1,488 research outputs found
A λ = 1.3 Millimeter Aperture Synthesis Molecular Line Survey of Orion Kleinmann-Low
We present a 1".3 spatial resolution interferometric spectral line survey of the core of the Orion molecular cloud, obtained with the OVRO millimeter array. Covering 4 GHz bandwidth in total, the survey contains ~100 emission lines from 18 chemical species. The spatial distributions of a number of molecules point to source I near the IRc2 complex as the dominant energy source in the region but do not rule out the presence of additional lower luminosity objects. At arcsecond resolution, the offsets between dust emission and various molecular tracers suggest that the spectacular "hot core" emission in the Orion core arises via the heating and ablation of material from the surfaces of very high density clumps located ≳500 AU from source I and traced by the dust emission. We find no evidence for a strong internal heating source within the hot core condensation(s)
The Owens Valley Millimeter Array
The present status and projected two year developments for the Owens Valley Millimeter Array are described and a brief summary of the astronomical research is presented
Deprojection of Rich Cluster Images
We consider a general method of deprojecting 2D images to reconstruct the 3D
structure of the projected object, assuming axial symmetry. The method consists
of the application of the Fourier Slice Theorem to the general case where the
axis of symmetry is not necessarily perpendicular to the line of sight, and is
based on an extrapolation of the image Fourier transform into the so-called
cone of ignorance. The method is specifically designed for the deprojection of
X-ray, Sunyaev-Zeldovich (SZ) and gravitational lensing maps of rich clusters
of galaxies. For known values of the Hubble constant, H0, and inclination
angle, the quality of the projection depends on how exact is the extrapolation
in the cone of ignorance. In the case where the axis of symmetry is
perpendicular to the line of sight and the image is noise-free, the
deprojection is exact. Given an assumed value of H0, the inclination angle can
be found by matching the deprojected structure out of two different images of a
given cluster, e.g., SZ and X-ray maps. However, this solution is degenerate
with respect to its dependence on the assumed H0, and a third independent image
of the given cluster is needed to determine H0 as well. The application of the
deprojection algorithm to upcoming SZ, X-ray and weak lensing projected mass
images of clusters will serve to determine the structure of rich clusters, the
value of H0, and place constraints on the physics of the intra-cluster gas and
its relation to the total mass distribution.Comment: 7 pages, LaTeX, 2 Postscript figures, uses as2pp4.sty. Accepted for
publication in ApJ Letters. Also available at:
http://astro.berkeley.edu:80/~squires/papers/deproj.ps.g
Determination of the Cosmic Distance Scale from Sunyaev-Zel'dovich Effect and Chandra X-ray Measurements of High Redshift Galaxy Clusters
We determine the distance to 38 clusters of galaxies in the redshift range
0.14 < z < 0.89 using X-ray data from Chandra and Sunyaev-Zeldovich Effect data
from the Owens Valley Radio Observatory and the Berkeley-Illinois-Maryland
Association interferometric arrays. The cluster plasma and dark matter
distributions are analyzed using a hydrostatic equilibrium model that accounts
for radial variations in density, temperature and abundance, and the
statistical and systematic errors of this method are quantified. The analysis
is performed via a Markov chain Monte Carlo technique that provides
simultaneous estimation of all model parameters. We measure a Hubble constant
of 76.9 +3.9-3.4 +10.0-8.0 km/s/Mpc (statistical followed by systematic
uncertainty at 68% confidence) for an Omega_M=0.3, Omega_Lambda=0.7 cosmology.
