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[show abstract]
[hide abstract]
ABSTRACT: A large fraction of the stellar mass in galaxy clusters is thought to be
contained in the diffuse low surface brightness intracluster light (ICL). Being
bound to the gravitational potential of the cluster rather than any individual
galaxy, the ICL contains much information about the evolution of its host
cluster and the interactions between the galaxies within. However due its low
surface brightness it is notoriously difficult to study. We present the first
detection and measurement of the flux contained in the ICL at z~1. We find that
the fraction of the total cluster light contained in the ICL may have increased
by factors of 2-4 since z~1, in contrast to recent findings for the lack of
mass and scale size evolution found for brightest cluster galaxies. Our results
suggest that late time buildup in cluster cores may occur more through
stripping than merging and we discuss the implications of our results for
hierarchical simulations.
11/2012;
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[show abstract]
[hide abstract]
ABSTRACT: A significant fraction of the total photospheric light in nearby galaxy
clusters is thought to be contained within the diffuse intracluster light
(ICL), which extends 100s of kpc from cluster cores. The study of the ICL can
reveal details of the evolutionary histories and processes occurring within
galaxy clusters, however since it has a very low surface brightness it is often
difficult to detect. We present here the first measurements of the ICL as a
fraction of total cluster light at z \sim 1 using deep J-band (1.2 {\mu}m)
imaging from HAWK-I on the VLT. We investigate the ICL in 6 X-ray selected
galaxy clusters at 0.8< z <1.2 and find that the ICL below isophotes {\mu}(J) =
22 mag/arcsec2 constitutes 1-4% of the total cluster light within a radius
R500. This is broadly consistent with simulations of the ICL at a similar
redshift and when compared to nearby observations suggests that the fraction of
the total cluster light that is in the ICL has increased by a factor 2 - 4
since z\sim1. We also find the fraction of the total cluster light contained
within the Brightest Cluster Galaxy (BCG) to be 2.0-6.3% at these redshifts,
which in 5 out of 6 cases is larger than the fraction of the ICL component, in
contrast to results from nearby clusters. This suggests that the evolution in
cluster cores involves substantial stripping activity at late times, in
addition to the early build up of the BCG stellar mass through merging. The
presence of significant amounts of stellar light at large radii from these BCGs
may help towards solving the recent disagreement between the semi-analytic
model predictions of BCG mass growth (e.g. De Lucia & Blaziot, 2007) and the
observed large masses and scale sizes reported for BCGs at high redshift.
06/2012;
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Nicola Mehrtens,
A. Kathy Romer, Matt Hilton,
E. J. Lloyd-Davies,
Christopher J. Miller,
S. A. Stanford,
Mark Hosmer,
Ben Hoyle,
Chris A. Collins,
Andrew R. Liddle, [......],
Michael West,
Heather C. Campbell,
Alastair C. Edge,
Robert G. Mann,
Kivanc Sabirli,
David Wake,
Christophe Benoist,
Luiz da Costa,
Marcio A. G. Maia,
Ricardo Ogando
[show abstract]
[hide abstract]
ABSTRACT: The XMM Cluster Survey (XCS) is a serendipitous search for galaxy
clusters using all publicly available data in the XMM-Newton Science
Archive. Its main aims are to measure cosmological parameters and trace
the evolution of X-ray scaling relations. In this paper we present the
first data release from the XMM Cluster Survey (XCS-DR1). This consists
of 503 optically confirmed, serendipitously detected, X-ray clusters.
Of these clusters, 256 are new to the literature and 357 are new X-ray
discoveries. We present 463 clusters with a redshift estimate (0.06
< z < 1.46), including 261 clusters with spectroscopic redshifts.
