Publication Search Results

ID: 155847
Type: article
Authors: Baug, T.; Wang, Ke; Liu, Tie; Tang, Mengyao; Zhang, Qizhou; Li, Di; Eswaraiah, Chakali; Liu, Sheng-Yuan; Tej, Anandmayee; Goldsmith, Paul F.; Bronfman, Leonardo; Qin, Sheng-Li; Tóth, Viktor L.; Li, Pak-Shing; Kim, Kee-Tae
Abstract: We present a statistical study of the orientation of outflows with respect to large-scale filaments and magnetic fields. Although filaments are widely observed toward Galactic star-forming regions, the exact role of filaments in star formation is unclear. Studies toward low-mass star- forming regions revealed both preferred and random orientations of outflows with respect to the filament long axes, while outflows in massive star-forming regions are mostly oriented perpendicular to the host filaments and parallel to the magnetic fields at similar physical scales. Here, we explore outflows in a sample of 11 protoclusters in H ii regions, a more evolved stage compared to infared dark clouds, using Atacama Large Millimeter/submillimeter Array CO (3─2) line observations. We identify a total of 105 outflow lobes in these protoclusters. Among the 11 targets, 7 are embedded within parsec-scale filamentary structures detected in ¹³CO line and 870 μm continuum emissions. The angles between outflow axes and corresponding filaments (γ_Fil) do not show any hint of preferred orientations (i.e., orthogonal or parallel as inferred in numerical models) with respect to the position angle of the filaments. Identified outflow lobes are also not correlated with the magnetic fields and Galactic plane position angles. Outflows associated with filaments aligned along the large-scale magnetic fields are also randomly oriented. Our study presents the first statistical results of outflow orientation with respect to large-scale filaments and magnetic fields in evolved massive star-forming regions. The random distribution suggests a lack of alignment of outflows with filaments, which may be a result of the evolutionary stage of the clusters.

ID: 156882
Type: article
Authors: Liu, Junhao; Zhang, Qizhou; Qiu, Keping; Baobab Liu, Hauyu; Pillai, Thushara; Miquel Girart, Josep; Li, Zhi-Yun; Wang, Ke
Abstract: We present 1.3 mm ALMA dust polarization observations at a resolution of ∼0.02 pc for three massive molecular clumps, MM1, MM4, and MM9, in the infrared dark cloud G28.34+0.06. With these sensitive and high- resolution continuum data, MM1 is resolved into a cluster of condensations. The magnetic field structure in each clump is revealed by the polarized emission. We found a trend of decreasing polarized emission fraction with increasing Stokes I intensities in MM1 and MM4. Using the angular dispersion function method (a modified Davis- Chandrasekhar-Fermi method), the plane-of-sky magnetic field strengths in two massive dense cores, MM1-Core1 and MM4-Core4, are estimated to be ∼1.6 mG and ∼0.32 mG, respectively. The virial parameters in MM1-Core1 and MM4-Core4 are calculated to be ∼0.76 and ∼0.37, respectively, suggesting that massive star formation does not start in equilibrium. Using the polarization-intensity gradient-local gravity method, we found that the local gravity is closely aligned with intensity gradient in the three clumps, and the magnetic field tends to be aligned with the local gravity in MM1 and MM4 except for regions near the emission peak, which suggests that the gravity plays a dominant role in regulating the gas collapse. Half of the outflows in MM4 and MM9 are found to be aligned within 10° of the condensation-scale (<0.05 pc) magnetic field, indicating that the magnetic field could play an important role from condensation to disk scale in the early stage of massive star formation.

