86 research outputs found
Planck intermediate results: IV. The XMM-Newton validation programme for new Planck galaxy clusters
We present the final results from the XMM-Newton validation follow-up of new Planck galaxy cluster candidates. We observed 15 new candidates, detected with signal-to-noise ratios between 4.0 and 6.1 in the 15.5-month nominal Planck survey. The candidates were selected using ancillary data flags derived from the ROSAT All Sky Survey (RASS) and Digitized Sky Survey all-sky maps, with the aim of pushing into the low SZ flux, high-z regime and testing RASS flags as indicators of candidate reliability. Fourteen new clusters were detected by XMM-Newton, ten single clusters and two double systems. Redshifts from X-ray spectroscopy lie in the range 0.2 to 0.9, with six clusters at z > 0.5. Estimated masses (M500) range from 2.5 × 1014 to 8 × 1014 MM·. We discuss our results in the context of the full XMM-Newton validation programme, in which 51 new clusters have been detected. This includes four double and two triple systems, some of which are chance projections on the sky of clusters at different redshifts. We find thatassociation with a source from the RASS-Bright Source Catalogue is a robust indicator of the reliability of a candidate, whereas association with a source from the RASS-Faint Source Catalogue does not guarantee that the SZ candidate is a bona fide cluster. Nevertheless, most Planck clusters appear in RASS maps, with a significance greater than 2σ being a good indication that the candidate is a real cluster. Candidate validation from association with SDSS galaxy overdensity at z > 0.5 is also discussed. The full sample gives a Planck sensitivity threshold of Y500 4 × 10-4 arcmin2, with indication for Malmquist bias in the Y X-Y500 relation below this threshold. The corresponding mass threshold depends on redshift. Systems with M500 > 5 × 1014 MM at z > 0.5 are easily detectable with Planck. The newly-detected clusters follow the YX-Y500 relation derived from X-ray selected samples. Compared to X-ray selected clusters, the new SZ clusters have a lower X-ray luminosity on average for their mass. There is no indication of departure from standard self-similar evolution in the X-ray versus SZ scaling properties. In particular, there is no significant evolution of the YX/Y500 ratio. © ESO, 2013.The Planck Collaboration acknowledges the support of: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN and JA (Spain); Tekes, AoF and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and DEISA (EU).Peer Reviewe
Two fossil groups of galaxies at z~0.4 in the COSMOS: accelerated stellar-mass build-up, different progenitors
We report on 2 fossil groups of galaxies at z=0.425 and 0.372 discovered in
the Cosmic Evolution Survey (COSMOS) area. Selected as X-ray extended sources,
they have total masses (M_200) of 1.9(+/-0.41)E13 and 9.5(+/-0.42)E13 M_sun,
respectively, as obtained from a recent X-ray luminosity-mass scaling relation.
The lower mass system appears isolated, whereas the other sits in a well-known
large-scale structure (LSS) populated by 27 other X-ray emitting groups. The
identification as fossil is based on the i-band photometry of all the galaxies
with a photo-z consistent with that of the group at the 2-sigma confidence
level and within a projected group-centric distance equal to 0.5R_200, and
i_AB<=22.5-mag limited spectroscopy. Both fossil groups exhibit high
stellar-to-total mass ratios compared to all the X-ray selected groups of
similar mass at 0.3<=z<=0.5 in the COSMOS. At variance with the composite
galaxy stellar mass functions (GSMFs) of similarly massive systems, both fossil
group GSMFs are dominated by passively evolving galaxies down to M^stars~1E10
M_sun (according to the galaxy broad-band spectral energy distributions). The
relative lack of star-forming galaxies with 1E10<=M^stars<=1E11 M_sun is
confirmed by the galaxy distribution in the b-r vs i color-magnitude diagram.