The remainder have photometric redshifts. In addition, we have measured
X-ray temperatures (TX) for 401 clusters (0.4 <
TX < 14.7 keV). We highlight seven interesting subsamples
of XCS-DR1 clusters: (i) 10 clusters at high redshift (z > 1.0,
including a new spectroscopically confirmed cluster at z= 1.01); (ii) 66
clusters with high TX (>5 keV) (iii) 130 clusters/groups
with low TX (<2 keV) (iv) 27 clusters with measured
TX values in the Sloan Digital Sky Survey (SDSS)
‘Stripe 82’ co-add region; (v) 77 clusters with measured
TX values in the Dark Energy Survey region; (vi) 40 clusters
detected with sufficient counts to permit mass measurements (under the
assumption of hydrostatic equilibrium); (vii) 104 clusters that can be
used for applications such as the derivation of cosmological parameters
and the measurement of cluster scaling relations. The X-ray analysis
methodology used to construct and analyse the XCS-DR1 cluster sample has
been presented in a companion paper, Lloyd-Davies et al.
Monthly Notices of the Royal Astronomical Society 05/2012; 423:1024-1052. · 4.90 Impact Factor
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Matt Hilton,
A. Kathy Romer,
Scott T. Kay,
Nicola Mehrtens,
E. J. Lloyd-Davies,
Peter A. Thomas,
Chris J. Short,
Julian A. Mayers,
Philip J. Rooney,
John P. Stott, [......],
Robert G. Mann,
Christopher J. Miller,
Martin Sahlen,
Pedro T. P. Viana,
Michael Davidson,
Mark Hosmer,
Robert C. Nichol,
Kivanc Sabirli,
S. A. Stanford,
Michael J. West
[show abstract]
[hide abstract]
ABSTRACT: We measure the evolution of the X-ray luminosity-temperature (L_X-T) relation
since z~1.5 using a sample of 211 serendipitously detected galaxy clusters with
spectroscopic redshifts drawn from the XMM Cluster Survey first data release
(XCS-DR1). This is the first study spanning this redshift range using a single,
large, homogeneous cluster sample. Using an orthogonal regression technique, we
find no evidence for evolution in the slope or intrinsic scatter of the
relation since z~1.5, finding both to be consistent with previous measurements
at z~0.1. However, the normalisation is seen to evolve negatively with respect
to the self-similar expectation: we find E(z)^{-1} L_X = 10^{44.67 +/- 0.09}
(T/5)^{3.04 +/- 0.16} (1+z)^{-1.5 +/- 0.5}, which is within 2 sigma of the zero
evolution case. We see milder, but still negative, evolution with respect to
self-similar when using a bisector regression technique. We compare our results
to numerical simulations, where we fit simulated cluster samples using the same
methods used on the XCS data. Our data favour models in which the majority of
the excess entropy required to explain the slope of the L_X-T relation is
injected at high redshift. Simulations in which AGN feedback is implemented
using prescriptions from current semi-analytic galaxy formation models predict
positive evolution of the normalisation, and differ from our data at more than
5 sigma. This suggests that more efficient feedback at high redshift may be
needed in these models.
05/2012;
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Craig D. Harrison,
Christopher J. Miller,
Joseph W. Richards,
E. J. Lloyd-Davies,
Ben Hoyle,
A. Kathy Romer,
Nicola Mehrtens, Matt Hilton,
John P. Stott,
Diego Capozzi,
Chris A. Collins,
Paul-James Deadman,
Andrew R. Liddle,
Martin Sahlén,
S. Adam Stanford,
Pedro T. P. Viana
[show abstract]
[hide abstract]
ABSTRACT: This paper presents both the result of a search for fossil systems (FSs)
within the XMM Cluster Survey and the Sloan Digital Sky Survey and the results
of a study of the stellar mass assembly and stellar populations of their fossil
galaxies. In total, 17 groups and clusters are identified at z < 0.25 with
large magnitude gaps between the first and fourth brightest galaxies. All the
information necessary to classify these systems as fossils is provided. For
both groups and clusters, the total and fractional luminosity of the brightest
galaxy is positively correlated with the magnitude gap. The brightest galaxies
in FSs (called fossil galaxies) have stellar populations and star formation
histories which are similar to normal brightest cluster galaxies (BCGs).
However, at fixed group/cluster mass, the stellar masses of the fossil galaxies
are larger compared to normal BCGs, a fact that holds true over a wide range of
group/cluster masses. Moreover, the fossil galaxies are found to contain a
significant fraction of the total optical luminosity of the group/cluster
within 0.5R200, as much as 85%, compared to the non-fossils, which can have as
little as 10%. Our results suggest that FSs formed early and in the highest
density regions of the universe and that fossil galaxies represent the end
products of galaxy mergers in groups and clusters. The online FS catalog can be
found at http://www.astro.ljmu.ac.uk/~xcs/Harrison2012/XCSFSCat.html.
