Publications (9)6.02 Total impact
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Article: LoCuSS: A Dynamical Analysis of X-ray AGN in Local Clusters
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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; -
Article: A bright z=5.2 lensed submillimeter galaxy in the field of Abell 773: HLSJ091828.6+514223
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ABSTRACT: 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 (\sim 200mJy at 500\micron) 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 L_FIR= 1.1 10^{14}/\mu Lo, where \mu is the magnification factor, likely \sim 11. We report here the redshift identification through CO lines with the IRAM-30m, 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\kms apart. Assuming the ultraluminous galaxy (ULIRG) CO-to-H2 conversion ratio, the H2 mass is 5.8 10^{11}/\mu Mo, of which one third is in a cool component. From the CI line we derive a CI/H2 number abundance of 6 10^{-5} similar to that in other ULIRGs. The H2O line is strong only in the red velocity component, with an intensity ratio I(H_2O)/I(CO) \sim 0.5, suggesting a strong local FIR radiation field, possibly from an active nucleus (AGN) component. We detect the [NII]205\mics 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.01/2012; -
Article: LoCuSS: Calibrating Mass-observable Scaling Relations for Cluster Cosmology with Subaru Weak-lensing Observations
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ABSTRACT: We present a joint weak-lensing/X-ray study of galaxy cluster mass-observable scaling relations motivated by the critical importance of accurate calibration of mass proxies for future X-ray missions, including eROSITA. We use a sample of 12 clusters at z 0.2 that we have observed with Subaru and XMM-Newton to construct relationships between the weak-lensing mass (M) and three X-ray observables, gas temperature (T), gas mass (M gas), and quasi-integrated gas pressure (Y X), at overdensities of Δ = 2500, 1000, and 500 with respect to the critical density. We find that M gas at Δ ≤ 1000 appears to be the most promising mass proxy of the three because it has the lowest intrinsic scatter in mass at a fixed observable, σln M 0.1, independent of the cluster dynamical state. The scatter in mass at fixed T and Y X is a factor of ~2-3 larger than at fixed M gas, which are indicative of the structural segregation that we find in the M-T and M-Y X relationships. Undisturbed clusters are found to be ~40% and ~20% more massive than disturbed clusters at fixed T and Y X, respectively, at ~2σ significance. In particular, A 1914—a well-known merging cluster—significantly increases the scatter and lowers the normalization of the relation for disturbed clusters. We also investigated the covariance between the intrinsic scatter in M-M gas and M-T relations, finding that they are positively correlated. This contradicts the adaptive mesh refinement simulations that motivated the idea that Y X may be a low-scatter mass proxy, and agrees with more recent smoothed particle hydrodynamic simulations based on the Millennium Simulation. We also propose a method to identify a robust mass proxy based on principal component analysis. The statistical precision of our results is limited by the small sample size and the presence of the extreme merging cluster in our sample. We therefore look forward to studying a larger, more complete sample in the future.The Astrophysical Journal 08/2010; 721(1):875. · 6.02 Impact Factor -
Article: LoCuSS: A Herschel view of obscured star formation in Abell 1835
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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 Issue05/2010; -
Article: LoCuSS: Luminous infrared galaxies in the merging cluster Abell 1758 at z=0.28
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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; -
Article: The Local Cluster Substructure Survey (LoCuSS): I. Joint KPNO/Spitzer/Herschel/Subaru Study of the Star Formation amp Assembly Histories of Massive Clusters
NOAO Proposal. 08/2008; -
Chapter: Observational Constraints on the ICM Temperature Enhancement by Cluster Mergers
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ABSTRACT: We present results from a combined weak lensing and X-ray analysis of the merging cluster A1914 at a redshift of z = 0.1712, based on R-band imaging data with Subaru/Suprime-Cam and archival Chandra X-ray data. Using the weak-lensing and X-ray data we explore the relationships between cluster global properties, namely the gravitational mass, the bolometric X-lay luminosity and temperature, the gas mass and the gas mass fraction, as a function of radius. We found that the gas mass fractions within r2500 and rvir are consistent with the results of earlier X-ray cluster studies and with cosmic microwave background studies based on the WMAP observations, respectively. However, the observed X-ray temperature, kBTave = 9.6±0.3keV, is signi?cantly higher than the virial temperature, kBTvir = 4.7 ± 0.3keV derived from the weak lensing distortion measurement. The X-ray bolometric luminosity-temperature (LX - T) relation is consistent with the LX - T relation derived by previous statistical X-ray studies of galaxy clusters. Such correlations among the global cluster properties are invaluable observational tools for studying the cluster merger physics. Our results demonstrate that the combination of X-ray and weak-lensing observations is a promising, powerful probe of the physical processes associated with cluster mergers as well as of their mass properties.01/1970: pages 278-281; -
Article: LoCuSS: A
http://dx.doi.org/10.1051/0004-6361/201014695. -
Article: LoCuSS: Probing galaxy transformation physics with
http://dx.doi.org/10.1051/0004-6361/201014691.
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Institutions
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2010
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Tohoku University
- Astronomical Institute
Sendai, Kagoshima-ken, Japan
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