1,382 research outputs found
CS J = 2 yields 1 emission toward the central region of M82
M82 is an irregular (Type II) galaxy located at a distance of approximately 3.5 Mpc. Its unusual appearance and high luminosity, particularly in the infrared, has led many astronomers to classify it as a starburst galaxy. This interpretation is supported by the observation of a large number of radio continuum sources within the central arcminute of the galaxy. These sources are thought to be associated with supernova remnants. The starburst in the central region of the galaxy is believed to have been triggered by tidal interaction with either M81 or the HI cloud surrounding the M81 group. High angular resolution CO-12 J=1 to 0 maps by Nakai (1984) and Lo et al. (1987) indicate the existence of a 400 to 450 pc rotating ring of molecular material about the central region of M82. Red- and blue-shifted absorption components of the HI and OH lines measured by Weliachew et al. (1984) provided the first evidence for the presence of the ring. Many astronomers, each using a different angular resolution, have compared CO-12 J=1 to 0, J=2 to 1, and J=3 to 2 emission and concluded that a large fraction of the CO emission is optically thin. Additional observations suggest that the molecular material toward the center of M82 is clumpy and dense. Unlike the lower rotational transitions of CO, CS is excited only at relatively high densities, n sub H sub 2 greater than or equal to 10(exp 4) cm(-3). It is in clouds with these densities that stars are expected to form. This makes CS an excellent probe of star formation regions. Researchers observed the CS J=2 to 1 transition (97.981 GHz) toward 52 positions in M82 using the National Radio Astronomy Observatory (NRAO) 12 m telescope
Imaging the Sunyaev-Zel'dovich Effect
We report on results of interferometric imaging of the Sunyaev-Zel'dovich
Effect (SZE) with the OVRO and BIMA mm-arrays. Using low-noise cm-wave
receivers on the arrays, we have obtained high quality images for 27 distant
galaxy clusters. We review the use of the SZE as a cosmological tool. Gas mass
fractions derived from the SZE data are given for 18 of the clusters, as well
as the implied constraint on the matter density of the universe, . We
find . A best guess for the matter
density obtained by assuming a reasonable value for the Hubble constant and
also by attempting to account for the baryons contained in the galaxies as well
as those lost during the cluster formation process gives .
We also give preliminary results for the Hubble constant. Lastly, the power for
investigating the high redshift universe with a non-targeted high sensitivity
SZE survey is discussed and an interferometric survey is proposed.Comment: 14 pages, 7 figures, latex, contribution to Nobel Symposium "Particle
Physics and the Universe" to appear in Physica Scripta and World Scientific,
eds L. Bergstrom, P. Carlson and C. Fransso
A Sunyaev-Zel'dovich Effect Survey for High Redshift Clusters
Interferometric observations of the Sunyaev-Zel'dovich Effect (SZE) toward
clusters of galaxies provide sensitive cosmological probes. We present results
from 1 cm observations (at BIMA and OVRO) of a large, intermediate redshift
cluster sample. In addition, we describe a proposed, higher sensitivity array
which will enable us to survey large portions of the sky. Simulated
observations indicate that we will be able to survey one square degree of sky
per month to sufficient depth that we will detect all galaxy clusters more
massive than 2x10^{14} h^{-1}_{50}M_\odot, regardless of their redshift. We
describe the cluster yield and resulting cosmological constraints from such a
survey.Comment: 7 pages, 6 figures, latex, contribution to VLT Opening Symposiu
Plans for a 10-m Submillimeter-wave Telescope at the South Pole
A 10 meter diameter submillimeter-wave telescope has been proposed for the
NSF Amundsen-Scott South Pole Station. Current evidence indicates that the
South Pole is the best submillimeter-wave telescope site among all existing or
proposed ground-based observatories. Proposed scientific programs place
stringent requirements on the optical quality of the telescope design. In
particular, reduction of the thermal background and offsets requires an
off-axis, unblocked aperture, and the large field of view needed for survey
observations requires shaped optics. This mix of design elements is well-suited
for large scale (square degree) mapping of line and continuum radiation from
submillimeter-wave sources at moderate spatial resolutions (4 to 60 arcsecond
beam size) and high sensitivity (milliJansky flux density levels). the
telescope will make arcminute angular scale, high frequency Cosmic Microwave
Background measurements from the best possible ground-based site, using an
aperture which is larger than is currently possible on orbital or airborne
platforms. Effective use of this telescope will require development of large
(1000 element) arrays of submillimeter detectors which are background-limited
when illuminated by antenna temperatures near 50 K.Comment: 12 pages, 3 figure
Markov Chain Monte Carlo joint analysis of Chandra X-ray imaging spectroscopy and Sunyaev-Zeldovich Effect data
X-ray and Sunyaev-Zeldovich Effect data can be combined to determine the
distance to galaxy clusters. High-resolution X-ray data are now available from
the Chandra Observatory, which provides both spatial and spectral information,
and Sunyaev-Zeldovich Effect data were obtained from the BIMA and OVRO arrays.
