3,833 research outputs found
Measuring the 3D Clustering of Undetected Galaxies Through Cross Correlation of their Cumulative Flux Fluctuations from Multiple Spectral Lines
We discuss a method for detecting the emission from high redshift galaxies by
cross correlating flux fluctuations from multiple spectral lines. If one can
fit and subtract away the continuum emission with a smooth function of
frequency, the remaining signal contains fluctuations of flux with frequency
and angle from line emitting galaxies. Over a particular small range of
observed frequencies, these fluctuations will originate from sources
corresponding to a series of different redshifts, one for each emission line.
It is possible to statistically isolate the fluctuations at a particular
redshift by cross correlating emission originating from the same redshift, but
in different emission lines. This technique will allow detection of clustering
fluctuations from the faintest galaxies which individually cannot be detected,
but which contribute substantially to the total signal due to their large
numbers. We describe these fluctuations quantitatively through the line cross
power spectrum. As an example of a particular application of this technique, we
calculate the signal-to-noise ratio for a measurement of the cross power
spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the
proposed Space Infrared Telescope for Cosmology and Astrophysics. We find that
the cross power spectrum can be measured beyond a redshift of z=8. Such
observations could constrain the evolution of the metallicity, bias, and duty
cycle of faint galaxies at high redshifts and may also be sensitive to the
reionization history through its effect on the minimum mass of galaxies. As
another example, we consider the cross power spectrum of CO line emission
measured with a large ground based telescope like CCAT and 21-cm radiation
originating from hydrogen in galaxies after reionization with an interferometer
similar in scale to MWA, but optimized for post-reionization redshifts.Comment: 21 pages, 6 figures; Replaced with version accepted by JCAP; Added an
example of cross correlating CO line emission and 21cm line emission from
galaxies after reionizatio
Cosmological Origin of the Stellar Velocity Dispersions in Massive Early-Type Galaxies
We show that the observed upper bound on the line-of-sight velocity
dispersion of the stars in an early-type galaxy, sigma<400km/s, may have a
simple dynamical origin within the LCDM cosmological model, under two main
hypotheses. The first is that most of the stars now in the luminous parts of a
giant elliptical formed at redshift z>6. Subsequently, the stars behaved
dynamically just as an additional component of the dark matter. The second
hypothesis is that the mass distribution characteristic of a newly formed dark
matter halo forgets such details of the initial conditions as the stellar
"collisionless matter" that was added to the dense parts of earlier generations
of halos. We also assume that the stellar velocity dispersion does not evolve
much at z<6, because a massive host halo grows mainly by the addition of
material at large radii well away from the stellar core of the galaxy. These
assumptions lead to a predicted number density of ellipticals as a function of
stellar velocity dispersion that is in promising agreement with the Sloan
Digital Sky Survey data.Comment: ApJ, in press (2003); matches published versio
Early Cosmic Formation of Massive Black Holes
The evolution of nonlinear density fluctuations around the Jeans mass shortly
after cosmological recombination is analyzed using a 3D
hydrodynamics/dark--matter code. The Cosmic Background Radiation (CBR) exerts
Compton friction on free electrons due to peculiar velocities. The dynamics
therefore depends strongly on the gas ionization history. Under a variety of
ionization conditions and in systems with or without non-baryonic components,
the baryons lose angular momentum efficiently and collapse to form a compact
optically--thick object which would probably quickly evolve into a massive
black hole. Attention is concentrated on elucidating some of the novel physical
effects in early cosmological collapses, but ways in which more realistic
calculations might be made and in which the scenario could be incorporated into
a more complete cosmogonic model are discussed.Comment: LaTeX file, figures not included. For hardcopy of figures contact
[email protected]. Institute for Advanced Study number AST 93/11-
Measuring disability and monitoring the UN Convention on the Rights of Persons with Disabilities: the work of the Washington Group on Disability Statistics
