5,640 research outputs found
COrE (Cosmic Origins Explorer) A White Paper
COrE (Cosmic Origins Explorer) is a fourth-generation full-sky,
microwave-band satellite recently proposed to ESA within Cosmic Vision
2015-2025. COrE will provide maps of the microwave sky in polarization and
temperature in 15 frequency bands, ranging from 45 GHz to 795 GHz, with an
angular resolution ranging from 23 arcmin (45 GHz) and 1.3 arcmin (795 GHz) and
sensitivities roughly 10 to 30 times better than PLANCK (depending on the
frequency channel). The COrE mission will lead to breakthrough science in a
wide range of areas, ranging from primordial cosmology to galactic and
extragalactic science. COrE is designed to detect the primordial gravitational
waves generated during the epoch of cosmic inflation at more than
for . It will also measure the CMB gravitational lensing
deflection power spectrum to the cosmic variance limit on all linear scales,
allowing us to probe absolute neutrino masses better than laboratory
experiments and down to plausible values suggested by the neutrino oscillation
data. COrE will also search for primordial non-Gaussianity with significant
improvements over Planck in its ability to constrain the shape (and amplitude)
of non-Gaussianity. In the areas of galactic and extragalactic science, in its
highest frequency channels COrE will provide maps of the galactic polarized
dust emission allowing us to map the galactic magnetic field in areas of
diffuse emission not otherwise accessible to probe the initial conditions for
star formation. COrE will also map the galactic synchrotron emission thirty
times better than PLANCK. This White Paper reviews the COrE science program,
our simulations on foreground subtraction, and the proposed instrumental
configuration.Comment: 90 pages Latex 15 figures (revised 28 April 2011, references added,
minor errors corrected
Spitzer observations of a gravitationally lensed quasar, QSO 2237+0305
The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by
stars in the lens galaxy. The amplitude of microlensing variability can be used
to infer the relative size of the quasar as a function of wavelength; this
provides a test of quasar models. Toward this end, we present Spitzer Space
Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations
of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy
distribution (SED) is similar to that of other bright radio-quiet quasars,
contrary to an earlier claim. (2) A dusty torus model with a small opening
angle fits the overall shape of the IR SED well, but the quantitative agreement
is poor due to an offset in wavelength of the silicate feature. (3) The flux
ratios of the four lensed images can be derived from the IRAC data despite
being unresolved. We find that the near-IR fluxes are increasingly affected by
microlensing toward shorter wavelengths. (4) The wavelength dependence of the
IRAC flux ratios is consistent with the standard quasar model in which an
accretion disk and a dusty torus both contribute near 1 micron in the rest
frame. This is also consistent with recent IR spectropolarimetry of nearby
quasars
Stabilization of Ultracold Molecules Using Optimal Control Theory
In recent experiments on ultracold matter, molecules have been produced from
ultracold atoms by photoassociation, Feshbach resonances, and three-body
recombination. The created molecules are translationally cold, but
vibrationally highly excited. This will eventually lead them to be lost from
the trap due to collisions. We propose shaped laser pulses to transfer these
highly excited molecules to their ground vibrational level. Optimal control
theory is employed to find the light field that will carry out this task with
minimum intensity. We present results for the sodium dimer. The final target
can be reached to within 99% if the initial guess field is physically
motivated. We find that the optimal fields contain the transition frequencies
required by a good Franck-Condon pumping scheme. The analysis is able to
identify the ranges of intensity and pulse duration which are able to achieve
this task before other competing process take place. Such a scheme could
produce stable ultracold molecular samples or even stable molecular
Bose-Einstein condensates
The WFIRST Galaxy Survey Exposure Time Calculator
This document describes the exposure time calculator for the Wide-Field
Infrared Survey Telescope (WFIRST) high-latitude survey. The calculator works
in both imaging and spectroscopic modes. In addition to the standard ETC
functions (e.g. background and S/N determination), the calculator integrates
over the galaxy population and forecasts the density and redshift distribution
of galaxy shapes usable for weak lensing (in imaging mode) and the detected
emission lines (in spectroscopic mode). The source code is made available for
public use.Comment: 44 pages. The current C source code and version history can be found
at http://www.tapir.caltech.edu/~chirata/web/software/space-etc/ ; IPAC
maintains a web interface at
http://wfirst-web.ipac.caltech.edu/wfDepc/wfDepc.js
The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectrum at 148 and 218 GHz from the 2008 Southern Survey
We present measurements of the cosmic microwave background (CMB) power
spectrum made by the Atacama Cosmology Telescope at 148 GHz and 218 GHz, as
well as the cross-frequency spectrum between the two channels. Our results
clearly show the second through the seventh acoustic peaks in the CMB power
spectrum. The measurements of these higher-order peaks provide an additional
test of the {\Lambda}CDM cosmological model. At l > 3000, we detect power in
excess of the primary anisotropy spectrum of the CMB. At lower multipoles 500 <
l < 3000, we find evidence for gravitational lensing of the CMB in the power
spectrum at the 2.8{\sigma} level. We also detect a low level of Galactic dust
in our maps, which demonstrates that we can recover known faint, diffuse
signals.Comment: 19 pages, 13 figures. Submitted to ApJ. This paper is a companion to
Hajian et al. (2010) and Dunkley et al. (2010
Science-driven 3D data compression
Photometric redshift surveys map the distribution of matter in the Universe
through the positions and shapes of galaxies with poorly resolved measurements
of their radial coordinates. While a tomographic analysis can be used to
recover some of the large-scale radial modes present in the data, this approach
suffers from a number of practical shortcomings, and the criteria to decide on
a particular binning scheme are commonly blind to the ultimate science goals.
