45 research outputs found
All-sky component separation in the presence of anisotropic noise and dust temperature variations
We present an extension of the harmonic-space maximum-entropy component
separation method (MEM) for multi-frequency CMB observations that allows one to
perform the separation with more plausible assumptions about the receiver noise
and foreground astrophysical components. Component separation is considered in
the presence of spatially-varying noise variance and spectral properties of the
foreground components. It is shown that, if not taken properly into account,
the presence of spatially-varying foreground spectra, in particular, can
severely reduce the accuracy of the component separation. Nevertheless, by
extending the basic method to accommodate such behaviour and the presence of
anisotropic noise, we find that the accuracy of the component separation can be
improved to a level comparable with previous investigations in which these
effects were not present.Comment: 11 pages, 15 figures, submitted to MNRAS. A fine-resolution colour
copy can be downloaded from http://www.mrao.cam.ac.uk/projects/cpac/pub.htm
"Author! Author!" : Shakespeare and biography
Original article can be found at: http://www.informaworld.com/smpp/title~content=t714579626~db=all Copyright Informa / Taylor & Francis Group. DOI: 10.1080/17450910902764454Since 1996, not a year has passed without the publication of at least one Shakespeare biography. Yet for many years the place of the author in the practice of understanding literary works has been problematized, and even on occasions eliminated. Criticism reads the âworksâ, and may or may not refer to an author whose âlifeâ contributed to their meaning. Biography seeks the author in the works, the personality that precedes the works and gives them their characteristic shape and meaning. But the form of literary biography addresses the unusual kind of âlifeâ that puts itself into âworksâ, and this is particularly challenging where the âworksâ predominate massively over the salient facts of the âlifeâ. This essay surveys the current terrain of Shakespeare biography, and considers the key questions raised by the medium: can we know anything of Shakespeare's âpersonalityâ from the facts of his life and the survival of his works? What is the status of the kind of speculation that inevitably plays a part in biographical reconstruction? Are biographers in the end telling us as much about themselves as they tell us about Shakespeare?Peer reviewe
A blind detection of a large, complex, Sunyaev--Zel'dovich structure
We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of
the Arcminute Microkelvin Imager (AMI) 'blind', degree-square fields to have
been observed down to our target sensitivity of 100{\mu}Jy/beam. In follow-up
deep pointed observations the SZ effect is detected with a maximum peak
decrement greater than 8 \times the thermal noise. No corresponding emission is
visible in the ROSAT all-sky X-ray survey and no cluster is evident in the
Palomar all-sky optical survey. Compared with existing SZ images of distant
clusters, the extent is large (\approx 10') and complex; our analysis favours a
model containing two clusters rather than a single cluster. Our Bayesian
analysis is currently limited to modelling each cluster with an ellipsoidal or
spherical beta-model, which do not do justice to this decrement. Fitting an
ellipsoid to the deeper candidate we find the following. (a) Assuming that the
Evrard et al. (2002) approximation to Press & Schechter (1974) correctly gives
the number density of clusters as a function of mass and redshift, then, in the
search area, the formal Bayesian probability ratio of the AMI detection of this
cluster is 7.9 \times 10^4:1; alternatively assuming Jenkins et al. (2001) as
the true prior, the formal Bayesian probability ratio of detection is 2.1
\times 10^5:1. (b) The cluster mass is MT,200 = 5.5+1.2\times 10^14h-1M\odot.
(c) Abandoning a physical model with num- -1.3 70 ber density prior and instead
simply modelling the SZ decrement using a phenomenological {\beta}-model of
temperature decrement as a function of angular distance, we find a central SZ
temperature decrement of -295+36 {\mu}K - this allows for CMB primary
anisotropies, receiver -15 noise and radio sources. We are unsure if the
cluster system we observe is a merging system or two separate clusters.Comment: accepted MNRAS. 12 pages, 9 figure
Probing the cosmic microwave background temperature using the Sunyaev-Zeldovich effect
We discuss the possibility to constrain the relation between redshift and
temperature of the cosmic microwave background (CMB) using multifrequency
Sunyaev-Zeldovich (SZ) observations. We have simulated a catalog of clusters of
galaxies detected through their SZ signature assuming the sensitivities that
will be achieved by the {\it Planck} satellite at 100, 143 and 353 GHz, taking
into account the instrumental noise and the contamination from the Cosmic
Infrared Background and from unresolved radiosources. We have parametrized the
cosmological temperature-redshift law as . Using two
sets of SZ flux density ratios (100/143 GHz, which is most sensitive to the
parametrization of the law, and 143/353 GHz, which is most sensitive to
the peculiar velocities of the clusters) we show that it is possible to recover
the law assuming that the temperatures and redshifts of the clusters are
known. From a simulated catalog of clusters, the parameter can
be recovered to an accuracy of 10. Sensitive SZ observations thus appear
as a potentially useful tool to test the standard law. Most cosmological models
predict a linear variation of the CMB temperature with redshift. The discovery
of an alternative law would have profound implications on the cosmological
model, implying creation of energy in a manner that would still maintain the
black-body shape of the CMB spectrum at redshift zero.Comment: 8 pages, 9 figures, submitted to A&
The XMM Cluster Survey: Forecasting cosmological and cluster scaling-relation parameter constraints
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.Comment: 28 pages, 17 figures. Revised version, as accepted for publication in
MNRAS. High-resolution figures available at http://xcs-home.org (under
"Publications"
Statistics of the Sunyaev-Zel'dovich Effect power spectrum
Using large numbers of simulations of the microwave sky, incorporating the
Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich (SZ) effect due to
clusters, we investigate the statistics of the power spectrum at microwave
frequencies between spherical multipoles of 1000 and 10000. From these virtual
sky maps, we find that the spectrum of the SZ effect has a larger standard
deviation by a factor of 3 than would be expected from purely Gaussian
realizations, and has a distribution that is significantly skewed towards
higher values, especially when small map sizes are used. The standard deviation
is also increased by around 10 percent compared to the trispectrum calculation
due to the clustering of galaxy clusters. We also consider the effects of
including residual point sources and uncertainties in the gas physics. This has
implications for the excess power measured in the CMB power spectrum by the
Cosmic Background Imager and BIMA experiments. Our results indicate that the
observed excess could be explained using a lower value of than
previously suggested, however the effect is not enough to match
. The uncertainties in the gas physics could also play a
substantial role. We have made our maps of the SZ effect available online.Comment: 21 pages, 23 figures, 3 tables. Accepted by MNRAS. We have made our
maps of the SZ effect available onlin