Hence, the 2 fossil groups appear as more mature than the coeval, similarly
massive groups. Their overall star formation activity ended rapidly after an
accelerated build up of the total stellar mass; no significant infall of
galaxies with M^stars>=1E10 M_sun took place in the last 3 to 6 Gyr. This
similarity holds although the 2 fossil groups are embedded in two very
different density environments of the LSS, which suggests that their galaxy
populations were shaped by processes that do not depend on the LSS. However,
their progenitors may do so. ...Comment: 12 pages, 5 color figures, 1 table; to be published in the MNRA
Mapping the kinetic Sunyaev-Zel'dovich effect toward MACS J0717.5+3745 with NIKA
Measurement of the gas velocity distribution in galaxy clusters provides
insight into the physics of mergers, through which large scale structures form
in the Universe. Velocity estimates within the intracluster medium (ICM) can be
obtained via the Sunyaev-Zel'dovich (SZ) effect, but its observation is
challenging both in term of sensitivity requirement and control of systematic
effects, including the removal of contaminants. In this paper we report
resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple
merger MACS J0717.5+3745 (z=0.55), using data obtained with the NIKA camera at
the IRAM 30m telescope. Assuming that the SZ signal is the sum of a thermal
(tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we
extract for the first time a resolved map of the kSZ signal in a cluster. The
kSZ signal is dominated by a dipolar structure that peaks at -5.1 and +3.4
sigma, corresponding to two subclusters moving respectively away and toward us
and coincident with the cold dense X-ray core and a hot region undergoing a
major merging event. We model the gas electron density and line-of-sight
velocity of MACS J0717.5+3745 as four subclusters. Combining NIKA data with
X-ray observations from XMM-Newton and Chandra, we fit this model to constrain
the gas line-of-sight velocity of each component, and we also derive, for the
first time, a velocity map from kSZ data (i.e. that is model-dependent). Our
results are consistent with previous constraints on the merger velocities, and
thanks to the high angular resolution of our data, we are able to resolve the
structure of the gas velocity. Finally, we investigate possible contamination
and systematic effects with a special care given to radio and submillimeter
galaxies. Among the sources that we detect with NIKA, we find one which is
likely to be a high redshift lensed submillimeter galaxy.Comment: 19 pages, 9 figures, accepted in A&
Testing adiabatic contraction of dark matter in fossil group candidates
We present deep XMM observations and ESO WFI optical imaging of two
X-ray-selected fossil group candidates, RXCJ0216.7-4749 and RXCJ2315.7-0222.
Using the X-ray data, we derive total mass profiles under the hydrostatic
equilibrium assumption. The central regions of RXCJ0216.7-4749 are found to be
dominated by an X-ray bright AGN, and although we derive a mass profile,
uncertainties are large and the constraints are significantly weakened due to
the presence of the central source. The total mass profile of RXCJ2315.7-0222
is of high quality, being measured in fifteen bins from [0.075 - 0.75]R500 and
containing three data points interior to 30 kpc, allowing comprehensive
investigation of its properties. We probe several mass models based on the
standard NFW profile or on the Sersic-like model recently suggested by
high-resolution N-body simulations. We find that the addition of a stellar
component due to the presence of the central galaxy is necessary for a good
analytical model fit. In all mass profile models fitted, the mass concentration
is not especially high compared to non-fossil systems. In addition, the
modification of the dark matter halo by adiabatic contraction slightly improves
the fit. However, our result depends critically on the choice of IMF used to
convert galaxy luminosity to mass, which leads to a degeneracy between the
central slope of the dark matter profile and the normalisation of the stellar
component. While we argue on the basis of the range of M_*/L_R ratios that
lower M_*/L_R ratios are preferred on physical grounds and that adiabatic
contraction has thus operated in this system, better theoretical and
observational convergence on this problem is needed to make further progess.Comment: to appear in Astronomy & Astrophysics, 16 pages, 24 figure
The XXL Survey IV. Mass-temperature relation of the bright cluster sample
The XXL survey is the largest survey carried out by XMM-Newton. Covering an area of 50deg, the survey contains galaxy clusters out to a redshift 2 and to an X-ray flux limit of . This paper is part of the first release of XXL results focussed on the bright cluster sample. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation is used to estimate the mass of all 100 clusters in XXL-100-GC. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS catalog, we derive the of each system with careful considerations of the systematics. The clusters lie at and span a range of . We combine our sample with 58 clusters from the literature, increasing the range out to 10keV. To date, this is the largest sample of clusters with measurements that has been used to study the mass-temperature relation. The fit () to the XXL clusters returns a slope and intrinsic scatter ; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, and . Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further
