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ABSTRACT: We present a study of the distribution of X-ray AGN in a representative
sample of 26 massive clusters at 0.15<z<0.30, combining Chandra observations
with highly complete spectroscopy of cluster members down to M_K*+2. In total
we identify 48 X-ray AGN among the cluster members, with luminosities
2x10^41-1x10^44erg/s. In the stacked caustic diagram, the X-ray AGN appear to
preferentially lie along the caustics, suggestive of an infalling population.
They also appear to avoid the region with lowest cluster-centric radii and
relative velocities (r_proj<0.4 r_500; |v- |/sigma_v<0.8), which is dominated
by the virialized population of galaxies accreted earliest into the clusters.
Moreover the velocity dispersion of the 48 X-ray AGN is 1.51x that of the
overall cluster population, which is consistent with the sqrt(2) ratio expected
by simple energetic arguments when comparing infalling versus virialized
populations. This kinematic segregation is significant at the 4.66-sigma level.
When splitting the X-ray AGN sample into two according to X-ray or infrared
(IR) luminosity, both X-ray bright and IR-bright sub-samples show higher
velocity dispersions than their X-ray dim and IR-dim counterparts at >2sigma
significance. This is consistent with the nuclear activity responsible for the
X-ray and IR emission being slowly shut down as the host galaxies are accreted
into the cluster. Overall our results provide the strongest observational
evidence to date that X-ray AGN found in massive clusters are an infalling
population, and that the cluster environment very effectively suppresses
radiatively-efficient nuclear activity in its member galaxies. These results
are consistent with the view that for galaxies to host an X-ray AGN they should
be the central galaxy within their dark matter halo and have a ready supply of
cold gas.
05/2012;
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J Richard,
G ~P Smith,
J -P Kneib,
R ~S Ellis,
A ~J ~R Sanderson,
L Pei,
T ~A Targett,
D ~J Sand,
A ~M Swinbank,
H Dannerbauer,
P Mazzotta,
M Limousin,
E Egami,
E Jullo,
V Hamilton-Morris, S ~M Moran
VizieR Online Data Catalog. 05/2011; 740:40325.
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ABSTRACT: We present the results of a panoramic (15 Mpc scale) survey of the Cl 0016+16 (z= 0.55) supercluster using Spitzer Space Telescope Multiband Infrared Photometer (MIPS) 24-μm and Galaxy Evolution Explorer near-ultraviolet (2500 Å; NUV) imaging. The supercluster regions probed are characterized by several dense nodes connected by a pronounced intermediate-density filamentary structure. We have studied the mid-infrared and NUV properties of potential cluster members within a Δz= 0.1 photometric redshift slice compared to an identical blank field selection. We have two main findings: (i) the star formation rates of individual star-forming galaxies throughout the cluster are not significantly different from identically selected field galaxies, and (ii) the cluster harbours pockets of ‘accelerated’ activity where galaxies have an enhanced probability of undergoing star formation. This observation could be explained in a simple model of ‘pre-processing’ of galaxies during cluster infall: galaxies in satellite groups have an increased chance of having star formation triggered via gravitational tidal interactions compared to their counterparts in the field, but there is no environmental mechanism boosting the individual star formation rates of galaxies. We estimate a lower limit for the total star formation rate of galaxies in the supercluster as ∼850 M⊙ yr−1 (field corrected). If this rate is maintained over the typical infall time of a few Gyr, then the infall population could contribute ∼1–2 × 1012 M⊙ of stellar mass to the structure.
Monthly Notices of the Royal Astronomical Society 04/2011; 413(1):177 - 182. · 4.90 Impact Factor
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ABSTRACT: We present the results of a panoramic (15 Mpc-scale) survey of the Cl0016+16 supercluster (z=0.55) using Spitzer Space Telescope MIPS 24um and Galaxy Evolution Explorer near-UV (2500A; NUV) imaging. The supercluster regions probed are characterised by several dense nodes connected by a pronounced intermediate-density filamentary structure. We have studied the mid-IR and NUV properties of potential cluster members within a Dz=0.1 photometric redshift slice, compared to an identical blank field selection. We have two main findings: (a) the star-formation rates of individual star-forming galaxies throughout the cluster are not significantly different to identically selected field galaxies, and (b) the cluster harbours pockets of 'accelerated' activity where galaxies have an enhanced probability of undergoing star formation. This observation could be explained in a simple model of 'pre-processing' of galaxies during cluster infall: galaxies in satellite groups have an increased chance of having star-formation triggered via gravitational tidal interactions compared to their counterparts in the field, but there is no environmental mechanism boosting the individual star-formation rates of galaxies. We estimate a lower-limit for the total star-formation rate of galaxies in the supercluster as ~850 Msun/yr (field corrected). If this rate is maintained over the typical infall time of a few Gyr, then the infall population could contribute ~1-2x10^12 Msun of stellar mass to the structure. Comment: 6 pages, 2 figures, accepted for publication in MNRAS
11/2010;
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ABSTRACT: We present Herschel/PACS, MMT/Hectospec and XMM-Newton observations of Abell 1835, one of the brightest X-ray clusters on the sky, and the host of a strong cool core. Even though Abell 1835 has a prototypically "relaxed" X-ray morphology and no signs of ongoing merger activity in strong- and weak-lensing mass maps, it has a complex velocity distribution, suggesting that it is still accreting significant amounts of mass in the form of smaller satellite systems. Indeed, we find strong dynamical segregation of star-forming dusty galaxies from the optically selected cluster population. Most Herschel sources are found close to the virial radius of the cluster, and almost a third appear to be embedded within a filament feeding the cluster from the SW. We find that the most luminous infrared galaxies are likely involved in galaxy-galaxy interactions that may have triggered the current phase of star formation. Comment: 4 pages,5 figures. Accepted for publication in upcoming A&A Herschel Special Issue
