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J. P. Stott, C. A. Collins,
M. Sahlén,
M. Hilton,
E. Lloyd-Davies,
D. Capozzi,
M. Hosmer,
A. R. Liddle,
N. Mehrtens,
C. J. Miller,
A. K. Romer,
S. A. Stanford,
P. T. P. Viana,
M. Davidson,
B. Hoyle,
S. T. Kay,
and R. C. Nichol
[show abstract]
[hide abstract]
ABSTRACT: We present deep J- and Ks -band photometry of 20 high redshift galaxy clusters between z = 0.8 and1.5, 19 of which are observed with the MOIRCS instrument on the Subaru telescope. By using near-infrared light as a proxy for stellar mass we find the surprising result that the average stellar mass of Brightest Cluster Galaxies (BCGs) has remained constant at ~9 × 1011 M ☉ since z ~ 1.5. We investigate the effect on this result of differing star formation histories generated by three well-known and independent stellar population codes and find it to be robust for reasonable, physically motivated choices of age and metallicity. By performing Monte Carlo simulations we find that the result is unaffected by any correlation between BCG mass and cluster mass in either the observed or model clusters. The large stellar masses imply that the assemblage of these galaxies took place at the same time as the initial burst of star formation. This result leads us to conclude that dry merging has had little effect on the average stellar mass of BCGs over the last 9-10 Gyr in stark contrast to the predictions of semi-analytic models, based on the hierarchical merging of dark matter halos, which predict a more protracted mass build-up over a Hubble time. However, we discuss that there is potential for reconciliation between observation and theory if there is a significant growth of material in the intracluster light over the same period.
The Astrophysical Journal 06/2010; 718(1):23. · 6.02 Impact Factor
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L. Guzzo,
P. Schuecker,
H. Boehringer, C. A. Collins,
A. Ortiz-Gil,
S. De Grandi,
A. C. Edge,
D. M. Neumann,
S. Schindler,
C. Altucci,
P. A. Shaver
[show abstract]
[hide abstract]
ABSTRACT: We present the final data from the spectroscopic survey of the ROSAT-ESO Flux-Limited X-ray (REFLEX) catalog of galaxy clusters. The REFLEX survey covers 4.24 steradians (34% of the entire sky) below a declination of 2.5 deg and at high Galactic latitude (|b| > 20 deg). The REFLEX catalog includes 447 entries with a median redshift of 0.08 and is better than 90% complete to a limiting flux fx = 3x10^{-12} erg s^{-1} cm^{-2} (0.1 to 2.4 keV), representing the largest statistically homogeneous sample of clusters drawn from the ROSAT All-Sky Survey (RASS) to date. Here we describe the details of the spectroscopic observations carried out at the ESO 1.5 m, 2.2 m, and 3.6 m telescopes, as well as the data reduction and redshift measurement techniques. The spectra typically cover the wavelength range 3600-7500 A at a FWHM resolution of ~14 A, and the measured redshifts have a total rms error of ~100 km s^{-1}. In total we present 1406 new galaxy redshifts in 192 clusters, most of which previously did not have any redshift measured. Finally, the luminosity/redshift distributions of the cluster sample and a comparison to the no-evolution expectations from the cluster X-ray luminosity function are presented. Comment: 16 pages, 8 figures (with multiple PS files) at low resolution due to size limits. Published version with higher-resolution figures, redshift catalogue and X-ray/DSS overlays available from http://www.brera.inaf.it/reflex
07/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We present the z = 0.3-0.7 cluster X-ray luminosity function (XLF) determined from the Southern Serendipitous High-Redshift Archival ROSAT Cluster (SHARC) survey. Over the luminosity range L ~ (0.3-3) × 1044 ergs s-1 (0.5-2.0 keV), the XLF is in close agreement with that of the low-redshift X-ray cluster population. This result greatly strengthens our previous claim of no evolution of the cluster population, at these luminosities, at a median redshift of z=0.44.
