Joint Center for Astrophysics

Lhasa, China

Joint Center for Astrophysics

Lhasa, China

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Liu X.-L.,CAS National Astronomical Observatories | Liu X.-L.,University of Chinese Academy of Sciences | Wang J.-J.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We studied 14 southern infrared dark clouds (IRDCs) using data taken from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey and the GLIMPSE and MIPSGAL midinfrared surveys of the inner Galaxy. The physical and chemical characteristics of the 14 IRDCs were investigated using N2H+(1-0), HNC(1-0), HCO+(1-0) and HCN(1-0) molecular lines. We found that the 14 IRDCs are in different evolutionary stages, from 'starless' to sources with an ultra-compact H II region. Three IRDCs were detected to have star-forming activity. The integrated intensity ratios IHCO+/HCN, IN2H+/HCN and IHNC/HCN are all ~1.5, which is different from previous measurements, suggesting that the integrated intensity ratios may be affected by the cloud environments. The integrated intensities of HNC, HCO+ and HCN show a tight correlation for the 14 IRDCs, implying a close link to the chemical evolution of these three species in the IRDCs. The derived excitation temperature for each IRDC is less than 25 K. We estimated the abundances of the four molecules to be from 10-11 to 10-9, and the average abundance ratios are NHNC/NHCN = 1.47 ± 0.50, NHNC/NHCO+ = 1.74 ± 0.22 and NHCN/NHCO+ = 1.21 ± 0.41. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Xu J.L.,CAS National Astronomical Observatories | Xu J.L.,Joint Center for Astrophysics | Wang J.J.,CAS National Astronomical Observatories | Wang J.J.,Joint Center for Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present Submillimeter Array (SMA) observations of the the massive star-forming region G20.08-0.14N at 335 and 345 GHz. With the SMA data, 41 molecular transitions were detected related to 11 molecular species and their isotopologues, including SO2, SO, C34S, NS, C17O, SiO, CH3OH, HC3N, H13CO+, HCOOCH3 and NH2CHO. In G20.08-0.14N, 10 transition lines out ofthe 41 detected belong to SO2, which dominates the appearance of the submillimetre-wave spectrum. To obtain the spatial kinematic distribution of molecules in G20.08-0.14N, we chose the strongest and unblended lines for the channel maps. The channel maps of C34S and SiO, together with their position-velocity diagrams, show that there are two accretion flows in G20.08-0.14N. Additionally, SiO emission shows a collimated outflow in the north-east-south-west direction. The direction ofthe outflow is revealed for the first time. The rotational temperature and column density of CH3OH are 105 K and 3.1 ×1017cm-2, respectively. Our results confirm that a hot core is associated with G20.08-0.14N. The hot core is heated by a protostar radiation at its centre, not by external excitation from shocks. Images of the spatial distribution of differentspecies have shown that the different molecules are located at different positions of the hot core. By comparing the spatialdistributions and abundances of molecules, we discuss possible chemical processes for producing the complex sulphur-bearing,nitrogen-bearing and oxygen-bearing molecules in G20.08-0.14N. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Xu J.-L.,CAS National Astronomical Observatories | Xu J.-L.,University of Chinese Academy of Sciences | Xu J.-L.,Joint Center for Astrophysics | Wang J.-J.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics
Astronomy and Astrophysics | Year: 2012

Aims.We investigate the environment in the vicinity of the supernova remnant (SNR) G59.5+0.1 and identify all the young stellar objects (YSOs) around the SNR, to derive the physical properties, obtain insight into the star-formation history, and determine whether SNR G59.5+0.1 can trigger star formation in this region. Methods. We perform the submillimeter/millimeter observations in CO lines toward the southeast of SNR G59.5+0.1 with the KOSMA 3 m Telescope. High values of the integrated CO line-intensity ratio R ICO(3-2)/ICO(2-1) is identified as one good signature of the SNR-MC (molecular cloud) interacting system. To investigate the impact of SNR G59.5+0.1 on the process of star formation, we use GLIMPSE I catalog to select YSOs (including Class I and Class II sources). Results.The CO emission forming an arc-like shape and mid-infrared 8.28 μ m emission are coincident with SNR G59.5+0.1, which has a totalmass of 1.1×104 M· and fully covers the open cluster NGC 6823. Three molecular clumps are identified in the COmolecular arc, each clump tracing the broad-line wing emission, indicating that there are three outflows in motion. The integrated CO line intensity ratio (R ICO(3-2)/ICO(2-1) ) for the whole molecular arc is between 0.48 and 1.57. The maximum value is 1.57, which ismuch higher than previous measurements of individual Galactic MCs. The CO molecular arc has a line-intensity ratio gradient. The SNR G59.5+0.1 is in adiabatic expansion phase. The age of the SNR is 8.6 × 10 4 yr. Based on the GLIMPSE I catalog, we select 625 YSOs candidates (including 176 Class I sources and 449 Class II sources). The timescales for Class 0, Class I and Class II sources are =10 4 yr, ∼ 10 5 yr, and ∼ 10 6 yr, respectively. The number of YSOs are significantly enhanced in the interacting regions, indicating the presence of some recently formed stars. © 2012 ESO.