Fossil Groups Origins: I. RX J105453.3+552102 a very massive and relaxed system at z~0.5
The most accepted scenario for the origin of fossil groups (FGs) is that they
are galaxy associations in which the merging rate was fast and efficient. These
systems have assembled half of their mass at early epoch of the Universe,
subsequently growing by minor mergers. They could contain a fossil record of
the galaxy structure formation. We have started a project in order to
characterize a large sample of FGs. In this paper we present the analysis of
the fossil system RX J105453.3+552102. Optical deep images were used for
studying the properties of the brightest group galaxy and for computing the
photometric luminosity function of the group. We have also performed a detail
dynamical analysis of the system based on redshift data for 116 galaxies. This
galaxy system is located at z=0.47, and shows a quite large line-of-sight
velocity dispersion \sigma_{v}~1000 km/s. Assuming the dynamical equilibrium,
we estimated a virial mass of M ~ 10^{15} h_{70} M_{\odot}. No evidence of
substructure was found within 1.4 Mpc radius. We found a statistically
significant departure from Gaussianity of the group members velocities in the
most external regions of the group. This could indicate the presence of
galaxies in radial orbits in the external region of the group. We also found
that the photometrical luminosity function is bimodal, showing a lack of M_{r}
~ -19.5 galaxies. The brightest group galaxy shows low Sersic parameter (n~2)
and a small peculiar velocity. Indeed, our accurate photometry shows that the
difference between the brightest and the second brightest galaxies is 1.9 mag
in the r-band, while the classical definition of FGs is based on a magnitude
gap of 2. We conclude that this fossil system does not follow the empirical
definition of FGs. Nevertheless, it is a massive, old and undisturbed galaxy
system with little infall of L^{*} galaxies since its initial collapse.Comment: 17 pages, 14 figures, accepted for publication at A&
Planck intermediate results. III. The relation between galaxy cluster mass and Sunyaev-Zeldovich signal
We examine the relation between the galaxy cluster mass M and
Sunyaev-Zeldovich (SZ) effect signal D_A^2 Y for a sample of 19 objects for
which weak lensing (WL) mass measurements obtained from Subaru Telescope data
are available in the literature. Hydrostatic X-ray masses are derived from
XMM-Newton archive data and the SZ effect signal is measured from Planck
all-sky survey data. We find an M_WL-D_A^2 Y relation that is consistent in
slope and normalisation with previous determinations using weak lensing masses;
however, there is a normalisation offset with respect to previous measures
based on hydrostatic X-ray mass-proxy relations. We verify that our SZ effect
measurements are in excellent agreement with previous determinations from
Planck data. For the present sample, the hydrostatic X-ray masses at R_500 are
on average ~ 20 per cent larger than the corresponding weak lensing masses, at
odds with expectations. We show that the mass discrepancy is driven by a
difference in mass concentration as measured by the two methods, and, for the
present sample, the mass discrepancy and difference in mass concentration is
especially large for disturbed systems. The mass discrepancy is also linked to
the offset in centres used by the X-ray and weak lensing analyses, which again
is most important in disturbed systems. We outline several approaches that are
needed to help achieve convergence in cluster mass measurement with X-ray and
weak lensing observations.Comment: 19 pages, 9 figures, matches accepted versio
Planck Intermediate Results. IV. The XMM-Newton validation programme for new Planck galaxy clusters
We present the final results from the XMM-Newton validation follow-up of new
Planck galaxy cluster candidates. We observed 15 new candidates, detected with
signal-to-noise ratios between 4.0 and 6.1 in the 15.5-month nominal Planck
survey. The candidates were selected using ancillary data flags derived from
the ROSAT All Sky Survey (RASS) and Digitized Sky Survey all-sky maps, with the
aim of pushing into the low SZ flux, high-z regime and testing RASS flags as
indicators of candidate reliability. 14 new clusters were detected by XMM,
including 2 double systems. Redshifts lie in the range 0.2 to 0.9, with 6
clusters at z>0.5. Estimated M500 range from 2.5 10^14 to 8 10^14 Msun. We
discuss our results in the context of the full XMM validation programme, in
which 51 new clusters have been detected. This includes 4 double and 2 triple
systems, some of which are chance projections on the sky of clusters at
different z. We find that association with a RASS-BSC source is a robust
indicator of the reliability of a candidate, whereas association with a FSC
source does not guarantee that the SZ candidate is a bona fide cluster.
