4,738 research outputs found
Cosmological implications of the KATRIN experiment
The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will put
unprecedented constraints on the absolute mass of the electron neutrino,
\mnue. In this paper we investigate how this information on \mnue will
affect our constraints on cosmological parameters. We consider two scenarios;
one where \mnue=0 (i.e., no detection by KATRIN), and one where
\mnue=0.3eV. We find that the constraints on \mnue from KATRIN will affect
estimates of some important cosmological parameters significantly. For example,
the significance of and the inferred value of depend
on the results from the KATRIN experiment.Comment: 13 page
Primordial non-Gaussianity from the large scale structure
Primordial non-Gaussianity is a potentially powerful discriminant of the
physical mechanisms that generated the cosmological fluctuations observed
today. Any detection of non-Gaussianity would have profound implications for
our understanding of cosmic structure formation. In this paper, we review past
and current efforts in the search for primordial non-Gaussianity in the large
scale structure of the Universe.Comment: Invited review article for the CQG special issue on nonlinear
cosmological perturbations
Cosmological Parameters from Observations of Galaxy Clusters
Studies of galaxy clusters have proved crucial in helping to establish the
standard model of cosmology, with a universe dominated by dark matter and dark
energy. A theoretical basis that describes clusters as massive,
multi-component, quasi-equilibrium systems is growing in its capability to
interpret multi-wavelength observations of expanding scope and sensitivity. We
review current cosmological results, including contributions to fundamental
physics, obtained from observations of galaxy clusters. These results are
consistent with and complementary to those from other methods. We highlight
several areas of opportunity for the next few years, and emphasize the need for
accurate modeling of survey selection and sources of systematic error.
Capitalizing on these opportunities will require a multi-wavelength approach
and the application of rigorous statistical frameworks, utilizing the combined
strengths of observers, simulators and theorists.Comment: 53 pages, 21 figures. To appear in Annual Review of Astronomy &
Astrophysic
The Peaks Formalism and the Formation of Cold Dark Matter Haloes
We use two cosmological simulations of structure formation to study the
conditions under which dark matter haloes emerge from the linear density field.
Our analysis focuses on matching sites of halo collapse to local density
maxima, or "peaks", in the initial conditions of the simulations and provides a
crucial test of the central ansatz of the peaks formalism. By identifying peaks
on a variety of smoothed, linearly extrapolated density fields we demonstrate
that as many as ~70% of well-resolved dark matter haloes form preferentially
near peaks whose characteristic masses are similar to that of the halo, with
more massive haloes showing a stronger tendency to reside near peaks initially.
We identify a small but significant fraction of haloes that appear to evolve
from peaks of substantially lower mass than that of the halo itself. We refer
to these as "peakless haloes" for convenience. By contrasting directly the
properties of these objects with the bulk of the proto-halo population we find
two clear differences: 1) their initial shapes are significantly flatter and
more elongated than the predominantly triaxial majority, and 2) they are, on
average, more strongly compressed by tidal forces associated with their
surrounding large scale structure. Using the two-point correlation function we
show that peakless haloes tend to emerge from highly clustered regions of the
initial density field implying that, at fixed mass, the accretion geometry and
mass accretion histories of haloes in highly clustered environments differ
significantly from those in the field. This may have important implications for
understanding the origin of the halo assembly bias, of galaxy properties in
dense environments and how environment affects the morphological transformation
of galaxies near groups and rich galaxy clusters.Comment: 13 pages, 11 figures, published in MNRA
A GMBCG Galaxy Cluster Catalog of 55,424 Rich Clusters from SDSS DR7
We present a large catalog of optically selected galaxy clusters from the
application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG)
algorithm to SDSS Data Release 7 data. The algorithm detects clusters by
identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which
is unique for galaxy clusters and does not exist among field galaxies. Red
sequence clustering in color space is detected using an Error Corrected
Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data
from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog,
consisting of over 55,000 rich clusters across the redshift range from 0.1 < z
< 0.55. We present Monte Carlo tests of completeness and purity and perform
cross-matching with X-ray clusters and with the maxBCG sample at low redshift.
These tests indicate high completeness and purity across the full redshift
range for clusters with 15 or more members.Comment: Updated to match the published version. The catalog can be accessed
from: http://home.fnal.gov/~jghao/gmbcg_sdss_catalog.htm
The Evolution of X-ray Clusters of Galaxies
Considerable progress has been made over the last decade in the study of the
evolutionary trends of the population of galaxy clusters in the Universe. In
this review we focus on observations in the X-ray band. X-ray surveys with the
ROSAT satellite, supplemented by follow-up studies with ASCA and Beppo-SAX,
have allowed an assessment of the evolution of the space density of clusters
out to z~1, and the evolution of the physical properties of the intra-cluster
medium out to z~0.5. With the advent of Chandra and Newton-XMM, and their
unprecedented sensitivity and angular resolution, these studies have been
extended beyond redshift unity and have revealed the complexity of the
thermodynamical structure of clusters. The properties of the intra-cluster gas
are significantly affected by non-gravitational processes including star
formation and Active Galactic Nucleus (AGN) activity. Convincing evidence has
emerged for modest evolution of both the bulk of the X-ray cluster population
and their thermodynamical properties since redshift unity. Such an
observational scenario is consistent with hierarchical models of structure
formation in a flat low density universe with Omega_m=0.3 and sigma_8=0.7-0.8
for the normalization of the power spectrum. Basic methodologies for
construction of X-ray-selected cluster samples are reviewed and implications of
cluster evolution for cosmological models are discussed.Comment: 40 pages, 15 figures. Full resolution figures can be downloaded from
http://www.eso.org/~prosati/ARAA
CMB-S4 Science Book, First Edition
This book lays out the scientific goals to be addressed by the
next-generation ground-based cosmic microwave background experiment, CMB-S4,
envisioned to consist of dedicated telescopes at the South Pole, the high
Chilean Atacama plateau and possibly a northern hemisphere site, all equipped
with new superconducting cameras. CMB-S4 will dramatically advance cosmological
studies by crossing critical thresholds in the search for the B-mode
polarization signature of primordial gravitational waves, in the determination
of the number and masses of the neutrinos, in the search for evidence of new
light relics, in constraining the nature of dark energy, and in testing general
relativity on large scales
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