Pressure profiles of distant galaxy clusters in the Planck catalog

Successive releases of Planck data have demonstrated the strength of the Sunyaev--Zeldovich (SZ) effect in detecting hot baryons out to the galaxy cluster peripheries. To infer the hot gas pressure structure from nearby galaxy clusters to more distant objects, we developed a parametric method that models the spectral energy distribution and spatial anisotropies of both the Galactic thermal dust and the Cosmic Microwave Background, that are mixed-up with the cluster SZ and dust signals. Taking advantage of the best angular resolution of the High Frequency Instrument channels (5 arcmin) and using X-ray priors in the innermost cluster regions that are not resolved with Planck, this modelling allowed us to analyze a sample of 61 nearby members of the Planck catalog of SZ sources ($0 < z < 0.5$, $\tilde{z} = 0.15$) using the full mission data, as well as to examine a distant sample of 23 clusters ($0.5 < z < 1$, $\tilde{z} = 0.56$) that have been recently followed-up with XMM-Newton and Chandra observations. We find that (i) the average shape of the mass-scaled pressure profiles agrees with results obtained by the Planck collaboration in the nearby cluster sample, and that (ii) no sign of evolution is discernible between averaged pressure profiles of the low- and high-redshift cluster samples. In line with theoretical predictions for these halo masses and redshift ranges, the dispersion of individual profiles relative to a self-similar shape stays well below 10 % inside $r_{500}$ but increases in the cluster outskirts.Comment: 12 pages, 10 figure

Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster

We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10 Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in ugriK bands and in Halpha narrow-band are used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending respectively 30kpc and 41kpc in projection from their disks. The galaxies' gaseous disks are truncated and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting about 250Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS-90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte

Selecting background galaxies in weak-lensing analysis of galaxy clusters

In this paper, we present a new method to select the faint, background galaxies used to derive the mass of galaxy clusters by weak lensing. The method is based on the simultaneous analysis of the shear signal, that should be consistent with zero for the foreground, unlensed galaxies, and of the colors of the galaxies: photometric data from the COSMic evOlution Survey are used to train the color selection. In order to validate this methodology, we test it against a set of state-of-the-art image simulations of mock galaxy clusters in different redshift [$0.23-0.45$] and mass [$0.5-1.55\times10^{15}M_\odot$] ranges, mimicking medium-deep multicolor imaging observations (e.g. SUBARU, LBT). The performance of our method in terms of contamination by unlensed sources is comparable to a selection based on photometric redshifts, which however requires a good spectral coverage and is thus much more observationally demanding. The application of our method to simulations gives an average ratio between estimated and true masses of $\sim 0.98 \pm 0.09$. As a further test, we finally apply our method to real data, and compare our results with other weak lensing mass estimates in the literature: for this purpose we choose the cluster Abell 2219 ($z=0.228$), for which multi-band (BVRi) data are publicly available.Comment: MNRAS, Accepted 2016 February 2

A2163: Merger events in the hottest Abell galaxy cluster II. Subcluster accretion with galaxy-gas separation

Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster medium (ICM) that exhibits extraordinary properties, including an exceptionally high X-ray luminosity, average temperature, and a powerful and extended radio halo. The irregular and complex morphology of its gas and galaxy structure suggests that this cluster has recently undergone major merger events that involve two or more cluster components. In this paper, we study the gas structure and dynamics by means of spectral-imaging analysis of X-ray data obtained from XMM-Newton and Chandra observations. From the evidence of a cold front, we infer the westward motion of a cool core across the E-W elongated atmosphere of the main cluster A2163-A. Located close to a galaxy over-density, this gas 'bullet' appears to have been spatially separated from its galaxy (and presumably dark matter component) as a result of high-velocity accretion. From gas brightness and temperature profile analysis performed in two opposite regions of the main cluster, we show that the ICM has been adiabatically compressed behind the crossing 'bullet' possibly because of shock heating, leading to a strong departure of the ICM from hydrostatic equilibrium in this region. Assuming that the mass estimated from the Yx proxy best indicates the overall mass of the system and that the western cluster sector is in approximate hydrostatic equilibrium before subcluster accretion, we infer a merger scenario between two subunits of mass ratio 1:4, leading to a present total system mass of M500 $\propto 1.9 \times 1015 M_{\odot}$. The exceptional properties of A2163 present various similarities with those of 1E0657-56, the so-called 'bullet-cluster'. These similarities are likely to be related to a comparable merger scenario.Comment: A&A, in pres