ArXiv e-prints. 02/2012;
-
John P. Stott,
Ryan C. Hickox,
Alastair C. Edge,
Chris A. Collins, Matt Hilton,
Craig D. Harrison,
A. Kathy Romer,
Philip J. Rooney,
Scott T. Kay,
Christopher J. Miller,
Martin Sahlen,
Ed J. Lloyd-Davies,
Nicola Mehrtens,
Ben Hoyle,
Andrew R. Liddle,
Pedro T. P. Viana,
Ian G. McCarthy,
Joop Schaye,
C. M. Booth
[show abstract]
[hide abstract]
ABSTRACT: Using a sample of 123 X-ray clusters and groups drawn from the XMM-Cluster
Survey first data release, we investigate the interplay between the brightest
cluster galaxy (BCG), its black hole, and the intra-cluster/group medium (ICM).
It appears that for groups and clusters with a BCG likely to host significant
AGN feedback, gas cooling dominates in those with Tx > 2 keV while AGN feedback
dominates below. This may be understood through the sub-unity exponent found in
the scaling relation we derive between the BCG mass and cluster mass over the
halo mass range 10^13 < M500 < 10^15Msol and the lack of correlation between
radio luminosity and cluster mass, such that BCG AGN in groups can have
relatively more energetic influence on the ICM. The Lx - Tx relation for
systems with the most massive BCGs, or those with BCGs co-located with the peak
of the ICM emission, is steeper than that for those with the least massive and
most offset, which instead follows self-similarity. This is evidence that a
combination of central gas cooling and powerful, well fuelled AGN causes the
departure of the ICM from pure gravitational heating, with the steepened
relation crossing self-similarity at Tx = 2 keV. Importantly, regardless of
their black hole mass, BCGs are more likely to host radio-loud AGN if they are
in a massive cluster (Tx > 2 keV) and again co-located with an effective fuel
supply of dense, cooling gas. This demonstrates that the most massive black
holes appear to know more about their host cluster than they do about their
host galaxy. The results lead us to propose a physically motivated, empirical
definition of 'cluster' and 'group', delineated at 2 keV.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We study the evolution of the K-band luminosity function (LF) and the Halo
Occupation Distribution (HOD) using Subaru observations of 15 X-ray clusters at
z=0.8-1.5 and compare the results with mock clusters (0<z<1.3) extracted from
the Millennium Simulation and populated with galaxies using the semi-analytic
model (SAM) of Bower et al., matched in mass to our observed sample. We find
that the characteristic luminosity K* defined by a Shechter LF is consistent
with SAM predictions, which mimic well the evolution of K* in z>1 rich
clusters. However, we cannot distinguish between this model and a simple
stellar population synthesis model invoking passive evolution with a formation
redshift z~5 - consistent with the presence of an old red galaxy population
ubiquitous in rich clusters at z=1.5. We also see a small difference (\Delta
K*~0.5) between our clusters and studies of the field population at similar
redshifts, suggesting only a weak dependence of the luminous (L>L*) part of the
LF on environment. Turning to our HOD study, we find that within R_{500},
high-z clusters tend to host smaller numbers of galaxies to a magnitude K*+2
compared to their low-z counterparts. This behavior is also seen in the mock
samples and is relatively insensitive to the average mass of the cluster
haloes. In particular, we find significant correlations of the observed number
of member cluster galaxies (N) with both z and cluster mass:
$N(M,z)=(53\pm1)(1+z)^{-0.61^{+0.18}_{-0.20}}(M/10^{14.3})^{0.86\pm0.05}$.
Finally, we examine the spatial distribution of galaxies and provide a new
estimate of the concentration parameter for clusters at high z
($c_{g}=2.8^{+1.0}_{-0.8}$). Our result is consistent with predictions from
both our SAM mock clusters and literature's predictions for dark matter haloes.
