G. P. Smith

LoCuSS: Subaru Weak Lensing Study of 30 Galaxy Clusters

(Abridged) We use Subaru data to conduct a detailed weak-lensing study of the dark matter distribution in a sample of 30 X-ray luminous galaxy clusters at 0.15<z<0.3. A weak-lensing signal is detected at high statistical significance in each cluster, the total detection S/N ranging from 5 to 13. In this paper we concentrate on fitting spherical models to the tangential distortion profiles of the clusters. When the models are fitted to the clusters individually, we are unable to discriminate statistically between SIS and NFW models. However when the tangential distortion profiles of the individual clusters are combined, and models fitted to the stacked profile, the SIS model is rejected at 6- and 11-sigma, respectively, for low- and high-mass bins. We also use the individual cluster NFW model fits to investigate the relationship between cluster mass (M_vir) and concentration (c_vir), finding an anti-correlation of c_vir and M_vir. The best-fit c_vir-M_vir relation is: c_vir(M_vir) propto M_vir^{-alpha} with alpha=0.41+/-0.19 -- i.e. a non-zero slope is detected at 2sigma significance. We then investigate the optimal radius within which to measure cluster mass, finding that the typical fractional errors are improved to sigma(M_Delta)/M_Delta ~ 0.1-0.2 for cluster masses at higher over-densities Delta=500-2000, from 0.2-0.3 for the virial over-density (~110). Further comparisons between mass measurements based on spherical model fitting and the model-independent aperture mass method reveal that the 2D aperture mass enclosed within a cylinder of a given aperture radius is systematically greater than the 3D spherical mass obtained from NFW model fitting: M_2D/M_3D= 1.34 and 1.40 for Delta=500 and 110, respectively. The amplitude of this effect agrees well with that predicted by integrating the NFW model along the line-of-sight.

LoCuSS: the connection between brightest cluster galaxy activity, gas cooling and dynamical disturbance of X-ray cluster cores

We study the distribution of projected offsets between the cluster X-ray centroid and the brightest cluster galaxy (BCG) for 65 X-ray-selected clusters from the Local Cluster Substructure Survey, with a median redshift of z = 0.23. We find a clear correlation between X-ray/BCG projected offset and the logarithmic slope of the cluster gas density profile at 0.04r 500 (α), implying that more dynamically disturbed clusters have weaker cool cores. Furthermore, there is a close correspondence between the activity of the BCG, in terms of detected Hα and radio emission, and the X-ray/BCG offset, with the line-emitting galaxies all residing in clusters with X-ray/BCG offsets of ≤15 kpc. Of the BCGs with α 0.02r 500 , indicating that the total mass may be systematically underestimated in clusters with larger X-ray/BCG offsets. Our results imply a link between cool core strength and cluster dynamical state consistent with the view that cluster mergers can significantly perturb cool cores, and set new constraints on models of the evolution of the intracluster medium.

LoCuSS: a comparison of cluster mass measurements from XMM-Newton and Subaru-testing deviation from hydrostatic equilibrium and non-thermal pressure support

We acknowledge support from KICP in Chicago for hospitality, and thank our LoCuSS collaborators, especially Masahiro Takada and Keiichi Umetsu, for helpful comments on the manuscript. Y.Y.Z. thanks Massimo Meneghetti and Gabriel Pratt for useful discussion. Y.Y.Z. acknowledges support by the DFG through Emmy Noether Research Grant RE 1462/ 2, through Schwerpunkt Program 1177, and through project B6 “Gravitational Lensing and X-ray Emission by Non-Linear Structures” of Transregional Collaborative Research Centre TRR 33 The Dark Universe, and support by the German BMBF through the Verbundforschung under grant 50 OR 0601. This work is supported by a Grant-in-Aid for the COE Program “Exploring New Science by Bridging Particle-Matter Hierarchy” and G-COE Program “Weaving Science Web beyond Particle-Matter Hierarchy” in Tohoku University, funded by theMinistry of Education, Science, Sports and Culture of Japan. This work is, in part, supported by a Grant-in-Aid for Science Research in a Priority Area “Probing the Dark Energy through an Extremely Wide and Deep Survey with Subaru Telescope” (18072001) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. N.O. is, in part, supported by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (20740099). A.F. acknowledges support from BMBF/DLR under grant 50 OR 0207 and MPG, and was partially supported by a NASA grant NNX08AX46G to UMBC. G.P.S. acknowledges support from the Royal Society and STFC. D.P.M. acknowledges support provided by NASA through Hubble Fellowship grant HF-51259.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.