ID: 158092
Type: article
Authors: Liu, Tie; Evans, Neal J.; Kim, Kee-Tae; Goldsmith, Paul F.; Liu, Sheng-Yuan; Zhang, Qizhou; Tatematsu, Ken'ichi; Wang, Ke; Juvela, Mika; Bronfman, Leonardo; Cunningham, Maria R.; Garay, Guido; Hirota, Tomoya; Lee, Jeong-Eun; Kang, Sung-ju; Li, Di; Li, Pak-Shing; Mardones, Diego; Qin, Sheng-Li; Ristorcelli, Isabelle; Tej, Anandmayee; Toth, L. Viktor; Wu, Jing-Wen; Wu, Yue-Fang; Yi, Hee-Weon; Yun, Hyeong-Sik; Liu, Hong-Li; Peng, Ya-Ping; Li, Juan; Li, Shang Huo; Lee, Chang Won; Shen, Zhi-Qiang; Baug, Tapas; Wang, Jun-Zhi; Zhang, Yong; Issac, Namitha; Zhu, Feng-Yao; Luo, Qiu-Yi; Liu, Xun-Chuan; Xu, Feng-Wei; Wang, Yu; Zhang, Chao; Ren, Zhiyuan; Zhang, Chao
Abstract: We report studies of the relationships between the total bolometric luminosity (L_bol or L_TIR) and the molecular line luminosities of J = 1 - 0 transitions of H¹³CN, H¹³CO⁺, HCN, and HCO⁺ with data obtained from ACA observations in the 'ATOMS' survey of 146 active Galactic star-forming regions. The correlations between L_bol and molecular line luminosities $L^{\prime }_{\rm mol}$ of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in L_bol- $L^{\prime }_{\rm mol}$ relations as their main line emission. The log(L_bol/ $L^{\prime }_{\rm mol}$ ) for different molecular line tracers have similar distributions. The L_bol-to- $L^{\prime }_{\rm mol}$ ratios do not change with galactocentric distances (R_GC) and clump masses (M_clump). The molecular line luminosity ratios (HCN-to-HCO⁺, H¹³CN-to-H¹³CO⁺, HCN-to-H¹³CN, and HCO⁺-to-H¹³CO⁺) all appear constant against L_bol, dust temperature (T_d), M_clump, and R_GC. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the 'ATOMS' survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales.

ID: 158091
Type: article
Authors: Liu, Tie; Evans, Neal J.; Kim, Kee-Tae; Goldsmith, Paul F.; Liu, Sheng-Yuan; Zhang, Qizhou; Tatematsu, Ken'ichi; Wang, Ke; Juvela, Mika; Bronfman, Leonardo; Cunningham, Maria R.; Garay, Guido; Hirota, Tomoya; Lee, Jeong-Eun; Kang, Sung-ju; Li, Di; Li, Pak-Shing; Mardones, Diego; Qin, Sheng-Li; Ristorcelli, Isabelle; Tej, Anandmayee; Toth, L. Viktor; Wu, Jing-Wen; Wu, Yue-Fang; Yi, Hee-Weon; Yun, Hyeong-Sik; Liu, Hong-Li; Peng, Ya-Ping; Li, Juan; Li, Shang-Huo; Lee, Chang Won; Shen, Zhi-Qiang; Baug, Tapas; Wang, Jun-Zhi; Zhang, Yong; Issac, Namitha; Zhu, Feng-Yao; Luo, Qiu-Yi; Soam, Archana; Liu, Xun-Chuan; Xu, Feng-Wei; Wang, Yu; Zhang, Chao; Ren, Zhiyuan; Zhang, Chao
Abstract: The ATOMS, standing for ALMA Three-millimeter Observations of Massive Star-forming regions, survey has observed 146 active star-forming regions with ALMA band 3, aiming to systematically investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary structures inside massive clumps. In this work, the observations, data analysis, and example science of the ATOMS survey are presented, using a case study for the G9.62+0.19 complex. Toward this source, some transitions, commonly assumed to trace dense gas, including CS J = 2-1, HCO⁺J = 1-0, and HCN J = 1-0, are found to show extended gas emission in low-density regions within the clump; less than 25 per cent of their emission is from dense cores. SO, CH₃OH, H¹³CN, and HC₃N show similar morphologies in their spatial distributions and reveal well the dense cores. Widespread narrow SiO emission is present (over ∼1 pc), which may be caused by slow shocks from large-scale colliding flows or H II regions. Stellar feedback from an expanding H II region has greatly reshaped the natal clump, significantly changed the spatial distribution of gas, and may also account for the sequential high-mass star formation in the G9.62+0.19 complex. The ATOMS survey data can be jointly analysed with other survey data, e.g. MALT90, Orion B, EMPIRE, ALMA_IMF, and ALMAGAL, to deepen our understandings of 'dense gas' star formation scaling relations and massive protocluster formation.

ID: 154700
Type: article
Authors: Lu, Xing; Mills, Elisabeth A. C.; Ginsburg, Adam; Walker, Daniel L.; Barnes, Ashley T.; Butterfield, Natalie; Henshaw, Jonathan D.; Battersby, Cara; Kruijssen, J. M. Diederik; Longmore, Steven N.; Zhang, Qizhou; Bally, John; Kauffmann, Jens; Ott, Jürgen; Rickert, Matthew; Wang, Ke
Abstract: We present new observations of the C-band continuum emission and masers to assess high-mass (>8 {M}_☉ ) star formation at early evolutionary phases in the inner 200 pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuum observation is complete to free-free emission from stars above 10-11 {M}_☉ in 91% of the covered area. We identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact H II regions, 12 are candidates of ultracompact H II regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. We detect class II CH₃OH masers at 23 positions, among which six are new detections. We confirm six known H₂CO masers in two high-mass star-forming regions and detect two new H₂CO masers toward the Sgr C cloud, making it the ninth region in the Galaxy that contains masers of this type. In spite of these detections, we find that current high-mass star formation in the inner CMZ is only taking place in seven isolated clouds. The results suggest that star formation at early evolutionary phases in the CMZ is about 10 times less efficient than expected from the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. This means that if there will be any impending, next burst of star formation in the CMZ, it has not yet begun.

