This paper presents an overview of the QUARKS survey,which stands for Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures."The QUARKS survey is observing139 m...This paper presents an overview of the QUARKS survey,which stands for Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures."The QUARKS survey is observing139 massive clumps covered by 156 pointings at Atacama Large Millimeter/submillimeter Array(ALMA)Band 6(λ~1.3 mm).In conjunction with data obtained from the ALMA-ATOMS survey at Band 3(λ~3 mm),QUARKS aims to carry out an unbiased statistical investigation of massive star formation process within protoclusters down to a scale of 1000 au.This overview paper describes the observations and data reduction of the QUARKS survey,and gives a first look at an exemplar source,the mini-starburst Sgr B2(M).The wide-b and width(7.5 GHz)and high-angular-resolution(~0."3)observations of the QUARKS survey allow for the resolution of much more compact cores than those could be done by the ATOMS survey,and to detect previously unrevealed fainter filamentary structures.The spectral windows cover transitions of species including CO,SO,N_(2)D^(+),SiO,H_(30)α,H_(2)CO,CH_(3)CN,and many other complex organic molecules,tracing gas components with different temperatures and spatial extents.QUARKS aims to deepen our understanding of several scientific topics of massive star formation,such as the mass transport within protoclusters by(hub-)filamentary structures,the existence of massive starless cores,the physical and chemical properties of dense cores within protoclusters,and the feedback from already formed high-mass young protostars.展开更多
A series of plane-parallel photodissociation region （PDR） models are calculated using the spectral synthesis code CLOUDY. These models span a wide range of physical conditions, with gas densities of n=10^2-10^6cm^-3...A series of plane-parallel photodissociation region （PDR） models are calculated using the spectral synthesis code CLOUDY. These models span a wide range of physical conditions, with gas densities of n=10^2-10^6cm^-3 and incident far-ultraviolet （FUV） fields of Go=10^0-10^6 （where Go is the FUV flux in units of the local interstellar value）, which are comparable with various astrophysical environments from interstellar diffuse clouds to the dense neutral gas around galactic compact H Ⅱ regions. Based on the calculated results, we study the thermal balance of PDR gas and the emissions of [C Ⅱ], [C I] and [O I] fine-structure lines under different physical conditions. The intensities and strength ratios of the studied lines, which are frequently used as PDR diagnostics, are presented using contour diagrams as functions of n and Go. We compare the calculated PDR surface gas temperatures Ts with those from Kaufman et al. and find that Ts from our models are systematically higher over most of the adopted n-Go parameter space. The predicated line intensities and ratios from our work and those from Kaufman et al. can be different by a factor greater than 10, and such large differences usually occur near the border of our parameter space. The different methods of treating the dust grain physics, the change of H2 formation and dissociation rates, and the improvement in the radiation transfer of line emissions in our CLOUDY models are likely to be the major reasons for the divergences. Our models represent an up-to-date treatment of PDR diagnostic calculations and can be used to interpret observational data. Meanwhile, the uncertainties in the treatment of microphysics and chemical processes in PDR models have significant effects on PDR diagnostics.展开更多
We describe the general structure of the well known S255IR high mass star forming region, as revealed by our recent ALMA observations. The data indicate a physical relation exists between the major clumps SMA1 and SMA...We describe the general structure of the well known S255IR high mass star forming region, as revealed by our recent ALMA observations. The data indicate a physical relation exists between the major clumps SMA1 and SMA2. The driving source of the extended high velocity, well collimated bipolar outflow, is not the most pronounced disk-like SMA1 clump harboring a 20M⊙ young star （S255 NIRS3）, as was assumed earlier. Apparently, it is the less evolved SMA2 clump, which drives the outflow and contains a compact rotating structure （probably a disk）. At the same time, the SMA 1 clump drives another outflow, with a larger opening angle. The molecular line data do not show an outflow from the SMA3 clump （NIRS 1）, which was suggested by IR studies of this region.展开更多
We present results of a high resolution study of the filamentary infrared dark cloud G192.76＋00.10 in the S254-S258 OB complex in several molecular species tracing different physical conditions. These include three i...We present results of a high resolution study of the filamentary infrared dark cloud G192.76＋00.10 in the S254-S258 OB complex in several molecular species tracing different physical conditions. These include three isotopologues of carbon monoxide （CO）, ammonia （NH3） and carbon monosulfide （CS）. The aim of this work is to study the general structure and kinematics of the filamen- tary cloud, and its fragmentation and physical parameters. The gas temperature is derived from the NH3 （J, K） = （1, 1）, （2, 2） and 12CO（2-1） lines, and the 13CO（1-0）, 13CO（2-1） emission is used to inves- tigate the overall gas distribution and kinematics. Several dense clumps are identified from the CS（2-1） data. Values of the gas temperature lie in the range 10 - 35 K, and column density N（H2） reaches the value 5.1 ×1022 cm-2. The width of the filament is of order 1 pc. The masses of the dense clumps range from ×30 M⊙ to - 160 M⊙. They appear to be gravitationally unstable. The molecular emission shows a gas dynamical coherence along the filament, The velocity pattern may indicate longitudinal collapse.展开更多