Nevertheless, most Planck clusters appear in RASS maps, with a significance
greater than 2 sigma being a good indication that the candidate is a real
cluster. The full sample gives a Planck sensitivity threshold of Y500 ~ 4 10^-4
arcmin^2, with indication for Malmquist bias in the YX-Y500 relation below this
level. The corresponding mass threshold depends on z. Systems with M500 > 5
10^14 Msun at z > 0.5 are easily detectable with Planck. The newly-detected
clusters follow the YX-Y500 relation derived from X-ray selected samples.
Compared to X-ray selected clusters, the new SZ clusters have a lower X-ray
luminosity on average for their mass. There is no indication of departure from
standard self-similar evolution in the X-ray versus SZ scaling properties.
(abridged)Comment: accepted by A&
Planck Intermediate Results II: Comparison of Sunyaev-Zeldovich measurements from Planck and from the Arcminute Microkelvin Imager for 11 galaxy clusters
A comparison is presented of Sunyaev-Zeldovich measurements for 11 galaxy
clusters as obtained by Planck and by the ground-based interferometer, the
Arcminute Microkelvin Imager. Assuming a universal spherically-symmetric
Generalised Navarro, Frenk & White (GNFW) model for the cluster gas pressure
profile, we jointly constrain the integrated Compton-Y parameter (Y_500) and
the scale radius (theta_500) of each cluster. Our resulting constraints in the
Y_500-theta_500 2D parameter space derived from the two instruments overlap
significantly for eight of the clusters, although, overall, there is a tendency
for AMI to find the Sunyaev-Zeldovich signal to be smaller in angular size and
fainter than Planck. Significant discrepancies exist for the three remaining
clusters in the sample, namely A1413, A1914, and the newly-discovered Planck
cluster PLCKESZ G139.59+24.18. The robustness of the analysis of both the
Planck and AMI data is demonstrated through the use of detailed simulations,
which also discount confusion from residual point (radio) sources and from
diffuse astrophysical foregrounds as possible explanations for the
discrepancies found. For a subset of our cluster sample, we have investigated
the dependence of our results on the assumed pressure profile by repeating the
analysis adopting the best-fitting GNFW profile shape which best matches X-ray
observations. Adopting the best-fitting profile shape from the X-ray data does
not, in general, resolve the discrepancies found in this subset of five
clusters. Though based on a small sample, our results suggest that the adopted
GNFW model may not be sufficiently flexible to describe clusters universally.Comment: update to metadata author list onl
The XXL survey XV: Evidence for dry merger driven BCG growth in XXL-100-GC X-ray clusters
The growth of brightest cluster galaxies is closely related to the properties of their host cluster. We present evidence for dry mergers as the dominant source of BCG mass growth at in the XXL 100 brightest cluster sample. We use the global red sequence, H emission and mean star formation history to show that BCGs in the sample possess star formation levels comparable to field ellipticals of similar stellar mass and redshift. XXL 100 brightest clusters are less massive on average than those in other X-ray selected samples such as LoCuSS or HIFLUGCS. Few clusters in the sample display high central gas concentration, rendering inefficient the growth of BCGs via star formation resulting from the accretion of cool gas. Using measures of the relaxation state of their host clusters, we show that BCGs grow as relaxation proceeds. We find that the BCG stellar mass corresponds to a relatively constant fraction 1\%\ of the total cluster mass in relaxed systems. We also show that, following a cluster scale merger event, the BCG stellar mass lags behind the expected value from the M - M relation but subsequently accretes stellar mass via dry mergers as the BCG and cluster evolve towards a relaxed state
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