ID: 150520
Type: article
Authors: Pillai, Thushara; Kauffmann, Jens; Zhang, Qizhou; Sanhueza, Patricio; Leurini, Silvia; Wang, Ke; Sridharan, Tirupati K.; König, Carsten
Abstract: The infrared dark clouds (IRDCs) G11.11-0.12 and G28.34+0.06 are two of the best-studied IRDCs in our Galaxy. These two clouds host clumps at different stages of evolution, including a massive dense clump in both clouds that is dark even at 70 and 100 μm. Such seemingly quiescent massive dense clumps have been speculated to harbor cores that are precursors of high-mass stars and clusters. We observed these two "prestellar" regions at 1 mm with the Submillimeter Array (SMA) with the aim of characterizing the nature of such cores. We show that the clumps fragment into several low- to high-mass cores within the filamentary structure of the enveloping cloud. However, while the overall physical properties of the clump may indicate a starless phase, we find that both regions host multiple outflows. The most massive core though 70 μm dark in both clumps is clearly associated with compact outflows. Such low-luminosity, massive cores are potentially the earliest stage in the evolution of a massive protostar. We also identify several outflow features distributed in the large environment around the most massive core. We infer that these outflows are being powered by young, low-mass protostars whose core mass is below our detection limit. These findings suggest that low-mass protostars have already formed or are coevally formed at the earliest phase of high-mass star formation.

ID: 154631
Type: article
Authors: Saajasto, Mika; Harju, Jorma; Juvela, Mika; Tie, Liu; Zhang, Qizhou; Liu, Sheng-Yuan; Hirano, Naomi; Wu, Yuefang; Kim, Kee-Tae; Tatematsu, Ken'ichi; Wang, Ke; Thompson, Mark
Abstract: Context. We present molecular line and dust continuum observations of a Planck-detected cold cloud, G074.11+00.11. The cloud consists of a system of curved filaments and a central star-forming clump. The clump is associated with several infrared sources and H₂O maser emission.
Aims: We aim to determine the mass distribution and gas dynamics within the clump to investigate if the filamentary structure seen around the clump repeats itself on a smaller scale, and to estimate the fractions of mass contained in dense cores and filaments. The velocity distribution of pristine dense gas can be used to investigate the global dynamical state of the clump, the role of filamentary inflows, filament fragmentation, and core accretion.
Methods: We used molecular line and continuum observations from single dish observatories and interferometric facilities to study the kinematics of the region.
Results: The molecular line observations show that the central clump may have formed as a result of a large-scale filament collision. The central clump contains three compact cores. Assuming a distance of 2.3 kpc, based on Gaia observations and a three-dimensional extinction method of background stars, the mass of the central clump exceeds 700 M_☉, which is roughly 25% of the total mass of the cloud. Our virial analysis suggests that the central clump and all identified substructures are collapsing. We find no evidence for small- scale filaments associated with the cores.
Conclusions: Our observations indicate that the clump is fragmented into three cores with masses in the range [10, 50] M_☉ and that all three are collapsing. The presence of an H₂O maser emission suggests active star formation. However, the CO lines show only weak signs of outflows. We suggest that the region is young and any processes leading to star formation have just recently begun.
The reduced radio datacubes and spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/630/A69Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.