Young protoclusters （embedded stellar clusters） are responsible for the vast majority of star formation currently occurring in the Galaxy. Recent observations suggest a scenario in which filamen-tary structures in t...Young protoclusters （embedded stellar clusters） are responsible for the vast majority of star formation currently occurring in the Galaxy. Recent observations suggest a scenario in which filamen-tary structures in the interstellar medium represent the first step towards precluster clumps and even- tually star formation. Whether filaments continuously fuel the star formation process when the cluster accretes material is still an open question. In this paper, we present a case study of the famous ＇integral shaped filament＇ （ISF） in the Orion A molecular cloud and we seek to study the kinematics which is truly originated from the ISF. We firstly define the central ridge of the ISF with NHa, ^12CO, ^13CO and N2H^＋. Undulations are present in all the ridges. Moreover, a large scale offset is apparent in the ridges as derived by different tracers, which may be explained by the slingshot mechanism proposed by Stutz ＆ Gould. We fit the velocity field of the ISF and find the derived velocity gradient is about 0.7 km s^- 1 pc^- 1 which may come from an overall contraction. We propose a method to check the accretion flow along the ISF by using the velocity deviations of different molecular tracers, which is better than the common method of using the velocity distribution of one tracer alone. Using the velocity deviations, we also find that OMC-1 to 5 are located close to the local extrema of the fluctuations, which may demonstrate that gas flows toward each clump along the ISE展开更多
We report the results of ^12CO of Ultra-Compact （UC） HII regions with and ^13CO J=1-0 observations of eight candidates the Purple Mountain Observatory （PMO） Qinghai 13.7 -m telescope, which resulted in revealing 1...We report the results of ^12CO of Ultra-Compact （UC） HII regions with and ^13CO J=1-0 observations of eight candidates the Purple Mountain Observatory （PMO） Qinghai 13.7 -m telescope, which resulted in revealing 11 molecular cores. Their masses range from 130 to 1.7 × 10^4 M⊙, with different spatial scales （1 - 6 pc）. Also presented are the relevant HCO＋ j=1-0 maps, which enabled us to investigate more detailed structures of these cores. Further comparisons show that four of the cores deviated from the centers of infrared （MIR） emission of Midcourse Space Experiment （MSX）, while others correspond either to bright MIR sources or diffuse MIR background. This indicates various evolutionary phases of the cores, including quite early ones for those without MIR sources.展开更多
We present large-scale(2°×2°)observations toward the molecular cloud M120.1+3.0,using ^(12)CO,^(13)CO and C^(18)O(J=1-0)data from the Purple Mountain Observatory 13.7 m millimeter telescope.The distance...We present large-scale(2°×2°)observations toward the molecular cloud M120.1+3.0,using ^(12)CO,^(13)CO and C^(18)O(J=1-0)data from the Purple Mountain Observatory 13.7 m millimeter telescope.The distance of the cloud is measured to be~1.1 kpc.Using the ^(13)CO data,we identify a main filament F1 and two sub-filaments F2 and F3 in the cloud,which together show a"hub-filament"structure.Filaments F1 and F2 are thermally supercritical.Furthermore,F1 displays clear localized systematic motions in the ^(13)CO position-velocity diagram,which could be explained by accretion along the filament.The mean estimated accretion rate is~132M_(⊙)Myr^(-1).Approximately 150 ^(13)CO clumps are identified in the cloud,of which 39 are gravitationally bound.Most of these virialized clumps are well distributed along the supercritical filaments F1 and F2.Based on the complementary infrared and optical data,we identify~186 young stellar objects in the observed area and extract five clusters within the dense ridge of F1.The calculated star formation rate(SFR)surface densities(∑_(SFR))in the clusters range from 1.4 to 2.5 M_(⊙)Myr^(-1)pc^(-2),with a mean value of~2.0M_(⊙)Myr^(-1)pc^(-2).We therefore regard them as mini-starburst cluster candidates.The comparison between ∑_(SFR) and column density N_(gas) along the skeleton of F1 suggests that star formation is closely related to the dense gas in the cloud.Along the main filament F1,five bipolar outflows are also found.All these results indicate intense star-forming activities in the M120.1+3.0 molecular cloud.展开更多
The most extensive survey of carbon monoxide(CO)gas in the Taurus molecular cloud relied on ^(12)CO and ^(13)CO J=1→0 emission only,distinguishing the region where ^(12)CO is detected without ^(13)CO(named mask 1 reg...The most extensive survey of carbon monoxide(CO)gas in the Taurus molecular cloud relied on ^(12)CO and ^(13)CO J=1→0 emission only,distinguishing the region where ^(12)CO is detected without ^(13)CO(named mask 1 region)from the one where both are detected(mask 2 region)(Goldsmith et al.2008;Pineda et al.2010).We have taken advantage of recent ^(12)CO J=3→2 James Clerk Maxwell Telescope observations,where they include mask 1regions to estimate density,temperature,and N(CO)with a large velocity gradient model.This represents 1395 pixels out of~1.2 million in the mark 1 region.Compared to Pineda et al.(2010)results and assuming a Tkin of 30 K,we find a higher volume density of molecular hydrogen of 3.3×10^(3) cm^(-3),compared to their 250-700 cm^(-3),and a CO column density of 5.7×10^(15)cm^(-2),about a quarter of their value.The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium.Future observations to extend the ^(12)CO J=3→2 mapping further away from the ^(13)COdetected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.展开更多
In order to search for intensity fluctuations on the HCN（1-0） and HCO＋（1-0） line pro- files, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming...In order to search for intensity fluctuations on the HCN（1-0） and HCO＋（1-0） line pro- files, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming cores S140 and S199 were carried out. The data were processed by the Fourier filtering method. Line temperature fluctuations that exceed the noise level were detected. Assuming the cores consist of a large number of randomly moving small thermal fragments, the total number of frag- ments is - 4 × 106 for the region with linear size - 0.1 pc in S140 and - 106 for the region with linear size - 0.3 pc in S 199. Physical parameters of fragments in S 140 were obtained from detailed modeling of the HCN emission in the framework of the clumpy cloud model.展开更多
