estimated at r > 0:4R500 in CC (NCC) objects. We find that the values of the emission-weighted metallicity are well-fitted by the relation Z(z) = Z0 (1 + z) at given radius. A significant scatter, intrinsic to the observed distribution and of the order of 0:05 0:15, is observed below 0:4R500. The nominal best-fit value of is significantly different from zero (> 3 ) in the inner cluster regions ( = 1:6 0:2) and in CC clusters only. These results are confirmed also with a bootstrap analysis, which provides a still significant negative evolution in the core of CC systems (P > 99:9 per cent, when counting the number of random repetitions which provides > 0). No redshift-evolution is observed when regions above the core (r > 0:15R500) are considered. A reasonable good fit of both the radial and redshift dependence is provided from the functional form Z(r;z) = Z0 (1 + (r=0:15R500) 2 ) (1 + z) , with (Z0;; ) = (0:83 0:13;0:55 0:07;1:7 0:6) in CC clusters and (0:39 0:04;0:37 0:15;0:5 0:5) for NCC systems. Conclusions. Our results represent the most extensive study of the spatially-resolved metal distribution in the cluster plasma as function of redshift. It defines the limits that numerical and analytic models describing the metal enrichment in the ICM have to meet.

A study of the core of the Shapley Concentration – VI. Spectral properties of galaxies★

ABSTRACT We present the results of a study of the spectral properties of galaxies in the cen-tral part of the Shapley Concentration, covering an extremely wide range of densities,from the rich cluster cores to the underlying supercluster environment.Our sample is homogeneous, in a well defined magnitude range (17 ≤ b J ≤ 18.8) andcontains ∼ 1300 spectra of galaxies at the same distance, covering an area of ∼ 26deg 2 . These characteristics allowed an accurate spectral classification, that we per-formed using a Principal Components Analysis technique.This spectral classification, together with the [OII] equivalent widths and the star for-mation rates, has been used to study the properties of galaxies at different densities:cluster, intercluster (i.e. galaxies in the supercluster but outside clusters) and fieldenvironment.No significant differences are present between samples at low density regimes (i.e.intercluster and field galaxies). Cluster galaxies, instead, not only have values signifi-cantly different from the field ones, but also show a dependence on the local density.Moreover, a well defined morphology-density relation is present in the cluster com-plexes, although these structures are known to be involved in major merging events.Also the mean equivalent width of [OII] shows a trend with the local environment,decreasing at increasing densities, even if it is probably induced by the morphology-density relation.Finally we analyzed the mean star formation rate as a function of the density, findingagain a decreasing trend (at ∼ 3σ significance level). Our analysis is consistent withthe claim of Balogh et al. (1998) that the star formation in clusters is depressed.Key words: galaxies: distances and redshifts – galaxies: spectra and morphology –galaxies: clusters: general – galaxies: clusters: individuals: A3528 - A3530 - A3532 -A3535 - A3556 - A3558 - A3562 –