352 research outputs found
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
Detection of Anomalous Microwave Emission in the Pleiades Reflection Nebula with WMAP and the COSMOSOMAS Experiment
We present evidence for anomalous microwave emission (AME) in the Pleiades
reflection nebula, using data from the seven-year release of the Wilkinson
Microwave Anisotropy Probe (WMAP) and from the COSMOSOMAS experiment. The flux
integrated in a 1-degree radius around R.A.=56.24^{\circ}, Dec.=23.78^{\circ}
(J2000) is 2.15 +/- 0.12 Jy at 22.8 GHz, where AME is dominant. COSMOSOMAS data
show no significant emission, but allow to set upper limits of 0.94 and 1.58 Jy
(99.7% C.L.) respectively at 10.9 and 14.7 GHz, which are crucial to pin down
the AME spectrum at these frequencies, and to discard any other emission
mechanisms which could have an important contribution to the signal detected at
22.8 GHz. We estimate the expected level of free-free emission from an
extinction-corrected H-alpha template, while the thermal dust emission is
characterized from infrared DIRBE data and extrapolated to microwave
frequencies. When we deduct the contribution from these two components at 22.8
GHz the residual flux, associated with AME, is 2.12 +/- 0.12 Jy (17.7-sigma).
The spectral energy distribution from 10 to 60 GHz can be accurately fitted
with a model of electric dipole emission from small spinning dust grains
distributed in two separated phases of molecular and atomic gas, respectively.
The dust emissivity, calculated by correlating the 22.8 GHz data with
100-micron data, is found to be 4.36+/-0.17 muK/MJy/sr, a value that is rather
low compared with typical values in dust clouds. The physical properties of the
Pleiades nebula indicate that this is indeed a much less opaque object than
others were AME has usually been detected. This fact, together with the broad
knowledge of the stellar content of this region, provides an excellent testbed
for AME characterization in physical conditions different from those generally
explored up to now.Comment: Accepted for publication in ApJ. 12 pages, 8 figure
Detailed study of the microwave emission of the supernova remnant 3C 396
We have observed the supernova remnant 3C~396 in the microwave region using
the Parkes 64-m telescope. Observations have been made at 8.4 GHz, 13.5 GHz,
and 18.6 GHz and in polarisation at 21.5 GHz. We have used data from several
other observatories, including previously unpublished observations performed by
the Green Bank Telescope at 31.2 GHz, to investigate the nature of the
microwave emission of 3C 396. Results show a spectral energy distribution
dominated by a single component power law emission with . Data do not favour the presence of anomalous microwave emission coming
from the source. Polarised emission at 21.5 GHz is consistent with
synchrotron-dominated emission. We present microwave maps and correlate them
with infrared (IR) maps in order to characterise the interplay between thermal
dust and microwave emission. IR vs. microwave TT plots reveal poor correlation
between mid-infrared and microwave emission from the core of the source. On the
other hand, a correlation is detected in the tail emission of the outer shell
of 3C 396, which could be ascribed to Galactic contamination.Comment: published in MNRA
New radio observations of anomalous microwave emission in the HII region RCW175
We have observed the HII region RCW175 with the 64m Parkes telescope at
8.4GHz and 13.5GHz in total intensity, and at 21.5GHz in both total intensity
and polarization. High angular resolution, high sensitivity, and polarization
capability enable us to perform a detailed study of the different constituents
of the HII region. For the first time, we resolve three distinct regions at
microwave frequencies, two of which are part of the same annular diffuse
structure. Our observations enable us to confirm the presence of anomalous
microwave emission (AME) from RCW175. Fitting the integrated flux density
across the entire region with the currently available spinning dust models,
using physically motivated assumptions, indicates the presence of at least two
spinning dust components: a warm component with a relatively large hydrogen
number density n_H=26.3/cm^3 and a cold component with a hydrogen number
density of n_H=150/cm^3. The present study is an example highlighting the