The nucleus of 103P/Hartley 2, target of the EPOXI mission

103P/Hartley 2 was selected as the target comet for the Deep Impact extended mission, EPOXI, in October 2007. There have been no direct optical observations of the nucleus of this comet, as it has always been highly active when previously observed. We aimed to recover the comet near to aphelion, to a) confirm that it had not broken up and was in the predicted position, b) to provide astrometry and brightness information for mission planning, and c) to continue the characterisation of the nucleus. We observed the comet at heliocentric distances between 5.7 and 5.5 AU, using FORS2 at the VLT, at 4 epochs between May and July 2008. We performed VRI photometry on deep stacked images to look for activity and measure the absolute magnitude and therefore estimate the size of the nucleus. We recovered the comet near the expected position, with a magnitude of m_R = 23.74 \pm 0.06 at the first epoch. The comet had no visible coma, although comparison of the profile with a stellar one showed that there was faint activity, or possibly a contribution to the flux from the dust trail from previous activity. This activity appears to fade at further epochs, implying that this is a continuation of activity past aphelion from the previous apparition rather than an early start to activity before the next perihelion. Our data imply a nucleus radius of \le 1 km for an assumed 4% albedo; we estimate a ~6% albedo. We measure a colour of (V-R) = 0. 26 \pm 0.09.Comment: 5 pages, 4 figures, accepted for publication in A&

Non-hydrostatic gas in the core of the relaxed galaxy cluster A1795

Chandra data on A1795 reveal a mild edge-shaped discontinuity in the gas density and temperature in the southern sector of the cluster at r=60/h kpc. The gas inside the edge is 1.3-1.5 times denser and cooler than outside, while the pressure is continuous, indicating that this is a "cold front", the surface of contact between two moving gases. The continuity of the pressure indicates that the current relative velocity of the gases is near zero, making the edge appear to be in hydrostatic equilibrium. However, a total mass profile derived from the data in this sector under the equilibrium assumption, exhibits an unphysical jump by a factor of 2, with the mass inside the edge being lower. We propose that the cooler gas is "sloshing" in the cluster gravitational potential well and is now near the point of maximum displacement, where it has zero velocity but nonzero centripetal acceleration. The distribution of this non-hydrostatic gas should reflect the reduced gravity force in the accelerating reference frame, resulting in the apparent mass discontinuity. Assuming that the gas outside the edge is hydrostatic, the acceleration of the moving gas can be estimated from the mass jump, a ~ 800 h km/s/(10^8 yr). The gravitational potential energy of this gas that is available for dissipation is about half of its current thermal energy. The length of the cool filament extending from the cD galaxy (Fabian et al.) may give the amplitude of the gas sloshing, 30-40/h kpc. Such gas bulk motion might be caused by a disturbance of the central gravitational potential by past subcluster infall.Comment: Minor text clarifications to correspond to published version. 5 pages, 1 figure in color, uses emulateapj.sty. ApJ Letters in pres

Shapley Supercluster Survey (ShaSS): Galaxy Evolution from Filaments to Cluster Cores