05/2010;
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ABSTRACT: We present wide-field Herschel/PACS observations of Abell 1689, a massive galaxy cluster at z=0.1832, from our Open Time Key Programme. We detect 39 spectroscopically confirmed 100micron-selected cluster members down to 1.5x10^10 Lsun. These galaxies are forming stars at rates in the range 1-10 Msun/yr, and appear to comprise two distinct populations: two-thirds are unremarkable blue, late-type spirals found throughout the cluster; the remainder are dusty red sequence galaxies whose star formation is heavily obscured with A(Halpha)~2 mag, and are found only in the cluster outskirts. The specific-SFRs of these dusty red galaxies are lower than the blue late-types, suggesting that the former are in the process of being quenched, perhaps via pre-processing, the unobscured star formation being terminated first. We also detect an excess of 100micron-selected galaxies extending ~6 Mpc in length along an axis that runs NE-SW through the cluster centre at >95% confidence. Qualitatively this structure is consistent with previous reports of substructure in X-ray, lensing, and near-infrared maps of this cluster, further supporting the view that this cluster is a dynamically active, merging system. Comment: 5 pages, 5 figures. Letter accepted for publication in the Herschel special issue of Astronomy and Astrophysics
05/2010;
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Johan Richard,
Graham P. Smith,
Jean-Paul Kneib,
Richard S. Ellis,
A. J. R. Sanderson,
L. Pei,
T. A. Targett,
D. J. Sand,
A. M. Swinbank,
H. Dannerbauer,
P. Mazzotta,
M. Limousin,
E. Egami,
E. Jullo,
V. Hamilton-Morris, S. M. Moran
[show abstract]
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ABSTRACT: 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 〈log10θE(z= 2)〉= 1.16 ± 0.28; (ii) we detect an X-ray/lensing mass discrepancy of 〈MSL/MX〉= 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.
Monthly Notices of the Royal Astronomical Society 04/2010; 404(1):325 - 349. · 4.90 Impact Factor
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ABSTRACT: We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy clusters at 0.02<z<0.40, using panoramic Spitzer/MIPS 24micron and NIR data. This is the largest sample of clusters to date with MIR data covering not only the cluster cores, but extending into the infall regions. We revisit the Butcher-Oemler effect, measuring the fraction of massive infrared-luminous galaxies (K<K*+1.5, L_IR>5x10^10L_sun) 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 is of the form f_SF ~ (1+z)^5.7, 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, implying that the MIR Butcher-Oemler 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 semi-analytic 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. 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. Comment: 11 pages, 7 figures, accepted for publication in ApJ
08/2009;
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ABSTRACT: We present the first galaxy evolution results from the Local Cluster Substructure Survey (LoCuSS), a multi-wavelength survey of 100 X-ray selected galaxy clusters at 0.15<z<0.30. LoCuSS combines far-UV through far-IR observations of cluster galaxies with gravitational lensing analysis and X-ray data to investigate the interplay between the hierarchical assembly of clusters and the evolution of cluster galaxies. Here we present new panoramic Spitzer/MIPS 24micron observations of the merging cluster Abell 1758 at z=0.279 spanning 6.5x6.5Mpc and reaching a 90% completeness limit of 400uJy. We estimate a global cluster SFR of 910\pm320 M_sun/yr within 3 Mpc of the cluster centre, originating from 42 galaxies with L_IR > 5x10^10 L_sun. The obscured activity in A1758 is therefore comparable with that in Cl 0024+1654, the most active cluster previously studied at 24um. The obscured galaxies faithfully trace the cluster potential as revealed by the weak-lensing mass map of the cluster, including numerous mass peaks at R~2-3Mpc that are likely associated with infalling galaxy groups and filamentary structures. However the core (R<500kpc) of A1758N is 2x more active in the IR than that of A1758S, likely reflecting differences in the recent dynamical history of the two clusters. The 24micron results from A1758 therefore suggest that dust-obscured cluster galaxies are common in merging clusters and suggests that obscured activity in clusters is triggered by both the details of cluster-cluster mergers and processes that operate at larger radii including those within in-falling groups. Our ongoing far-UV through far-IR observations of a large sample of clusters should allow us to disentangle the different physical processes responsible for triggering obscured star formation in clusters.
04/2009;
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[show abstract]
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ABSTRACT: (abridged) We present panoramic Spitzer MIPS 24um observations covering 9x9Mpc (25'x25') fields around two massive clusters, Cl0024+16 and MS0451-03, at z=0.39 and z=0.55. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turn-around radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24um members. The much more significant excess is associated with Cl0024+16, whereas MS0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to A_V~1-2 mags) rather than emission from dusty tori around active galactic nuclei (AGN) in early-type hosts. The inferred total-infrared star-formation rates in Cl0024+16 are typically >5x greater than those found from a similar Halpha survey, indicating significant obscured activity in the cluster population. We find evidence for strong evolution of the level of dust-obscured star-formation in dense environments out to z=0.5, analogous to the rise in fraction of optically-selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.
07/2006;
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http://dx.doi.org/10.1051/0004-6361/201014692.
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http://dx.doi.org/10.1051/0004-6361/201014695.
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G P Smith,
C. P. Haines,
M. J. Pereira,
E. Egami, S. M. Moran,
E. Hardegree-Ullman,
A. Babul,
M. Rex,
T. D. Rawle,
Y Y Zhang,
A. Finoguenov,
N. Okabe,
A. J. R. Sanderson,
A. C. Edge,
M. Takada
http://dx.doi.org/10.1051/0004-6361/201014691.
