543 research outputs found
The Lx-T Relation and Intracluster Gas Fractions of X-ray Clusters
We re-examine the X-ray luminosity-temperature relation using a nearly
homogeneous data set of 24 clusters selected for statistically accurate
temperature measurements and absence of strong cooling flows. The data exhibit
a remarkably tight power-law relation between bolometric luminosity and
temperature with a slope 2.88 \pm 0.15. With reasonable assumptions regarding
cluster structure, we infer an upper limit on fractional variations in the
intracluster gas fraction <(\delta\fgas/\fgas)^2)^1/2 \le 15%. Imaging data
from the literature are employed to determine absolute values of fgas within
spheres encompassing density contrast 500 and 200 with respect to the critical
density. Comparing binding mass estimates based on the virial theorem (VT) and
the hydrostatic, betamodel (BM), we find a temperature-dependent discrepancy in
fgas between the two methods caused by sytematic variation of the outer slope
parameter beta with temperature. There is evidence that cool clusters have a
lower mean gas fraction that hot clusters, but it is not possible to assess the
statistical significance of this effect in the present dataset. The temperature
dependance of the ICM density structure, coupled with the increase of the gas
fraction with T in the VT aproach, explains the steepening of the Lx-T
relation. The small variation about the mean gas fraction within this majority
sub-population of clusters presents an important constraint for theories of
galaxy formation and supports arguments against an Einstein-deSitter universe
based on the population mean gas fraction and primordial nucleosynthesis. The
apparent trend of lower gas fractions and more extended atmospheres in low T
systems are consistent with expectations of models incorporating the effects of
galactic winds on the ICM. ABRIDGEDComment: 11 pages, 4 figures, uses mn.sty and epsf.sty, accepted for
publication in MNRAS; minor modifications: discussion added on CF LX (Sec.
3.1);comparison with Allen & Fabian L-T results (Sec.3.1 & Sec.4.4);
statistics precised (3.1), discussion clarified (Sec. 2.2,Sec. 4.4); slight
mistake in the r-T and M-T relation calibration corrected and thus fgas in
Fig.3, Fig 4, Tab 2 slightly change
The matter distribution in z ~ 0.5 redshift clusters of galaxies. II : The link between dark and visible matter
We present an optical analysis of a sample of 11 clusters built from the
EXCPRES sample of X-ray selected clusters at intermediate redshift (z ~ 0.5).
With a careful selection of the background galaxies we provide the mass maps
reconstructed from the weak lensing by the clusters. We compare them with the
light distribution traced by the early-type galaxies selected along the red
sequence for each cluster. The strong correlations between dark matter and
galaxy distributions are confirmed, although some discrepancies arise, mostly
for merging or perturbed clusters. The average M/L ratio of the clusters is
found to be: M/L_r = 160 +/- 60 in solar units (with no evolutionary
correction), in excellent agreement with similar previous studies. No strong
evolutionary effects are identified even if the small sample size reduces the
significance of the result. We also provide a individual analysis of each
cluster in the sample with a comparison between the dark matter, the galaxies
and the gas distributions. Some of the clusters are studied for the first time
in the optical.Comment: 25 pages, 9 figues + 11 figures in Annex, 4 tables. Accepted for
publication in A&A. 1 reference correcte
Joint signal extraction from galaxy clusters in X-ray and SZ surveys: A matched-filter approach
The hot ionized gas of the intra-cluster medium emits thermal radiation in
the X-ray band and also distorts the cosmic microwave radiation through the
Sunyaev-Zel'dovich (SZ) effect. Combining these two complementary sources of
information through innovative techniques can therefore potentially improve the
cluster detection rate when compared to using only one of the probes. Our aim
is to build such a joint X-ray-SZ analysis tool, which will allow us to detect
fainter or more distant clusters while maintaining high catalogue purity. We
present a method based on matched multifrequency filters (MMF) for extracting
cluster catalogues from SZ and X-ray surveys. We first designed an X-ray
matched-filter method, analogous to the classical MMF developed for SZ
observations. Then, we built our joint X-ray-SZ algorithm by combining our
X-ray matched filter with the classical SZ-MMF, for which we used the physical
relation between SZ and X-ray observations. We show that the proposed X-ray
matched filter provides correct photometry results, and that the joint matched
filter also provides correct photometry when the relation
of the clusters is known. Moreover, the proposed joint algorithm provides a
better signal-to-noise ratio than single-map extractions, which improves the
detection rate even if we do not exactly know the relation.
The proposed methods were tested using data from the ROSAT all-sky survey and
from the Planck survey.Comment: 22 pages (before appendices), 19 figures, 3 tables, 5 appendices.