ID: 154437
Type: article
Authors: Soam, Archana; Liu, Tie; Andersson, B. -G; Lee, Chang Won; Liu, Junhao; Juvela, Mika; Li, Pak Shing; Goldsmith, Paul F.; Zhang, Qizhou; Koch, Patrick M.; Kim, Kee-Tae; Qiu, Keping; Evans, Neal J., II; Johnstone, Doug; Thompson, Mark; Ward-Thompson, Derek; di Francesco, James; Tang, Ya-Wen; Montillaud, Julien; Kim, Gwanjeong; Mairs, Steve; Sanhueza, Patricio; Kim, Shinyoung; Berry, David; Gordon, Michael S.; Tatematsu, Ken'ichi; Liu, Sheng-Yuan; Pattle, Kate; Eden, David; McGehee, Peregrine M.; Wang, Ke; Ristorcelli, I.; Graves, Sarah F.; Alina, Dana; Lacaille, Kevin M.; Montier, Ludovic; Park, Geumsook; Kwon, Woojin; Chung, Eun Jung; Pelkonen, Veli-Matti; Micelotta, Elisabetta R.; Saajasto, Mika; Fuller, Gary
Abstract: We present the B-fields mapped in IRDC G34.43+0.24 using 850 μm polarized dust emission observed with the POL-2 instrument at the James Clerk Maxwell telescope. We examine the magnetic field geometries and strengths in the northern, central, and southern regions of the filament. The overall field geometry is ordered and aligned closely perpendicular to the filament's main axis, particularly in regions containing the central clumps MM1 and MM2, whereas MM3 in the north has field orientations aligned with its major axis. The overall field orientations are uniform at large (POL-2 at 14″ and SHARP at 10″) to small scales (TADPOL at 2.″5 and SMA at 1.″5) in the MM1 and MM2 regions. SHARP/CSO observations in MM3 at 350 μm from Tang et al. show a similar trend as seen in our POL-2 observations. TADPOL observations demonstrate a well-defined field geometry in MM1/MM2 consistent with MHD simulations of accreting filaments. We obtained a plane-of-sky magnetic field strength of 470 ± 190 μG, 100 ± 40 μG, and 60 ± 34 μG in the central, northern, and southern regions of G34, respectively, using the updated Davis-Chandrasekhar-Fermi relation. The estimated value of field strength, combined with column density and velocity dispersion values available in the literature, suggests G34 to be marginally critical with criticality parameter λ values 0.8 ± 0.4, 1.1 ± 0.8, and 0.9 ± 0.5 in the central, northern, and southern regions, respectively. The turbulent motions in G34 are sub-Alfvénic with Alfvénic Mach numbers of 0.34 ± 0.13, 0.53 ± 0.30, and 0.49 ± 0.26 in the three regions. The observed aligned B-fields in G34.43+0.24 are consistent with theoretical models suggesting that B-fields play an important role in guiding the contraction of the cloud driven by gravity.

ID: 145792
Type: article
Authors: Liu, Tie; Kim, Kee-Tae; Juvela, Mika; Wang, Ke; Tatematsu, Ken'ichi; di Francesco, James; Liu, Sheng-Yuan; Wu, Yuefang; Thompson, Mark; Fuller, Gary; Eden, David; Li, Di; Ristorcelli, I.; Kang, Sung-ju; Lin, Yuxin; Johnstone, D.; He, J. H.; Koch, P. M.; Sanhueza, Patricio; Qin, Sheng-Li; Zhang, Qizhou; Hirano, N.; Goldsmith, Paul F.; Evans, Neal J., II; White, Glenn J.; Choi, Minho; Lee, Chang Won; Toth, L. V.; Mairs, Steve; Yi, H. -W; Tang, Mengyao; Soam, Archana; Peretto, N.; Samal, Manash R.; Fich, Michel; Parsons, Harriet; Yuan, Jinghua; Zhang, Chuan-Peng; Malinen, Johanna; Bendo, George J.; Rivera-Ingraham, A.; Liu, Hong-Li; Wouterloot, Jan; Li, Pak Shing; Qian, Lei; Rawlings, Jonathan; Rawlings, Mark G.; Feng, Siyi; Aikawa, Yuri; Akhter, S.; Alina, Dana; Bell, Graham; Bernard, J. -P; Blain, Andrew; Bőgner, Rebeka; Bronfman, L.; Byun, D. -Y; Chapman, Scott; Chen, Huei-Ru; Chen, M.; Chen, Wen-Ping; Chen, X.; Chen, Xuepeng; Chrysostomou, A.; Cosentino, Giuliana; Cunningham, M. R.; Demyk, K.; Drabek-Maunder, Emily; Doi, Yasuo; Eswaraiah, C.; Falgarone, Edith; Fehér, O.; Fraser, Helen; Friberg, Per; Garay, G.; Ge, J. X.; Gear, W. K.; Greaves, Jane; Guan, X.; Harvey-Smith, Lisa; Hasegawa, Tetsuo; Hatchell, J.; He, Yuxin; Henkel, C.; Hirota, T.; Holland, W.; Hughes, A.; Jarken, E.; Ji, Tae-Geun; Jimenez-Serra, Izaskun; Kang, Miju; Kawabata, Koji S.; Kim, Gwanjeong; Kim, Jungha; Kim, Jongsoo; Kim, Shinyoung; Koo, B. -C; Kwon, Woojin; Kuan, Yi-Jehng; Lacaille, K. M.; Lai, Shih-Ping; Lee, C. F.; Lee, J. -E; Lee, Y. -U; Li, Dalei; Li, Hua-Bai; Lo, N.; Lopez, John A. P.; Lu, Xing; Lyo, A. -Ran; Mardones, D.; Marston, A.; McGehee, P.; Meng, F.; Montier, L.; Montillaud, Julien; Moore, T.; Morata, O.; Moriarty-Schieven, Gerald H.; Ohashi, S.; Pak, Soojong; Park, Geumsook; Paladini, R.; Pattle, Kate M.; Pech, Gerardo; Pelkonen, V. -M; Qiu, K.; Ren, Zhi-Yuan; Richer, John; Saito, M.; Sakai, Takeshi; Shang, H.; Shinnaga, Hiroko; Stamatellos, Dimitris; Tang, Y. -W; Traficante, Alessio; Vastel, Charlotte; Viti, S.; Walsh, Andrew; Wang, Bingru; Wang, Hongchi; Wang, Junzhi; Ward-Thompson, D.; Whitworth, Anthony; Xu, Ye; Yang, J.; Yang, Yao-Lun; Yuan, Lixia; Zavagno, A.; Zhang, Guoyin; Zhang, H. -W; Zhou, Chenlin; Zhou, Jianjun; Zhu, Lei; Zuo, Pei; Zhang, Chao
Abstract: The low dust temperatures (_⊙, ∼12 pc, and ∼500 M _⊙ pc^‑1, respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (β) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.

