- ID:
- ivo://CDS.VizieR/J/ApJ/839/113
- Title:
- Molecular clouds with GLIMPSE/MIPSGAL data
- Short Name:
- J/ApJ/839/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the star-formation (SF) law in 12 Galactic molecular clouds with ongoing high-mass star-formation (HMSF) activity, as traced by the presence of a bright IRAS source and other HMSF tracers. We define the molecular cloud (MC) associated with each IRAS source using ^13^CO line emission, and count the young stellar objects (YSOs) within these clouds using GLIMPSE and MIPSGAL 24{mu}m Spitzer databases. The masses for high-luminosity YSOs (L_bol_>10L_{sun}_) are determined individually using pre-main-sequence evolutionary tracks and the evolutionary stages of the sources, whereas a mean mass of 0.5M_{sun}_ was adopted to determine the masses in the low-luminosity YSO population. The star-formation rate surface density ({Sigma}SFR) corresponding to a gas surface density ({Sigma}gas) in each MC is obtained by counting the number of the YSOs within successive contours of ^13^CO line emission. We find a break in the relation between {Sigma}SFR and {Sigma}gas, with the relation being a power law ({Sigma}SFR{propto}{Sigma}gas^N^) with the index N varying between 1.4 and 3.6 above the break. The {Sigma}gas at the break is between 150-360M_{sun}_/pc^2^ for the sample clouds, which compares well with the threshold gas density found in recent studies of Galactic star-forming regions. Our clouds treated as a whole lie between the Kennicutt relation and the linear relation for Galactic and extra-galactic dense star-forming regions. We find a tendency for the high- mass YSOs to be found preferentially in dense regions at densities higher than 1200M_{sun}_/pc^2^ (~0.25g/cm^2^).
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/other/RAA/20.115
- Title:
- Molecular clumps CO, HCO and HCN data
- Short Name:
- J/other/RAA/20.1
- Date:
- 19 Jan 2022 00:26:13
- Publisher:
- CDS
- Description:
- Gravitational accretion accumulates the original mass. This process is crucial for us to understand the initial phases of star formation. Using the specific infall profiles in optically thick and thin lines, we searched the clumps with infall motion from the Milky Way Imaging Scroll Painting (MWISP) CO data in previous work. In this study, we selected 133 sources as a sub-sample for further research and identification. The excitation temperatures of these sources are between 7.0 and 38.5K, while the H_2_ column densities are between 10^21^ and 10^23^cm^-2^. We have observed optically thick lines HCO+(1-0) and HCN(1-0) using the DLH 13.7-m telescope, and found 56 sources with a blue profile and no red profile in these two lines, which are likely to have infall motions, with a detection rate of 42%. This suggests that using CO data to restrict the sample can effectively improve the infall detection rate. Among these confirmed infall sources are 43 associated with Class 0/I young stellar objects (YSOs), and 13 which are not. These 13 sources are probably associated with the sources in the earlier evolutionary stage. In comparison, the confirmed sources that are associated with Class 0/I YSOs have higher excitation temperatures and column densities, while the other sources are colder and have lower column densities. Most infall velocities of the sources that we confirmed are between 10^-1^ to 100km/s, which is consistent with previous studies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/424/1658
- Title:
- Molecular clumps in W51 giant molecular cloud
- Short Name:
- J/MNRAS/424/1658
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present a catalogue of dense molecular clumps located within the W51 giant molecular cloud (GMC). This work is based on Heterodyne Array Receiver Programme ^13^CO J=3-2 observations of the W51 GMC and uses the automated CLUMPFIND algorithm to decompose the region into a total of 1575 clumps of which 1130 are associated with the W51 GMC. We clearly see the distinct structures of the W51 complex and the high-velocity stream previously reported.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A95
- Title:
- Molecular DNM in Chamaeleon CO spectra
- Short Name:
- J/A+A/627/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To determine carbon monoxide column densities along sightlines through the Chamaeleon cloud complex where molecular absorption had been observed but CO emission had not been detected. We took ^12^CO J=1-0 absorption profiles toward 6 of 8 members of a group of sightlines in Chamaeleon having abundant dark neutral matter and molecular hydrogen but no detectable CO emission. CO absorption was detected along five of the six sightlines at column densities 4x10^+13^cm^-2^<~N(CO)<~10^15^cm^-2^ that are below typical survey detection limits of 1-2K-km/s. Dark gas absent in CO emission along sightlines in the outskirts of the Chamaeleon complex where molecular gas is readily detected in HCO^+^ absorption results from small CO column densities around the onset of CO formation at the HI/H_2_ transition. Relative abundances N(CO)/H_2_<3x10^-6^ in Chamaeleon are comparable to those seen in UV absorption toward early-type stars and in a CO absorption/emission line survey toward local quasar background targets away from the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A97
- Title:
- Molecular emission from the Perseus cloud
- Short Name:
- J/A+A/646/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The traditional technique to characterize the structure of molecular clouds is mapping their line emission. We aim to test and apply a sampling technique that can characterize the line emission from a molecular cloud more efficiently than mapping. We have sampled the molecular emission from the Perseus cloud using the H_2_ column density as a proxy. We have divided the cloud into 10 logarithmically- spaced column density bins, and we have selected 10 random positions from each bin. The resulting 100 cloud positions have been observed with the IRAM 30m telescope covering the 3mm-wavelength band and parts of the 2mm and 1mm bands. We focus our analysis on the eleven molecular species (plus isotopologs) detected toward most column density bins. In all cases, the line intensity is tightly correlated with the H_2_ column density. For the CO isotopologs, the correlation is relatively flat, while for most dense gas tracers, the correlation is approximately linear. To reproduce these trends, we have developed a cloud model in which most species have abundance profiles characterized by an outer photo-dissociation edge and an inner freeze-out drop. With this model we determine that the intensity behavior of the dense gas tracers arises from a combination of excitation effects and molecular freeze out, with some modulation from optical depth. The quasi-linear dependence of the dense-gas tracer emission with H_2_ column density makes the gas at low column densities dominate the cloud- integrated emission. It also makes this emission proportional to the cloud mass inside the photodissociation edge. Stratified random sampling is an efficient technique to characterize the emission from molecular clouds. Despite its complex appearance, the molecular emission from Perseus presents a relatively simple behavior that, from a limited comparison with other clouds, seems to reflect a general pattern.