LoCuSS: First Results from Strong-lensing Analysis of 20 Massive Galaxy Clusters at z=0.2

We present a statistical analysis of a sample of 20 strong lensing clusters drawn from the Local Cluster Substructure Survey, based on high-resolution Hubble Space Telescope imaging of the cluster cores and follow-up spectroscopic observations using the Keck-I telescope. We use detailed parametrized models of the mass distribution in the cluster cores, to measure the total cluster mass and fraction of that mass associated with substructures within R ≤ 250 kpc. These measurements are compared with the distribution of baryons in the cores, as traced by the old stellar populations and the X-ray emitting intracluster medium. Our main results include: (i) the distribution of Einstein radii is lognormal, with a peak and 1σ width of〈log_(10)θ_E(z=2)〉= 1.16 ± 0.28; (ii) we detect an X-ray/lensing mass discrepancy of〈M_(SL)/M_X〉= 1.3 at 3σ significance – clusters with larger substructure fractions displaying greater mass discrepancies, and thus greater departures from hydrostatic equilibrium and (iii) cluster substructure fraction is also correlated with the slope of the gas density profile on small scales, implying a connection between cluster–cluster mergers and gas cooling. Overall our results are consistent with the view that cluster–cluster mergers play a prominent role in shaping the properties of cluster cores, in particular causing departures from hydrostatic equilibrium, and possibly disturbing cool cores. Our results do not support recent claims that large Einstein radius clusters present a challenge to the cold dark matter paradigm.

Direct measurement of dark matter halo ellipticity from two-dimensional lensing shear maps of 25 massive clusters★

We present new measurements of dark matter distributions in 25 X-ray luminous clusters by making a full use of the two-dimensional (2D) weak-lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. Our approach to directly compare the measured lensing shear pattern with elliptical model predictions allows us to extract new information on the mass distributions of individual clusters, such as the halo ellipticity and mass centroid. We find that these parameters on the cluster shape are little degenerate with cluster mass and concentration parameters. By combining the 2D fitting results for a subsample of 18 clusters, the elliptical shape of dark matter haloes is detected at 7σ significance level. The mean ellipticity is found to be (e) = 〈1 ― b/a〉 = 0.46 ± 0.04 (1σ), which is in excellent agreement with a theoretical prediction based on the standard collisionless cold dark matter model. The mass centroid can be constrained with a typical accuracy of ∼20 arcsec (∼50 h ―1 kpc) in radius for each cluster. The mass centroid position fairly well matches the position of the brightest cluster galaxy, with some clusters showing significant offsets. Thus, the 2D shear fitting method enables us to assess one of the most important systematic errors inherent in the stacked cluster weak-lensing technique, the mass centroid uncertainty. In addition, the shape of the dark mass distribution is found to be only weakly correlated with that of the member galaxy distribution or the brightest cluster galaxy. We carefully examine possible sources of systematic errors in our measurements including the effect of substructures, the cosmic shear contamination, fitting regions and the dilution effect, and find none of them to be significant. Our results demonstrate the power of high-quality imaging data for exploring the detailed spatial distribution of dark matter, which should improve the ability of future surveys to conduct cluster cosmology experiments.

A bright z=5.2 lensed submillimeter galaxy in the field of Abell 773: HLSJ091828.6+514223

During our Herschel Lensing Survey (HLS) of massive galaxy clusters, we have discovered an exceptionally bright source behind the z = 0.22 cluster Abell 773, which appears to be a strongly lensed submillimeter galaxy (SMG) at z = 5.2429. This source is unusual compared to most other lensed sources discovered by Herschel so far, because of its higher submm flux (~200 mJy at 500 μm) and its high redshift. The dominant lens is a foreground z = 0.63 galaxy, not the cluster itself. The source has a far-infrared (FIR) luminosity of LFIR = 1.1 × 1014/μ Ls, where μ is the magnification factor, likely ~11. We report here the redshift identification through CO lines with the IRAM-30 m, and the analysis of the gas excitation, based on CO(7-6), CO(6-5), CO(5-4) detected at IRAM and the CO(2-1) at the EVLA. All lines decompose into a wide and strong red component, and a narrower and weaker blue component, 540 km s-1 apart. Assuming the ultraluminous galaxy (ULIRG) CO-to-H2 conversion ratio, the H2 mass is 5.8 × 1011/μ Ms, of which one third is in a cool component. From the C I(3P2-3P1) line we derive a C I/H2 number abundance of 6 × 10-5 similar to that in other ULIRGs. The H2Op(2,0,2-1,1,1) line is strong only in the red velocity component, with an intensity ratio I(H2O)/I(CO) ~ 0.5, suggesting a strong local FIR radiation field, possibly from an active nucleus (AGN) component. We detect the [NII]205 μm line for the first time at high-z. It shows comparable blue and red components, with a strikingly broad blue one, suggesting strong ionized gas flows.