The mock sample predictions rise slowly with decreasing redshift reaching
$c_{g}=6.3^{+0.39}_{-0.36}$ at z=0.
09/2011;
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Pedro T. P. Viana,
António da Silva,
Elsa P. R. G. Ramos,
Andrew R. Liddle,
E. J. Lloyd-Davies,
A. Kathy Romer,
Scott T. Kay,
Chris A. Collins, Matt Hilton,
Mark Hosmer,
Ben Hoyle,
Nicola Mehrtens,
Christopher J. Miller,
Martin Sahlén,
S. Adam Stanford,
John P. Stott
[show abstract]
[hide abstract]
ABSTRACT: We present a list of 15 clusters of galaxies, serendipitously detected by the
XMM Cluster Survey (XCS), that have a high probability of detection by the
Planck satellite. Three of them already appear in the Planck Early
Sunyaev-Zel'dovich (ESZ) catalogue. The estimation of the Planck detection
probability assumes the flat Lambda cold dark matter (LambdaCDM) cosmology most
compatible with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) data. It
takes into account the XCS selection function and Planck sensitivity, as well
as the covariance of the cluster X-ray luminosity, temperature, and integrated
comptonization parameter, as a function of cluster mass and redshift,
determined by the Millennium Gas Simulations. We also characterize the
properties of the galaxy clusters in the final data release of the XCS that we
expect Planck will have detected by the end of its extended mission. Finally,
we briefly discuss possible joint applications of the XCS and Planck data.
09/2011;
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Nicola Mehrtens,
A. Kathy Romer,
E. J. Lloyd-Davies, Matt Hilton,
Christopher J. Miller,
S. A. Stanford,
Mark Hosmer,
Ben Hoyle,
Chris A. Collins,
Andrew R Liddle, [......],
Edward M. Edmondson,
Michael West,
Heather C. Campbell,
Alastair C. Edge,
Robert G. Mann,
David Wake,
Christophe Benoist,
Luiz da Costa,
Marcio A. G. Maia,
Ricardo Ogando
[show abstract]
[hide abstract]
ABSTRACT: The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters
using all publicly available data in the XMM-Newton Science Archive. Its main
aims are to measure cosmological parameters and trace the evolution of X-ray
scaling relations. In this paper we present the first data release from the XMM
Cluster Survey (XCS-DR1). This consists of 503 optically confirmed,
serendipitously detected, X-ray clusters. Of these clusters, 255 are new to the
literature and 356 are new X-ray discoveries. We present 464 clusters with a
redshift estimate (0.06 < z < 1.46), including 261 clusters with spectroscopic
redshifts. In addition, we have measured X-ray temperatures (Tx) for 402
clusters (0.4 < Tx < 14.7 keV). We highlight seven interesting subsamples of
XCS-DR1 clusters: (i) 10 clusters at high redshift (z > 1.0, including a new
spectroscopically-confirmed cluster at z = 1.01); (ii) 67 clusters with high Tx
(> 5 keV); (iii) 131 clusters/groups with low Tx (< 2 keV); (iv) 27 clusters
with measured Tx values in the SDSS `Stripe 82' co-add region; (v) 78 clusters
with measured Tx values in the Dark Energy Survey region; (vi) 40 clusters
detected with sufficient counts to permit mass measurements (under the
assumption of hydrostatic equilibrium); (vii) 105 clusters that can be used for
applications such as the derivation of cosmological parameters and the
measurement of cluster scaling relations. The X-ray analysis methodology used
to construct and analyse the XCS-DR1 cluster sample has been presented in a
companion paper, Lloyd-Davies et al. (2010).
