1,299 research outputs found
On the Presence of Thermal SZ Induced Signal in the First Year WMAP Temperature Maps
Using available optical and X-ray catalogues of clusters and superclusters of
galaxies, we build templates of tSZ emission as they should be detected by the
WMAP experiment. We compute the cross-correlation of our templates with WMAP
temperature maps, and interpret our results separately for clusters and for
superclusters of galaxies. For clusters of galaxies, we claim 2-5
detections in our templates built from BCS Ebeling et al. (1998), NORAS
(Boehringer et al. 2000) and de Grandi et al. (1999) catalogues. In these
templates, the typical cluster temperature decrements in WMAP maps are around
15-35 K in the RJ range (no beam deconvolution applied). Several tests
probing the possible influence of foregrounds in our analyses demonstrate that
our results are robust against galactic contamination. On supercluster scales,
we detect a diffuse component in the V & W WMAP bands which cannot be generated
by superclusters in our catalogues (Einasto et al. 1994, 1997), and which is
not present in the clean map of Tegmark, de Oliveira-Costa & Hamilton (2003).
Using this clean map, our analyses yield, for Einasto's supercluster
catalogues, the following upper limit for the comptonization parameter
associated to supercluster scales: y_{SC} < 2.18 \time s 10^{-8} at the 95%
confidence limit.Comment: MNRAS accepted. New section and minor changes include
Limits on Hot Intracluster Gas Contributions to the Tenerife Temperature Anisotropy Map
We limit the contribution of the hot intracluster gas, by means of the
Sunyaev-Zel'dovich effect, to the temperature anisotropies measured by the
Tenerife experiment. The data is cross-correlated with maps generated from the
ACO cluster catalogue, the ROSAT PSPC catalogue of clusters of galaxies, a
catalogue of superclusters and the HEAO 1 A-1 map of X-ray sources. There is no
evidence of contamination by such sources at an rms level of K at
99% confidence level at angular resolution. We place an upper limit on
the mean Comptonization parameter of at the same
level of confidence. These limits are slightly more restrictive than those
previously found by a similar analysis on the COBE/DMR data and indicate that
most of the signal measured by Tenerife is cosmological.Comment: To be published in ApJ (main journal
The origin of the LMC stellar bar: clues from the SFH of the bar and inner disk
We discuss the origin of the LMC stellar bar by comparing the star formation
histories (SFH) obtained from deep color-magnitude diagrams (CMDs) in the bar
and in a number of fields in different directions within the inner disk. The
CMDs, reaching the oldest main sequence turnoffs in these very crowded fields,
have been obtained with VIMOS on the VLT in service mode, under very good
seeing conditions. We show that the SFHs of all fields share the same patterns,
with consistent variations of the star formation rate as a function of time in
all of them. We therefore conclude that no specific event of star formation can
be identified with the formation of the LMC bar, which instead likely formed
from a redistribution of disk material that occurred when the LMC disk became
bar unstable, and shared a common SFH with the inner disk thereafter. The
strong similarity between the SFH of the center and edge of the bar rules out
significant spatial variations of the SFH across the bar, which are predicted
by scenarios of classic bar formation through buckling mechanisms.Comment: MNRAS Letters, accepte
Radial velocities and metallicities from infrared Ca II triplet spectroscopy of open clusters II. Berkeley 23, King 1, NGC 559, NGC 6603 and NGC 7245
Context: Open clusters are key to studying the formation and evolution of the
Galactic disc. However, there is a deficiency of radial velocity and chemical
abundance determinations for open clusters in the literature. Aims: We intend
to increase the number of determinations of radial velocities and metallicities
from spectroscopy for open clusters. Methods: We acquired medium-resolution
spectra (R~8000) in the infrared region Ca II triplet lines (~8500 AA) for
several stars in five open clusters with the long-slit IDS spectrograph on the
2.5~m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain).
Radial velocities were obtained by cross-correlation fitting techniques. The
relationships available in the literature between the strength of infrared Ca
II lines and metallicity were also used to derive the metallicity for each
cluster. Results: We obtain = 48.6+/-3.4, -58.4+/-6.8, 26.0+/-4.3 and
-65.3+/-3.2 km s-1 for Berkeley 23, NGC 559, NGC 6603 and NGC 7245,
respectively. We found [Fe/H] =-0.25+/-0.14 and -0.15+/-0.18 for NGC 559 and
NGC 7245, respectively. Berkeley 23 has a low metallicity, [Fe/H]
=-0.42+/-0.13, similar to other open clusters in the outskirts of the Galactic
disc. In contrast, we derived a high metallicity ([Fe/H] =+0.43+/-0.15) for NGC
6603, which places this system among the most metal rich known open clusters.
To our knowledge, this is the first determination of radial velocities and
metallicities from spectroscopy for these clusters, except NGC 6603, for which
radial velocities had been previously determined. We have also analysed ten
stars in the line of sight to King 1. Because of the large dispersion obtained
in both radial velocity and metallicity, we cannot be sure that we have sampled
true cluster members.Comment: 10 pages, 5 figures, accepted for publication in A&A (minor
modifications
Implementation of a Fourier Matched Filter in CMB Analyses. Application to ISW Studies
Aims: Implement a matched filter (MF) cross-correlation algorithm in
multipole space and compare it to the standard Angular Cross Power Spectrum
(ACPS) method. Apply both methods on a Integrated Sachs Wolfe (ISW) - Large
Scale Structure (LSS) cross correlation scenario and study how sky masks
influence the multipole range where signal arises and its comparison to
theoretical predictions.