We present a method designed to separate and compress the data into a small
number of uncorrelated radial modes, circumventing some of the problems of
standard tomographic analyses. The method is based on the Karhunen-Lo\`{e}ve
transform (KL), and is connected to other 3D data compression bases advocated
in the literature, such as the Fourier-Bessel decomposition. We apply this
method to both weak lensing and galaxy clustering. In the case of galaxy
clustering, we show that the resulting optimal basis is closely associated with
the Fourier-Bessel basis, and that for certain observables, such as the effects
of magnification bias or primordial non-Gaussianity, the bulk of the signal can
be compressed into a small number of modes. In the case of weak lensing we show
that the method is able to compress the vast majority of the signal-to-noise
into a single mode, and that optimal cosmological constraints can be obtained
considering only three uncorrelated KL eigenmodes, considerably simplifying the
analysis with respect to a traditional tomographic approach.Comment: 14 pages, 11 figures. Comments welcom
Distributed feedback lasers
A ridge waveguide distributed feedback laser was developed in InGaAsP. These devices have demonstrated CW output powers over 7 mW with threshold currents as low as 60 mA at 25 C. Measurements of the frequency response of these devices show a 3 dB bandwidth of about 2 GHz, which may be limited by the mount. The best devices have a single mode spectra over the entire temperature range tested with a side mode suppression of about 20 dB in both CW and pulsed modes. The design of this device, including detailed modeling of the ridge guide structure, effective index calculations, and a discussion of the grating configuration are presented. Also, the fabrication of the devices is presented in some detail, especially the fabrication of and subsequent growth over the grating. In addition, a high frequency fiber pigtailed package was designed and tested, which is a suitable prototype for a commercial package
CCAT-prime: Science with an Ultra-widefield Submillimeter Observatory at Cerro Chajnantor
We present the detailed science case, and brief descriptions of the telescope
design, site, and first light instrument plans for a new ultra-wide field
submillimeter observatory, CCAT-prime, that we are constructing at a 5600 m
elevation site on Cerro Chajnantor in northern Chile. Our science goals are to
study star and galaxy formation from the epoch of reionization to the present,
investigate the growth of structure in the Universe, improve the precision of
B-mode CMB measurements, and investigate the interstellar medium and star
formation in the Galaxy and nearby galaxies through spectroscopic,
polarimetric, and broadband surveys at wavelengths from 200 um to 2 mm. These
goals are realized with our two first light instruments, a large field-of-view
(FoV) bolometer-based imager called Prime-Cam (that has both camera and an
imaging spectrometer modules), and a multi-beam submillimeter heterodyne
spectrometer, CHAI. CCAT-prime will have very high surface accuracy and very
low system emissivity, so that combined with its wide FoV at the unsurpassed
CCAT site our telescope/instrumentation combination is ideally suited to pursue
this science. The CCAT-prime telescope is being designed and built by Vertex
Antennentechnik GmbH. We expect to achieve first light in the spring of 2021.Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared
Detectors and Instrumentation for Astronomy IX, June 14th, 201
Classification and analysis of emission-line galaxies using mean field independent component analysis
We present an analysis of the optical spectra of narrow emission-line
galaxies, based on mean field independent component analysis (MFICA). Samples
of galaxies were drawn from the Sloan Digital Sky Survey (SDSS) and used to
generate compact sets of `continuum' and `emission-line' component spectra.
These components can be linearly combined to reconstruct the observed spectra
of a wider sample of galaxies. Only 10 components - five continuum and five
emission line - are required to produce accurate reconstructions of essentially
all narrow emission-line galaxies; the median absolute deviations of the
reconstructed emission-line fluxes, given the signal-to-noise ratio (S/N) of
the observed spectra, are 1.2-1.8 sigma for the strong lines. After applying
the MFICA components to a large sample of SDSS galaxies we identify the regions
of parameter space that correspond to pure star formation and pure active
galactic nucleus (AGN) emission-line spectra, and produce high S/N
reconstructions of these spectra.
The physical properties of the pure star formation and pure AGN spectra are
investigated by means of a series of photoionization models, exploiting the
faint emission lines that can be measured in the reconstructions. We are able
to recreate the emission line strengths of the most extreme AGN case by
assuming the central engine illuminates a large number of individual clouds
with radial distance and density distributions, f(r) ~ r^gamma and g(n) ~
n^beta, respectively. The best fit is obtained with gamma = -0.75 and beta =
-1.4. From the reconstructed star formation spectra we are able to estimate the
starburst ages. These preliminary investigations serve to demonstrate the
success of the MFICA-based technique in identifying distinct emission sources,
and its potential as a tool for the detailed analysis of the physical
properties of galaxies in large-scale surveys.Comment: MNRAS accepted. 29 pages, 24 figures, 3 table
- …