63 research outputs found
The Detection of Hot Molecular Cores in the Small Magellanic Cloud
We report the first detection of hot molecular cores in the Small Magellanic
Cloud, a nearby dwarf galaxy with 0.2 solar metallicity. We observed two
high-mass young stellar objects in the SMC with ALMA, and detected emission
lines of CO, HCO+, H13CO+, SiO, H2CO, CH3OH, SO, and SO2. Compact hot-core
regions are traced by SO2, whose spatial extent is about 0.1 pc, and the gas
temperature is higher than 100 K based on the rotation diagram analysis. In
contrast, CH3OH, a classical hot-core tracer, is dominated by extended (0.2-0.3
pc) components in both sources, and the gas temperature is estimated to be
39+-8 K for one source. Protostellar outflows are also detected from both
sources as high-velocity components of CO. The metallicity-scaled abundances of
SO2 in hot cores are comparable among the SMC, LMC, and Galactic sources,
suggesting that the chemical reactions leading to SO2 formation would be
regulated by elemental abundances. On the other hand, CH3OH shows a large
abundance variation within SMC and LMC hot cores. The diversity in the initial
condition of star formation (e.g., degree of shielding, local radiation field
strength) may lead to the large abundance variation of organic molecules in hot
cores. This work, in conjunction with previous hot-core studies in the LMC and
outer/inner Galaxy, suggests that the formation of a hot core would be a common
phenomenon during high-mass star formation across the metallicity range of
0.2-1 solar metallicity. High-excitation SO2 lines will be a useful hot-core
tracer in the low-metallicity environments of the SMC and LMC.Comment: Accepted for publication in ApJL, 17 pages, 8 figures, 4 tables.
arXiv admin note: text overlap with arXiv:2109.1112
Molecular-Cloud-Scale Chemical Composition I: Mapping Spectral Line Survey toward W51 in the 3 mm Band
We have conducted a mapping spectral line survey toward the Galactic giant
molecular cloud W51 in the 3 mm band with the Mopra 22 m telescope in order to
study an averaged chemical composition of the gas extended over a molecular
cloud scale in our Galaxy. We have observed the area of , which
corresponds to 39 pc 47 pc. The frequency ranges of the observation
are 85.1 - 101.1 GHz and 107.0 - 114.9 GHz. In the spectrum spatially averaged
over the observed area, spectral lines of 12 molecular species and 4 additional
isotopologues are identified. An intensity pattern of the spatially-averaged
spectrum is found to be similar to that of the spiral arm in the external
galaxy M51, indicating that these two sources have similar chemical
compositions. The observed area has been classified into 5 sub-regions
according to the integrated intensity of CO() (), and contributions of the fluxes of 11 molecular lines from each
sub-region to the averaged spectrum have been evaluated. For most of molecular
species, 50 % or more of the flux come from the sub-regions with from 25 K km s to 100 K km s, which does not involve
active star forming regions. Therefore, the molecular-cloud-scale spectrum
observed in the 3 mm band hardly represents the chemical composition of star
forming cores, but mainly represents the chemical composition of an extended
quiescent molecular gas. The present result constitutes a sound base for
interpreting the spectra of external galaxies at a resolution of a molecular
cloud scale ( pc) or larger.Comment: Accepted for publication in Ap
AKARI Infrared Camera Survey of the Large Magellanic Cloud. I. Point Source Catalog
We present a near- to mid-infrared point source catalog of 5 photometric
bands at 3.2, 7, 11, 15 and 24 um for a 10 deg2 area of the Large Magellanic
Cloud (LMC) obtained with the Infrared Camera (IRC) onboard the AKARI
satellite. To cover the survey area the observations were carried out at 3
separate seasons from 2006 May to June, 2006 October to December, and 2007
March to July.
The 10-sigma limiting magnitudes of the present survey are 17.9, 13.8, 12.4,
9.9, and 8.6 mag at 3.2, 7, 11, 15 and 24 um, respectively. The photometric
accuracy is estimated to be about 0.1 mag at 3.2 um and 0.06--0.07 mag in the
other bands. The position accuracy is 0.3" at 3.2, 7 and 11um and 1.0" at 15
and 24 um. The sensitivities at 3.2, 7, and 24 um are roughly comparable to
those of the Spitzer SAGE LMC point source catalog, while the AKARI catalog
provides the data at 11 and 15 um, covering the mid-infrared spectral range
contiguously. Two types of catalog are provided: a Catalog and an Archive. The
Archive contains all the detected sources, while the Catalog only includes the
sources that have a counterpart in the Spitzer SAGE point source catalog. The
Archive contains about 650,000, 140,000, 97,000, 43,000, and 52,000 sources at
3.2, 7, 11, 15, and 24 um, respectively. Based on the catalog, we discuss the
luminosity functions at each band, the color-color diagram, and the
color-magnitude diagram using the 3.2, 7, and 11 um band data. Stars without
circumstellar envelopes, dusty C-rich and O-rich stars, young stellar objects,
and background galaxies are located at distinct regions in the diagrams,
suggesting that the present catalog is useful for the classification of objects
towards the LMC.Comment: 59 pages, 12 figures, accepted for the Astronomical Journa
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
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