The Astrophysical Journal 01/2009; 488(2):L83. · 6.02 Impact Factor
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A. K. Romer,
R. C. Nichol,
B. P. Holden,
M. P. Ulmer,
R. A. Pildis,
A. J. Merrelli,
C. Adami,
D. J. Burke, C. A. Collins,
A. J. Metevier,
R. G. Kron,
and K. Commons
[show abstract]
[hide abstract]
ABSTRACT: We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 deg2 and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified 37 clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696 < z < 0.83 and a luminosity range of 0.065 < LX < 8.3 × 1044 ergs s-1 [0.5-2.0 keV] (assuming H0 = 50 km s-1 Mpc-1 and q0 = 0.5). Twelve of the clusters have redshifts greater than z = 0.3, eight of which are at luminosities brighter than LX = 3 × 1044 ergs s-1. Seventeen of the 37 optically confirmed Bright SHARC clusters have not been listed in any previously published catalog. We also report the discovery of three candidate "fossil groups" of the kind proposed by Ponman et al.
The Astrophysical Journal Supplement Series 12/2008; 126(2):209. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We examine the central galaxy luminosity–host halo mass relation for 54 brightest group galaxies (BGGs) and 92 brightest cluster galaxies (BCGs) at z < 0.1 and present the first measurement of this relation for a sample of known BCGs at . At z < 0.1 we find LK∝M0.24±0.08200 for the BCGs and the early-type BGGs in groups with extended X-ray emission and LK∝M0.11±0.10200 for the BCGs alone. At 0.1 < z < 0.8 we find LK∝M0.28±0.11200. We conclude that there is no evidence for evolution in this relationship between z < 0.1 and z < 0.8: BCG growth appears to still be limited by the time-scale for dynamical friction at these earlier times, not proceeding according to the predictions of present semi-analytic models.
Monthly Notices of the Royal Astronomical Society Letters 03/2008; 385(1):L103 - L107.
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Joshua A. Frieman,
B. Bassett,
A. Becker,
C. Choi,
D Cinabro,
F. DeJongh,
D. L. DePoy,
B. Dilday,
M Doi,
P. M. Garnavich, [......],
C. Stoughton,
M. Stritzinger,
M. Subbarao,
D. Tucker,
P. Vaisanen,
L. C. Watson,
S. Watters,
J. C. Wheeler,
B. Yanny,
D. York
[show abstract]
[hide abstract]
ABSTRACT: The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5 degrees wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for discovery of new objects. Supernova imaging observations are being acquired between 1 September and 30 November of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.
09/2007;
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[show abstract]
[hide abstract]
ABSTRACT: We present an examination of the kinematics and stellar populations of a sample of three brightest group galaxies (BGGs) and three brightest cluster galaxies (BCGs) in X-ray groups and clusters. We have obtained high signal-to-noise ratio Gemini/Gemini South Multi-Object Spectrograph (GMOS) long-slit spectra of these galaxies and use Lick indices to determine ages, metallicities and α-element abundance ratios out to at least their effective radii. We find that the BGGs and BCGs have very uniform masses, central ages and central metallicities. Examining the radial dependence of their stellar populations, we find no significant velocity dispersion, age, or α-enhancement gradients. However, we find a wide range of metallicity gradients, suggesting a variety of formation mechanisms. The range of metallicity gradients observed is surprising, given the homogeneous environment these galaxies probe and their uniform central stellar populations. However, our results are inconsistent with any single model of galaxy formation and emphasize the need for more theoretical understanding of both the origins of metallicity gradients and galaxy formation itself. We postulate two possible physical causes for the different formation mechanisms.