06/2011;
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E. J. Lloyd-Davies,
A. Kathy Romer,
Nicola Mehrtens,
Mark Hosmer,
Michael Davidson,
Kivanc Sabirli,
Robert G. Mann, Matt Hilton,
Andrew R Liddle,
Pedro T. P. Viana, [......],
Peter Freeman,
Craig D. Harrison,
Ben Hoyle,
Scott T. Kay,
Emma Kuwertz,
Christopher J. Miller,
Robert C. Nichol,
Martin Sahlen,
S. A. Stanford,
John P. Stott
[show abstract]
[hide abstract]
ABSTRACT: The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters
using all publicly available data in the XMM-Newton Science Archive. Its main
aims are to measure cosmological parameters and trace the evolution of X-ray
scaling relations. In this paper we describe the data processing methodology
applied to the 5,776 XMM observations used to construct the current XCS source
catalogue. A total of 3,675 > 4-sigma cluster candidates with > 50
background-subtracted X-ray counts are extracted from a total non-overlapping
area suitable for cluster searching of 410 deg^2. Of these, 993 candidates are
detected with > 300 background-subtracted X-ray photon counts, and we
demonstrate that robust temperature measurements can be obtained down to this
count limit. We describe in detail the automated pipelines used to perform the
spectral and surface brightness fitting for these candidates, as well as to
estimate redshifts from the X-ray data alone. A total of 587 (122) X-ray
temperatures to a typical accuracy of < 40 (< 10) per cent have been measured
to date. We also present the methodology adopted for determining the selection
function of the survey, and show that the extended source detection algorithm
is robust to a range of cluster morphologies by inserting mock clusters derived
from hydrodynamical simulations into real XMM images. These tests show that the
simple isothermal beta-profiles is sufficient to capture the essential details
of the cluster population detected in the archival XMM observations. The
redshift follow-up of the XCS cluster sample is presented in a companion paper,
together with a first data release of 503 optically-confirmed clusters.
10/2010;
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Matt Hilton,
Ed Lloyd-Davies,
S. Adam Stanford,
John P. Stott,
Chris A. Collins,
A. Kathy Romer,
Mark Hosmer,
Ben Hoyle,
Scott T. Kay,
Andrew R. Liddle,
Nicola Mehrtens,
Christopher J. Miller,
Martin Sahlén,
and Pedro T. P. Viana
[show abstract]
[hide abstract]
ABSTRACT: We use Chandra X-ray and Spitzer infrared (IR) observations to explore the active galactic nucleus (AGN) and starburst populations of XMMXCS J2215.9–1738 at z = 1.46, one of the most distant spectroscopically confirmed galaxy clusters known. The high-resolution X-ray imaging reveals that the cluster emission is contaminated by point sources that were not resolved in XMM-Newton observations of the system, and have the effect of hardening the spectrum, leading to the previously reported temperature for this system being overestimated. From a joint spectroscopic analysis of the Chandra and XMM-Newton data, the cluster is found to have temperature T = 4.1+0.6 –0.9 keV and luminosity L X = (2.92+0.24 –0.35) × 1044 erg s–1, extrapolated to a radius of 2 Mpc. As a result of this revised analysis, the cluster is found to lie on the σ v -T relation, but the cluster remains less luminous than would be expected from self-similar evolution of the local L X-T relation. Two of the newly discovered X-ray AGNs are cluster members, while a third object, which is also a prominent 24 μm source, is found to have properties consistent with it being a high-redshift, highly obscured object in the background. We find a total of eight >5σ 24 μm sources associated with cluster members (four spectroscopically confirmed and four selected using photometric redshifts) and one additional 24 μm source with two possible optical/near-IR counterparts that may be associated with the cluster. Examining the Infrared Array Camera colors of these sources, we find that one object is likely to be an AGN. Assuming that the other 24 μm sources are powered by star formation, their IR luminosities imply star formation rates ~100 M ☉ yr–1. We find that three of these sources are located at projected distances of <250 kpc from the cluster center, suggesting that a large amount of star formation may be taking place in the cluster core, in contrast to clusters at low redshift.