We present simultaneous observations of 12CO,13CO and C18O J=1-0 emission in 11 nearby（cz1000 km s-1） bright infrared galaxies.Both 12CO and 13CO are detected in the centers of all the galaxies,except for 13CO in NG...We present simultaneous observations of 12CO,13CO and C18O J=1-0 emission in 11 nearby（cz1000 km s-1） bright infrared galaxies.Both 12CO and 13CO are detected in the centers of all the galaxies,except for 13CO in NGC 3031. We have also detected C18O,CSJ=2-1 and HCO＋J=1-0 emission in the nuclear regions of M82 and M51.These are the first systematical extragalactic detections of 12CO and its isotopes from the PMO 14 m telescope.We have conducted half-beam-spaced mapping of M82 over an area of 4×2.5 and major axis mapping of NGC 3627,NGC 3628,NGC 4631 and M51.The radial distributions of 12CO and 13CO in NGC 3627,NGC 3628 and M51 can be well fitted by an exponential profile. The 12CO/13CO intensity ratio,R,decreases monotonically with the galactocentric radius in all mapped sources.The average R in the center and disk of the galaxies are 9.9±3.0 and 5.6±1.9,respectively,much lower than the peculiar R（～24） found in the center of M82.The intensity ratios of 13CO/C18O,13CO/HCO＋and 13CO/CS（either our or literature data） show little variation with galactocentric radius,in sharp contrast with the greatly varied R.This supports the notion that the observed gradient in R could be the result of the variations of the physical conditions across the disks.The H2 column density derived from C18O shows that the Galactic standard conversion factor（X-factor） overestimates the amount of the molecular gas in M82 by a factor of～2.5.These observations suggest that the X-factor in active star-forming regions（i.e.,nuclear regions） should be lower than that in normal star-forming disks and the gradient in R can be used to trace the variations of the X-factor.展开更多
Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines ...Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines have been detected in all. We found that in most sources, emissions of HC3N, HN13C, CH3CN, HNCO and SiO show more compact distributions than those of HCO＋, HNC, HCN and N2H＋. By comparing with other molecular lines, we found that the abun- dance of HNCO （x（HNCO）） correlates well with other species such as HC3N, HNC, C2H, H13CO＋ and N2H＋. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we find the abundance of HNCO does not correlate well with that of SiO, which is also a good tracer of shocks. We suggest this may be because HNCO and SiO trace different parts of shocks. Our analysis indicates that the velocity of a shock traced by HNCO tends to be lower than that traced by SiO. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of SiO. While in the relatively high-velocity shocks traced by SiO, the SiO abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud MSXDC G331.71＋00.59, high-velocity shocks are destroying the molecule HNCO.展开更多
We present high angular resolution images of both NH3 (1, 1) and (2, 2) lines toward NGC 7538 IRS 1. The density and velocity-position plots have been used to study the interaction among the outflows, winds and their ...We present high angular resolution images of both NH3 (1, 1) and (2, 2) lines toward NGC 7538 IRS 1. The density and velocity-position plots have been used to study the interaction among the outflows, winds and their environment. For the first time we have found an expanding half-shell of molecular gas around the HII region associated with IRS 1, which may be produced by the interaction of the bipolar outflows and the winds originating in IRS 1-3, and optical HII region NGC 7538 with ambient molecular gas.展开更多
We carried out observations toward the giant molecular cloud W 37 with the J = 1 - 0 transitions of 12CO, 13CO and C180 using the 13.7 m single-dish telescope at the Delingha station of Purple Mountain Observatory. Ba...We carried out observations toward the giant molecular cloud W 37 with the J = 1 - 0 transitions of 12CO, 13CO and C180 using the 13.7 m single-dish telescope at the Delingha station of Purple Mountain Observatory. Based on these CO lines, we calculated the column densities and cloud masses for molecular clouds with radial velocities around ＋20 km s-1. The gas mass of W 37, calculated from 13CO emission, is 1.7 × 10^5 M, above the criterion to be considered a giant molecular cloud. The dense ridge of W 37 is a dense filament, which is supercritical in terms of linear mass ratio. Dense clumps found by C180 emission are aligned along the dense ridge at regular intervals of about 2.8 pc, similar to the clump separation caused by large-scale ＇sausage instability＇. We confirm the identification of the giant molecular filament （GMF） G 18.0-16.8 and find a new giant filament, G 16.5-15.8, located ~ 0.7° to the west of G 18.0-16.8. Both GMFs are not gravitationally bound, as indicated by their low linear mass ratio （- 80 M pc-l）. We compared the gas temperature map with the dust temperature map from Herschel images, and found similar structures. The spatial distributions of class I objects and the dense clumps are reminiscent of triggered star formation occurring in the northwestern part of W 37, which is close to NGC 6611.展开更多
We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant an...We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds, we tentatively identify the clouds that are respectively interacting with the two SNRs.展开更多
For the first time, the OMC-2/3 region was mapped in C2H （1–0）, HC3N （10–9） and HNC （1–0） lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The di...For the first time, the OMC-2/3 region was mapped in C2H （1–0）, HC3N （10–9） and HNC （1–0） lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The distribution of C2H cores almost follows that of the 1300μm condensations, which might suggest that C2H is a good tracer to study the core structure of molecular clouds. The core masses traced by HNC are rather ？at, ranging from 18.8 to 49.5 M , while also presenting a large span for those from C2H, ranging from 6.4 to 36.0 M . The line widths of both HNC and C2H look very similar, and both are wider than that of HC3N. The line widths of the three lines are all wider than those from dark clouds, implying that the former is more active than the latter, and has larger turbulence caused by winds and UV radiation from the surrounding massive stars.展开更多