Monthly Notices of the Royal Astronomical Society 07/2007; 378(4):1507 - 1530. · 4.90 Impact Factor
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S. A. Stanford,
A. K. Romer,
K. Sabirli,
M. Davidson,
M. Hilton,
P. T. P. Viana, C. A. Collins,
S. T. Kay,
A. R. Liddle,
R. G. Mann,
C. J. Miller,
R. C. Nichol,
M. J. West,
C. J. Conselice,
H. Spinrad,
D. Stern,
K. Bundy
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of XMMXCS J2215.9-1738, a massive galaxy cluster at z =1.45, which was found in the XMM Cluster Survey. The cluster candidate was initially identified as an extended X-ray source in archival XMM data. Optical spectroscopy shows that 6 galaxies within a 60 arcsec diameter region lie at z = 1.45 +/- 0.01. Model fits to the X-ray spectra of the extended emission yield kT = 7.4 (+2.7,-1.8) keV (90 % confidence); if there is an undetected central X-ray point source then kT = 6.5 (+2.6,-1.8) keV. The bolometric X-ray luminosity is Lx = 4.4 (+0.8,-0.6) x 10^44 ergs/s over a 2 Mpc radial region. The measured Tx, which is the highest known for a cluster at z > 1, suggests that this cluster is relatively massive for such a high redshift. The redshift of XMMXCS J2215.9-1738 is the highest currently known for a spectroscopically-confirmed cluster of galaxies. Comment: Accepted for publication in the The Astrophysical Journal Letters. 5 pages, 5 figures
06/2006;
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Kivanc Sabirli,
A. K. Romer,
M. Davidson,
S. A. Stanford,
P. T. Viana,
M. Hilton, C. A. Collins,
S. T. Kay,
A. R. Liddle,
R. G. Mann,
C. J. Miller,
R. C. Nichol,
M. J. West,
C. J. Conselice,
H. Spinrad,
D. Stern,
XCS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of the hottest cluster known at z > 1. It was
identified as an extended X-ray source in the XMM Cluster Survey (XCS,
Romer et al., 2001) and optical spectroscopy shows that 6 galaxies
within a 60 arcsec diameter region lie at z = 1.45 ± 0.01.
Hence its redshift is the highest currently known for a
spectroscopically-confirmed cluster. Analysis of the X-ray spectra
yields kT = 7.9+2.8-1.8 keV (90% confidence) and
suggests that it is relatively massive for such a high redshift
cluster.We acknowledge financial support from NASA grant NAG-11634 (AKR,
RCN, KS, MD, PTPV), The Royal Astronomical Society's Hosie Request (MD,
KS), PPARC (ARL, STK, RGM), the NASA XMM program (KS), the Institute of
Astronomy at the University of Edinburgh (MD), Liverpool John Moores
University (MH), Carnegie Mellon University (KS, AKR), and NSF grant
AST-0205960 (MJW).
05/2006; 38:106.
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[show abstract]
[hide abstract]
ABSTRACT: We review recent results from the SHARC Survey for distant X-ray clusters of galaxies. We first discuss the SHARC South project which finds no evidence for evolution in the faint end of the X-ray cluster luminosity function out to a redshift of z ≲ 0.7. We then give an overview of the Bright SHARC project; this project will provide an independent measurement of the evolution of bright (Lx[0.5 - 2keV] > 3 × 1044 erg s−1) X-ray clusters and allow us to put strong constraints on the value of ω0.
Astronomische Nachrichten 02/2006; 319(1‐2):83 - 86. · 1.01 Impact Factor
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H. Böhringer,
L. Guzzo, C. A. Collins,
P. Schuecker,
S. Schindler,
W. Voges,
D. M. Neumann,
R. Cruddace,
S. DeGrandi,
G. Chincarini,
T. H. Reiprich,
A. C. Edge,
H. T. MacGillivray,
P. Shaver
[show abstract]
[hide abstract]
ABSTRACT: Clusters of galaxies detected in X-rays are ideal probes for the study of the large scale structure in the Universe. Based
on the ROSAT All-Sky Survey we have conducted a large redshift survey as an ESO key programme to identify the X-ray brightest
clusters found in the southern hemisphere. We present first results from the bright part of the survey comprising 460 identified
clusters for an X-ray flux limit of
310-123\cdot 10^{-12}
erg s-1 cm-2. We show results for the X-ray luminosity function and discuss the assessment of the large-scale structure be means of the
cluster distribution power spectrum on a scale of 400h
-1 Mpc.
02/2006: pages 157-163;
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12/2005; 604:759.
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05/2005; -1:131-133.