Zhang C.P.,CAS National Astronomical Observatories | Zhang C.P.,Joint Center for Astrophysics | Zhang C.P.,University of Chinese Academy of Sciences | Wang J.J.,CAS National Astronomical Observatories | Wang J.J.,Joint Center for Astrophysics
Astronomy and Astrophysics | Year: 2012

Aims. We investigate the environment of the infrared dust bubble S51 and search for evidence of triggered star formation in its surroundings. Methods. We performed a multiwavelength study of the region around S51 with data taken from large-scale surveys: 2MASS, GLIMPSE, MIPSGAL, IRAS, and MALT90. We analyzed the spectral profile and the distribution of the molecular gas ( 13CO, C 18O, HCN, HNC, HCO +, C 2H, N 2H +, and HC 3N), and dust in the environment of S51. We used a mid-infrared emission three-color image to explore the physical environment and GLIMPSE color-color diagram [5.8]-[8.0] versus [3.6]-[4.5] to search for young stellar objects and identify the ionizing star candidates. Results. From a comparison of the morphology of the molecular gas and the Spitzer 8.0 μm emission, we conclude that the dust bubble is interacting with CO at a kinematic distance of 3.4 kpc. The bubble S51 structure, carried with shell and front side, is exhibited with 13CO and C 18O emission. Both outflow and inflow may exist in sources in the shell of bubble S51. We discover a small bubble G332.646-0.606 (R in = 26′′, r in = 15′′, R out = 35′′ and r out = 25′′) located at the northwest border of S51. A water maser, a methanol maser, and IRAS 16158-5055 are located at the junction of the two bubbles. Several young stellar objects are distributed along an arc-shaped structure near the S51 shell. They may represent a second generation of stars whose formation was triggered by the bubble expanding into the molecular gas. © 2012 ESO.


Liu X.-L.,CAS National Astronomical Observatories | Liu X.-L.,University of Chinese Academy of Sciences | Wang J.-J.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The physical, chemical and kinetic characteristics of 12 northern infrared dark clouds (IRDCs) are systematic studied using the 13CO (1-0) and C18O (1-0) lines, observed with the Purple MountainObservatory 13.7mradio telescope, the 1.1mmBolocam Galactic Plane Survey data and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Spitzer Infrared Array Camera 8 μm data. The molecular lines emission and 1.1 mm continuum emission almost coincide in morphology for each IRDC and both are associated well with the IRDCs. 10 IRDCs present the filamentary structure and substructures. Totally, 41 IRDC cores are identified, and a statistic research for them shows that the northern IRDC cores have a typical excitation temperature of 8-10 K, an integrated intensity ratio of 13CO to C18O of 3-6 and the column density (1-6) × 1022 cm-2. About 57.5 per cent of the IRDC cores are gravitationally bound, which are more compact, warmer and denser. In addition, we study the mass distribution functions of the whole IRDC cores as well as the gravitationally bound cores, finding that they almost have the same power-law indices. This indicates that the evolution of the IRDC cores almost has no effect on the mass spectrum of the molecular cores and thus can be used to study the stellar initial mass function. Moreover, three IRDC cores G24.00-3, G31.38-1 and G34.43-4 are detected to have large-scaled infall motions. Two different outflows are further found for the IRDC core G34.43-4 and one of them is in high collimation. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Yu N.,CAS National Astronomical Observatories | Yu N.,Joint Center for Astrophysics | Wang J.-J.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present a molecular line study towards 31 extended green object (EGO) clumps in the southern sky using data from MALT90 (Millimetre Astronomy Legacy Team 90 GHz). According to previous multiwavelength observations, we divide our sample into two groups: massive young stellar objects (MYSOs) and H II regions. The most detected lines are N2H+ (J = 1 - 0), HCO+ (J = 1 - 0), HNC (J = 1 - 0), HCN (J = 1 - 0), HC3N (J = 10 - 9), H13CO+ (J = 1 - 0), C2H (N = 1 - 0) and SiO (J = 2 - 1), indicating that most EGOs are indeed associated with dense clumps and recent outflow activities. The velocity widths of the N2H+ (J = 1 - 0), H13CO+ (J = 1 - 0), C2H (N = 1 - 0) and HC3N (J = 10 - 9) lines are comparable to each other in MYSOs. However, in H II regions the velocity widths of the N2H+ (J = 1 - 0) and C2H (N = 1 - 0) lines tend to be narrower than those of H13CO+ (J = 1 - 0) and HC3N (J = 10 - 9). Our results seem to support that N2H+ and C2H emissions mainly come from the gas inside quiescent clumps. In addition, we also find that the [N2H+]/[H13CO+] and [C2H]/[H13CO+] relative abundance ratios decrease from MYSOs to H II regions. These results suggest depletion of N2H+ and C2H in the late stages of massive-star formation, probably caused by the formation of H II regions inside. N2H+ and C2H might be used as chemical clocks for massive-star formation by comparing with other molecules such as H13CO+ and HC3N. © 2015 The Authors.