ID: 150206
Type: article
Authors: Liu, Tie; Kim, Kee-Tae; Liu, Sheng-Yuan; Juvela, Mika; Zhang, Qizhou; Wu, Yuefang; Li, Pak Shing; Parsons, Harriet; Soam, Archana; Goldsmith, Paul F.; Su, Yu-Nung; Tatematsu, Ken'ichi; Qin, Sheng-Li; Garay, Guido; Hirota, Tomoya; Wouterloot, Jan; Chen, Huei-Ru; Evans, Neal J., II; Graves, Sarah; Kang, Sung-ju; Li, Di; Mardones, Diego; Rawlings, Mark G.; Ren, Zhiyuan; Wang, Ke
Abstract: How stellar feedback from high-mass stars (e.g., H II regions) influences the surrounding interstellar medium and regulates new star formation is still unclear. To address this question, we observed the G9.62+0.19 complex in 850 μm continuum with the James Clerk Maxwell Telescope/POL-2 polarimeter. An ordered magnetic field has been discovered in its youngest clump, the G9.62 clump. The magnetic field strength is determined to be ∼1 mG. Magnetic field plays a larger role than turbulence in supporting the clump. However, the G9.62 clump is still unstable against gravitational collapse even if thermal, turbulent, and magnetic field support are taken into account together. The magnetic field segments in the outskirts of the G9.62 clump seem to point toward the clump center, resembling a dragged-in morphology, indicating that the clump is likely undergoing magnetically regulated global collapse. However, the magnetic field in its central region is aligned with the shells of the photodissociation regions and is approximately parallel to the ionization (or shock) front, indicating that the magnetic field therein is likely compressed by the expanding H II regions that formed in the same complex.

ID: 146169
Type: article
Authors: Sokolov, Vlas; Wang, Ke; Pineda, Jaime E.; Caselli, Paola; Henshaw, Jonathan D.; Barnes, Ashley T.; Tan, Jonathan C.; Fontani, Francesco; Jiménez-Serra, Izaskun; Zhang, Qizhou
Abstract: High-mass star forming regions are typically thought to be dominated by supersonic motions. We present combined Very Large Array and Green Bank Telescope (VLA+GBT) observations of NH₃ (1,1) and (2,2) in the infrared dark cloud (IRDC) G035.39-00.33, tracing cold and dense gas down to scales of 0.07 pc. We find that, in contrast to previous, similar studies of IRDCs, more than a third of the fitted ammonia spectra show subsonic non-thermal motions (mean line width of 0.71 km s^-1), and sonic Mach number distribution peaks around ℳ = 1. As possible observational and instrumental biases would only broaden the line profiles, our results provide strong upper limits to the actual value of ℳ, further strengthening our findings of narrow line widths. This finding calls for a re-evaluation of the role of turbulent dissipation and subsonic regions in massive-star and cluster formation. Based on our findings in G035.39, we further speculate that the coarser spectral resolution used in the previous VLA NH₃ studies may have inhibited the detection of subsonic turbulence in IRDCs. The reduced turbulent support suggests that dynamically important magnetic fields of the 1 mG order would be required to support against possible gravitational collapse. Our results offer valuable input into the theories and simulations that aim to recreate the initial conditions of high-mass star and cluster formation.