potential of using high angular-resolution microwave data to break model
parameter degeneracies. Thanks to our spectral coverage and angular resolution,
we have been able to derive one of the first AME maps, at 13.5GHz, showing
clear evidence that the bulk of the AME arises in particular from one of the
source components, with some additional contribution from the diffuse
structure. A cross-correlation analysis with thermal dust emission has shown a
high degree of correlation with one of the regions within RCW175. In the center
of RCW175, we find an average polarized emission at 21.5GHz of
2.2\pm0.2(rand.)\pm0.3(sys.)% of the total emission, where we have included
both systematic and statistical uncertainties at 68% CL. This polarized
emission could be due to sub-dominant synchrotron emission from the region and
is thus consistent with very faint or non-polarized emission associated with
AME.Comment: Accepted for publication in the Astrophysical Journa
A VSA search for the extended Sunyaev-Zel'dovich Effect in the Corona Borealis Supercluster
We present interferometric imaging at 33 GHz of the Corona Borealis
supercluster, using the extended configuration of the Very Small Array. A total
area of 24 deg^2 has been imaged, with an angular resolution of 11 arcmin and a
sensitivity of 12 mJy/beam. The aim of these observations is to search for
Sunyaev-Zel'dovich (SZ) detections from known clusters of galaxies in this
supercluster and for a possible extended SZ decrement due to diffuse warm/hot
gas in the intercluster medium. We measure negative flux values in the
positions of the ten richest clusters in the region. Collectively, this implies
a 3.0-sigma detection of the SZ effect. In the clusters A2061 and A2065 we find
decrements of approximately 2-sigma. Our main result is the detection of two
strong and resolved negative features at -70+-12 mJy/beam (-157+-27 microK) and
-103+-10 mJy/beam (-230+-23 microK), respectively, located in a region with no
known clusters, near the centre of the supercluster. We discuss their possible
origins in terms of primordial CMB anisotropies and/or SZ signals related to
either unknown clusters or to a diffuse extended warm/hot gas distribution. Our
analyses have revealed that a primordial CMB fluctuation is a plausible
explanation for the weaker feature (probability of 37.82%). For the stronger
one, neither primordial CMB (probability of 0.33%) nor SZ can account alone for
its size and total intensity. The most reasonable explanation, then, is a
combination of both primordial CMB and SZ signal. Finally, we explore what
characteristics would be required for a filamentary structure consisting of
warm/hot diffuse gas in order to produce a significant contribution to such a
spot taking into account the constraints set by X-ray data.Comment: 16 pages, 10 figures. Accepted in MNRA
Radio source calibration for the VSA and other CMB instruments at around 30 GHz
Accurate calibration of data is essential for the current generation of CMB
experiments. Using data from the Very Small Array (VSA), we describe procedures
which will lead to an accuracy of 1 percent or better for experiments such as
the VSA and CBI. Particular attention is paid to the stability of the receiver
systems, the quality of the site and frequent observations of reference
sources. At 30 GHz the careful correction for atmospheric emission and
absorption is shown to be essential for achieving 1 percent precision. The
sources for which a 1 percent relative flux density calibration was achieved
included Cas A, Cyg A, Tau A and NGC7027 and the planets Venus, Jupiter and
Saturn. A flux density, or brightness temperature in the case of the planets,
was derived at 33 GHz relative to Jupiter which was adopted as the fundamental
calibrator. A spectral index at ~30 GHz is given for each. Cas A,Tau A, NGC7027
and Venus were examined for variability. Cas A was found to be decreasing at
percent per year over the period March 2001 to August 2004.
In the same period Tau A was decreasing at percent per year. A
survey of the published data showed that the planetary nebula NGC7027 decreased
at percent per year over the period 1967 to 2003. Venus showed
an insignificant ( percent) variation with Venusian illumination.
The integrated polarization of Tau A at 33 GHz was found to be
percent at pa .}Comment: 13 pages, 15 figures, submitted to MNRA
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