The study of multiple molecular spectral lines in gas infalling sources can provide the physical and chemica properties of these sources and help us estimate their evolutionary stages.We report line detections within ...The study of multiple molecular spectral lines in gas infalling sources can provide the physical and chemica properties of these sources and help us estimate their evolutionary stages.We report line detections within the 3 mm band using the FTS wide-sideband mode of the IRAM 30 m telescope toward 20 gas-infalling sources.Using XCLASS,we identify the emission lines of up to 22 molecular species(including a few isotopologues)and on hydrogen radio recombination line in these sources.H^(13)CO^(+),HCO^(+),HCN,HNC,c-C_(3)H_(2),and CCH lines are detected in 15 sources.We estimate the rotation temperatures and column densities of these molecular species using the LTE radiative transfer model,and compare the molecular abundances of these sources with those from nine high mass star-forming regions reported in previous studies and with those from the chemical model.Our results sugges that G012.79-0.20,G012.87-0.22 clump A and B,and G012.96-0.23 clump A may be in the high-mass protostella object stage,while sources with fewer detected species may be in the earlier evolutionary stage.Additionally,th CCH and c-C_(3)H_(2)column densities in our sources reveal a linear correlation,with a ratio of N(CCH)/N(c-C_(3)H_(2)=89.2±5.6),which is higher than the ratios reported in the literature.When considering only sources with lowe column densities,this ratio decreases to 29.0±6.1,consistent with those of diffuse clouds.Furthermore,comparison between the N(CCH)/N(c-C_(3)H_(2))ratio and the sources’physical parameters reveals a correlation,with sources exhibiting higher ratios tending to have higher kinetic temperatures and H2column densities.展开更多
Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson’s first relation,which is often attributed to the turbulent nature of molecular...Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson’s first relation,which is often attributed to the turbulent nature of molecular ISM and imprints the dynamics of molecular cloud structures.Using the^(13)CO(J=1-0)data from the Milky Way Imaging Scroll Painting survey,we built a sample with 360 structures having relatively accurate distances obtained from either the reddened background stars with Gaia parallaxes or associated maser parallaxes,spanning from 0.4 to~15 kpc.Using this sample and about 0.3 million pixels,we analyzed the correlations between velocity dispersion,surface/column density,and spatial scales.Our structure-wise results show power-law indices smaller than 0.5 in both theσ_(v)-R_(eff)andσ_(v)-R_(eff)·Σrelations.In the pixel-wise results,the v spix is statistically scaling with the beam physical size(R_(s)≡ΘD/2)in form ofσ_(v)^(pix)■R_(s)^(0.43±0.03).Meanwhile,σ_(v)_(pix)in the inner Galaxy is statistically larger than the outer side.We also analyzed correlations betweenσ_(v)_(pix)and the H_(2)column density N(H_(2)),finding thatσ_(v)_(pix)stops increasing with N(H_(2))after>10^(22)cm^(-2).The structures with and without high-column-density(>10^(22)cm^(-2))pixels show differentσ_(v)_(pix)■N(H_(2))^(ξ)relations,where the mean(std)ξvalues are 0.38(0.14)and 0.62(0.27),respectively.展开更多
We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation.Our first step is to utilize the data products by MWISP to make an unbiased survey for blue a...We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation.Our first step is to utilize the data products by MWISP to make an unbiased survey for blue asymmetric line profiles of CO isotopical molecules.Within a total area of~2400 square degrees nearby the Galactic plane,we have found 3533 candidates showing blue-profiles,in which 3329 are selected from the^(12)CO&^(13)CO pair and 204 are from the^(13)CO&C^(18)O pair.Exploration of the parametric spaces suggests our samples are in the cold phase with relatively high column densities ready for star formation.Analysis of the spatial distribution of our samples suggests that they exist virtually in all major components of the galaxy.The vertical distribution suggest that the sources are located mainly in the thick disk of~85 pc,but still a small part are located far beyond Galactic midplane.Our follow-up observation indicates that these candidates are a good sample to start a search for infall motions,and to study the condition of very early phase of star formation.展开更多
The research of infall motion is a common means to study molecular cloud dynamics and the early process of star formation. Many works had been done in-depth research on infall. We searched the literature related to in...The research of infall motion is a common means to study molecular cloud dynamics and the early process of star formation. Many works had been done in-depth research on infall. We searched the literature related to infall study of molecular cloud since 1994, summarized the infall sources identified by the authors. A total of 456 infall sources are cataloged. We classify them into high-mass and low-mass sources, in which the high-mass sources are divided into three evolutionary stages: prestellar, protostellar and H II region. We divide the sources into clumps and cores according to their sizes. The H2 column density values range from 1.21 × 10^(21) to 9.75 × 10^(24) cm^(-2), with a median value of 4.17 × 10^(22) cm^(-2). The H_(2) column densities of high-mass and low-mass sources are significantly separated. The median value of infall velocity for high-mass clumps is 1.12 km s^(-1), and the infall velocities of lowmass cores are virtually all less than 0.5 km s^(-1). There is no obvious difference between different stages of evolution. The mass infall rates of low-mass cores are between 10^(-7) and 10^(-4) M⊙yr^(-1), and those of high-mass clumps are between 10^(-4 )and 10-1 M⊙yr^(-1) with only one exception. We do not find that the mass infall rates vary with evolutionary stages.展开更多