ID: 143372
Type: article
Authors: Sanhueza, Patricio; Jackson, James M.; Zhang, Qizhou; Guzmán, Andrés E.; Lu, Xing; Stephens, Ian W.; Wang, Ke; Tatematsu, Ken'ichi
Abstract: The infrared dark cloud (IRDC) G028.23-00.19 hosts a massive (1500 M _⊙), cold (12 K), and 3.6–70 μm IR dark clump (MM1) that has the potential to form high-mass stars. We observed this prestellar clump candidate with the Submillimeter Array (∼3.″5 resolution) and Jansky Very Large Array (∼2.″1 resolution) in order to characterize the early stages of high-mass star formation and to constrain theoretical models. Dust emission at 1.3 mm wavelength reveals five cores with masses ≤15 M _⊙. None of the cores currently have the mass reservoir to form a high-mass star in the prestellar phase. If the MM1 clump will ultimately form high-mass stars, its embedded cores must gather a significant amount of additional mass over time. No molecular outflows are detected in the CO (2-1) and SiO (5-4) transitions, suggesting that the SMA cores are starless. By using the NH₃ (1, 1) line, the velocity dispersion of the gas is determined to be transonic or mildly supersonic (ΔV _nt/ΔV _th ∼ 1.1–1.8). The cores are not highly supersonic as some theories of high-mass star formation predict. The embedded cores are four to seven times more massive than the clump thermal Jeans mass and the most massive core (SMA1) is nine times less massive than the clump turbulent Jeans mass. These values indicate that neither thermal pressure nor turbulent pressure dominates the fragmentation of MM1. The low virial parameters of the cores (0.1–0.5) suggest that they are not in virial equilibrium, unless strong magnetic fields of ∼1–2 mG are present. We discuss high-mass star formation scenarios in a context based on IRDC G028.23-00.19, a study case believed to represent the initial fragmentation of molecular clouds that will form high-mass stars.

ID: 140787
Type: article
Authors: Feng, Siyi; Beuther, Henrik; Zhang, Qizhou; Liu, Hauyu Baobab; Zhang, Zhiyu; Wang, Ke; Qiu, Keping
Abstract: We present observations toward a high-mass (\gt 40 {M}_? ), low-luminosity (\lt 10 {L}_? ) 70 µ {{m}} dark molecular core G28.34 S-A at 3.4 mm, using the IRAM 30 m telescope and the NOEMA interferometer. We report the detection of {SiO} J=2\to 1 line emission, which is spatially resolved in this source at a linear resolution of ˜0.1 pc, while the 3.4 mm continuum image does not resolve any internal sub-structures. The SiO emission exhibits two W-E oriented lobes centering on the continuum peak. Corresponding to the redshifted and blueshifted gas with velocities up to 40 {km} {{{s}}}^-1 relative to the quiescent cloud, these lobes clearly indicate the presence of a strong bipolar outflow from this 70 µ {{m}} dark core, a source previously considered as one of the best candidates of “starless” core. Our SiO detection is consistent with ALMA archival data of {SiO} J=5\to 4, whose high-velocity blueshifted gas reveals a more compact lobe spatially closer to the dust center. This outflow indicates that the central source may be in an early evolutionary stage of forming a high-mass protostar. We also find that the low-velocity components (in the range of {{Vlsr}}_-5⁺³ {km} {{{s}}}^-1) have an extended, NW-SE oriented distribution. Discussing the possible accretion scenarios of the outflow-powering young stellar object, we argue that molecular line emission and the molecular outflows may provide a better indication of the accretion history of the forming young stellar object, than snapshot observations of the present bolometric luminosity. This is particularly significant for cases of episodic accretion, which may occur during the collapse of the parent molecular core.