The Astrophysical Journal 06/2010; 718(1):133. · 6.02 Impact Factor
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Matt Hilton,
Ed Lloyd-Davies,
S. Adam Stanford,
John P. Stott,
Chris A. Collins,
A. Kathy Romer,
Mark Hosmer,
Ben Hoyle,
Scott T. Kay,
Andrew R Liddle,
Nicola Mehrtens,
Christopher J. Miller,
Martin Sahlén,
Pedro T. P. Viana
[show abstract]
[hide abstract]
ABSTRACT: We use Chandra X-ray and Spitzer infrared observations to explore the AGN and starburst populations of XMMXCS J2215.9-1738 at z=1.46, one of the most distant spectroscopically confirmed galaxy clusters known. The high resolution X-ray imaging reveals that the cluster emission is contaminated by point sources that were not resolved in XMM observations of the system, and have the effect of hardening the spectrum, leading to the previously reported temperature for this system being overestimated. From a joint spectroscopic analysis of the Chandra and XMM data, the cluster is found to have temperature T=4.1_-0.9^+0.6 keV and luminosity L_X=(2.92_-0.35^+0.24)x10^44 erg/s extrapolated to a radius of 2 Mpc. As a result of this revised analysis, the cluster is found to lie on the sigma_v-T relation, but the cluster remains less luminous than would be expected from self-similar evolution of the local L_X-T relation. Two of the newly discovered X-ray AGN are cluster members, while a third object, which is also a prominent 24 micron source, is found to have properties consistent with it being a high redshift, highly obscured object in the background. We find a total of eight >5 sigma 24 micron sources associated with cluster members (four spectroscopically confirmed, and four selected using photometric redshifts), and one additional 24 micron source with two possible optical/near-IR counterparts that may be associated with the cluster. Examining the IRAC colors of these sources, we find one object is likely to be an AGN. Assuming that the other 24 micron sources are powered by star formation, their infrared luminosities imply star formation rates ~100 M_sun/yr. We find that three of these sources are located at projected distances of <250 kpc from the cluster center, suggesting that a large amount of star formation may be taking place in the cluster core, in contrast to clusters at low redshift. Comment: Accepted for publication in ApJ, 16 pages, 10 figures
05/2010;
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Chris A Collins,
John P Stott, Matt Hilton,
Scott T Kay,
S Adam Stanford,
Michael Davidson,
Mark Hosmer,
Ben Hoyle,
Andrew Liddle,
Ed Lloyd-Davies,
Robert G Mann,
Nicola Mehrtens,
Christopher J Miller,
Robert C Nichol,
A Kathy Romer,
Martin Sahlén,
Pedro T P Viana,
Michael J West
[show abstract]
[hide abstract]
ABSTRACT: The current consensus is that galaxies begin as small density fluctuations in the early Universe and grow by in situ star formation and hierarchical merging. Stars begin to form relatively quickly in sub-galactic-sized building blocks called haloes which are subsequently assembled into galaxies. However, exactly when this assembly takes place is a matter of some debate. Here we report that the stellar masses of brightest cluster galaxies, which are the most luminous objects emitting stellar light, some 9 billion years ago are not significantly different from their stellar masses today. Brightest cluster galaxies are almost fully assembled 4-5 billion years after the Big Bang, having grown to more than 90 per cent of their final stellar mass by this time. Our data conflict with the most recent galaxy formation models based on the largest simulations of dark-matter halo development. These models predict protracted formation of brightest cluster galaxies over a Hubble time, with only 22 per cent of the stellar mass assembled at the epoch probed by our sample. Our findings suggest a new picture in which brightest cluster galaxies experience an early period of rapid growth rather than prolonged hierarchical assembly.