In the 12CO （J=1-0） survey of 1331 cold 1RAS sources, 214 sources show profiles with multiple peaks and are selected as cloud-cloud collision candidates. In January 2005, 201 sources were detected with 12CO（1-0）, ...In the 12CO （J=1-0） survey of 1331 cold 1RAS sources, 214 sources show profiles with multiple peaks and are selected as cloud-cloud collision candidates. In January 2005, 201 sources were detected with 12CO（1-0）, 13CO（1-0）, and c18O（1-0） emissions by the 13.7 m telescope at Purple Mount Observatory. This is the first survey of CO and its isotope lines directed toward possible cloud-cloud collision regions. According to the statistics of the 201 sources in the Galactic distribution, the 201 sources show a similar distribution to the parent sample （1331 cold IRAS sources）. These sources are located over a wide range of Galactocentric distances, and are partly associated with the star forming region. Based on preliminary criteria which describe the spectral properties of the possible cloud-cloud collision region, the 201 sources are classified into four types by the fit of the spectral profiles between the optically thick and thin lines toward each source. The survey is focused on possible cloud-cloud collision regions, and gives some evidence to help us with selecting the target region. We will continue the process of mapping and studying multi-wavelength observations for the selected region in the future.展开更多
We analyze large scale mapping observations of the molecular lines in the ^12CO（J= 2-1）,^12CO（J=3-2）,^13CO（J=2-1）,and ^13CO（J=3-2） transition emissions toward the Cepheus B molecular cloud with the KOSMA 3mtel...We analyze large scale mapping observations of the molecular lines in the ^12CO（J= 2-1）,^12CO（J=3-2）,^13CO（J=2-1）,and ^13CO（J=3-2） transition emissions toward the Cepheus B molecular cloud with the KOSMA 3mtelescope. The integrated intensity map of the ^12CO （J = 2 - 1） transition has shown a structure with a compact core and a compact ridge extended to the north-west of the core. The cloud is surrounded by an optically bright rim, where the radiation-driven implosion （RDI） may greatly change the gas properties. The intensities of the CO （J = 3 - 2） transition are higher than those of the CO （J = 2 - 1） transition along the rim area. We find characteristic RDI structure in position-velocity diagrams. Non-LTE large velocity gradient （LVG） model analysis shows that the density and temperature at the edge are higher than that in the center. Our results provide evidences that an RDI is taking place in the Cepheus B molecular cloud.展开更多
We report the FCRAO observations that mapped HCN （1-0）, CS （2-1）, HNC （1-0） and HCO＋ （1-0） in ten high-mass star forming cores associated with water masers. We present velocity integrated intensity maps of th...We report the FCRAO observations that mapped HCN （1-0）, CS （2-1）, HNC （1-0） and HCO＋ （1-0） in ten high-mass star forming cores associated with water masers. We present velocity integrated intensity maps of the four lines for these dense cores, compare their line profiles, and derive physical properties of these cores. We find that these four tracers identify areas with similar properties in these massive dense cores, and in most cases, the emissions of HCN and HCO＋ are stronger than those of HNC and CS. We also use the line ratios of HCO＋/HCN, HNC/HCN and HNC/HCO＋ as the diagnostics to explore the environment of these high-mass star forming regions, and find that most of the cores agree with the model that photodominated regions dominate the radiation field, except for W44, for which the radiation field is similar to an X-ray dominated region.展开更多
Using the 13.7 m telescope of the Purple Mountain Observatory （PMO）, a survey of the 3 = 1 - 0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infr...Using the 13.7 m telescope of the Purple Mountain Observatory （PMO）, a survey of the 3 = 1 - 0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin. In the survey, except for 43 sources showing complex or multiple-peak profiles, almost all the ^13CO line profiles of the other 55 sources have large line widths of 4.5km s^-1 on average and are usually asymmetric. Fifty corresponding Infrared Astronomical Satellite （IRAS） sources of these 55 sources have Lbdl larger than 10^3 L⊙, which can be identified as possible high-mass young stellar sources. Statistics show that the ^13CO line widths correlate with the bolometric luminosity of the associated IRAS sources. Here, we also report the mapping results of two sources; IRAS 06117＋1350 and IRAS 07299-1651. Two cores were found in IRAS 06117＋1350 and one core was detected in IRAS 07299-1651. The northwest core in IRAS 06117＋1350 and the core in IRAS 07299-1651 can be identified as precursors of UC HII regions or high-mass protostellar objects （HMPOs）. The southeast core of IRAS 06117＋1350 has no infrared counterpart, seeming to be at a younger stage than the pre-UC HII phase.展开更多
The purpose of this paper is to explore the effect of magnetic fields on the dynamics of magnetized filamentary molecular clouds. We suppose there is a filament with cylindrical symmetry and two components of axial an...The purpose of this paper is to explore the effect of magnetic fields on the dynamics of magnetized filamentary molecular clouds. We suppose there is a filament with cylindrical symmetry and two components of axial and toroidal magnetic fields. In comparison to previous works, the novelty in the present work involves a similarity solution that does not define a function of the magnetic fields or density. We consider the effect of the magnetic field on the collapse of the filament in both axial and toroidal directions and show that the magnetic field has a braking effect, which means that the increasing intensity of the magnetic field reduces the velocity of collapse. This is consistent with other studies. We find that the magnetic field in the central region tends to be aligned with the filament axis. Also, the magnitude and the direction of the magnetic field depend on the magnitude and direction of the initial magnetic field in the outer region. Moreover, we show that more energy dissipation from the filament causes a rise in the infall velocity.展开更多
