148 research outputs found
Spectral Line Survey toward Spiral Arm of M51 in the 3 mm and 2 mm Bands
We have conducted a spectral line survey in the 3 mm and 2 mm bands toward
two positions in a spiral arm of M51 (NGC 5194) with the IRAM 30 m telescope.
In this survey, we have identified 13 molecular species, including CN, CCH,
N2H+, HNCO, and CH3OH. Furthermore, 6 isotopologues of the major species have
been detected. On the other hand, SiO, HC3N, CH3CN, and the deuterated species
such as DCN and DCO+ are not detected. The deuterium fractionation ratios are
evaluated to be less than 0.8 % and 1.2 % for DCN/HCN and DCO+/HCO+,
respectively. By comparing the results of the two positions with different star
formation activities, we have found that the observed chemical compositions do
not strongly depend on star formation activities. They seem to reflect a
chemical composition averaged over the 1-kpc scale region including many giant
molecular clouds. Among the detected molecules CN, CCH, and CH3OH are found to
be abundant. High abundances of CN, and CCH are consistent with the above
picture of a wide spread distribution of molecules, because they can be
produced by photodissociation. On the other hand, it seems likely that CH3OH is
liberated into the gas phase by shocks associated with large scale phenomena
such as cloud-cloud collisions and/or by non-thermal desorption processes such
as photoevaporation due to cosmic-ray induced UV photons. The present result
demonstrates a characteristic chemical composition of a giant molecular cloud
complex in the spiral arm, which can be used as a standard reference for
studying chemistry in AGNs and starbursts.Comment: 45 pages, 12 figures, accepted for publication in Ap
Molecular Distribution in the Spiral Arm of M51
Molecular line images of 13CO, C18O, CN, CS, CH3OH, and HNCO are obtained
toward the spiral arm of M51 at a 7" times 6" resolution with the Combined
Array for Research in Millimeter-wave Astronomy (CARMA). Distributions of the
molecules averaged over a 300 pc scale are found to be almost similar to one
another and to essentially trace the spiral arm. However, the principal
component analysis shows a slight difference of distributions among molecular
species particularly for CH3OH and HNCO. These two species do not correlate
well with star-formation rate, implying that they are not enhanced by local
star-formation activities but by galactic-scale phenomena such as spiral
shocks. Furthermore, the distribution of HNCO and CH3OH are found to be
slightly different, whose origin deserves further investigation. The present
results provide us with an important clue to understanding the 300 pc scale
chemical composition in the spiral arm and its relation to galactic-scale
dynamics.Comment: 20 pages, 9 figures, 8 tables, accepted for publication in Ap
An unbiased spectral line survey observation toward the low-mass star-forming region L1527
An unbiased spectral line survey toward a solar-type Class 0/I protostar,
IRAS04368+2557, in L1527 has been carried out in the 3 mm band with the
Nobeyama 45 m telescope. L1527 is known as a warm carbon-chain chemistry (WCCC)
source, which harbors abundant unsaturated organic species such as CH () in a warm and dense region near the protostar. The
observation covers the frequency range from 80 to 116 GHz. A supplementary
observation has also been conducted in the 70 GHz band to observe fundamental
transitions of deuterated species. In total, 69 molecular species are
identified, among which 27 species are carbon-chain species and their isomers,
including their minor isotopologues. This spectral line survey provides us with
a good template of the chemical composition of the WCCC source.Comment: published online in PAS
A 3 mm Spectral Line Survey toward the Barred Spiral Galaxy NGC 3627
We conduct spectral line survey observations in the 3 mm band toward a spiral
arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC
3627 with the IRAM 30 m telescope and the Nobeyama 45 m telescope. Additional
observations are performed toward the spiral arm and the bar-end in the 2 mm
band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end,
and the nuclear region, respectively. Star-formation activities are different
among the three regions, and in particular, the nucleus of NGC 3627 is known as
a LINER/Seyfert 2 type nucleus. In spite of these physical differences, the
chemical composition shows impressive similarities among the three regions.