The Washington Group on Disability Statistics is a voluntary working group made up of representatives of over 100 National Statistical Offices and international, non-governmental and disability organizations that was organized under the aegis of the United Nations Statistical Division. The purpose of the Washington Group is to deal with the challenge of disability definition and measurement in a way that is culturally neutral and reasonably standardized among the UN member states. The work, which began in 2001, took on added importance with the passage and ratification of the UN Convention on the Rights of Persons with Disabilities since the Convention includes a provision for monitoring whether those with and without disabilities have equal opportunities to participate in society and this will require the identification of persons with disabilities in each nation. The International Classification of Functioning, Disability and Health (ICF) developed by the World Health Organization provided a framework for conceptualizing disability. Operationalizing an ICF-based approach to disability has required the development of new measurement tools for use in both censuses and surveys. To date, a short set of six disability-related questions suitable for use in national censuses has been developed and adopted by the Washington Group and incorporated by the United Nations in their Principles and Recommendations for Population and Housing Censuses. A series of extended sets of questions is currently under development and some of the sets have been tested in several countries. The assistance of many National and International organizations has allowed for cognitive and field testing of the disability questionnaires in multiple languages and locations. This paper will describe the work of the Washington Group and explicate the applicability of its approach and the questions developed for monitoring the UN Convention on the Rights of Persons with Disabilities
The Expected Rate of Gamma-Ray Burst Afterglows In Supernova Searches
We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be
detected in supernova searches as a function of limiting flux. Although GRB
afterglows are rarer than supernovae, they are detectable at greater distances
because of their higher intrinsic luminosity. Assuming that GRBs trace the
cosmic star formation history and that every GRB gives rise to a bright
afterglow, we find that the average detection rate of supernovae and afterglows
should be comparable at limiting magnitudes brighter than K=18. The actual rate
of afterglows is expected to be somewhat lower since only a fraction of all
gamma-ray selected GRBs were observed to have associated afterglows. However,
the rate could also be higher if the initial gamma-ray emission from GRB
sources is more beamed than their late afterglow emission. Hence, current and
future supernova searches can place strong constraints on the afterglow
appearance fraction and the initial beaming angle of GRB sources.Comment: 13 pages, submitted to ApJ
Redshift determination in the X-ray band of gamma-ray bursts
If gamma-ray bursts originate in dense stellar forming regions, the
interstellar material can imprint detectable absorption features on the
observed X-ray spectrum. Such features can be detected by existing and planned
X-ray satellites, as long as the X-ray afterglow is observed after a few
minutes from the burst. If the column density of the interstellar material
exceeds ~10^{23} cm^{-2} there exists the possibility to detect the K_alpha
fluorescent iron line, which should be visible for more than one year, long
after the X-ray afterglow continuum has faded away. Detection of these X-ray
features will make possible the determination of the redshift of gamma-ray
bursts even when their optical afterglow is severely dimmed by extinction.Comment: 15 pages with 5 figures. Submitted to Ap
Constraining Parity Violation in Gravity with Measurements of Neutron-Star Moments of Inertia
Neutron stars are sensitive laboratories for testing general relativity,
especially when considering deviations where velocities are relativistic and
gravitational fields are strong. One such deviation is described by dynamical,
Chern-Simons modified gravity, where the Einstein-Hilbert action is modified
through the addition of the gravitational parity-violating Pontryagin density
coupled to a field. This four-dimensional effective theory arises naturally
both in perturbative and non-perturbative string theory, loop quantum gravity,
and generic effective field theory expansions. We calculate here Chern-Simons
modifications to the properties and gravitational fields of slowly spinning
neutron stars. We find that the Chern-Simons correction affects only the
gravitomagnetic sector of the metric to leading order, thus introducing
modifications to the moment of inertia but not to the mass-radius relation. We
show that an observational determination of the moment of inertia to an
accuracy of 10%, as is expected from near-future observations of the double
pulsar, will place a constraint on the Chern-Simons coupling constant of
\xi^{1/4} < 5 km, which is at least three-orders of magnitude stronger than the
previous strongest bound.Comment: 14 pages, 6 figures, replaced with version accepted for publication
in Phys. Rev.
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