Nature 05/2009; 458(7238):603-6. · 36.28 Impact Factor
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Matt Hilton,
S. Adam Stanford,
John P. Stott,
Chris A. Collins,
Ben Hoyle,
Michael Davidson,
Mark Hosmer,
Scott T. Kay,
Andrew R. Liddle,
Ed Lloyd-Davies, [......],
Kivanc Sabirli,
Martin Sahlén,
Pedro T. P. Viana,
Michael J. West,
Kyle Barbary,
Kyle S. Dawson,
Joshua Meyers,
Saul Perlmutter,
David Rubin,
and Nao Suzuki
[show abstract]
[hide abstract]
ABSTRACT: We present a study of the morphological fractions and color-magnitude relation (CMR) in the most distant X-ray selected galaxy cluster currently known, XMMXCS J2215.9 – 1738 at z = 1.46, using a combination of optical imaging data obtained with the Hubble Space Telescope Advanced Camera for Surveys, and infrared data from the Multi-Object Infrared Camera and Spectrograph, mounted on the 8.2 m Subaru telescope. We find that the morphological mix of the cluster galaxy population is similar to clusters at z ~ 1. Within the central 0.5 Mpc, approximately ~62% of the galaxies identified as likely cluster members are ellipticals or S0s; and ~38% are spirals or irregulars. Therefore, early-type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately ~4.5 Gyr after the big bang. We measure the CMRs for the early-type galaxies, finding that the slope in the z 850-J relation is consistent with that measured in the Coma cluster, some ~9 Gyr earlier, although the uncertainty is large. In contrast, the measured intrinsic scatter about the CMR is more than three times the value measured in Coma, after conversion to rest-frame U – V. From comparison with stellar population synthesis models, the intrinsic scatter measurements imply mean luminosity-weighted ages for the early-type galaxies in J2215.9 – 1738 of 3 Gyr, corresponding to the major epoch of star formation coming to an end at zf 3-5. We find that the cluster exhibits evidence of the "downsizing" phenomenon: the fraction of faint cluster members on the red sequence expressed using the Dwarf-to-Giant Ratio (DGR) is 0.32 ± 0.18 within a radius of 0.5R 200. This is consistent with extrapolation of the redshift evolution of the DGR seen in cluster samples at z < 1. In contrast to observations of some other z > 1 clusters, we find a lack of very bright galaxies within the cluster.
The Astrophysical Journal 04/2009; 697(1):436. · 6.02 Impact Factor
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Matt Hilton,
S. Adam Stanford,
John P. Stott,
Chris A. Collins,
Ben Hoyle,
Michael Davidson,
Mark Hosmer,
Scott T. Kay,
Andrew R Liddle,
Ed Lloyd-Davies, [......],
Kivanc Sabirli,
Martin Sahlen,
Pedro T. P. Viana,
Michael J. West,
Kyle Barbary,
Kyle S. Dawson,
Joshua Meyers,
Saul Perlmutter,
David Rubin,
Nao Suzuki
[show abstract]
[hide abstract]
ABSTRACT: We present a study of the morphological fractions and color-magnitude
relation in the most distant X-ray selected galaxy cluster currently known,
XMMXCS J2215.9-1738 at z=1.46, using a combination of optical imaging data
obtained with the Hubble Space Telescope Advanced Camera for Surveys, and
infrared data from the Multi-Object Infrared Camera and Spectrograph, mounted
on the 8.2m Subaru telescope. We find that the morphological mix of the cluster
galaxy population is similar to clusters at z~1: approximately ~62% of the
galaxies identified as likely cluster members are ellipticals or S0s; and ~38%
are spirals or irregulars. We measure the color-magnitude relations for the
early type galaxies, finding that the slope in the z_850-J relation is
consistent with that measured in the Coma cluster, some ~9 Gyr earlier,
although the uncertainty is large. In contrast, the measured intrinsic scatter
about the color-magnitude relation is more than three times the value measured
in Coma, after conversion to rest frame U-V. From comparison with stellar
population synthesis models, the intrinsic scatter measurements imply mean
luminosity weighted ages for the early type galaxies in J2215.9-1738 of ~3 Gyr,
corresponding to the major epoch of star formation coming to an end at z_f =
3-5. We find that the cluster exhibits evidence of the `downsizing' phenomenon:
the fraction of faint cluster members on the red sequence expressed using the
Dwarf-to-Giant Ratio (DGR) is 0.32+/-0.18. This is consistent with
extrapolation of the redshift evolution of the DGR seen in cluster samples at z
< 1. In contrast to observations of some other z > 1 clusters, we find a lack
of very bright galaxies within the cluster.
03/2009;
-
S. A. Stanford,
A. Kathy Romer,
Kivanc Sabirli,
Michael Davidson, Matt Hilton,
Pedro T. P. Viana,
Chris A. Collins,
Scott T. Kay,
Andrew R. Liddle,
Robert G. Mann,
Christopher J. Miller,
Robert C. Nichol,
Michael J. West,
Christopher J. Conselice,
Hyron Spinrad,
Daniel Stern,
and Kevin 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 six galaxies within a ~60'' diameter region lie at z = 1.45 ± 0.01. Model fits to the X-ray spectra of the extended emission yield kT = 7.4 keV (90% confidence); if there is an undetected central X-ray point source, then kT = 6.5 keV. The bolometric X-ray luminosity is LX = 4.4 × 1044 ergs s-1 over a 2 Mpc radial region. The measured TX, which is the highest for any known 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.
