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Register a new userLarge-scale CO (J=4-3) Mapping toward the Orion-A Giant Molecular Cloud
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We have mapped the Orion-A Giant Molecular Cloud in the CO (J=4-3) line with the Tsukuba 30-cm submillimeter telescope.The map covered a 7.125 deg^2 area with a 9 resolution, including main components of the cloud such as Orion Nebula, OMC-2/3, and L1641-N. The most intense emission was detected toward the Orion KL region. The integrated intensity ratio between CO (J=4-3) and CO (J=1-0) was derived using data from the Columbia-Univ. de Chile CO survey, which was carried out with a comparable angular resolution. The ratio was r_{4-3/1-0} ~ 0.2 in the southern region of the cloud and 0.4-0.8 at star forming regions. We found a trend that the ratio shows higher value at edges of the cloud. In particular the ratio at the north-eastern edge of the cloud at (l, b) = (208.375 deg, -19.0 deg) shows the specific highest value of 1.1. The physical condition of the molecular gas in the cloud was estimated by non-LTE calculation. The result indicates that the kinetic temperature has a gradient from north (Tkin=80 K) to south (20 K). The estimation shows that the gas associated with the edge of the cloud is warm (Tkin~60 K), dense (n_{H_2}~10^4 cm^{-3}), and optically thin, which may be explained by heating and sweeping of interstellar materials from OB clusters.
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Large scale mapping observations of the 3P1-3P0 fine structure transition of atomic carbon (CI, 492 GHz) and the J=3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mt. Fuji submillimeter-wave telescope. The observations cover 9 square degrees, and include the Orion nebula M42 and the L1641 dark cloud complex. The CI emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO(J=1-0).The CO(J=3-2) emission shows a more featureless and extended distribution than CI.The CI/CO(J=3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the CI/13CO(J=1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the CI and 13CO(J=1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.
We present the discovery of expanding spherical shells around low to intermediate-mass young stars in the Orion A giant molecular cloud using observations of $^{12}$CO (1-0) and $^{13}$CO (1-0) from the Nobeyama Radio Observatory 45-meter telescope. The shells have radii from 0.05 to 0.85 pc and expand outward at 0.8 to 5 km/s. The total energy in the expanding shells is comparable to protostellar outflows in the region. Together, shells and outflows inject enough energy and momentum to maintain the cloud turbulence. The mass-loss rates required to power the observed shells are two to three orders of magnitude higher than predicted for line-driven stellar winds from intermediate-mass stars. This discrepancy may be resolved by invoking accretion-driven wind variability. We describe in detail several shells in this paper and present the full sample in the online journal.
Context. Outflows provide indirect means to get an insight on diverse star formation associated phenomena. On scales of individual protostellar cores, outflows combined with intrinsic core properties can be used to study the mass accretion/ejection process of heavily embedded protostellar sources. Methods. An area comprising 460x230 of the Serpens cloud core has been mapped in 12 CO J = 3to 2 with the HARP-B heterodyne array at the James Clerk Maxwell Telescope; J = 3to 2 observations are more sensitive tracers of hot outflow gas than lower J CO transitions; combined with the high sensitivity of the HARP-B receptors outflows are sharply outlined, enabling their association with individual protostellar cores. Results. Most of ~20 observed outflows are found to be associated with known protostellar sources in bipolar or unipolar configurations. All but two outflow/core pairs in our sample tend to have a projected orientation spanning roughly NW-SE. The overall momentum driven by outflows in Serpens lies between 3.2 and 5.1 x 10^(-1) Modot km s^(-1), the kinetic energy from 4.3 to 6.7 x 10^(43) erg and momentum flux is between 2.8 and 4.4 x 10^(-4) Modot km s^(-1) yr^(-1). Bolometric luminosities of protostellar cores based on Spitzer photometry are found up to an order of magnitude lower than previous estimations derived with IRAS/ISO data. Conclusions. We confirm the validity of the existing correlations between the momentum flux and bolometric luminosity of Class I sources for the homogenous sample of Serpens, though we suggest that they should be revised by a shift to lower luminosities. All protostars classified as Class 0 sources stand well above the known Class I correlations, indicating a decline in momentum flux between the two classes.
Infrared Dark Clouds (IRDCs) are cold, high mass surface density and high density structures, likely to be representative of the initial conditions for massive star and star cluster formation. CO emission from IRDCs has the potential to be useful for tracing their dynamics, but may be affected by depleted gas phase abundances due to freeze-out onto dust grains. Here we analyze C18O J=1-0 and J=2-1 emission line data, taken with the IRAM 30m telescope, of the highly filamentary IRDC G035.39.-0033. We derive the excitation temperature as a function of position and velocity, with typical values of ~7K, and thus derive total mass surface densities, Sigma_C18O, assuming standard gas phase abundances and accounting for optical depth in the line, which can reach values of ~1. The mass surface densities reach values of ~0.07 g/cm^2. We compare these results to the mass surface densities derived from mid-infrared (MIR) extinction mapping, Sigma_SMF, by Butler & Tan, which are expected to be insensitive to the dust temperatures in the cloud. With a significance of >10sigma, we find Sigma_C18O/Sigma_SMF decreases by about a factor of 5 as Sigma increases from ~0.02 to ~0.2 g/cm^2, which we interpret as evidence for CO depletion. Several hundred solar masses are being affected, making this one of the most massive clouds in which CO depletion has been observed directly. We present a map of the depletion factor in the filament and discuss implications for the formation of the IRDC.
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 $25 times 30$, which corresponds to 39 pc $times$ 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 $^{13}$CO($J=1-0$) ($I_{rm ^{13}CO}$), 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 $I_{rm ^{13}CO}$ from 25 K km s$^{-1}$ to 100 K km s$^{-1}$, 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 ($sim10$ pc) or larger.
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