292 research outputs found
Limits on the Peculiar Velocities of Two Distant Clusters Using the Kinematic Sunyaev-Zel'dovich Effect
We report millimeter-wavelength observations of the Sunyaev-Zel'dovich (S-Z)
effect in two distant galaxy clusters. A relativistically correct analysis of
the S-Z data is combined with the results of X-ray observations to determine
the radial peculiar velocities v_r of the clusters. We observed Abell 2163
(z=.201) in three mm-wavelength bands centered at 2.1, 1.4, and 1.1 mm. We
report a significant detection of the thermal component of the S-Z effect seen
as both a decrement in the brightness of the CMB at 2.1 mm, and as an increment
at 1.1 mm. Including uncertainties due to the calibration of the instrument,
distribution and temperature of the IC gas, and astrophysical confusion, a
simultaneous fit to the data in all three bands gives v_r=+490 +1370/-880 km/s
at 68% confidence. We observed Abell 1689 (z=.181) in the 2.1 and 1.4 mm bands.
Including the same detailed accounting of uncertainty, a simultaneous fit to
the data in both bands gives v_r=+170 +815/-630 km/s. The limits on the
peculiar velocities of A2163 and A1689 correspond to deviations from the
uniform Hubble flow of <= 2-3%.Comment: 21 pages, 13 postscript figures, LaTeX(aaspptwo.sty), ApJ(in press
The Sunyaev-Zel'dovich Infrared Experiment: A Millimeter-wave Receiver for Cluster Cosmology
Measurements of the Sunyaev-Zel'dovich (S-Z) effect towards distant clusters
of galaxies can be used to determine the Hubble constant and the radial
component of cluster peculiar velocities. Determination of the cluster peculiar
velocity requires the separation of the two components of the S-Z effect, which
are due to the thermal and bulk velocities of the intracluster plasma. The two
components can be separated practically only at millimeter (mm) wavelengths.
Measurements of the S-Z effect at mm wavelengths are subject to minimal
astrophysical confusion and, therefore, provide an important test of results
obtained at longer wavelengths. We describe the instrument used to make the
first significant detections of the S-Z effect at millimeter wavelengths. This
instrument employs new filter, detector, and readout technologies to produce
sensitive measurements of differential sky brightness stable on long time
scales. These advances allow drift scan observations which achieve high
sensitivity while minimizing common sources of systematic error.Comment: 19 pages, 15 postscript figures, LaTeX(aaspptwo.sty), ApJ(in press
Understanding Climatic Impacts, Vulnerabilities, and Adaptation in the United States: Building a Capacity for Assessment
Based on the experience of the U.S. National Assessment, we propose a program of research and analysis to advance capability for assessment of climate impacts, vulnerabilities, and adaptation options. We identify specific priorities for scientific research on the responses of ecological and socioeconomic systems to climate and other stresses; for improvement in the climatic inputs to impact assessments; and for further development of assessment methods to improve their practical utility to decision-makers. Finally, we propose a new institutional model for assessment, based principally on regional efforts that integrate observations, research, data, applications, and assessment on climate and linked environmental-change issues. The proposed program will require effective collaboration between scientists, resource managers, and other stakeholders, all of whose expertise is needed to define and prioritize key regional issues, characterize relevant uncertainties, and assess potential responses. While both scientifically and organizationally challenging, such an integrated program holds the best promise of advancing our capacity to manage resources and the economy adaptively under a changing climate
Geocentrism reexamined
The universe is nearly isotropic on very large scales. It is much more
difficult to show that the universe is radially homogeneous (independent of
distance), or equivalently, that it is isotropic about distant points. This
taken as an axiom, since if it were not true, then we would occupy a preferred
position. This paper considers several empirical arguments for radial
homogeneity based on the cosmic microwave background (CMB). The tightest limits
on inhomogeneity on the scale of the horizon are of order ten percent but will
improve soon. These limits involve the Sunyaev-Zel'dovich effect in clusters of
galaxies, excitation of low-energy atomic transitions, and the accurately
thermal spectrum of the CMB. Weaker limits from primordial nucleosynthesis are
discussed briefly.Comment: RevTeX source, 14 pages, no figs. To appear Phys Rev
A Weak Gravitational Lensing and X-ray Analysis of Abell 2163
We report on the detection of dark matter in the cluster of galaxies
Abell~2163 using the weak gravitational distortion of background galaxies, and
an analysis of the cluster X-ray emission. We find that while the qualitative
distributions of the cluster light and the dark matter are similar -- shallow
and extended, with significant substructure -- the X-ray morphology shows a
more regular overall appearance. We interpret the joint lensing and X-ray
observations as a signature of a merger event in the cluster. We present new
ROSAT/HRI data and reanalyze ROSAT/PSPC data, accounting for the effect of a
varying background to determine the best fit parameters in the -model
formalism. We combine the surface brightness fits with two determinations of
the radial temperature profile to determine the total mass. Although there are
slight variations in the total mass determinations introduced by the
uncertainties in the -fit, the main contributor to the error arises from
the uncertainties in the temperature determinations. Even though the
morphologies of the dark matter/light and X-ray gas are quite different, we
find that the total mass determined from the X-ray and weak lensing estimates
are consistent with each other within the error bars, with the X-ray
inferred mass a factor of larger. However, as the lensing mass
estimates are differential (the surface density at any point is determined
relative to the mean in a control annulus), the shallow, extended nature of the
mass profile biases the lensing inferred mass downwards. We estimate the
correction for this effect and find very good agreement between the corrected
lensing and X-ray results. We determine the gas mass fraction and find at all radii and a constant mass-to-light ratio of $M/L_VComment: 30 pages, latex file. Postscript file also available at
ftp://magicbean.berkeley.edu/pub/squires/a2163/a2163_paper.ps.g
Measurement of the Hubble Constant from X-ray and 2.1 mm Observations of Abell 2163
We report 2.1 mm observations of the Sunyaev-Zel'dovich (S-Z) effect; these
observations confirm our previous detection of a decrement in the Cosmic
Microwave Background intensity towards the cluster Abell 2163. The S-Z data are
analyzed using the relativistically correct expression for the Comptonization.