基金supported by the National Key R&D Program of China(No.2022YFA1603100)the National Natural Science Foundation of China(NSFC)through grants Nos.12203086,12033005,12073061,12122307,and 12103045+12 种基金supported by CPSF No.2022M723278the international partnership program of Chinese Academy of Sciences through grant No.114231K YSB20200009Shanghai Pujiang Program 20PJ1415500the science research grants from the China Manned Space Project with no.CMS-CSST-2021-B06Yunnan Fundamental Research Project(grant No.202301AT070118)sponsored by Natural Science Foundation of Shanghai(No.23ZR1482100)support from the National Natural Science Foundation of China(NSFC)through grants Nos.12273090&12322305the Chinese Academy of Sciences(CAS)‘Light of West China’Program(No.xbzgzdsys-202212)support from the ANID BASAL project FB210003support from the Fondecyt Regular(project code 1220610)partially supported by a Grant-in-Aid for Scientific Research(KAKENHI Number JP22H01271 and JP23H01221)of JSPSsupported by JSPS KAKENHI(grant No.JP20H05645)sponsored(in part)by the Chinese Academy of Sciences(CAS),through a grant to the CAS South America Center for Astronomy(CASSACA)in Santiago,Chile。
文摘This paper presents an overview of the QUARKS survey,which stands for Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures."The QUARKS survey is observing139 massive clumps covered by 156 pointings at Atacama Large Millimeter/submillimeter Array(ALMA)Band 6(λ~1.3 mm).In conjunction with data obtained from the ALMA-ATOMS survey at Band 3(λ~3 mm),QUARKS aims to carry out an unbiased statistical investigation of massive star formation process within protoclusters down to a scale of 1000 au.This overview paper describes the observations and data reduction of the QUARKS survey,and gives a first look at an exemplar source,the mini-starburst Sgr B2(M).The wide-b and width(7.5 GHz)and high-angular-resolution(~0."3)observations of the QUARKS survey allow for the resolution of much more compact cores than those could be done by the ATOMS survey,and to detect previously unrevealed fainter filamentary structures.The spectral windows cover transitions of species including CO,SO,N_(2)D^(+),SiO,H_(30)α,H_(2)CO,CH_(3)CN,and many other complex organic molecules,tracing gas components with different temperatures and spatial extents.QUARKS aims to deepen our understanding of several scientific topics of massive star formation,such as the mass transport within protoclusters by(hub-)filamentary structures,the existence of massive starless cores,the physical and chemical properties of dense cores within protoclusters,and the feedback from already formed high-mass young protostars.
文摘A series of plane-parallel photodissociation region （PDR） models are calculated using the spectral synthesis code CLOUDY. These models span a wide range of physical conditions, with gas densities of n=10^2-10^6cm^-3 and incident far-ultraviolet （FUV） fields of Go=10^0-10^6 （where Go is the FUV flux in units of the local interstellar value）, which are comparable with various astrophysical environments from interstellar diffuse clouds to the dense neutral gas around galactic compact H Ⅱ regions. Based on the calculated results, we study the thermal balance of PDR gas and the emissions of [C Ⅱ], [C I] and [O I] fine-structure lines under different physical conditions. The intensities and strength ratios of the studied lines, which are frequently used as PDR diagnostics, are presented using contour diagrams as functions of n and Go. We compare the calculated PDR surface gas temperatures Ts with those from Kaufman et al. and find that Ts from our models are systematically higher over most of the adopted n-Go parameter space. The predicated line intensities and ratios from our work and those from Kaufman et al. can be different by a factor greater than 10, and such large differences usually occur near the border of our parameter space. The different methods of treating the dust grain physics, the change of H2 formation and dissociation rates, and the improvement in the radiation transfer of line emissions in our CLOUDY models are likely to be the major reasons for the divergences. Our models represent an up-to-date treatment of PDR diagnostic calculations and can be used to interpret observational data. Meanwhile, the uncertainties in the treatment of microphysics and chemical processes in PDR models have significant effects on PDR diagnostics.
基金supported by the Russian Foundation for Basic Research(Grant No.15–02–06098)during the preparation of the observations and initial data reductionthe Russian Science Foundation(Grant No.17–12–01256)during the spectral data analysissupport from the European Research Council under the Horizon 2020 Framework Program via the ERC Consolidator Grant CSF-648505
文摘We describe the general structure of the well known S255IR high mass star forming region, as revealed by our recent ALMA observations. The data indicate a physical relation exists between the major clumps SMA1 and SMA2. The driving source of the extended high velocity, well collimated bipolar outflow, is not the most pronounced disk-like SMA1 clump harboring a 20M⊙ young star （S255 NIRS3）, as was assumed earlier. Apparently, it is the less evolved SMA2 clump, which drives the outflow and contains a compact rotating structure （probably a disk）. At the same time, the SMA 1 clump drives another outflow, with a larger opening angle. The molecular line data do not show an outflow from the SMA3 clump （NIRS 1）, which was suggested by IR studies of this region.
基金supported by the Russian Foundation for Basic Research(Grant Nos.15–02–06098 and 17–52–45020)in part of the observations and preliminary data reductionby the Russian Science Foundation(Grant No.17–12–01256)in part of the data analysis
文摘We present results of a high resolution study of the filamentary infrared dark cloud G192.76＋00.10 in the S254-S258 OB complex in several molecular species tracing different physical conditions. These include three isotopologues of carbon monoxide （CO）, ammonia （NH3） and carbon monosulfide （CS）. The aim of this work is to study the general structure and kinematics of the filamen- tary cloud, and its fragmentation and physical parameters. The gas temperature is derived from the NH3 （J, K） = （1, 1）, （2, 2） and 12CO（2-1） lines, and the 13CO（1-0）, 13CO（2-1） emission is used to inves- tigate the overall gas distribution and kinematics. Several dense clumps are identified from the CS（2-1） data. Values of the gas temperature lie in the range 10 - 35 K, and column density N（H2） reaches the value 5.1 ×1022 cm-2. The width of the filament is of order 1 pc. The masses of the dense clumps range from ×30 M⊙ to - 160 M⊙. They appear to be gravitationally unstable. The molecular emission shows a gas dynamical coherence along the filament, The velocity pattern may indicate longitudinal collapse.