We introduce a Markov chain Monte Carlo procedure for the joint analysis of
X-ray and Sunyaev-Zeldovich Effect data. The advantages of this method are the
high computational efficiency and the ability to measure simultaneously the
probability distribution of all parameters of interest, such as the spatial and
spectral properties of the cluster gas and also for derivative quantities such
as the distance to the cluster. We demonstrate this technique by applying it to
the Chandra X-ray data and the OVRO radio data for the galaxy cluster Abell
611. Comparisons with traditional likelihood-ratio methods reveal the
robustness of the method. This method will be used in follow-up papers to
determine the distances to a large sample of galaxy clusters.Comment: ApJ accepted, scheduled for ApJ 10 October 2004, v614 issue. Title
changed, added more convergence diagnostic tests, Figure 7 converted to lower
resolution for easier download, other minor change
Development of a Sideband Separation Receiver at 100 GHz
We have built and tested a prototype SIS receiver operating at 100 GHz to
test the feasibility of sideband separation through quadrature mixing at millimeter
and submillimeter wavelengths. We achieved over 40 dB of separation with no
degradation of the mixer noise temperature due to the sideband separation. Both
the sky signal and atmospheric noise are separated, greatly reducing the system
temperature for millimeter and submillimeter observations in which spectral lines
are present in only one sideband
Final Results from the BIMA CMB Anisotropy Survey and Search for Signature of the SZ effect
We report the final results of our study of the cosmic microwave background
(CMB) with the BIMA array. Over 1000 hours of observation were dedicated to
this project exploring CMB anisotropy on scales between 1' and 2' in eighteen
6.6' FWHM fields. In the analysis of the CMB power spectrum, the visibility
data is divided into two bins corresponding to different angular scales.
Modeling the observed excess power as a flat band of average multipole ell=
5237, we find Delta T_1^2=220_{-120}^{+140} muK^2 at 68% confidence and Delta
T_1^2 >0 muK^2 with 94.7% confidence. In a second band with average multipole
of ell = 8748, we find Delta T_2^2 consistent with zero, and an upper limit 880
muK^2 at 95% confidence. An extensive series of tests and supplemental
observations with the VLA provide strong evidence against systematic errors or
radio point sources being the source of the observed excess power. The dominant
source of anisotropy on these scales is expected to arise from the
Sunyaev-Zel'dovich (SZ) effect in a population of distant galaxy clusters. If
the excess power is due to the SZ effect, we can place constraints on the
normalization of the matter power spectrum sigma_8 = 1.03^{+0.20}_{-0.29} at
68% confidence. The distribution of pixel fluxes in the BIMA images are found
to be consistent with simulated observations of the expected SZ background and
rule out instrumental noise or radio sources as the source of the observed
excess power with similar confidence to the detection of excess power.
Follow-up optical observations to search for galaxy over-densities
anti-correlated with flux in the BIMA images, as might be expected from the SZ
effect, proved to be inconclusive.Comment: Accepted by ApJ, 17 page
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