We also analyze the data using an isothermal beta model that does not invoke
the hydrostatic equilibrium assumption, and find H_0=73.7 +4.6-3.8 +9.5-7.6
km/s/Mpc; to avoid effects from cool cores in clusters, we repeated this
analysis excluding the central 100 kpc from the X-ray data, and find H_0=77.6
+4.8-4.3 +10.1-8.2 km/s/Mpc. The consistency between the models illustrates the
relative insensitivity of SZE/X-ray determinations of H_0 to the details of the
cluster model. Our determination of the Hubble parameter in the distant
universe agrees with the recent measurement from the Hubble Space Telescope key
project that probes the nearby universe.Comment: ApJ submitted (revised version
Low-resolution spectroscopy of the Sunyaev-Zel'dovich effect and estimates of cluster parameters
The Sunyaev-Zel'dovich (SZ) effect is a powerful tool for studying clusters
of galaxies and cosmology. Large mm-wave telescopes are now routinely detecting
and mapping the SZ effect in a number of clusters, measure their comptonisation
parameter and use them as probes of the large-scale structure and evolution of
the universe. We show that estimates of the physical parameters of clusters
(optical depth, plasma temperature, peculiar velocity, non-thermal components
etc.) obtained from ground-based multi-band SZ photometry can be significantly
biased, owing to the reduced frequency coverage, to the degeneracy between the
parameters and to the presence of a number of independent components larger
than the number of frequencies measured. We demonstrate that low-resolution
spectroscopic measurements of the SZ effect that also cover frequencies
GHz are effective in removing the degeneracy. We used accurate simulations of
observations with lines-of-sight through clusters of galaxies with different
experimental configurations (4-band photometers, 6-band photometer, multi-range
differential spectrometer, full coverage spectrometers) and different
intracluster plasma stratifications. We find that measurements carried out with
ground-based few-band photometers are biased towards high electron temperatures
and low optical depths, and require coverage of high frequency and/or
independent complementary observations to produce unbiased information; a
differential spectrometer that covers 4 bands with a resolution of $\sim 6 \
GHz$ eliminates most if not all bias; full-range differential spectrometers are
the ultimate resource that allows a full recovery of all parameters.Comment: in pres
X-ray and Sunyaev-Zel'dovich Effect Measurements of the Gas Mass Fraction in Galaxy Clusters
We present gas mass fractions of 38 massive galaxy clusters spanning
redshifts from 0.14 to 0.89, derived from Chandra X-ray data and OVRO/BIMA
interferometric Sunyaev-Zel'dovich Effect measurements. We use three models for
the gas distribution: (1) an isothermal beta-model fit jointly to the X-ray
data at radii beyond 100 kpc and to all of the SZE data,(2) a non-isothermal
double beta-model fit jointly to all of the X-ray and SZE data, and (3) an
isothermal beta-model fit only to the SZE spatial data. We show that the simple
isothermal model well characterizes the intracluster medium (ICM) outside of
the cluster core in clusters with a wide range of morphological properties. The
X-ray and SZE determinations of mean gas mass fractions for the 100 kpc-cut
isothermal beta-model are fgas(X-ray)=0.110 +0.003-0.003 +0.006-0.018 and
fgas(SZE)=0.116 +0.005-0.005 +0.009-0.026, where uncertainties are statistical
followed by systematic at 68% confidence. For the non-isothermal double
beta-model, fgas(X-ray)=0.119 +0.003-0.003 +0.007-0.014 and fgas(SZE)=0.121
+0.005-0.005 +0.009-0.016. For the SZE-only model, fgas(SZE)=0.120 +0.009-0.009
+0.009-0.027. Our results indicate that the ratio of the gas mass fraction
within r2500 to the cosmic baryon fraction is 0.68 +0.10-0.16 where the range
includes statistical and systematic uncertainties. By assuming that cluster gas
mass fractions are independent of redshift, we find that the results are in
agreement with standard LambdaCDM cosmology and are inconsistent with a flat
matter dominated universe.Comment: ApJ, submitted. 47 pages, 5 figures, 8 table
DASI First Results: A Measurement of the Cosmic Microwave Background Angular Power Spectrum
We present measurements of anisotropy in the Cosmic Microwave Background
(CMB) from the first season of observations with the Degree Angular Scale
Interferometer (DASI). The instrument was deployed at the South Pole in the
austral summer 1999--2000, and made observations throughout the following
austral winter. We have measured the angular power spectrum of the CMB in the
range 100<l<900 with high signal-to-noise. In this paper we review the
formalism used in the analysis, in particular the use of constraint matrices to
project out contaminants such as ground and point source signals, and to test
for correlations with diffuse foreground templates. We find no evidence of
foregrounds other than point sources in the data, and find a maximum likelihood
temperature spectral index beta = -0.1 +/- 0.2 (1 sigma), consistent with CMB.
We detect a first peak in the power spectrum at l approx 200, in agreement with
previous experiments. In addition, we detect a peak in the power spectrum at l
approx 550 and power of similar magnitude at l approx 800 which are consistent
with the second and third harmonic peaks predicted by adiabatic inflationary
cosmological models.Comment: 8 pages, 1 figure, minor changes in response to referee comment
The Cosmic Background Imager
Design and performance details are given for the Cosmic Background Imager
(CBI), an interferometer array that is measuring the power spectrum of
fluctuations in the cosmic microwave background radiation (CMBR) for multipoles
in the range 400 < l < 3500. The CBI is located at an altitude of 5000 m in the
Atacama Desert in northern Chile. It is a planar synthesis array with 13 0.9-m
diameter antennas on a 6-m diameter tracking platform. Each antenna has a
cooled, low-noise receiver operating in the 26-36 GHz band. Signals are
cross-correlated in an analog filterbank correlator with ten 1 GHz bands. This
allows spectral index measurements which can be used to distinguish CMBR
signals from diffuse galactic foregrounds. A 1.2 kHz 180-deg phase switching
scheme is used to reject cross-talk and low-frequency pick-up in the signal
processing system. The CBI has a 3-axis mount which allows the tracking
platform to be rotated about the optical axis, providing improved (u,v)
coverage and a powerful discriminant against false signals generated in the
receiving electronics. Rotating the tracking platform also permits polarization
measurements when some of the antennas are configured for the orthogonal
polarization.Comment: 14 pages. Accepted for publication in PASP. See also
http://www.astro.caltech.edu/~tjp/CBI
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