基金funded by the CAS“Light of West China”Program(2015-XBQN-B-03)the National Natural Science Foundation of China(Grant Nos.11433008 and 11603063)+1 种基金supported by the National Natural Science Foundation of China(Grant Nos.11703073,117030734,11373062 and 11303081)Recruitment Program of High-end Foreign Experts(20166500004)
文摘Young protoclusters （embedded stellar clusters） are responsible for the vast majority of star formation currently occurring in the Galaxy. Recent observations suggest a scenario in which filamen-tary structures in the interstellar medium represent the first step towards precluster clumps and even- tually star formation. Whether filaments continuously fuel the star formation process when the cluster accretes material is still an open question. In this paper, we present a case study of the famous ＇integral shaped filament＇ （ISF） in the Orion A molecular cloud and we seek to study the kinematics which is truly originated from the ISF. We firstly define the central ridge of the ISF with NHa, ^12CO, ^13CO and N2H^＋. Undulations are present in all the ridges. Moreover, a large scale offset is apparent in the ridges as derived by different tracers, which may be explained by the slingshot mechanism proposed by Stutz ＆ Gould. We fit the velocity field of the ISF and find the derived velocity gradient is about 0.7 km s^- 1 pc^- 1 which may come from an overall contraction. We propose a method to check the accretion flow along the ISF by using the velocity deviations of different molecular tracers, which is better than the common method of using the velocity distribution of one tracer alone. Using the velocity deviations, we also find that OMC-1 to 5 are located close to the local extrema of the fluctuations, which may demonstrate that gas flows toward each clump along the ISE
基金the National Natural Science Foundation of China
文摘We report the results of ^12CO of Ultra-Compact （UC） HII regions with and ^13CO J=1-0 observations of eight candidates the Purple Mountain Observatory （PMO） Qinghai 13.7 -m telescope, which resulted in revealing 11 molecular cores. Their masses range from 130 to 1.7 × 10^4 M⊙, with different spatial scales （1 - 6 pc）. Also presented are the relevant HCO＋ j=1-0 maps, which enabled us to investigate more detailed structures of these cores. Further comparisons show that four of the cores deviated from the centers of infrared （MIR） emission of Midcourse Space Experiment （MSX）, while others correspond either to bright MIR sources or diffuse MIR background. This indicates various evolutionary phases of the cores, including quite early ones for those without MIR sources.
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.12041305,12173090 and 12073079)+2 种基金the CAS International Cooperation Program(grant No.114332KYSB20190009)sponsored by the National Key R&D Program of China with grant 2017YFA0402701the CAS Key Research Program of Frontier Sciences with grant QYZDJ-SSW-SLH047。
文摘We present large-scale(2°×2°)observations toward the molecular cloud M120.1+3.0,using ^(12)CO,^(13)CO and C^(18)O(J=1-0)data from the Purple Mountain Observatory 13.7 m millimeter telescope.The distance of the cloud is measured to be~1.1 kpc.Using the ^(13)CO data,we identify a main filament F1 and two sub-filaments F2 and F3 in the cloud,which together show a"hub-filament"structure.Filaments F1 and F2 are thermally supercritical.Furthermore,F1 displays clear localized systematic motions in the ^(13)CO position-velocity diagram,which could be explained by accretion along the filament.The mean estimated accretion rate is~132M_(⊙)Myr^(-1).Approximately 150 ^(13)CO clumps are identified in the cloud,of which 39 are gravitationally bound.Most of these virialized clumps are well distributed along the supercritical filaments F1 and F2.Based on the complementary infrared and optical data,we identify~186 young stellar objects in the observed area and extract five clusters within the dense ridge of F1.The calculated star formation rate(SFR)surface densities(∑_(SFR))in the clusters range from 1.4 to 2.5 M_(⊙)Myr^(-1)pc^(-2),with a mean value of~2.0M_(⊙)Myr^(-1)pc^(-2).We therefore regard them as mini-starburst cluster candidates.The comparison between ∑_(SFR) and column density N_(gas) along the skeleton of F1 suggests that star formation is closely related to the dense gas in the cloud.Along the main filament F1,five bipolar outflows are also found.All these results indicate intense star-forming activities in the M120.1+3.0 molecular cloud.
基金the National Natural Science Foundation of China(NSFC,grant Nos.11988101,11725313,and U1931117)the International Partnership Program of Chinese Academy of Sciences(grant No.114A11KYSB20210010)supported by the Natural Science Foundation of Jiangsu Province(grant No.BK20201108)。
文摘The most extensive survey of carbon monoxide(CO)gas in the Taurus molecular cloud relied on ^(12)CO and ^(13)CO J=1→0 emission only,distinguishing the region where ^(12)CO is detected without ^(13)CO(named mask 1 region)from the one where both are detected(mask 2 region)(Goldsmith et al.2008;Pineda et al.2010).We have taken advantage of recent ^(12)CO J=3→2 James Clerk Maxwell Telescope observations,where they include mask 1regions to estimate density,temperature,and N(CO)with a large velocity gradient model.This represents 1395 pixels out of~1.2 million in the mark 1 region.Compared to Pineda et al.(2010)results and assuming a Tkin of 30 K,we find a higher volume density of molecular hydrogen of 3.3×10^(3) cm^(-3),compared to their 250-700 cm^(-3),and a CO column density of 5.7×10^(15)cm^(-2),about a quarter of their value.The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium.Future observations to extend the ^(12)CO J=3→2 mapping further away from the ^(13)COdetected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.