- ID:
- ivo://CDS.VizieR/J/A+A/496/153
- Title:
- Molecular hydrogen flows along Ori A cloud
- Short Name:
- J/A+A/496/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A census of molecular hydrogen flows across the entire Orion A giant molecular cloud is sought. With this paper we aim to associate each flow with its progenitor and associated molecular core, so that the characteristics of the outflows and outflow sources can be established. We present wide-field near-infrared images of Orion A, obtained with the Wide Field Camera, WFCAM, on the United Kingdom Infrared Telescope. Broad-band K and narrow-band H_2_ 1-0S(1) images of a contiguous ~8 square degree region are compared to mid-IR photometry from the Spitzer Space Telescope and (sub)millimetre dust-continuum maps obtained with the MAMBO and SCUBA bolometer arrays. Using previously-published H_2_ images, we also measured proper motions for H_2_ features in 33 outflows, and use these data to help associate flows with existing sources and/or dust cores.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A64
- Title:
- Molecular ions in L1157-B1
- Short Name:
- J/A+A/565/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we perform a complete census of molecular ions with an abundance larger than ~10^-10^ in the protostellar shock L1157-B1. This allows us to study the ionization structure and chemistry of the shock. An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30m and Herschel/HIFI as part of the CHESS and ASAI large programs allows searching for molecular ions emission. Then, by means of a radiative transfer code in the Large Velocity Gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem.
- ID:
- ivo://CDS.VizieR/J/A+A/570/A51
- Title:
- Molecular lines in 4 IRCS clumps
- Short Name:
- J/A+A/570/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The earliest phases of high-mass star formation are poorly understood. Aims. Our goal is to determine the physical conditions and kinematic structure of massive starforming cloud clumps. We analyse H_2_O 557GHz line profiles observed with HIFI toward four positions in two infrared-dark cloud clumps. By comparison with ground-based C_17_O, N_2_H^+^, CH_3_OH, and NH_3_ line observations, we constrain the volume density and kinetic temperature of the gas and estimate the column density and abundance of H_2_O and N_2_H^+^. The observed water lines are complex with emission and absorption components. The absorption is redshifted and consistent with a cold envelope, while the emission is interpreted as resulting from proto-stellar outflows. The gas density in the clumps is ~10^7^cm^-3^. The o-H_2_O outflow column density is 0.3-3.0x10^14^cm^-2^. The o-H_2_O absorption column density is between 1.5x10^14^ and 2.6x10^15^cm^-2^ with cold o-H_2_O abundances between 1.5x10^-9^ and 3.1x10^-8^. All clumps have high gas densities (~10^7^cm^-3^) and display infalling gas. Three of the four clumps have outflows. The clumps form an evolutionary sequence as probed by H_2_O N_2_H+, NH_3_, and CH_3_OH. We find that G28-MM is the most evolved, followed by G11-MM and then G28-NH3. The least evolved clump is G11-NH3 which shows no signposts of starformation; G11-NH3 is a high-mass pre-stellar core.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/85
- Title:
- Molecular line study of infrared dark clouds
- Short Name:
- J/ApJ/780/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is currently assumed that infrared dark clouds (IRDCs) represent the earliest evolutionary stages of high-mass stars (>8M_{sun}_). Submillimeter and millimeter-wave studies performed over the past 15yr show that IRDCs possess a broad variety of properties, and hence a wide range of problems and questions that can be tackled. In this paper, we report an investigation of the molecular composition and chemical processes in two groups of IRDCs. Using the Mopra, APEX, and IRAM radio telescopes over the last four years, we have collected molecular line data for CO, H_2_CO, HNCO, CH_3_CCH, CH_3_OH, CH_3_CHO, CH_3_OCHO, and CH_3_OCH_3_. For all of these species we estimated molecular abundances. We then undertook chemical modeling studies, concentrating on the source IRDC028.34+0.06, and compared observed and modeled abundances. This comparison showed that to reproduce observed abundances of complex organic molecules, a zero-dimensional gas-grain model with constant physical conditions is not sufficient. We achieved greater success with the use of a warm-up model, in which warm-up from 10K to 30K occurs following a cold phase.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A123
- Title:
- Molecular maps of NGC1333
- Short Name:
- J/A+A/606/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Are the initial conditions for clustered star formation the same as for non-clustered star formation? To investigate the initial gas properties in young proto-clusters we carried out a comprehensive and high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content of the NGC1333 region in Perseus, one of the nearest and best studied embedded clusters. The analysis of the gas velocities in the Position-Position-Velocity space reveals an intricate underlying gas organization both in space and velocity. We identified a total of 14 velocity-coherent, (tran-)sonic structures within NGC1333, with similar physical and kinematic properties than those quiescent, star-forming (aka fertile) fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. Our results demonstrate that the presence of fibers is not restricted to low-mass clouds but can be extended to regions of increasing mass and complexity. We propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of fertile fibers in these environments.