ID: 142013
Type: article
Authors: Liu, Tie; Kim, Kee-Tae; Yoo, Hyunju; Liu, Sheng-Yuan; Tatematsu, Ken'ichi; Qin, Sheng-Li; Zhang, Qizhou; Wu, Yuefang; Wang, Ke; Goldsmith, Paul F.; Juvela, Mika; Lee, Jeong-Eun; Tóth, L. Viktor; Mardones, Diego; Garay, Guido; Bronfman, Leonardo; Cunningham, Maria R.; Li, Di; Lo, Nadia; Ristorcelli, Isabelle; Schnee, Scott
Abstract: We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment 10 m telescope. A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift (z > 1) star forming galaxies (SFGs), indicating a constant gas depletion time of ˜100 Myr for molecular gas in both Galactic clumps and high z SFGs. However, low z galaxies do not follow this relation and seem to have a longer global gas depletion time. The correlations between total infrared luminosities (L _TIR) and molecular line luminosities ({L}_{mol}^\prime ) of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with L _TIR ˜ 10³ L _⊙. These correlations become linear when extended to external galaxies. A bimodal behavior in the L _TIR-{L}_{mol}^\prime correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and σ _line/σ _vir. Such bimodal behavior may be due to evolutionary effects. The slopes of L _TIR-L‧_mol correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in Wu et al. (2010). The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L _TIR larger than L _TIR ˜ 10^4.5 L _⊙. High effective excitation density tracers cannot linearly trace the total clump masses, leading to a sublinear correlations for both M _clump-L‧_mol and L _TIR-L‧_mol relations.

ID: 138760
Type: article
Authors: Liu, Tie; Zhang, Qizhou; Kim, Kee-Tae; Wu, Yuefang; Lee, Chang Won; Lee, Jeong-Eun; Tatematsu, Ken'ichi; Choi, Minho; Juvela, Mika; Thompson, Mark; Goldsmith, Paul F.; Liu, Sheng-Yuan; Naomi, Hirano; Koch, Patrick; Henkel, Christian; Sanhueza, Patricio; He, JinHua; Rivera-Ingraham, Alana; Wang, Ke; Cunningham, Maria R.; Tang, Ya-Wen; Lai, Shih-Ping; Yuan, Jinghua; Li, Di; Fuller, Gary; Kang, Miju; Nguyen Luong, Quang; Liu, Hauyu Baobab; Ristorcelli, Isabelle; Yang, Ji; Xu, Ye; Hirota, Tomoya; Mardones, Diego; Qin, Sheng-Li; Chen, Huei-Ru; Kwon, Woojin; Meng, FanYi; Zhang, Huawei; Kim, Mi-Ryang; Yi, Hee-Weon
Abstract: We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the λ Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound bright-rimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity (˜0.8 {L}_⊙ ) and accretion rate (6.3 × 10^-7 {M}_⊙ yr^-1) when compared with other young Class 0 sources (e.g., PACS Bright Red Sources) in the Orion complex. It has slightly larger internal luminosity (0.21 ± 0.01 {L}_⊙ ) and outflow velocity (˜14 km s^-1) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than an FHSC. Considering its low internal luminosity (0.08 ± 0.01 {L}_⊙ ) and accretion rate (2.8 × 10^-8 {M}_⊙ yr^-1), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency (˜0.3%-0.4%) and core formation efficiency (˜1%) in PGCC G192.32-11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed owing to stellar feedback.

ID: 140479
Type: article
Authors: Liu, Tie; Kim, Kee-Tae; Wu, Yuefang; Li, Di; Lee, Chang-Won; De Pree, Christopher G.; Qin, Sheng-Li; Wang, Ke; Tatematsu, Ken'ichi; Zhang, Qizhou; Mardones, Diego; Liu, Sheng-Yuan; Cho, Se-Hyung
Abstract: W49N is a mini-starburst in the Milky Way and is thus an ideal laboratory for high-mass star formation studies. Due to its large distance ({11.1}_-0.7^+0.9 kpc), the kinematics inside and between the dense molecular clumps in W49N are far from well-understood. The Submillimeter Array observations resolved the continuum emission into two clumps. The molecular line observation of SO₂ ({28}_{4,24}–{28}_{3,25}) suggests that the two clumps have a velocity difference of ∼7 km s^‑1. The eastern clump is very close to two radio sources "G1" and "G2," and the western clump coincides with a radio source "B." The HCN (3–2) line reveals an extremely energetic outflow, which is among the most energetic molecular outflows in the Milky Way. This is the first report of high-velocity molecular outflow detection in W49N. The outflow jet might be in precession, which could account for the distribution, velocity, and rotation of water maser spots. Three absorption systems are identified in {{HCO}}⁺ (3–2) spectra. The absorption features are blueshifted with respect to the emission of SO₂ ({28}_{4,24}–{28}_{3,25}) lines, indicating that a cold layer is expanding in front of the warm gas. Further analysis indicates that the expansion is decelerated from the geometric expansion centers.