基金support of the RFBR grants(projects 15–02–06098,16–02–00761 and18–02–00660)support of the Russian Science Foundation grant(project 17–12–01256)
文摘In order to search for intensity fluctuations on the HCN（1-0） and HCO＋（1-0） line pro- files, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming cores S140 and S199 were carried out. The data were processed by the Fourier filtering method. Line temperature fluctuations that exceed the noise level were detected. Assuming the cores consist of a large number of randomly moving small thermal fragments, the total number of frag- ments is - 4 × 106 for the region with linear size - 0.1 pc in S140 and - 106 for the region with linear size - 0.3 pc in S 199. Physical parameters of fragments in S 140 were obtained from detailed modeling of the HCN emission in the framework of the clumpy cloud model.
基金Supported by the National Natural Science Foundation of Chinafunded by the National Science Foundation of China(Distinguished Young Scholars,Nos.10425313,10833006 and 10621303)the Hundred Talent Program of the Chinese Academy of Sciences
文摘We present simultaneous observations of 12CO,13CO and C18O J=1-0 emission in 11 nearby（cz1000 km s-1） bright infrared galaxies.Both 12CO and 13CO are detected in the centers of all the galaxies,except for 13CO in NGC 3031. We have also detected C18O,CSJ=2-1 and HCO＋J=1-0 emission in the nuclear regions of M82 and M51.These are the first systematical extragalactic detections of 12CO and its isotopes from the PMO 14 m telescope.We have conducted half-beam-spaced mapping of M82 over an area of 4×2.5 and major axis mapping of NGC 3627,NGC 3628,NGC 4631 and M51.The radial distributions of 12CO and 13CO in NGC 3627,NGC 3628 and M51 can be well fitted by an exponential profile. The 12CO/13CO intensity ratio,R,decreases monotonically with the galactocentric radius in all mapped sources.The average R in the center and disk of the galaxies are 9.9±3.0 and 5.6±1.9,respectively,much lower than the peculiar R（～24） found in the center of M82.The intensity ratios of 13CO/C18O,13CO/HCO＋and 13CO/CS（either our or literature data） show little variation with galactocentric radius,in sharp contrast with the greatly varied R.This supports the notion that the observed gradient in R could be the result of the variations of the physical conditions across the disks.The H2 column density derived from C18O shows that the Galactic standard conversion factor（X-factor） overestimates the amount of the molecular gas in M82 by a factor of～2.5.These observations suggest that the X-factor in active star-forming regions（i.e.,nuclear regions） should be lower than that in normal star-forming disks and the gradient in R can be used to trace the variations of the X-factor.
基金supported by the National Natural Science Foundation of China(Grant No.11503037)
文摘Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines have been detected in all. We found that in most sources, emissions of HC3N, HN13C, CH3CN, HNCO and SiO show more compact distributions than those of HCO＋, HNC, HCN and N2H＋. By comparing with other molecular lines, we found that the abun- dance of HNCO （x（HNCO）） correlates well with other species such as HC3N, HNC, C2H, H13CO＋ and N2H＋. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we find the abundance of HNCO does not correlate well with that of SiO, which is also a good tracer of shocks. We suggest this may be because HNCO and SiO trace different parts of shocks. Our analysis indicates that the velocity of a shock traced by HNCO tends to be lower than that traced by SiO. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of SiO. While in the relatively high-velocity shocks traced by SiO, the SiO abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud MSXDC G331.71＋00.59, high-velocity shocks are destroying the molecule HNCO.
基金Supported by the National Natural Science Foundation of China.
文摘We present high angular resolution images of both NH3 (1, 1) and (2, 2) lines toward NGC 7538 IRS 1. The density and velocity-position plots have been used to study the interaction among the outflows, winds and their environment. For the first time we have found an expanding half-shell of molecular gas around the HII region associated with IRS 1, which may be produced by the interaction of the bipolar outflows and the winds originating in IRS 1-3, and optical HII region NGC 7538 with ambient molecular gas.
基金supported by the Strategic Priority Research Program ‘The Emergence of Cosmological Structure’ of the Chinese Academy of Sciences (Grant No. XDB09000000)the Millimeter Wave Radio Astronomy Database, and the Key Laboratory for Radio Astronomy, CAS. Z.J. acknowledges the support by the National Natural Science Foundation of China (Grant No. 11233007)a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration
文摘We carried out observations toward the giant molecular cloud W 37 with the J = 1 - 0 transitions of 12CO, 13CO and C180 using the 13.7 m single-dish telescope at the Delingha station of Purple Mountain Observatory. Based on these CO lines, we calculated the column densities and cloud masses for molecular clouds with radial velocities around ＋20 km s-1. The gas mass of W 37, calculated from 13CO emission, is 1.7 × 10^5 M, above the criterion to be considered a giant molecular cloud. The dense ridge of W 37 is a dense filament, which is supercritical in terms of linear mass ratio. Dense clumps found by C180 emission are aligned along the dense ridge at regular intervals of about 2.8 pc, similar to the clump separation caused by large-scale ＇sausage instability＇. We confirm the identification of the giant molecular filament （GMF） G 18.0-16.8 and find a new giant filament, G 16.5-15.8, located ~ 0.7° to the west of G 18.0-16.8. Both GMFs are not gravitationally bound, as indicated by their low linear mass ratio （- 80 M pc-l）. We compared the gas temperature map with the dust temperature map from Herschel images, and found similar structures. The spatial distributions of class I objects and the dense clumps are reminiscent of triggered star formation occurring in the northwestern part of W 37, which is close to NGC 6611.