The Astrophysical Journal 12/2008; 646(1):L13. · 6.02 Impact Factor
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Matt Hilton,
Chris A. Collins,
S. Adam Stanford,
Chris Lidman,
Kyle S. Dawson,
Michael Davidson,
Scott T. Kay,
Andrew R. Liddle,
Robert G. Mann,
Christopher J. Miller,
Robert C. Nichol,
A. Kathy Romer,
Kivanc Sabirli,
Pedro T. P. Viana,
and Michael J. West
[show abstract]
[hide abstract]
ABSTRACT: We present new spectroscopic observations of the most distant X-ray-selected galaxy cluster currently known, XMMXCS J2215.9-1738 at z = 1.457, obtained with the DEIMOS instrument at the W. M. Keck Observatory and the FORS2 instrument on the ESO Very Large Telescope. Within the cluster virial radius, as estimated from the cluster X-ray properties, we increase the number of known spectroscopic cluster members to 17 objects, and calculate the line-of-sight velocity dispersion of the cluster to be 580 ± 140 km s-1. We find mild evidence that the velocity distribution of galaxies within the virial radius deviates from a single Gaussian. We show that the properties of J2215.9-1738 are inconsistent with self-similar evolution of local X-ray scaling relations, finding that the cluster is underluminous given its X-ray temperature, and that the intracluster medium contains ~2-3 times the kinetic energy per unit mass of the cluster galaxies. These results can perhaps be explained if the cluster is observed in the aftermath of an off-axis merger. Alternatively, heating of the intracluster medium through supernovae and/or active galactic nucleus activity, as is required to explain the observed slope of the local X-ray luminosity-temperature relation, may be responsible.
The Astrophysical Journal 12/2008; 670(2):1000. · 6.02 Impact Factor
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Martin Sahlén,
Pedro T. P. Viana,
Andrew R Liddle,
A. Kathy Romer,
Michael Davidson,
Mark Hosmer,
Ed Lloyd-Davies,
Kivanc Sabirli,
Chris A. Collins,
Peter E. Freeman, Matt Hilton,
Ben Hoyle,
Scott T. Kay,
Robert G. Mann,
Nicola Mehrtens,
Christopher J. Miller,
Robert C. Nichol,
S. Adam Stanford,
Michael J. West,
for the XCS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We forecast the constraints on the values of sigma_8, Omega_m, and cluster
scaling relation parameters which we expect to obtain from the XMM Cluster
Survey (XCS). We assume a flat Lambda-CDM Universe and perform a Monte Carlo
Markov Chain analysis of the evolution of the number density of galaxy clusters
that takes into account a detailed simulated selection function. Comparing our
current observed number of clusters shows good agreement with predictions. We
determine the expected degradation of the constraints as a result of
self-calibrating the luminosity-temperature relation (with scatter), including
temperature measurement errors, and relying on photometric methods for the
estimation of galaxy cluster redshifts. We examine the effects of systematic
errors in scaling relation and measurement error assumptions. Using only (T,z)
self-calibration, we expect to measure Omega_m to +-0.03 (and Omega_Lambda to
the same accuracy assuming flatness), and sigma_8 to +-0.05, also constraining
the normalization and slope of the luminosity-temperature relation to +-6 and
+-13 per cent (at 1sigma) respectively in the process. Self-calibration fails
to jointly constrain the scatter and redshift evolution of the
luminosity-temperature relation significantly. Additional archival and/or
follow-up data will improve on this. We do not expect measurement errors or
imperfect knowledge of their distribution to degrade constraints significantly.
Scaling-relation systematics can easily lead to cosmological constraints 2sigma
or more away from the fiducial model. Our treatment is the first exact
treatment to this level of detail, and introduces a new `smoothed ML' estimate
of expected constraints.
02/2008;