We present an overview of a multi-wavelength survey of the Shapley supercluster (SSC; z~0.05) covering a contiguous area of 260 h^-2_70 Mpc^2 including the supercluster core. The project main aim is to quantify the influence of cluster-scale mass assembly on galaxy evolution in one of the most massive structures in the local Universe. The Shapley supercluster survey (ShaSS) includes nine Abell clusters (A3552, A3554, A3556, A3558, A3559, A3560, A3562, AS0724, AS0726) and two poor clusters (SC1327- 312, SC1329-313) showing evidence of cluster-cluster interactions. Optical (ugri) and near-infrared (K) imaging acquired with VST and VISTA allow us to study the galaxy population down to m*+6 at the supercluster redshift. A dedicated spectroscopic survey with AAOmega on the Anglo-Australian Telescope provides a magnitude-limited sample of supercluster members with 80% completeness at ~m*+3. We derive the galaxy density across the whole area, demonstrating that all structures within this area are embedded in a single network of clusters, groups and filaments. The stellar mass density in the core of the SSC is always higher than 9E09 M_sun Mpc^-3, which is ~40x the cosmic stellar mass density for galaxies in the local Universe. We find a new filamentary structure (~7 Mpc long in projection) connecting the SSC core to the cluster A3559, as well as previously unidentified density peaks. We perform a weak-lensing analysis of the central 1 sqdeg field of the survey obtaining for the central cluster A3558 a mass of M_500=7.63E14 M_sun, in agreement with X-ray based estimates.Comment: 22 pages, 11 figures. Accepted for publication on MNRA

An X-ray and optical study of the cluster A33

We report the first detailed X-ray and optical observations of the medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray and optical imaging and spectroscopic data allowed us to identify the X-ray source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint, F_{2-10 keV} \approx 2.4 \times 10^{-13} \ergscm2, X-ray source 1SAXJ0027.2-1930, $\sim 2$ arcmin away from the optical position of the cluster as given in the Abell catalogue, is identified with the central region of A33. Based on six cluster galaxy redshifts, we determine the redshift of A33, $z=0.2409$; this is lower than the value derived by Leir and Van Den Bergh (1977). The source X-ray luminosity, L_{2-10 keV} = 7.7 \times 10^{43} \ergs, and intracluster gas temperature, $T = 2.9$ keV, make this cluster interesting for cosmological studies of the cluster $L_X-T$ relation at intermediate redshifts. Two other X-ray sources in the A33 field are identified. An AGN at z$=$0.2274, and an M-type star, whose emission are blended to form an extended X-ray emission $\sim 4$ arcmin north of the A33 cluster. A third possibly point-like X-ray source detected $\sim 3$ arcmin north-west of A33 lies close to a spiral galaxy at z$=$0.2863 and to an elliptical galaxy at the same redshift as the cluster.Comment: 9 pages, 6 Figures, Latex (using psfig,l-aa), to appear in Astronomy and Astrophysics S. (To get better quality copies of Figs.1-3 send an email to: [email protected]). A&AS, in pres

The Feedback-Regulated Growth of Black Holes and Bulges through Gas Accretion and Starbursts in Cluster Central Dominant Galaxies

We present an analysis of the growth of black holes through accretion and bulges through star formation in 33 galaxies at the centers of cooling flows. Most of these systems show evidence of cavities in the intracluster medium (ICM) inflated by radio jets emanating from their active galactic nuclei (AGN). We present a new and extensive analysis of X-ray cavities in these systems. We find that AGN are energetically able to balance radiative losses (cooling) from the ICM in more than half of our sample. Using a subsample of 17 systems, we examine the relationship between cooling and star formation. We find that the star formation rates are approaching or are comparable to X-ray and far UV limits on the rates of gas condensation onto the central galaxy. The remaining radiative losses could be offset by AGN feedback. The vast gulf between radiative losses and the sink of cooling material, which has been the primary objection to cooling flows, has narrowed and, in some cases, is no longer a serious issue. Using the cavity (jet) powers, we place strong lower limits on the rate of growth of supermassive black holes in central galaxies, and we find that they are growing at an average rate of ~ 0.1 solar masses per year, with some systems growing as quickly as ~ 1 solar mass per year. We find a trend between bulge growth (star formation) and black hole growth that is approximately in accordance with the slope of the local (Magorrian) relation between black hole and bulge mass. However, the large scatter in the trend suggests that bulges and black holes do not always grow in lock step. (Abridged)Comment: 17 pages, 6 figures, accepted to ApJ. Minor changes to text and figure