基金Supported by the National Natural Science Foundation of China.
文摘We made the first CO（1-0） mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720MHz maser. Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds, we tentatively identify the clouds that are respectively interacting with the two SNRs.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11003046, 11073054, 10733030 and 10621303)the National Basic Research Program of China (973 Program, Grant 2007CB815403)
文摘For the first time, the OMC-2/3 region was mapped in C2H （1–0）, HC3N （10–9） and HNC （1–0） lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The distribution of C2H cores almost follows that of the 1300μm condensations, which might suggest that C2H is a good tracer to study the core structure of molecular clouds. The core masses traced by HNC are rather ？at, ranging from 18.8 to 49.5 M , while also presenting a large span for those from C2H, ranging from 6.4 to 36.0 M . The line widths of both HNC and C2H look very similar, and both are wider than that of HC3N. The line widths of the three lines are all wider than those from dark clouds, implying that the former is more active than the latter, and has larger turbulence caused by winds and UV radiation from the surrounding massive stars.
文摘In the 12CO （J=1-0） survey of 1331 cold 1RAS sources, 214 sources show profiles with multiple peaks and are selected as cloud-cloud collision candidates. In January 2005, 201 sources were detected with 12CO（1-0）, 13CO（1-0）, and c18O（1-0） emissions by the 13.7 m telescope at Purple Mount Observatory. This is the first survey of CO and its isotope lines directed toward possible cloud-cloud collision regions. According to the statistics of the 201 sources in the Galactic distribution, the 201 sources show a similar distribution to the parent sample （1331 cold IRAS sources）. These sources are located over a wide range of Galactocentric distances, and are partly associated with the star forming region. Based on preliminary criteria which describe the spectral properties of the possible cloud-cloud collision region, the 201 sources are classified into four types by the fit of the spectral profiles between the optically thick and thin lines toward each source. The survey is focused on possible cloud-cloud collision regions, and gives some evidence to help us with selecting the target region. We will continue the process of mapping and studying multi-wavelength observations for the selected region in the future.
文摘We analyze large scale mapping observations of the molecular lines in the ^12CO（J= 2-1）,^12CO（J=3-2）,^13CO（J=2-1）,and ^13CO（J=3-2） transition emissions toward the Cepheus B molecular cloud with the KOSMA 3mtelescope. The integrated intensity map of the ^12CO （J = 2 - 1） transition has shown a structure with a compact core and a compact ridge extended to the north-west of the core. The cloud is surrounded by an optically bright rim, where the radiation-driven implosion （RDI） may greatly change the gas properties. The intensities of the CO （J = 3 - 2） transition are higher than those of the CO （J = 2 - 1） transition along the rim area. We find characteristic RDI structure in position-velocity diagrams. Non-LTE large velocity gradient （LVG） model analysis shows that the density and temperature at the edge are higher than that in the center. Our results provide evidences that an RDI is taking place in the Cepheus B molecular cloud.
基金supported by the National Natural Science Foundation of China(Grant No.11390373)
文摘We report the FCRAO observations that mapped HCN （1-0）, CS （2-1）, HNC （1-0） and HCO＋ （1-0） in ten high-mass star forming cores associated with water masers. We present velocity integrated intensity maps of the four lines for these dense cores, compare their line profiles, and derive physical properties of these cores. We find that these four tracers identify areas with similar properties in these massive dense cores, and in most cases, the emissions of HCN and HCO＋ are stronger than those of HNC and CS. We also use the line ratios of HCO＋/HCN, HNC/HCN and HNC/HCO＋ as the diagnostics to explore the environment of these high-mass star forming regions, and find that most of the cores agree with the model that photodominated regions dominate the radiation field, except for W44, for which the radiation field is similar to an X-ray dominated region.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10733030 and 10873019)
文摘Using the 13.7 m telescope of the Purple Mountain Observatory （PMO）, a survey of the 3 = 1 - 0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin. In the survey, except for 43 sources showing complex or multiple-peak profiles, almost all the ^13CO line profiles of the other 55 sources have large line widths of 4.5km s^-1 on average and are usually asymmetric. Fifty corresponding Infrared Astronomical Satellite （IRAS） sources of these 55 sources have Lbdl larger than 10^3 L⊙, which can be identified as possible high-mass young stellar sources. Statistics show that the ^13CO line widths correlate with the bolometric luminosity of the associated IRAS sources. Here, we also report the mapping results of two sources; IRAS 06117＋1350 and IRAS 07299-1651. Two cores were found in IRAS 06117＋1350 and one core was detected in IRAS 07299-1651. The northwest core in IRAS 06117＋1350 and the core in IRAS 07299-1651 can be identified as precursors of UC HII regions or high-mass protostellar objects （HMPOs）. The southeast core of IRAS 06117＋1350 has no infrared counterpart, seeming to be at a younger stage than the pre-UC HII phase.
文摘The purpose of this paper is to explore the effect of magnetic fields on the dynamics of magnetized filamentary molecular clouds. We suppose there is a filament with cylindrical symmetry and two components of axial and toroidal magnetic fields. In comparison to previous works, the novelty in the present work involves a similarity solution that does not define a function of the magnetic fields or density. We consider the effect of the magnetic field on the collapse of the filament in both axial and toroidal directions and show that the magnetic field has a braking effect, which means that the increasing intensity of the magnetic field reduces the velocity of collapse. This is consistent with other studies. We find that the magnetic field in the central region tends to be aligned with the filament axis. Also, the magnitude and the direction of the magnetic field depend on the magnitude and direction of the initial magnetic field in the outer region. Moreover, we show that more energy dissipation from the filament causes a rise in the infall velocity.