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Rachida Sadat,
Alain Blanchard,
Sebastien C. Vauclair,
David H. Lumb,
James Bartlett,
A. K. Romer,
Jean-Philippe Bernard,
Michel Boer,
Philippe Marty,
Jukka Nevalainen,
Douglas. J. Burke, C. A. Collins,
Robert C. Nichol
[show abstract]
[hide abstract]
ABSTRACT: We study the gas mass fraction, $f\_{\rm gas},$ behavior in $XMM-Newton$ $\Omega$ project. The typical $f\_{\rm gas}$ shape of high redshift galaxy clusters follows the global shape inferred at low redshift quite well. This result is consistent with the gravitational instability picture leading to self similar structures for both the dark and baryonic matter. However, the mean $f\_{\rm gas} in distant clusters shows some differences to local ones, indicating a departure from strict scaling. This result is consistent with the observed evolution in the luminosity-temperature relation. We quantitatively investigate this departure from scaling laws. Within the local sample we used, a moderate but clear variation of the amplitude of the gas mass fraction with temperature is found, a trend that weakens in the outer regions. These variations do not explain departure from scaling laws of our distant clusters. An important implication of our results is that the gas fraction evolution, a test of the cosmological parameters, can lead to biased values when applied at radii smaller than the virial radius. From our $XMM$ clusters, the apparent gas fraction at the virial radius is consistent with a non-evolving universal value in a high matter density model and not with a concordance.
04/2005;
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[show abstract]
[hide abstract]
ABSTRACT: The precise determination of global properties of galaxy clusters, and their scaling relations, is a task of prime importance for the use of clusters as cosmological probes. We performed a detailed XMM-Newton study of 14 X-ray luminous REFLEX Survey clusters at z ∼ 0.3. We found that the properties of the galaxy clusters show a self-similar behavior at r > 0.1rvir. This helps us to establish tighter scaling relations. Peculiarities in the individual clusters are important to understand the scatter from the self-similar frame in the cluster central parts.
Advances in Space Research. 02/2005;
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[show abstract]
[hide abstract]
ABSTRACT: (abridged) We present a study based on XMM data of RX J0256.5+0006, a medium distant (z=0.36) galaxy cluster found in the Bright SHARC catalog. The intracluster medium shows a bimodal structure: one main cluster component and a substructure in the west. Despite the indication of interaction we do not find any sign of temperature gradients. Due to the non-symmetric form of the main cluster we extract surface brightness profiles in different sectors around its centre. We see large variations between the profiles, which we quantify by beta-model fitting. The corresponding r_c's vary between 0.1-0.5Mpc and the beta's between 0.5-1.2. The variations of the beta-model parameters indicate that the main cluster is not entirely relaxed. This hypothesis is strengthened by the fact that the cluster is over-luminous with respect to the (z-evolving) L_x-T relation found for nearby clusters. Comparing our profiles to the reference emission measure profile of Arnaud et al., we find that only the profile extracted north-east (NE) of the main cluster centre is similar to this reference profile. This indicates that only the NE profile is representative for the relaxed part of this cluster component. Using this profile and the spectroscopically fitted temperature of T=4.9^+0.5_-0.4keV we find M_500~4 10^14 solar masses. This value is in agreement with the value obtained using the z-evolving M_500-T relation from the HIFLUGCS sample. For the gas mass fraction we find f_g~18-20% which is in good agreement with other work. We also develop a simple on-axis merger model for the cluster. Together with a simple ram pressure model we find that the most likely physical distance of the subcluster to the main cluster lies between 0.6<d<1.0Mpc. We find for the ratio of subcluster to main cluster mass values between 20-30%. Comment: 19 pages including 19 figures (including 4 figures in jpg and png format), accepted for publication in A&A
06/2004;
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H. Boehringer,
P. Schuecker,
L. Guzzo, C. A. Collins,
W. Voges,
R. G. Cruddace,
A. Ortiz-Gil,
G. Chincarini,
S. De Grandi,
A. C. Edge,
H. T. MacGillivray,
D. M. Neumann,
S. Schindler,
P. Shaver
[show abstract]
[hide abstract]
