32 research outputs found
Cosmic-ray-driven enhancement of the C/CO abundance ratio in W51C
We examine spatial variations of the C/CO abundance ratio
() in the vicinity of the -ray supernova remnant
W51C, based on [CI] (-), CO(1-0), and CO(1-0)
observations with the ASTE and Nobeyama 45-m telescopes. We find that
varies in a range of 0.02-0.16 (0.05 in median) inside the
molecular clouds of 100 mag, where photodissociation of CO by the
interstellar UV is negligible. Furthermore, is locally
enhanced up to by a factor of four near the W51C center, depending on the
projected distance from the W51C center. In high- molecular clouds,
is determined by the ratio of the cosmic-ray (CR)
ionization rate to the H density, and we find no clear spatial variation of
the H density against the projected distance. Hence, the high CR ionization
rate may locally enhance near the W51C center. We also find
that the observed spatial extent of the enhanced (17
pc) is consistent with the diffusion distance of CRs with the energy of 100
MeV. The fact suggests that the low-energy CRs accelerated in W51C enhance
. The CR ionization rate at the -enhanced
cloud is estimated to be 310 s on the basis of
time-dependent PDR simulations of , the value of which is 30
times higher than that in the standard Galactic environment. These results
demonstrate that [CI] is a powerful probe to investigate the interaction
between CRs and the interstellar medium for a wide area in the vicinity of
supernova remnants.Comment: 17 pages, 8 figures, accepted for publication in PAS
Material properties of a low contraction and resistivity silicon-aluminum composite for cryogenic detectors
We report on the cryogenic properties of a low-contraction silicon-aluminum
composite, namely Japan Fine Ceramics SA001, to use as a packaging structure
for cryogenic silicon devices. SA001 is a silicon--aluminum composite material
(75% silicon by volume) and has a low thermal expansion coefficient (1/3
that of aluminum). The superconducting transition temperature of SA001 is
measured to be 1.18 K, which is in agreement with that of pure aluminum, and is
thus available as a superconducting magnetic shield material. The residual
resistivity of SA001 is 0.065 , which is considerably
lower than an equivalent silicon--aluminum composite material. The measured
thermal contraction of SA001 immersed in liquid nitrogen is
%, which is
consistent with the expected rate obtained from the volume-weighted mean of the
contractions of silicon and aluminum. The machinability of SA001 is also
confirmed with a demonstrated fabrication of a conical feedhorn array, with a
wall thickness of 100 . These properties are suitable for
packaging applications for large-format superconducting detector devices.Comment: 8 pages, 4 figures, 1 table, accepted for the Journal of Low
Temperature Physics for the LTD19 special issu
An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog
The nature of molecular clouds and their statistical behavior in sub-solar
metallicity environments are not fully explored yet. We analyzed an unbiased
CO( = 2-1) survey data at a spatial resolution of 2 pc in the northern
region of the Small Magellanic Cloud (SMC) with the Atacama Compact Array to
characterize the CO cloud properties. A cloud decomposition analysis identified
426 spatially/velocity-independent CO clouds and their substructures. Based on
the cross-matching with known infrared catalogs by Spitzer and Herschel, more
than 90% CO clouds show spatial correlations with point sources. We
investigated the basic properties of the CO clouds and found that the
radius-velocity linewidth (-) relation follows the Milky Way
(MW) like power-low exponent, but the intercept is 1.5 times lower than
that in the MW. The mass functions () of the CO luminosity and virial
mass are characterized by an exponent of 1.7, which is consistent with
previously reported values in the Large Magellanic Cloud and MW.Comment: 18 pages, 9 figures. Accepted for publication in The Astrophysical
Journa
Dense Clumps in Giant Molecular Clouds in the Large Magellanic Cloud: Density and Temperature Derived from CO() Observations
In order to precisely determine temperature and density of molecular gas in
the Large Magellanic Cloud, we made observations of optically thin
CO() transition by using the ASTE 10m telescope toward 9 peaks
where CO() clumps were previously detected with the same
telescope. The molecular clumps include those in giant molecular cloud (GMC)
Types I (with no signs of massive star formation), II (with HII regions only),
and III (with HII regions and young star clusters). We detected
CO() emission toward all the peaks and found that their
intensities are 3 -- 12 times lower than those of CO(). We
determined the intensity ratios of CO() to CO(),
, and CO() to CO(),
, at 45\arcsec resolution. These ratios were used for
radiative transfer calculations in order to estimate temperature and density of
the clumps. The parameters of these clumps range kinetic temperature
= 15 -- 200 K, and molecular hydrogen gas density
= 8 -- 7 cm. We confirmed
that the higher density clumps show higher kinetic temperature and that the
lower density clumps lower kinetic temperature at a better accuracy than in the
previous work. The kinetic temperature and density increase generally from a
Type I GMC to a Type III GMC. We interpret that this difference reflects an
evolutionary trend of star formation in molecular clumps. The
and kinetic temperature of the clumps are well correlated
with H flux, suggesting that the heating of molecular gas
= -- cm can be explained by stellar FUV
photons.Comment: 39 pages, 7 figures, 4 tables. Accepted for publication in The
Astronomical Journa
TiEMPO: Open-source time-dependent end-to-end model for simulating ground-based submillimeter astronomical observations
The next technological breakthrough in millimeter-submillimeter astronomy is
3D imaging spectrometry with wide instantaneous spectral bandwidths and wide
fields of view. The total optimization of the focal-plane instrument, the
telescope, the observing strategy, and the signal-processing software must
enable efficient removal of foreground emission from the Earth's atmosphere,
which is time-dependent and highly nonlinear in frequency. Here we present
TiEMPO: Time-Dependent End-to-End Model for Post-process Optimization of the
DESHIMA Spectrometer. TiEMPO utilizes a dynamical model of the atmosphere and
parametrized models of the astronomical source, the telescope, the instrument,
and the detector. The output of TiEMPO is a time-stream of sky brightness
temperature and detected power, which can be analyzed by standard
signal-processing software. We first compare TiEMPO simulations with an on-sky
measurement by the wideband DESHIMA spectrometer and find good agreement in the
noise power spectral density and sensitivity. We then use TiEMPO to simulate
the detection of a line emission spectrum of a high-redshift galaxy using the
DESHIMA 2.0 spectrometer in development. The TiEMPO model is open source. Its
modular and parametrized design enables users to adapt it to design and
optimize the end-to-end performance of spectroscopic and photometric
instruments on existing and future telescopes.Comment: Presented at SPIE Astronomical Telescopes + Instrumentation 2020.
Full published paper, poster and video available at
https://doi.org/10.1117/12.2561014 Open-source Python package of TiEMPO:
https://pypi.org/project/tiempo-deshima/ Open-source code of TiEMPO:
https://zenodo.org/record/4279086#.X_jAsdhKg2