Methods: The MF requires the inversion of a multipole covariance matrix that
if is generally non-diagonal and singular. We use a SVD
approach that focuses on those modes carrying most of the information. We
compare the MF to the ACPS in ISW-LSS Monte Carlo simulations, paying attention
on the effect that a limited sky coverage has on the cross-correlation results.
Results: Within the linear data model for which the MF is defined, the MF
performs comparatively better than the ACPS for smaller values of and
scale dependent (non-Poissonian) noise fields. In the context of ISW studies
both methods are comparable, although the MF performs slightly more sensitively
under more restrictive masks. A preliminary study predicts that most of the
ISW--LSS cross correlation S/N ratio should be found in the very large scales
(50% of the S/N at , 90% at ), and this is confirmed by
Monte Carlo simulations. The statistical significance of our cross-correlation
statistics reaches its maximum when considering , with
for all values of observed, despite of the
smoothing and power aliasing that aggressive masks introduce in Fourier space.
This -confinement of the ISW-LSS cross correlation should enable a safe
distinction from other secondary effects arising at smaller angular scales.Comment: 9 pages, 5 figures, submitted to A&
Missing baryons, bulk flows and the E-mode polarization of the Cosmic Microwave Background
If the peculiar motion of galaxy groups and clusters indeed resembles that of
the surrounding baryons, then the kinetic Sunyaev-Zel'dovich (kSZ) pattern of
those massive halos should be closely correlated to the kSZ pattern of all
surrounding electrons. Likewise, it should also be correlated to the CMB E-mode
polarization field generated via Thomson scattering after reionization. We
explore the cross-correlation of the kSZ generated in groups and clusters to
the all sky E-mode polarization in the context of upcoming CMB experiments like
Planck, ACT, SPT or APEX. We find that this cross-correlation is effectively
probing redshifts below (where most of baryons cannot be seen), and
that it arises in the very large scales (). The significance with which
this cross-correlation can be measured depends on the Poissonian uncertainty
associated to the number of halos where the kSZ is measured and on the accuracy
of the kSZ estimations themselves. Assuming that Planck can provide a cosmic
variance limited E-mode polarization map at and S/N kSZ
estimates can be gathered for all clusters more massive than , then this cross-correlation should be measured at the 2--3
level. Further, if an all-sky ACT or SPT type CMB experiment provides similar
kSZ measurements for all halos above , then the
cross-correlation total signal to noise (S/N) ratio should be at the level of
4--5. A detection of this cross-correlation would provide direct and definite
evidence of bulk flows and missing baryons simultaneously.Comment: 6 pages, 2 figures, submitted to A&
The Effect of Hot Gas in WMAP's First Year Data
By cross-correlating templates constructed from the 2 Micron All Sky Survey
(2MASS) Extended Source (XSC) catalogue with WMAP's first year data, we search
for the thermal Sunyaev-Zel'dovich signature induced by hot gas in the local
Universe. Assuming that galaxies trace the distribution of hot gas, we select
regions on the sky with the largest projected density of galaxies. Under
conservative assumptions on the amplitude of foreground residuals, we find a
temperature decrement of -35 7 K ( detection level,
the highest reported so far) in the 26 square degrees of the sky
containing the largest number of galaxies per solid angle. We show that most of
the reported signal is caused by known galaxy clusters which, when convolved
with the average beam of the WMAP W band channel, subtend a typical angular
size of 20--30 arcmins. Finally, after removing from our analyses all pixels
associated with known optical and X-ray galaxy clusters, we still find a tSZ
decrement of -96 37 K in pixels subtending about 0.8 square
degrees on the sky. Most of this signal is coming from five different cluster
candidates in the Zone of Avoidance (ZoA), present in the Clusters In the ZoA
(CIZA) catalogue. We found no evidence that structures less bound than clusters
contribute to the tSZ signal present in the WMAP data.Comment: 10 pages, 4 figures, matches accepted version in ApJ Letter
On the Number Density of Sunyaev-Zel'dovich Clusters of Galaxies
If the mean properties of clusters of galaxies are well described by the
entropy-driven model, the distortion induced by the cluster population on the
blackbody spectrum of the Cosmic Microwave Background radiation is proportional
to the total amount of intracluster gas while temperature anisotropies are
dominated by the contribution of clusters of about 10^{14} solar masses. This
result depends marginally on cluster parameters and it can be used to estimate
the number density of clusters with enough hot gas to produce a detectable
Sunyaev-Zel'dovich effect. Comparing different cosmological models, the
relation depends mainly on the density parameter Omega_m. If the number density
of clusters could be estimated by a different method, then this dependence
could be used to constrain Omega_m.Comment: 8 pages, 3 figures, submitted to ApJ Letter
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