ID: 136588
Type: article
Authors: Lu, Xing; Zhang, Qizhou; Wang, Ke; Gu, Qiusheng
Abstract: To study the fragmentation and gravitational collapse of dense cores in infrared dark clouds (IRDCs), we have obtained submillimeter continuum and spectral line data as well as multiple inversion transitions of NH₃ and H₂O maser data of four massive clumps in IRDC G28.53-0.25. Combining single-dish and interferometer NH₃ data, we derive a rotation temperature of G28.53. We identity 12 dense cores at a 0.1 pc scale based on submillimeter continuum, and obtain their physical properties using NH₃ and continuum data. By comparing the Jeans masses of cores with the core masses, we find that turbulent pressure is important for supporting the gas when 1 pc scale clumps fragment into 0.1 pc scale cores. All cores have a virial parameter that is smaller than 1 if we assume an inverse squared radial density profile, suggesting they are gravitationally bound, and the three most promising star-forming cores have a virial parameter that is smaller than 1 even when taking the magnetic field into account. We also associate the cores with star formation activities revealed by outflows, masers, or infrared sources. Unlike what previous studies have suggested, MM1 turns out to harbor a few star-forming cores and is likely a progenitor of a high-mass star cluster. MM5 is intermediate while MM7/8 are quiescent in terms of star formation, but they also harbor gravitationally bound dense cores and have the potential for forming stars, as in MM1.

ID: 136417
Type: article
Authors: Zhang, Qizhou; Wang, Ke; Lu, Xing; Jiménez-Serra, Izaskun
Abstract: Sufficiently massive clumps of molecular gas collapse under self-gravity and fragment to spawn a cluster of stars that have a range of masses. We investigate observationally the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, in the 1.3 mm continuum and spectral line emission using the Atacama Large Millimeter/Submillimeter Array. Sensitive continuum data reveal further fragmentation in five dusty cores at a resolution of several 10³ AU. Spectral line emission from C¹⁸O, CH₃OH, ¹³CS, H₂CO, and N₂D⁺ is detected for the first time toward these dense cores. We found that three cores are chemically more evolved as compared with the other two; interestingly, though, all of them are associated with collimated outflows as suggested by evidence from the CO, SiO, CH₃OH, H₂CO, and SO emission. The parsec-scale kinematics in exhibit velocity gradients along the filament, consistent with accretion flows toward the clumps and cores. The moderate luminosity and the chemical signatures indicate that the five cores harbor low- to intermediate-mass protostars that likely become massive ones at the end of the accretion. Despite the fact that the mass limit reached by the dust continuum sensitivity is 30 times lower than the thermal Jeans mass, there is a lack of a distributed low-mass protostellar population in the clump. Our observations indicate that in a protocluster, low-mass stars form at a later stage after the birth of more massive protostars.

ID: 120963
Type: article
Authors: Wang, Ke; Zhang, Qizhou; Testi, Leonardo; Tak, Floris van der; Wu, Yuefang; Zhang, Huawei; Pillai, Thushara; Wyrowski, Friedrich; Carey, Sean; Ragan, Sarah E.; Henning, Thomas
Abstract: We present Submillimeter Array (SMA) λ = 0.88 and 1.3 mm broad-band observations, and Very Large Array (VLA) observations in NH₃ (J, K) = (1,1) up to (5,5), H₂O and CH₃OH maser lines towards the two most massive molecular clumps in infrared dark cloud (IRDC) G11.11-0.12. Sensitive high-resolution images reveal hierarchical fragmentation in dense molecular gas from the ˜1 pc clump scale down to ˜0.01 pc condensation scale. At each scale, the mass of the fragments is orders of magnitude larger than the Jeans mass. This is common to all four IRDC clumps we studied, suggesting that turbulence plays an important role in the early stages of clustered star formation. Masers, shock heated NH₃ gas, and outflows indicate intense ongoing star formation in some cores while no such signatures are found in others. Furthermore, chemical differentiation may reflect the difference in evolutionary stages among these star formation seeds. We find NH₃ ortho/para ratios of 1.1 ± 0.4, 2.0 ± 0.4, and 3.0 ± 0.7 associated with three outflows, and the ratio tends to increase along the outflows downstream. Our combined SMA and VLA observations of several IRDC clumps present the most in-depth view so far of the early stages prior to the hot core phase, revealing snapshots of physical and chemical properties at various stages along an apparent evolutionary sequence.

ID: 109915
Type: article
Authors: Liu, Hauyu Baobab; Quintana-Lacaci, Guillermo; Wang, Ke; Ho, Paul T. P.; Li, Zhi-Yun; Zhang, Qizhou; Zhang, Zhi-Yu
Abstract: We observe the 1.2 mm continuum emission around the OB cluster-forming region G10.6-0.4, using the MAMBO-2 bolometer array of the IRAM 30 m telescope and the Submillimeter Array (SMA). Comparison of the Spitzer