ABSTRACT: We present the catalogue of the REFLEX Cluster Survey providing information on the X-ray properties, redshifts, and some identification details of the clusters in the REFLEX sample. The catalogue describes a statistically complete X-ray flux-limited sample of 447 galaxy clusters above an X-ray flux of 3 10(-12) erg /s/cm**2 (0.1 to 2.4 keV) in an area of 4.24 ster in the southern sky. The cluster candidates were first selected by their X-ray emission in the ROSAT-All Sky Survey and subsequently spectroscopically identified in the frame of an ESO key programme. In addition to the cluster catalogue we also describe the complete selection criteria as a function of the sky position and the conversion functions used to analyse the X-ray data. These are essential for the precise statistical analysis of the large-scale cluster distribution. This data set is at present the largest, statistically complete X-ray galaxy cluster sample. Together with these data set we also provide for the first time the full three-dimensional selection function. The sample forms the basis of several cosmological studies, one of the most important applications being the assessment of the statistics of the large-scale structure of the universe and the test of cosmological models. Comment: 31 pages, 12 Tables and 3 Postscript figures, uses psfig.tex. Astronomy & Astrophysics in press
05/2004;
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H. Boehringer,
P. Schuecker,
L. Guzzo, C. A. Collins,
W. Voges,
R. G. Cruddace,
A. Ortiz-Gil,
G. Chincarini,
S. de Grandi,
A. C. Edge,
H. T. MacGillivray,
D. M. Neumann,
S. Schindler,
P. Shaver
[show abstract]
[hide abstract]
ABSTRACT: The following tables provide the catalogue as well as several data files
necessary to reproduce the sample preparation. These files are also
required for the cosmological modeling of these observations in e.g. the
study of the statistics of the large-scale structure of the matter
distribution in the Universe and related cosmological tests.
(13 data files).
VizieR Online Data Catalog. 04/2004; 342:50367.
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[show abstract]
[hide abstract]
ABSTRACT: We present XMM-Newton results on the spatially resolved temperature profiles of eight massive galaxy clusters of a volume-limited sample at redshifts $z\sim0.3$ (REFLEX-DXL sample) and an additional luminous cluster at $z=0.2578$, selected from the REFLEX survey. Useful temperature measurements could be performed out to radii with overdensity 500 ($r_{500}$). The scaled temperature distributions show good similarities. We discovered diversities in the temperature gradients at the outer cluster radii with examples of both flat and strongly decreasing profiles which call for different physical interpretations. We found an indication of the 'warm-hot' gas existing in or around the hot clusters. Using RXCJ0307.0-2840 we demonstrate that the errors on the mass estimates are within 25% up to r_{500}.
03/2004;
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D. H. Lumb,
J G Bartlett,
A. K. Romer,
A. Blanchard,
D. J. Burke, C. A. Collins,
R. C. Nichol,
M. Giard,
P. Marty,
J. Nevalainen,
R. Sadat,
S. C. Vauclair
[show abstract]
[hide abstract]
ABSTRACT: (abridged) We describe XMM-Newton Guaranteed Time observations of a sample of eight high redshift (0.45<z<0.62) clusters. The goal of these observations was to measure the luminosity and the temperature of the clusters to a precision of \~10%, leading to constraints on the possible evolution of the luminosity--temperature relation, and ultimately on the values of the matter density, Omega_M and, to a lesser extent, the cosmological constant Omega_L. The clusters were drawn from the SHARC and 160 Square Degree (160SD) ROSAT surveys. Here we describe our data analysis techniques and present, for the first time with XMM-Newton,Lx-Tx relation. For each of the eight clusters in the sample, we have measured total bolometric luminosities, performed beta-model fits to the radial surface profiles and made spectral fits to a single temperature isothermal model. We describe data analysis techniques that pay particular attention to background mitigation. Characterizing the Lx-Tx relation as Lx = L_{6} (T/6keV)^{alpha},we find L_{6}=16.8 +7.6/-5.2 10^{44} erg/s and alpha=2.7 +/-0.4 for a EdS H=50 cosmology at a typical redshift z =0.55. Comparing with the low redshift study by Markevitch, assuming L-T to evolve as (1+z)^A, we find A=0.68 +/-0.26 for the same cosmology and A=1.52 +0.26/-0.27 for a concordance cosmology. We conclude that there is now evidence from both XMM-Newton and Chandra for an evolutionary trend in the L-T relation. Our observations lend support to the robustness and completeness of the SHARC and 160SD surveys. Comment: Accepted by A&A 22 pages, 20 figures. Replaced initial version with minor edits. Contains Table and Appendix that are in on-line version only
11/2003;
