48 research outputs found
The Standard Cosmology
These lectures provide an introductory review of big bang cosmology. I
discuss the expanding Friedmann-Robertson-Walker universe, summarizing the
observational evidence which has led to its adoption as the `standard'
cosmological model and reviewing its basic properties. Subsequent lectures
provide an overview of the early universe. The final lectures give an
introduction to the inflationary universe, beginning with the motivating
puzzles of the standard cosmology (the horizon and flatness problems) and
ending with the inflationary production of quantum field fluctuations and their
possible role in seeding the large-scale structure of the Universe.Comment: 49 pages, uuencoded postscript file (includes 7 figures),
Fermilab-Conf-94/090-
Loop Corrections in Non-Linear Cosmological Perturbation Theory II. Two-point Statistics and Self-Similarity
We calculate the lowest-order non-linear contributions to the power spectrum,
two-point correlation function, and smoothed variance of the density field, for
Gaussian initial conditions and scale-free initial power spectra, . These results extend and in some cases correct previous work in the
literature on cosmological perturbation theory. Comparing with the scaling
behavior observed in N-body simulations, we find that the validity of
non-linear perturbation theory depends strongly on the spectral index . For
, we find excellent agreement over scales where the variance \sigma^2(R)
\la 10; however, for , perturbation theory predicts deviations from
self-similar scaling (which increase with ) not seen in numerical
simulations. This anomalous scaling suggests that the principal assumption
underlying cosmological perturbation theory, that large-scale fields can be
described perturbatively even when fluctuations are highly non-linear on small
scales, breaks down beyond leading order for spectral indices . For
, the power spectrum, variance, and correlation function in the scaling
regime can be calculated using dimensional regularization.Comment: 48 pages, 19 figures, uses axodraw.sty; also available at
http://fnas08.fnal.gov
The Effect of Splashback on Weak Lensing Mass Estimates of Galaxy Clusters and Groups
The splashback radius of a dark matter halo, which corresponds to the first
apocenter radius reached by infalling matter and substructures, has been
detected around galaxy clusters using a multitude of observational methods,
including weak lensing measurements. In this manuscript, we present how the
splashback feature in the halo density profile affects galaxy cluster masses
derived through weak lensing measurements if it is not accounted for. We find
that the splashback radius has an increasingly large effect on group-sized
halos towards . Depending on the
model and the radial scale used, the cluster/group masses can be biased low by
more than 0.1 dex. This bias, in turn, would result in a slightly lower
value if propagated into a cluster cosmology analysis. The
splashback effect with group-sized dark matter halos may become important to
consider, given the increasingly stringent cosmological constraints coming from
optical wide-field surveys
Average Properties of a Large Sample of z_abs ~ z_em associated Mg II Absorption Line Systems
We have studied a sample of 415 associated (z_ab z_em; relative velocity with
respect to QSO <3000km/s) Mg II absorption systems with 1.0<=z_ab<=1.86, in the
spectra of SDSS DR3 QSOs, to determine the dust content and ionization state in
the absorbers. We studied the dependence of these properties on the properties
of the QSOs and also, compared the properties with those of a similarly
selected sample of 809 intervening systems (apparent relative velocity with
respect to the QSO of >3000km/s), so as to understand their origin. From the
analysis of the composite spectra, as well as from the comparison of measured
equivalent widths in individual spectra, we conclude that the associated Mg II
absorbers have higher apparent ionization, measured by the strength of the C IV
absorption lines compared to the Mg II absorption lines, than the intervening
absorbers. The ionization so measured appears to be related to apparent
ejection velocity, being lower as the apparent ejection velocity is more and
more positive. There is clear evidence, from the composite spectra, for SMC
like dust attenuation in these systems; the 2175AA absorption feature is not
present. The extinction is almost twice that observed in the similarly selected
sample of intervening systems. We reconfirm that QSOs with non-zero FIRST radio
flux are intrinsically redder than the QSOs with no detection in the FIRST
survey. The incidence of associated Mg II systems in QSOs with non-zero FIRST
radio flux is 1.7 times that in the QSOs with no detection in the FIRST survey.
The associated absorbers in radio-detected QSOs which comprise about 12% of our
sample, cause 3 times more reddening than the associated absorbers in
radio-undetected QSOs. This excess reddening possibly suggests an intrinsic
nature for the associated absorbers in radio-detected QSOs.Comment: Accepted for publication in Ap
The LSST Dark Energy Science Collaboration (DESC) Science Requirements Document
The Large Synoptic Survey Telescope (LSST) Dark Energy Science Collaboration
(DESC) will use five cosmological probes: galaxy clusters, large scale
structure, supernovae, strong lensing, and weak lensing. This Science
Requirements Document (SRD) quantifies the expected dark energy constraining
power of these probes individually and together, with conservative assumptions
about analysis methodology and follow-up observational resources based on our
current understanding and the expected evolution within the field in the coming
years. We then define requirements on analysis pipelines that will enable us to
achieve our goal of carrying out a dark energy analysis consistent with the
Dark Energy Task Force definition of a Stage IV dark energy experiment. This is
achieved through a forecasting process that incorporates the flowdown to
detailed requirements on multiple sources of systematic uncertainty. Future
versions of this document will include evolution in our software capabilities
and analysis plans along with updates to the LSST survey strategy.Comment: 32 pages + 60 pages of appendices. This is v1 of the DESC SRD, an
internal collaboration document that is being made public and is not planned
for submission to a journal. Data products for reproducing key plots are
available at the LSST DESC Zenodo community,
https://zenodo.org/communities/lsst-desc; see "Executive Summary and User
Guide" for instructions on how to use and cite those product
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
An r -process enhanced star in the dwarf galaxy Tucana III
Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate Tucana III. Because it is particularly bright for a star in an ultra-faint Milky Way (MW) satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. This star, DES J235532.66−593114.9 (DES J235532), shows a mild enhancement in neutron-capture elements associated with the r-process and can be classified as an r-I star. DES J235532 is the first r-I star to be discovered in an ultra-faint satellite, and Tuc III is the second extremely low-luminosity system found to contain rprocess enriched material, after Reticulum II. Comparison of the abundance pattern of DES J235532 with r-I and r-II stars found in other dwarf galaxies and in the MW halo suggests a common astrophysical origin for the neutron-capture elements seen in all r-process enhanced stars. We explore both internal and external scenarios for the r-process enrichment of Tuc III and show that with abundance patterns for additional stars, it should be possible to distinguish between them