We report on the near-infrared polarimetric observations of RCW 120 with the 1.4 m IRSF telescope.The starlight polarization of the background stars reveals for the first time the magnetic field of RCW 120.The global ...We report on the near-infrared polarimetric observations of RCW 120 with the 1.4 m IRSF telescope.The starlight polarization of the background stars reveals for the first time the magnetic field of RCW 120.The global magnetic field of RCW 120 is along the direction of 20°,parallel to the Galactic plane.The field strength on the plane of the sky is 100 ± 26 μG.The magnetic field around the eastern shell shows evidence of compression by the H Ⅱ region.The external pressure(turbulent pressure+ magnetic pressure) and the gas density of the ambient cloud are minimum along the direction where RCW 120 breaks out,which explains the observed elongation of RCW 120.The dynamical age of RCW 120,depending on the magnetic field strength,is~1.6 Myr for field strength of100 μG,older than the hydrodynamic estimates.In direction perpendicular to the magnetic field,the density contrast of the western shell is greatly reduced by the strong magnetic field.The strong magnetic field in general reduces the efficiency of triggered star formation,in comparison with the hydrodynamic estimates.Triggered star formation via the "collect and collapse" mechanism could occur in the direction along the magnetic field.Core formation efficiency(CFE) is found to be higher in the southern and eastern shells of RCW 120 than in the infrared dark cloud receiving little influence from the H Ⅱ region,suggesting increase in the CFE related to triggering from ionization feedback.展开更多
基金supported by the National Key R&D Program of China(No.2022YFA1603102)the National Natural Science Foundation of China(NSFC,Grant Nos.U2031202,12373030,and 11873093)。
文摘The study of multiple molecular spectral lines in gas infalling sources can provide the physical and chemica properties of these sources and help us estimate their evolutionary stages.We report line detections within the 3 mm band using the FTS wide-sideband mode of the IRAM 30 m telescope toward 20 gas-infalling sources.Using XCLASS,we identify the emission lines of up to 22 molecular species(including a few isotopologues)and on hydrogen radio recombination line in these sources.H^(13)CO^(+),HCO^(+),HCN,HNC,c-C_(3)H_(2),and CCH lines are detected in 15 sources.We estimate the rotation temperatures and column densities of these molecular species using the LTE radiative transfer model,and compare the molecular abundances of these sources with those from nine high mass star-forming regions reported in previous studies and with those from the chemical model.Our results sugges that G012.79-0.20,G012.87-0.22 clump A and B,and G012.96-0.23 clump A may be in the high-mass protostella object stage,while sources with fewer detected species may be in the earlier evolutionary stage.Additionally,th CCH and c-C_(3)H_(2)column densities in our sources reveal a linear correlation,with a ratio of N(CCH)/N(c-C_(3)H_(2)=89.2±5.6),which is higher than the ratios reported in the literature.When considering only sources with lowe column densities,this ratio decreases to 29.0±6.1,consistent with those of diffuse clouds.Furthermore,comparison between the N(CCH)/N(c-C_(3)H_(2))ratio and the sources’physical parameters reveals a correlation,with sources exhibiting higher ratios tending to have higher kinetic temperatures and H2column densities.
基金supported by the National Key R&D Program of China(grant No.2023YFA1608000)the National Natural Science Foundation of China(NSFC,grant Nos.U2031202,12373030,and 11873093)+2 种基金sponsored by the National Key R&D Program of China with grant 2023YFA1608000the CAS Key Research Program of Frontier Sciences with grant QYZDJ-SSW-SLH047Z.C.acknowledges the Natural Science Foundation of Jiangsu Province(grant No.BK20231509)。
文摘Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson’s first relation,which is often attributed to the turbulent nature of molecular ISM and imprints the dynamics of molecular cloud structures.Using the^(13)CO(J=1-0)data from the Milky Way Imaging Scroll Painting survey,we built a sample with 360 structures having relatively accurate distances obtained from either the reddened background stars with Gaia parallaxes or associated maser parallaxes,spanning from 0.4 to~15 kpc.Using this sample and about 0.3 million pixels,we analyzed the correlations between velocity dispersion,surface/column density,and spatial scales.Our structure-wise results show power-law indices smaller than 0.5 in both theσ_(v)-R_(eff)andσ_(v)-R_(eff)·Σrelations.In the pixel-wise results,the v spix is statistically scaling with the beam physical size(R_(s)≡ΘD/2)in form ofσ_(v)^(pix)■R_(s)^(0.43±0.03).Meanwhile,σ_(v)_(pix)in the inner Galaxy is statistically larger than the outer side.We also analyzed correlations betweenσ_(v)_(pix)and the H_(2)column density N(H_(2)),finding thatσ_(v)_(pix)stops increasing with N(H_(2))after>10^(22)cm^(-2).The structures with and without high-column-density(>10^(22)cm^(-2))pixels show differentσ_(v)_(pix)■N(H_(2))^(ξ)relations,where the mean(std)ξvalues are 0.38(0.14)and 0.62(0.27),respectively.