Accepted for publication in A&
Planck 2013 results. XXXI. Consistency of the Planck data
The Planck design and scanning strategy provide many levels of redundancy that can be exploited to provide tests of internal consistency. One of the most important is the comparison of the 70 GHz (amplifier) and 100 GHz (bolometer) channels. Based on different instrument technologies, with feeds located differently in the focal plane, analysed independently by different teams using different software, and near the minimum of diffuse foreground emission, these channels are in effect two different experiments. The 143 GHz channel has the lowest noise level on Planck, and is near the minimum of unresolved foreground emission. In this paper, we analyse the level of consistency achieved in the 2013 Planck data. We concentrate on comparisons between the 70, 100, and 143 GHz channel maps and power spectra, particularly over the angular scales of the first and second acoustic peaks, on maps masked for diffuse Galactic emission and for strong unresolved sources. Difference maps covering angular scales from 8° to 15′ are consistent with noise, and show no evidence of cosmic microwave background structure. Including small but important corrections for unresolved-source residuals, we demonstrate agreement (measured by deviation of the ratio from unity) between 70 and 100 GHz power spectra averaged over 70 ≤ ℓ ≤ 390 at the 0.8% level, and agreement between 143 and 100 GHz power spectra of 0.4% over the same ℓ range. These values are within and consistent with the overall uncertainties in calibration given in the Planck 2013 results. We also present results based on the 2013 likelihood analysis showing consistency at the 0.35% between the 100, 143, and 217 GHz power spectra. We analyse calibration procedures and beams to determine what fraction of these differences can be accounted for by known approximations or systematicerrors that could be controlled even better in the future, reducing uncertainties still further. Several possible small improvements are described. Subsequent analysis of the beams quantifies the importance of asymmetry in the near sidelobes, which was not fully accounted for initially, affecting the 70/100 ratio. Correcting for this, the 70, 100, and 143 GHz power spectra agree to 0.4% over the first two acoustic peaks. The likelihood analysis that produced the 2013 cosmological parameters incorporated uncertainties larger than this. We show explicitly that correction of the missing near sidelobe power in the HFI channels would result in shifts in the posterior distributions of parameters of less than 0.3σ except for As, the amplitude of the primordial curvature perturbations at 0.05 Mpc-1, which changes by about 1σ. We extend these comparisons to include the sky maps from the complete nine-year mission of the Wilkinson Microwave Anisotropy Probe (WMAP), and find a roughly 2% difference between the Planck and WMAP power spectra in the region of the first acoustic peak
The stellar mass function of galaxies in Planck-selected clusters at 0.5 < z < 0.7: new constraints on the timescale and location of satellite quenching
We study the abundance of star-forming and quiescent galaxies in a sample of
21 massive clusters at 0.5<z<0.7, detected with the Planck satellite. We
measure the cluster galaxy stellar mass function (SMF), which is a fundamental
observable to study and constrain the formation and evolution of galaxies. Our
measurements are based on homogeneous and deep multi-band photometry spanning
u- to the Ks-band for each cluster and are supported by spectroscopic data from
different programs. The galaxy population is separated between quiescent and
star-forming galaxies based on their rest-frame U-V and V-J colours. The SMF is
compared to that of field galaxies at the same redshifts, using data from the
COSMOS/UltraVISTA survey. We find that the shape of the SMF of star-forming
galaxies does not depend on environment, while the SMF of quiescent galaxies
has a significantly steeper low-mass slope in the clusters compared to the
field. We estimate the environmental quenching efficiency (f_EQ), i.e. the
probability for a galaxy that would normally be star forming in the field, to
be quenched due to its environment. The f_EQ shows no stellar-mass dependence
in any environment, but it increases from 40% in the cluster outskirts to ~90%
in the cluster centres. The radial signature of f_EQ provides constraints on
where the dominant quenching mechanism operates in these clusters and on what
timescale. Exploring these using a simple model based on galaxy orbits obtained
from an N-body simulation, we find a clear degeneracy between both parameters.
For example, the quenching process may either be triggered on a long (~3 Gyr)
time scale at large radii (r~8R_500), or happen well within 1 Gyr at r<R_500.
The radius where quenching is triggered is at least r_quench> 0.67R_500
(95%CL). The ICM density at this location suggests that ram-pressure stripping
of the cold gas is a likely cause of quenching. [Abridged]Comment: 16 pages, 12 figures, accepted for publication in A&
Planck intermediate results XXV. The Andromeda galaxy as seen by Planck
The Andromeda galaxy (M 31) is one of a few galaxies that has sufficient angular size on the sky to be resolved by the Planck satellite. Planck has detected M 31 in all of its frequency bands, and has mapped out the dust emission with the High Frequency Instrument, clearly resolving multiple spiral arms and sub-features. We examine the morphology of this long-wavelength dust emission as seen by Planck, including a study of its outermost spiral arms, and investigate the dust heating mechanism across M 31. We find that dust dominating the longer wavelength emission (greater than or similar to 0.3 mm) is heated by the diffuse stellar population (as traced by 3.6 mu m emission), with the dust dominating the shorter wavelength emission heated by a mix of the old stellar population and star-forming regions (as traced by 24 mu m emission). We also fit spectral energy distributions for individual 5\u27 pixels and quantify the dust properties across the galaxy, taking into account these different heating mechanisms, finding that there is a linear decrease in temperature with galactocentric distance for dust heated by the old stellar population, as would be expected, with temperatures ranging from around 22 K in the nucleus to 14 K outside of the 10 kpc ring. Finally, we measure the integrated spectrum of the whole galaxy, which we find to be well-fitted with a global dust temperature of (18.2 +/- 1.0) K with a spectral index of 1.62 +/- 0.11 (assuming a single modified blackbody), and a significant amount of free-free emission at intermediate frequencies of 20-60 GHz, which corresponds to a star formation rate of around 0.12 M-circle dot yr(-1). We find a 2.3 sigma detection of the presence of spinning dust emission, with a 30 GHz amplitude of 0.7 +/- 0.3 Jy, which is in line with expectations from our Galaxy
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