Xu J.-L.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics
Research in Astronomy and Astrophysics | Year: 2010

The mapping observations of CO J 2-1, CO J 3-2, 13CO J 2-1 and 13CO J 3-2 lines in the direction of IRAS 22506+5944 have been made. The results show that the cores in the J 2-1 transition lines have a similar morphology to those in the J 3-2 transition lines. Bipolar molecular outflows are verified. The prior IRAS 22506+5944 observations indicated that two IRAS sources and three H2O masers were located close to the peak position of the core. One of the IRAS sources may be the driving source of the outflows. In addition, the H2O masers may occur in relatively warm environments. The parameters of the dense core and outflow, obtained by the LTE method, indicate that IRAS 22506+5944 is a high-mass star formation region. © 2010 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.


Yu N.-P.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics
Research in Astronomy and Astrophysics | Year: 2013

We present the results of a high-resolution study with the Submillimeter Array (SMA) toward the massive star-forming complex G20.08-0.14N. With the SMA data, we have detected and analyzed the transitions in the 12CO (3-2) and 12CO (2-1) molecular lines as well as CH3CN. The millimeter observations reveal highly collimated bipolar molecular outflows, traced by high-velocity 12CO (2-1) and 12CO (3-2) emissions. Using a rotation temperature diagram, we derive that the rotational temperature and the column density of CH3CN are 244 K and 1.2 × 1015 cm-2, respectively. We also suggest that the minor outflow is probably driven by the hypercompact (HC) HII region A that is inside. We find the molecular gas (traced by C17O, SO, CH3OH and SO2) surrounding G20.08-0.14N appears to be undergoing bulk rotation. The HCHII region A that is inside is most probably the main source of accretion and heating for G20.08-0.14N. © 2013 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.


Zhang C.-P.,CAS National Astronomical Observatories | Zhang C.-P.,Joint Center for Astrophysics | Zhang C.-P.,University of Chinese Academy of Sciences | Wang J.-J.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics
Research in Astronomy and Astrophysics | Year: 2013

We investigated the environment of the infrared dust bubble N68 and searched for evidence of triggered star formation in its surroundings. We performed a multiwavelength study of the nebula with data taken from several large-scale surveys: GLIMPSE, MIPSGAL, IRAS, NVSS, GRS and JCMT. We analyzed the spectral profile and the distribution of the molecular gas (13CO J = 1 - 0 and J = 3 - 2), and the dust in the environment of N68. The position-velocity diagram clearly shows that N68 may be expanding outward. We used two three-color images of the mid-infrared emission to explore the physical environment, and one color-color diagram to investigate the distribution of young stellar objects (YSOs). We found that the 24 μm emission is surrounded by the 8.0 μm emission. Morphologically, the 1.4 GHz continuum strongly correlates with the 24 μm emission, and the 13CO J = 1 - 0 and J = 3 - 2 emissions correlate well with the 8.0 μm emission. We investigated two compact cores located in the shell of N68. The spectral intensity ratios of 13CO J = 3 - 2 to J = 1 - 0 range from 5 to 0.3. In addition, YSOs, masers, IRAS and UC HII regions are distributed in the shell of the bubble. The active region may be triggered by the expansion of the bubble N68. © 2013 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd..


Xu J.-L.,CAS National Astronomical Observatories | Xu J.-L.,Joint Center for Astrophysics | Wang J.-J.,CAS National Astronomical Observatories | Wang J.-J.,Joint Center for Astrophysics | Miller M.,University of Cologne
Astrophysical Journal | Year: 2011

We have performed submillimeter and millimeter observations in CO lines toward supernova remnant (SNR) IC443. The CO molecular shell coincides well with the partial shell of the SNR detected in radio continuum observations. Broad emission lines and three 1720 MHz OH masers were detected in the CO molecular shell. The present observations have provided further evidence in support of the interaction between the SNR and the adjoining molecular clouds (MCs). The total mass of the MCs is 9.26 × 103 M⊙. The integrated CO line intensity ratio (RICO(3-2)/I CO(2-1)) for the whole MC is between 0.79 and 3.40. The average value is 1.58, which is much higher than previous measurements of individual Galactic MCs. Higher line ratios imply that shocks have driven into the MCs. We conclude that high RICO(3-2)/ICO(2-1) is identified as a good signature of the SNR-MC interacting system. Based on the IRAS Point Source Catalog and the Two Micron All Sky Survey near-infrared database, 12 protostellar object and 1666 young stellar object (YSO) candidates (including 154 classical T Tauri stars and 419 Herbig Ae/Be stars) are selected. In the interacting regions, the significant enhancement of the number of protostellar objects and YSOs indicates the presence of some recently formed stars. After comparing the characteristic timescales of star formation with the age of IC443, we conclude that the protostellar objects and YSO candidates are not triggered by IC443. For the age of the stellar winds shell, we have performed our calculation on the basis of a stellar wind shell expansion model. The results and analysis suggest that the formation of these stars may be triggered by the stellar winds of the IC443 progenitor. © 2011. The American Astronomical Society.

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