This result means that the characteristic chemical composition associated with
these regions is insensitive to the local physical conditions such as star
formation rate, because such local effects are smeared out by extended
quiescent molecular gas on scales of 1 kpc. Moreover, the observed chemical
compositions are also found to be similar to those of molecular clouds in our
Galaxy and the spiral arm of M51, whose elemental abundances are close to those
in NGC 3627. Therefore, this study provides us with a standard template of the
chemical composition of extended molecular clouds with the solar metalicity in
nearby galaxies.Comment: Accepted for publication in The Astrophysical Journal Supplement
Series, 10 figures, 10 table
RePair in Compressed Space and Time
Given a string of length , the goal of grammar compression is to
construct a small context-free grammar generating only . Among existing
grammar compression methods, RePair (recursive paring) [Larsson and Moffat,
1999] is notable for achieving good compression ratios in practice. Although
the original paper already achieved a time-optimal algorithm to compute the
RePair grammar RePair() in expected time, the study to reduce its
working space is still active so that it is applicable to large-scale data. In
this paper, we propose the first RePair algorithm working in compressed space,
i.e., potentially space for highly compressible texts. The key idea is
to give a new way to restructure an arbitrary grammar for into
RePair() in compressed space and time. Based on the recompression technique,
we propose an algorithm for RePair() in space and
expected time or
time, where is the size of and is the number of variables in
RePair(). We implemented our algorithm running in
time and show it can actually run in compressed space. We also present a new
approach to reduce the peak memory usage of existing RePair algorithms
combining with our algorithms, and show that the new approach outperforms, both
in computation time and space, the most space efficient linear-time RePair
implementation to date
The role of SiO as a tracer of past star-formation events: The case of the high-mass protocluster NGC 2264-C
NGC 2264-C is a high-mass protocluster where several star-formation events
are known to have occurred. To investigate whether past protostellar activity
has left a chemical imprint in this region, we mapped it in SiO(), a
shock tracer, and several other molecular lines with the Nobeyama 45 m
telescope. Our observations show the presence of a complex network of
protostellar outflows. The strongest SiO emission lies beyond a radius of pc with respect to the center of the clump, and is characterized by broad
( km s) lines and abundances of with
respect to H. Interestingly, SiO appears relatively depleted
() within this radius, despite it
being affected by molecular outflow activity. We attribute this to fast
condensation of SiO back onto dust grains and/or rapid gas-phase destruction of
SiO, favored by the high density present in this area ( cm).
Finally, we identify a peripheral, narrow-line ( km s)
component, where SiO has an abundance of a few times 10. After
considering different options, we conclude that this weak emission may be
tracing protostellar shocks from the star formation episode that preceded the
current one, which have decelerated over time and eventually resulted in SiO
being largely depleted/destroyed. Alternatively, a population of unresolved
low-mass protostars may be responsible for the narrow SiO emission.
High-angular resolution observations are necessary to distinguish between these
two possibilities and thus understand the role of SiO as a chemical tracer of
past star-formation episodes in massive protoclusters.Comment: 33 pages, 5 figure
Discovery of Striking Difference of Molecular-Emission-Line Richness in the Potential Proto-Binary System NGC 2264 CMM3
We have conducted an interferometric line survey in the 0.8 mm band toward
the young high-mass protostar candidate NGC 2264 CMM3 with ALMA. CMM3 is
resolved into the two continuum peaks, CMM3A and CMM3B, at an angular
separation of 0.9". Thus, CMM3 is found to be a binary system candidate. We
have detected molecular outflows associated with CMM3A and CMM3B each,
indicating active star formation. In addition to the two peaks, six faint
continuum peaks are detected around CMM3A and CMM3B, most of which are thought
to be evolved low-mass protostars. CMM3A is found to be rich in molecular line
emission including complex organic molecules such as HCOOCH3 and CH3OCH3. The
emission of complex organic molecules is distributed within a compact region
around the continuum peak of CMM3A. Hence, CMM3A apparently harbors a hot core.
On the other hand, CMM3B is deficient in molecular line emission, although its
continuum flux is almost comparable to that of CMM3A. Possible origins of the
striking difference between CMM3A and CMM3B are discussed.Comment: Accepted for publication in ApJ, 7 figures, 2 table
Molecular-Cloud-Scale Chemical Composition III: Constraints of Average Physical Properties through Chemical Models
It is important to understand the origin of molecular line intensities and
chemical composition in the molecular-cloud scale in the Galactic sources
because it serves as a benchmark to compare with the chemical compositions of
extragalactic sources. Recent observations of the 3-mm spectra averaged over
the 10-pc scale show similar spectral pattern among sources for molecular lines
HCN, HCO, CCH, HNC, HNCO, c-CH, CS, SO, NH, and CN. To
constrain the average physical property emitting such spectral pattern, we
model molecular spectra using a time-dependent gas-grain chemical model
followed by a radiative transfer calculation. We use a grid of physical
parameters such as the density cm, the
temperature, K, the visual extinction mag, the
cosmic-ray ionization rate s, and the
sulfur elemental abundance .