We begin by assuming the intracluster (IC) gas to be isothermal at the emission
weighted average temperature determined by a combined analysis of the ASCA and
GINGA X-ray satellite observations. Combining the X-ray and S-Z measurements,
we determine the Hubble constant to be H_0(q_0=0.5)= 60 +40/-23 km/s/Mpc, where
the uncertainty is dominated by the systematic difference in the ASCA and GINGA
determined IC gas temperatures. ASCA observations suggest the presence of a
significant thermal gradient in the IC gas. We determine as a function of
the assumed IC gas thermal structure. Using the ASCA determined thermal
structure and keeping the emission weighted average temperature the same as in
the isothermal case, we find H_0(q_0=0.5)= 78 +54/-28 km/s/Mpc. Including
additional uncertainties due to cluster asphericity, peculiar velocity, IC gas
clumping, and astrophysical confusion, we find H_0(q_0=0.5)= 78 +60/-40
km/s/Mpc.Comment: 24 pages, 10 postscript figures, LaTeX(aaspptwo.sty), ApJ(in press
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The First State of the Carbon Cycle Report (SOCCR)
A primary objective of the U.S. Climate Change Science Program (CCSP) is to provide the best possible scientific information to support public discussion, as well as government and private sector decision making, on key climate-related issues. To help meet this objective, the CCSP has identified an initial set of 21 Synthesis and Assessment Products (SAPs) that address its highest priority research, observation, and decision support needs. This report-CCSP SAP 2.2-addresses Goal 2 of the CCSP Strategic Plan: Improve quantification of the forces bringing about changes in the Earth's climate and related systems. The report provides a synthesis and integration of the current knowledge of the North American carbon budget and its context within the global carbon cycle. In a format useful to decision makers, it (1) summarizes our knowledge of carbon cycle properties and changes relevant to the contributions of and impacts upon North America and the rest of the world, and (2) provides scientific information for decision support focused on key issues for carbon management and policy. Consequently, this report is aimed at both the decision-maker audience and to the expert scientific and stakeholder communities
US National Climate Assessment (NCA) Scenarios for Assessing Our Climate Future: Issues and Methodological Perspectives Background Whitepaper for Participants
This whitepaper is intended to provide a starting point for discussion at a workshop for the National Climate Assessment (NCA) that focuses on the use and development of scenarios. The paper will provide background needed by participants in the workshop in order to review options for developing and using scenarios in NCA. The paper briefly defines key terms and establishes a conceptual framework for developing consistent scenarios across different end uses and spatial scales. It reviews uses of scenarios in past U.S. national assessments and identifies potential users of and needs for scenarios for both the report scheduled for release in June 2013 and to support an ongoing distributed assessment process in sectors and regions around the country. Because scenarios prepared for the NCA will need to leverage existing research, the paper takes account of recent scientific advances and activities that could provide needed inputs. Finally, it considers potential approaches for providing methods, data, and other tools for assessment participants. We note that the term 'scenarios' has many meanings. An important goal of the whitepaper (and portions of the workshop agenda) is pedagogical (i.e., to compare different meanings and uses of the term and make assessment participants aware of the need to be explicit about types and uses of scenarios). In climate change research, scenarios have been used to establish bounds for future climate conditions and resulting effects on human and natural systems, given a defined level of greenhouse gas emissions. This quasi-predictive use contrasts with the way decision analysts typically use scenarios (i.e., to consider how robust alternative decisions or strategies may be to variation in key aspects of the future that are uncertain). As will be discussed, in climate change research and assessment, scenarios describe a range of aspects of the future, including major driving forces (both human activities and natural processes), changes in climate and related environmental conditions (e.g., sea level), and evolution of societal capability to respond to climate change. This wide range of scenarios is needed because the implications of climate change for the environment and society depend not only on changes in climate themselves, but also on human responses. This degree of breadth introduces and number of challenges for communication and research
Technical summary
Human interference with the climate system is occurring. Climate change poses risks for human and natural systems. The assessment of impacts, adaptation, and vulnerability in the Working Group II contribution to the IPCC's Fifth Assessment Report (WGII AR5) evaluates how patterns of risks and potential benefits are shifting due to climate change and how risks can be reduced through mitigation and adaptation. It recognizes that risks of climate change will vary across regions and populations, through space and time, dependent on myriad factors including the extent of mitigation and adaptation
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