基金supported by the National Key R&D Program of China(Grant No.2017YFA0402702)the National Natural Science Foundation of China(NSFC,Grant Nos.,11873093,U2031202,and 11903083)+1 种基金sponsored by the National Key R&D Program of China with Grant 2017YFA0402701CAS Key Research Program of Frontier Sciences with grant QYZDJ-SSW-SLH047。
文摘We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation.Our first step is to utilize the data products by MWISP to make an unbiased survey for blue asymmetric line profiles of CO isotopical molecules.Within a total area of~2400 square degrees nearby the Galactic plane,we have found 3533 candidates showing blue-profiles,in which 3329 are selected from the^(12)CO&^(13)CO pair and 204 are from the^(13)CO&C^(18)O pair.Exploration of the parametric spaces suggests our samples are in the cold phase with relatively high column densities ready for star formation.Analysis of the spatial distribution of our samples suggests that they exist virtually in all major components of the galaxy.The vertical distribution suggest that the sources are located mainly in the thick disk of~85 pc,but still a small part are located far beyond Galactic midplane.Our follow-up observation indicates that these candidates are a good sample to start a search for infall motions,and to study the condition of very early phase of star formation.
基金supported by the National Key R&D Program of China (Grant No. 2017YFA0402702)National Natural Science Foundation of China (NSFC, Grant Nos.11873093 and U2031202)support from the NSFC (Grant No. 11903083)。
文摘The research of infall motion is a common means to study molecular cloud dynamics and the early process of star formation. Many works had been done in-depth research on infall. We searched the literature related to infall study of molecular cloud since 1994, summarized the infall sources identified by the authors. A total of 456 infall sources are cataloged. We classify them into high-mass and low-mass sources, in which the high-mass sources are divided into three evolutionary stages: prestellar, protostellar and H II region. We divide the sources into clumps and cores according to their sizes. The H2 column density values range from 1.21 × 10^(21) to 9.75 × 10^(24) cm^(-2), with a median value of 4.17 × 10^(22) cm^(-2). The H_(2) column densities of high-mass and low-mass sources are significantly separated. The median value of infall velocity for high-mass clumps is 1.12 km s^(-1), and the infall velocities of lowmass cores are virtually all less than 0.5 km s^(-1). There is no obvious difference between different stages of evolution. The mass infall rates of low-mass cores are between 10^(-7) and 10^(-4) M⊙yr^(-1), and those of high-mass clumps are between 10^(-4 )and 10-1 M⊙yr^(-1) with only one exception. We do not find that the mass infall rates vary with evolutionary stages.
基金supported by the National Key Research & Development Program of China (2017YFA0402702)the general Grant Nos. 11903083, 12173090, U2031202, 11873093, 11873094 from the National Natural Science Foundation of Chinathe science research grants from the China Manned Space Project with No. CMS-CSST2021-B06。
文摘We report on the near-infrared polarimetric observations of RCW 120 with the 1.4 m IRSF telescope.The starlight polarization of the background stars reveals for the first time the magnetic field of RCW 120.The global magnetic field of RCW 120 is along the direction of 20°,parallel to the Galactic plane.The field strength on the plane of the sky is 100 ± 26 μG.The magnetic field around the eastern shell shows evidence of compression by the H Ⅱ region.The external pressure(turbulent pressure+ magnetic pressure) and the gas density of the ambient cloud are minimum along the direction where RCW 120 breaks out,which explains the observed elongation of RCW 120.The dynamical age of RCW 120,depending on the magnetic field strength,is~1.6 Myr for field strength of100 μG,older than the hydrodynamic estimates.In direction perpendicular to the magnetic field,the density contrast of the western shell is greatly reduced by the strong magnetic field.The strong magnetic field in general reduces the efficiency of triggered star formation,in comparison with the hydrodynamic estimates.Triggered star formation via the "collect and collapse" mechanism could occur in the direction along the magnetic field.Core formation efficiency(CFE) is found to be higher in the southern and eastern shells of RCW 120 than in the infrared dark cloud receiving little influence from the H Ⅱ region,suggesting increase in the CFE related to triggering from ionization feedback.
