52 research outputs found
Submillimeter Line Emission from LMC 30Dor: The Impact of a Starburst on a Low Metallicity Environment
(Abridged) The 30 Dor region in the Large Magellanic Cloud (LMC) is the most
vigorous star-forming region in the Local Group. Star formation in this region
is taking place in low-metallicity molecular gas that is exposed to an extreme
far--ultraviolet (FUV) radiation field powered by the massive compact star
cluster R136. We used the NANTEN2 telescope to obtain high-angular resolution
observations of the 12CO 4-3, 7-6, and 13CO 4-3 rotational lines and [CI]
3P1-3P0 and 3P2-3P1 fine-structure submillimeter transitions in 30Dor-10, the
brightest CO and FIR-emitting cloud at the center of the 30Dor region. We
derived the properties of the low-metallicity molecular gas using an
excitation/radiative transfer code and found a self-consistent solution of the
chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR
model. We compared the derived properties with those in the N159W region, which
is exposed to a more moderate far-ultraviolet radiation field compared with
30Dor-10, but has similar metallicity. We also combined our CO detections with
previously observed low-J CO transitions to derive the CO spectral-line energy
distribution in 30Dor-10 and N159W. The separate excitation analysis of the
submm CO lines and the neutral carbon fine structure lines shows that the mid-J
CO and [CI]-emitting gas in the 30Dor-10 region has a temperature of about 160
K and a H2 density of about 10^4 cm^-3. We find that the molecular gas in
30Dor-10 is warmer and has a lower beam filling factor compared to that of
N159W, which might be a result of the effect of a strong FUV radiation field
heating and disrupting the low--metallicity molecular gas. We use a clumpy PDR
model (including the [CII] line intensity reported in the literature) to
constrain the FUV intensity to about chi_0 ~ 3100 and an average total H
density of the clump ensemble of about 10^5 cm^-3 in 30Dor-10.Comment: 11 pages, 8 figures. Accepted for publication in A&
Molecular Clouds associated with the Type Ia SNR N103B in the Large Magellanic Cloud
N103B is a Type Ia supernova remnant (SNR) in the Large Magellanic Cloud
(LMC). We carried out new CO( = 3-2) and CO( = 1-0)
observations using ASTE and ALMA. We have confirmed the existence of a giant
molecular cloud (GMC) at 245 km s towards the
southeast of the SNR using ASTE CO( = 3-2) data at an angular
resolution of 25 (6 pc in the LMC). Using the ALMA CO(
= 1-0) data, we have spatially resolved CO clouds along the southeastern edge
of the SNR with an angular resolution of 1.8 (0.4 pc in the
LMC). The molecular clouds show an expanding gas motion in the
position-velocity diagram with an expansion velocity of km s.
The spatial extent of the expanding shell is roughly similar to that of the
SNR. We also find tiny molecular clumps in the directions of optical nebula
knots. We present a possible scenario that N103B exploded in the wind-bubble
formed by the accretion winds from the progenitor system, and is now
interacting with the dense gas wall. This is consistent with a
single-degenerate scenario.Comment: 12 pages, 1 table, 8 figures, accepted for publication in The
Astrophysical Journal (ApJ
ALMA CO Observations of Supernova Remnant N63A in the Large Magellanic Cloud: Discovery of Dense Molecular Clouds Embedded within Shock-Ionized and Photoionized Nebulae
We carried out new CO( = 1-0, 3-2) observations of a N63A supernova
remnant (SNR) from the LMC using ALMA and ASTE. We find three giant molecular
clouds toward the northeast, east, and near the center of the SNR. Using the
ALMA data, we spatially resolved clumpy molecular clouds embedded within the
optical nebulae in both the shock-ionized and photoionized lobes discovered by
previous H and [S II] observations. The total mass of the molecular
clouds is for the shock-ionized region and
for the photoionized region. Spatially resolved X-ray spectroscopy
reveals that the absorbing column densities toward the molecular clouds are
- cm, which are - times less
than the averaged interstellar proton column densities for each region. This
means that the X-rays are produced not only behind the molecular clouds, but
also in front of them. We conclude that the dense molecular clouds have been
completely engulfed by the shock waves, but have still survived erosion owing
to their high-density and short interacting time. The X-ray spectrum toward the
gas clumps is well explained by an absorbed power-law or high-temperature
plasma models in addition to the thermal plasma components, implying that the
shock-cloud interaction is efficiently working for both the cases through the
shock ionization and magnetic field amplification. If the hadronic gamma-ray is
dominant in the GeV band, the total energy of cosmic-ray protons is calculated
to be - erg with the estimated ISM proton density
of cm, containing both the shock-ionized gas and
neutral atomic hydrogen.Comment: 18 pages, 4 tables, 8 figures, accepted for publication in The
Astrophysical Journal (ApJ
Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association
Furukawa et al. 2009 reported the existence of a large mass of molecular gas
associated with the super star cluster Westerlund 2 and the surrounding HII
region RCW49, based on a strong morphological correspondence between NANTEN2
12CO(J=2-1) emission and Spitzer IRAC images of the HII region. We here present
temperature and density distributions in the associated molecular gas at 3.5 pc
resolution, as derived from an LVG analysis of the 12CO(J=2-1), 12CO(J=1-0) and
13CO(J=2-1) transitions. The kinetic temperature is as high as 60-150 K within
a projected distance of 5-10 pc from Westerlund 2 and decreases to as low as 10
K away from the cluster. The high temperature provides robust verification that
the molecular gas is indeed physically associated with the HII region,
supporting Furukawa et al.'s conclusion. The derived temperature is also
roughly consistent with theoretical calculations of photo dissociation regions
(PDRs), while the low spatial resolution of the present study does not warrant
a more detailed comparison with PDR models. We suggest that the molecular
clouds presented here will serve as an ideal laboratory to test theories on
PDRs in future higher resolution studies.Comment: 23 pages, 5 figures, accepted for publication in Ap
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