3,834 research outputs found
The Kinematic Composition of MgII Absorbers
The study of galaxy evolution using quasar absorption lines requires an
understanding of what components of galaxies and their surroundings are
contributing to the absorption in various transitions. This paper considers the
kinematic composition of the class of 0.4 < z < 1.0 MgII absorbers,
particularly addressing the question of what fraction of this absorption is
produced in halos and what fraction arises from galaxy disks. We design models
with various fractional contributions from radial infall of halo material and
from a rotating thick disk component. We generate synthetic spectra from lines
of sight through model galaxies and compare the resulting ensembles of MgII
profiles with the 0.4 < z < 1.0 sample observed with HIRES/Keck. We apply a
battery of statistical tests and find that pure disk and pure halo models can
be ruled out, but that various models with rotating disk and infall/halo
contributions can produce an ensemble that is nearly consistent with the data.
A discrepancy in all models that we considered requires the existence of a
kinematic component intermediate between halo and thick disk. The variety of
MgII profiles can be explained by the gas in disks and halos of galaxies not
very much different than galaxies in the local Universe.
In any one case there is considerable ambiguity in diagnosing the kinematic
composition of an absorber from the low ionization high resolution spectra
alone. Future data will allow galaxy morphologies, impact parameters, and
orientations, FeII/MgII of clouds, and the distribution of high ionization gas
to be incorporated into the kinematic analysis. Combining all these data will
permit a more accurate diagnosis of the physical conditions along the line of
sight through the absorbing galaxy.Comment: 34 pages including 14 postscript figures; Accepted by the
Astrophysical Journal; URL http://www.astro.psu.edu/users/cwc/pubs.htm
Effect of pooling samples on the efficiency of comparative studies using microarrays
Many biomedical experiments are carried out by pooling individual biological
samples. However, pooling samples can potentially hide biological variance and
give false confidence concerning the data significance. In the context of
microarray experiments for detecting differentially expressed genes, recent
publications have addressed the problem of the efficiency of sample-pooling,
and some approximate formulas were provided for the power and sample size
calculations. It is desirable to have exact formulas for these calculations and
have the approximate results checked against the exact ones. We show that the
difference between the approximate and exact results can be large. In this
study, we have characterized quantitatively the effect of pooling samples on
the efficiency of microarray experiments for the detection of differential gene
expression between two classes. We present exact formulas for calculating the
power of microarray experimental designs involving sample pooling and technical
replications. The formulas can be used to determine the total numbers of arrays
and biological subjects required in an experiment to achieve the desired power
at a given significance level. The conditions under which pooled design becomes
preferable to non-pooled design can then be derived given the unit cost
associated with a microarray and that with a biological subject. This paper
thus serves to provide guidance on sample pooling and cost effectiveness. The
formulation in this paper is outlined in the context of performing microarray
comparative studies, but its applicability is not limited to microarray
experiments. It is also applicable to a wide range of biomedical comparative
studies where sample pooling may be involved.Comment: 8 pages, 1 figure, 2 tables; to appear in Bioinformatic
Preface: symposium on progressive politics
Introduction to a special issue of Political Studies Review, based on papers presented at a conference on ‘Progressivism: Past and Present’ held at Senate House in London on 3 July 2012
Fluid physics, thermodynamics, and heat transfer experiments in space
An overstudy committee was formed to study and recommend fundamental experiments in fluid physics, thermodynamics, and heat transfer for experimentation in orbit, using the space shuttle system and a space laboratory. The space environment, particularly the low-gravity condition, is an indispensable requirement for all the recommended experiments. The experiments fell broadly into five groups: critical-point thermophysical phenomena, fluid surface dynamics and capillarity, convection at reduced gravity, non-heated multiphase mixtures, and multiphase heat transfer. The Committee attempted to assess the effects of g-jitter and other perturbations of the gravitational field on the conduct of the experiments. A series of ground-based experiments are recommended to define some of the phenomena and to develop reliable instrumentation
On the Spatial and Kinematic Distributions of Mg II Absorbing Gas in <z>=0.7 Galaxies
(Abridged) We present HIRES/Keck spectra having resolution 6 km/s of Mg II
2796 absorption profiles which arise in the gas associated with 15 identified
galaxies over the redshift range 0.5 < z < 0.9. Using non-parametric rank
correlation tests, we searched for correlations of the absorption strengths,
saturation, and line-of-sight kinematics with the galaxy redshifts, rest frame
B and K luminosities, rest colors, and impact parameters D. We found no
correlations at the 2.5-sigma level between these properties. Of primary
significance is the fact that the QSO-galaxy impact parameter apparently does
not provide the primary distinguishing factor by which absorption properties
can be characterized. The galaxy absorption properties exhibit a large scatter,
which, we argue, is suggestive of a picture in which the gas arises from a
variety of on-going dynamical events. Inferences from our study include: (1)
The spatial distribution of absorbing gas in galaxies does not appear to follow
a simple galactocentric functional dependence. (2) A single systematic
kinematic model apparently cannot describe the observed velocity spreads in the
absorbing gas. It is more that a heterogeneous population of sub-galaxy scale
structures are giving rise to the observed cloud velocities. (3) The absorbing
gas spatial distribution and kinematics may depend upon gas producing events
and mechanisms that are recent to the epoch at which the absorption is
observed. These distributions likely change over a few Gyr timescale. Based
upon these inferences, we note that any evolution in the absorption gas
properties over a larger redshift range should be directly quantifiable from a
larger dataset of high-resolution absorption profiles.Comment: uuencoded: 22 pages, AASTeX file, 5 encapsulated PostScript figures;
Accepted for publication in The Astrophysical Journal; Also available for
pick-up at http://www.ucolick.org/~cwc/qso/abstract.htm
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