LOCUSS: THE MID-INFRARED BUTCHER-OEMLER EFFECT

We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy clusters at 0.02 ≤ z ≤ 0.40, using panoramic Spitzer/MIPS 24 μm and near-infrared data, including 27 new observations from the LoCuSS and ACCESS surveys. This is the largest sample of clusters to date with such high-quality and uniform MIR data covering not only the cluster cores, but extending into the infall regions. We use these data to revisit the so-called Butcher-Oemler (BO) effect, measuring the fraction of massive infrared luminous galaxies (K 5 × 10^(10) L_☉) within r_(200), finding a steady increase in the fraction with redshift from ~3% at z = 0.02 to ~10% by z = 0.30, and an rms cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift evolution model of the form f_(SF) ∝ (1 + z)^n has n = 5.7^(+2.1)_(–1.8), which is stronger redshift evolution than that of L*_(IR) in both clusters and the field. We find that, statistically, this excess is associated with galaxies found at large cluster-centric radii, specifically r_(500) < r < r_(200), implying that the MIR BO effect can be explained by a combination of both the global decline in star formation in the universe since z ~ 1 and enhanced star formation in the infall regions of clusters at intermediate redshifts. This picture is supported by a simple infall model based on the Millennium Simulation semianalytic galaxy catalogs, whereby star formation in infalling galaxies is instantaneously quenched upon their first passage through the cluster, in that the observed radial trends of f_(SF) trace those inferred from the simulations. The observed f SF values, however, lie systematically above the predictions, suggesting an overall excess of star formation, either due to triggering by environmental processes, or a gradual quenching. We also find that f SF does not depend on simple indicators of the dynamical state of clusters, including the offset between the brightest cluster galaxy and the peak of the X-ray emission. This is consistent with the picture described above in that most new star formation in clusters occurs in the infall regions, and is thus not sensitive to the details of cluster-cluster mergers in the core regions.

An increase in the faint red galaxy population in massive clusters since z ∼ 0.5

We compare the luminosity functions for red galaxies lying on the rest-frame (U - V) color-magnitude sequence in a homogeneous sample of 10 X-ray-luminous clusters from the MACS survey at z ~ 0.5 to a similarly selected X-ray cluster sample at z ~ 0.1. We exploit deep Hubble Space Telescope ACS imaging in the F555W and F814W passbands of the central 1.2 Mpc diameter regions of the distant clusters to measure precise colors for the galaxies in these regions and statistically correct for contamination by field galaxies using observations of blank fields. We apply an identical analysis to ground-based photometry of the z ~ 0.1 sample. This comparison demonstrates that the number of faint, MV ~ -19, red galaxies relative to the bright population seen in the central regions of massive clusters has roughly doubled over the 4 Gyr between z ~ 0.5 and z ~ 0.1. We quantify this difference by measuring the dwarf-giant ratio on the red sequence, which increases by a factor of at least 2.2 ± 0.4 since z ~ 0.5. This is consistent with the idea that many faint, blue, star-forming galaxies in high-density environments are transforming onto the red sequence in the last half of the Hubble time.

LoCuSS: THE MASS DENSITY PROFILE OF MASSIVE GALAXY CLUSTERS AT z = 0.2* , **

We present a stacked weak-lensing analysis of an approximately mass-selected sample of 50 galaxy clusters at 0.15 < z < 0.3, based on observations with Suprime-Cam on the Subaru Telescope. We develop a new method for selecting lensed background galaxies from which we estimate that our sample of red background galaxies suffers just 1% contamination. We detect the stacked tangential shear signal from the full sample of 50 clusters, based on this red sample of background galaxies, at a total signal-to-noise ratio of 32.7. The Navarro-Frenk-White model is an excellent fit to the data, yielding sub-10% statistical precision on mass and concentration: , (). Tests of a range of possible systematic errors, including shear calibration and stacking-related issues, indicate that they are subdominant to the statistical errors. The concentration parameter obtained from stacking our approximately mass-selected cluster sample is broadly in line with theoretical predictions. Moreover, the uncertainty on our measurement is comparable with the differences between the different predictions in the literature. Overall, our results highlight the potential for stacked weak-lensing methods to probe the mean mass density profile of cluster-scale dark matter halos with upcoming surveys, including Hyper-Suprime-Cam, Dark Energy Survey, and KIDS.

Truncation of galaxy dark matter halos in high density environments

Aims. Our aim is to constrain the properties of dark matter halos inhabiting high density environments, such as is the case in massive galaxy clusters. Methods. We use galaxy-galaxy lensing techniques that utilize a maximum likelihood method to constrain the parameters of the lenses. It has been demonstrated that such a technique provides strong constraints on the parameters that characterize a galaxy halo, as well as on the aperture mass of these halos. In this analysis, we only use weak shear data and do not include strong lensing constraints. Results. We present the results of a study of galaxy-galaxy lensing in a homogeneous sample of massive x-ray luminous clusters at z ∼ 0.2. These have been observed in three bands with the cfh12k instrument. We find dark matter halos in these clusters to be compact compared to those inferred around isolated field galaxies of equivalent luminosity at this redshift: the half mass radius is found to be smaller than 50 kpc, with a mean total mass of order 0.2× 10 12 M� . This is in good agreement with previous galaxy-galaxy lensing results and with numerical simulations, in particular with the tidal stripping scenario. We thus provide a strong confirmation of tidal truncation from a homogeneous sample of galaxy clusters. Moreover, it is the first time that cluster galaxies are probed successfully using galaxy-galaxy lensing techniques from ground based data.