12,395 research outputs found
CMB Likelihood Functions for Beginners and Experts
Although the broad outlines of the appropriate pipeline for cosmological
likelihood analysis with CMB data has been known for several years, only
recently have we had to contend with the full, large-scale, computationally
challenging problem involving both highly-correlated noise and extremely large
datasets (). In this talk we concentrate on the beginning and end of
this process. First, we discuss estimating the noise covariance from the data
itself in a rigorous and unbiased way; this is essentially an iterated
minimum-variance mapmaking approach. We also discuss the unbiased determination
of cosmological parameters from estimates of the power spectrum or experimental
bandpowers.Comment: Long-delayed submission. In AIP Conference Proceedings "3K Cosmology"
held in Rome, Oct 5-10, 1998, edited by Luciano Maiani, Francesco Melchiorri
and Nicola Vittorio, 343-347, New York, American Institute of Physics 199
Constraining Large Scale Structure Theories with the Cosmic Background Radiation
We review the relevant 10+ parameters associated with inflation and matter
content; the relation between LSS and primary and secondary CMB anisotropy
probes; COBE constraints on energy injection; current anisotropy band-powers
which strongly support the gravitational instability theory and suggest the
universe could not have reionized too early. We use Bayesian analysis methods
to determine what current CMB and CMB+LSS data imply for inflation-based
Gaussian fluctuations in tilted CDM, hCDM and oCDM model
sequences with age 11-15 Gyr, consisting of mixtures of baryons, cold (and
possibly hot) dark matter, vacuum energy, and curvature energy in open
cosmologies. For example, we find the slope of the initial spectrum is within
about 5% of the (preferred) scale invariant form when just the CMB data is
used, and for CDM when LSS data is combined with CMB; with both, a
nonzero value of is strongly preferred ( for a 13
Gyr sequence, similar to the value from SNIa). The CDM sequence prefers
, but is overall much less likely than the flat
sequence with CMB+LSS. We also review the rosy forecasts
of angular power spectra and parameter estimates from future balloon and
satellite experiments when foreground and systematic effects are ignored.Comment: 20 pages, LaTeX, 5 figures, 2 tables, uses rspublic.sty To appear in
Philosophical Transactions of the Royal Society of London A, 1998.
"Discussion Meeting on Large Scale Structure in the Universe," Royal Society,
London, March 1998. Text and colour figures also available at
ftp://ftp.cita.utoronto.ca/bond/roysoc9
The Exotic Eclipsing Nucleus of the Ring Planetary Nebula SuWt2
SuWt2 is a planetary nebula (PN) consisting of a bright ionized thin ring
seen nearly edge-on. It has a bright (V=12) central star, too cool to ionize
the PN, which we discovered to be an eclipsing binary. A spectrum from IUE did
not reveal a UV source. We present extensive ground-based photometry and
spectroscopy of the central binary collected over the ensuing two decades,
resulting in the determination that the orbital period of the eclipsing pair is
4.9 d, and consists of two nearly identical A1 V stars, each of mass ~2.7
M_sun. The physical parameters of the A stars, combined with evolutionary
tracks, show that both are in the short-lived "blue-hook" evolutionary phase
that occurs between the main sequence and the Hertzsprung gap, and that the age
of the system is about 520 Myr. One puzzle is that the stars' rotational
velocities are different from each other, and considerably slower than
synchronous with the orbital period. It is possible that the center-of-mass
velocity of the eclipsing pair is varying with time, suggesting that there is
an unseen third orbiting body in the system. We propose a scenario in which the
system began as a hierarchical triple, consisting of a ~2.9 M_sun star orbiting
the close pair of A stars. Upon reaching the AGB stage, the primary engulfed
the pair into a common envelope, leading to a rapid contraction of the orbit
and catastrophic ejection of the envelope into the orbital plane. In this
picture, the exposed core of the initial primary is now a white dwarf of ~0.7
M_sun, orbiting the eclipsing pair, which has already cooled below the
detectability possible by IUE at our derived distance of 2.3 kpc and a
reddening of E(B-V)=0.40. The SuWt2 system may be destined to perish as a Type
Ia supernova. (Abridged)Comment: 60 pages, 11 figure, to appear in the Astronomical Journa
Simulation of seismic events induced by CO2 injection at In Salah, Algeria
Date of Acceptance: 18/06/2015 Acknowledgments The authors would like to thank the operators of the In Salah JV and JIP, BP, Statoil and Sonatrach, for providing the data shown in this paper, and for giving permission to publish. Midland Valley Exploration are thanked for the use of their Move software for geomechanical restoration. JPV is a Natural Environment Research Council (NERC) Early Career Research Fellow (Grant NE/I021497/1) and ALS is funded by a NERC Partnership Research Grant (Grant NE/I010904).Peer reviewedPublisher PD
The Evolution of the Cosmic Microwave Background
We discuss the time dependence and future of the Cosmic Microwave Background
(CMB) in the context of the standard cosmological model, in which we are now
entering a state of endless accelerated expansion. The mean temperature will
simply decrease until it reaches the effective temperature of the de Sitter
vacuum, while the dipole will oscillate as the Sun orbits the Galaxy. However,
the higher CMB multipoles have a richer phenomenology. The CMB anisotropy power
spectrum will for the most part simply project to smaller scales, as the
comoving distance to last scattering increases, and we derive a scaling
relation that describes this behaviour. However, there will also be a dramatic
increase in the integrated Sachs-Wolfe contribution at low multipoles. We also
discuss the effects of tensor modes and optical depth due to Thomson
scattering. We introduce a correlation function relating the sky maps at two
times and the closely related power spectrum of the difference map. We compute
the evolution both analytically and numerically, and present simulated future
sky maps.Comment: 23 pages, 11 figures; references added; one figure dropped and minor
changes to match published version. For high-resolution versions of figures
and animations, see http://www.astro.ubc.ca/people/scott/future.htm
The Imprint of Gravitational Waves on the Cosmic Microwave Background
Long-wavelength gravitational waves can induce significant temperature
anisotropy in the cosmic microwave background. Distinguishing this from
anisotropy induced by energy density fluctuations is critical for testing
inflationary cosmology and theories of large-scale structure formation. We
describe full radiative transport calculations of the two contributions and
show that they differ dramatically at angular scales below a few degrees. We
show how anisotropy experiments probing large- and small-angular scales can
combine to distinguish the imprint due to gravitational waves.Comment: 11 pages, Penn Preprint-UPR-
Statistics of Dark Matter Halos from Gravitational Lensing
We present a new approach to measure the mass function of dark matter halos
and to discriminate models with differing values of Omega through weak
gravitational lensing. We measure the distribution of peaks from simulated
lensing surveys and show that the lensing signal due to dark matter halos can
be detected for a wide range of peak heights. Even when the signal-to-noise is
well below the limit for detection of individual halos, projected halo
statistics can be constrained for halo masses spanning galactic to cluster
halos. The use of peak statistics relies on an analytical model of the noise
due to the intrinsic ellipticities of source galaxies. The noise model has been
shown to accurately describe simulated data for a variety of input ellipticity
distributions. We show that the measured peak distribution has distinct
signatures of gravitational lensing, and its non-Gaussian shape can be used to
distinguish models with different values of Omega. The use of peak statistics
is complementary to the measurement of field statistics, such as the
ellipticity correlation function, and possibly not susceptible to the same
systematic errors.Comment: 5 pages, 4 figures, matches version accepted for ApJ
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