14,457 research outputs found
Addendum to "Superimposed Oscillations in the WMAP Data?"
We elaborate further on the possibility that the inflationary primordial
power spectrum contains superimposed oscillations. We study various effects
which could influence the calculation of the multipole moments in this case. We
also present the theoretical predictions for two other cosmological
observables, the matter power spectrum and the EE polarization channel.Comment: 4 pages, 3 figures, uses RevTex4, matches published versio
Viking orbiter stereo imaging catalog
The extremely long mission of the two Viking Orbiter spacecraft produced a wealth of photos of surface features. Many of these photos can be used to form stereo images allowing the student of Mars to examine a subject in three dimensional. This catalog is a technical guide to the use of stereo coverage within the complex Viking imaging data set
The Canis Major Dwarf Galaxy
Recent observational evidence suggests that the Sagittarius dwarf galaxy
represents the only major ongoing accretion event in the Galactic halo,
accounting for the majority of stellar debris identified there. This paper
summarizes the recent discovery of another potential Milky Way accretion event,
the Canis Major dwarf galaxy. This dwarf satellite galaxy is found to lie just
below the Galactic plane and appears to be on an equatorial orbit. Unlike
Sagittarius, which is contributing to the Galactic halo, the location and
eventual demise of Canis Major suggests that it represents a building block of
the thick disk.Comment: Refereed contribution to "Structure & Dynamics in the Local Universe,
a workshop to honour Brent Tully's 60th birthday", Nov 2003. 4 pages + 2
figures (quality reduced due to size restrictions). To appear in PAS
Correcting the influence of an asymmetric line spread function in 2-degree Field spectrograph data
We investigate the role of asymmetries in the line spread function of the
2-degree field spectrograph and the variations in these asymmetries with the
CCD, the plate, the time of observation and the fibre. A data-reduction
pipeline is developed that takes these deformations into account for the
calibration and cross-correlation of the spectra. We show that, using the
emission lines of calibration lamp observations, we can fit the line spread
function with the sum of two Gaussian functions representing the theoretical
signal and a perturbation of the system. This model is then used to calibrate
the spectra and generate templates by downgrading high resolution spectra.
Thus, we can cross-correlate the observed spectra with templates degraded in
the same way. Our reduction pipeline is tested on real observations and
provides a significant improvement in the accuracy of the radial velocities
obtained. In particular, the systematic errors that were as high as ~20 km/s
when applying the AAO reduction package 2dfDR are now reduced to ~5 km/s. Even
though the 2-degree Field spectrograph is to be decommissioned at the end of
2005, the analysis of archival data and previous studies could be improved by
the reduction procedure we propose here.Comment: 9 pages, 9 figures, accepted to PASA, minor change
CMB power spectrum parameter degeneracies in the era of precision cosmology
Cosmological parameter constraints from the CMB power spectra alone suffer
several well-known degeneracies. These degeneracies can be broken by numerical
artefacts and also a variety of physical effects that become quantitatively
important with high-accuracy data e.g. from the Planck satellite. We study
degeneracies in models with flat and non-flat spatial sections, non-trivial
dark energy and massive neutrinos, and investigate the importance of various
physical degeneracy-breaking effects. We test the CAMB power spectrum code for
numerical accuracy, and demonstrate that the numerical calculations are
accurate enough for degeneracies to be broken mainly by true physical effects
(the integrated Sachs-Wolfe effect, CMB lensing and geometrical and other
effects through recombination) rather than numerical artefacts. We quantify the
impact of CMB lensing on the power spectra, which inevitably provides
degeneracy-breaking information even without using information in the
non-Gaussianity. Finally we check the numerical accuracy of sample-based
parameter constraints using CAMB and CosmoMC. In an appendix we document recent
changes to CAMB's numerical treatment of massive neutrino perturbations, which
are tested along with other recent improvements by our degeneracy exploration
results.Comment: 27 pages, 28 figures. Latest CAMB version available from
http://camb.info/. Reduced number of figures, plot legend corrected and minor
edits to match published versio
The PAndAS view of the Andromeda satellite system - I. A Bayesian search for dwarf galaxies using spatial and color-magnitude information
We present a generic algorithm to search for dwarf galaxies in photometric
catalogs and apply it to the Pan-Andromeda Archaeological Survey (PAndAS). The
algorithm is developed in a Bayesian framework and, contrary to most
dwarf-galaxy-search codes, makes use of both the spatial and color-magnitude
information of sources in a probabilistic approach. Accounting for the
significant contamination from the Milky Way foreground and from the structured
stellar halo of the Andromeda galaxy, we recover all known dwarf galaxies in
the PAndAS footprint with high significance, even for the least luminous ones.
Some Andromeda globular clusters are also recovered and, in one case,
discovered. We publish a list of the 143 most significant detections yielded by
the algorithm. The combined properties of the 39 most significant isolated
detections show hints that at least some of these trace genuine dwarf galaxies,
too faint to be individually detected. Follow-up observations by the community
are mandatory to establish which are real members of the Andromeda satellite
system. The search technique presented here will be used in an upcoming
contribution to determine the PAndAS completeness limits for dwarf galaxies.
Although here tuned to the search of dwarf galaxies in the PAndAS data, the
algorithm can easily be adapted to the search for any localised overdensity
whose properties can be modeled reliably in the parameter space of any catalog.Comment: 20 pages, 16 figures, 1 table; accepted for publication in ApJ. High
res pdf available at
https://www.dropbox.com/s/7zk7pme2wunwkjv/PAndAS_dwarf_galaxies.pd
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