Comparison with the observed spectra indicates that spectra are well reproduced
with the relatively low density of cm, K,
s, and the short chemistry timescale of yrs.
This short chemistry timescale may indicate that molecular clouds are
constantly affected by the turbulence, and exposed to low-density, low regions that "refreshes" the chemical clock by UV radiation. The relatively
low density obtained is orders of magnitude lower than the commonly-quoted
critical density in the optically thin case. Meanwhile, this range of density
is consistent with results from recent observational analysis of
molecular-cloud-scale mapping.Comment: 30 pages, 21 figures, accepted for publication in The Astrophysical
Journa
Spectral Line Survey toward Molecular Clouds in the Large Magellanic Cloud
Spectral line survey observations of 7 molecular clouds in the Large
Magellanic Cloud (LMC) have been conducted in the 3 mm band with the Mopra 22 m
telescope to reveal chemical compositions in low metallicity conditions.
Spectral lines of fundamental species such as CS, SO, CCH, HCN, HCO+, and HNC
are detected in addition to those of CO and 13CO, while CH3OH is not detected
in any source and N2H+ is marginally detected in two sources. The
molecular-cloud scale (10 pc scale) chemical composition is found to be similar
among the 7 sources regardless of different star formation activities, and
hence, it represents the chemical composition characteristic to the LMC without
influences of star formation activities. In comparison with chemical
compositions of Galactic sources, the characteristic features are (1) deficient
N-bearing molecules, (2) abundant CCH, and (3) deficient CH3OH. The feature (1)
is due to a lower elemental abundance of nitrogen in the LMC, whereas the
features (2) and (3) seem to originate from extended photodissociation regions
and warmer temperature in cloud peripheries due to a lower abundance of dust
grains in the low metallicity condition. In spite of general resemblance of
chemical abundances among the seven sources, the CS/HCO+ and SO/HCO+ ratios are
found to be slightly higher in a quiescent molecular cloud. An origin of this
trend is discussed in relation to possible depletion of sulfur along molecular
cloud formation.Comment: 45 pages, 7 figures, 7 tables, accepted for publication in Ap
Spectrometer Using superconductor MIxer Receiver (SUMIRE) for Laboratory Submillimeter Spectroscopy
Recent spectroscopic observations by sensitive radio telescopes require
accurate molecular spectral line frequencies to identify molecular species in a
forest of lines detected. To measure rest frequencies of molecular spectral
lines in the laboratory, an emission-type millimeter and submillimeter-wave
spectrometer utilizing state-of-the-art radio-astronomical technologies is
developed. The spectrometer is equipped with a 200 cm glass cylinder cell, a
two sideband (2SB) Superconductor-Insulator-Superconductor (SIS) receiver in
the 230 GHz band, and wide-band auto-correlation digital spectrometers. By
using the four 2.5 GHz digital spectrometers, a total instantaneous bandwidth
of the 2SB SIS receiver of 8 GHz can be covered with a frequency resolution of
88.5 kHz. Spectroscopic measurements of CHCN and HDO are carried out in the
230 GHz band so as to examine frequency accuracy, stability, sensitivity, as
well as intensity calibration accuracy of our system. As for the result of
CHCN, we confirm that the frequency accuracy for lines detected with
sufficient signal to noise ratio is better than 1 kHz, when the high resolution
spectrometer having a channel resolution of 17.7 kHz is used. In addition, we
demonstrate the capability of this system by spectral scan measurement of
CHOH from 216 GHz to 264 GHz. We assign 242 transitions of CHOH, 51
transitions of CHOH, and 21 unidentified emission lines for 295
detected lines. Consequently, our spectrometer demonstrates sufficient
sensitivity, spectral resolution, and frequency accuracy for in-situ
experimental-based rest frequency measurements of spectral lines on various
molecular species.Comment: Accepted for publication in Publications of the Astronomical Society
of Japan (PASJ) , 15 figures, 4 tables, typos correcte
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