Publication Search Results

ID: 159432
Type: article
Authors: Lu, Xing; Li, Shanghuo; Ginsburg, Adam; Longmore, Steven N.; Kruijssen, J. M. Diederik; Walker, Daniel L.; Feng, Siyi; Zhang, Qizhou; Battersby, Cara; Pillai, Thushara; Mills, Elisabeth A. C.; Kauffmann, Jens; Cheng, Yu; Inutsuka, Shu-ichiro
Abstract: We observe 1.3 mm spectral lines at 2000 au resolution toward four massive molecular clouds in the Central Molecular Zone (CMZ) of the Galaxy to investigate their star formation activities. We focus on several potential shock tracers that are usually abundant in protostellar outflows, including SiO, SO, CH₃OH, H₂CO, HC₃N, and HNCO. We identify 43 protostellar outflows, including 37 highly likely ones and 6 candidates. The outflows are found toward both known high-mass star-forming cores and less massive, seemingly quiescent cores, while 791 out of the 834 cores identified based on the continuum do not have detected outflows. The outflow masses range from less than 1 M_⊙ to a few tens of M_⊙, with typical uncertainties of a factor of 70. We do not find evidence of disagreement between relative molecular abundances in these outflows and in nearby analogs such as the well-studied L1157 and NGC 7538S outflows. The results suggest that (i) protostellar accretion disks driving outflows ubiquitously exist in the CMZ environment, (ii) the large fraction of candidate starless cores is expected if these clouds are at very early evolutionary phases, with a caveat on the potential incompleteness of the outflows, (iii) high-mass and low-mass star formation is ongoing simultaneously in these clouds, and (iv) current data do not show evidence of a difference between the shock chemistry in the outflows that determines the molecular abundances in the CMZ environment and in nearby clouds.

ID: 159433
Type: article
Authors: Olguin, Fernando A.; Sanhueza, Patricio; Guzmán, Andrés E.; Lu, Xing; Saigo, Kazuya; Zhang, Qizhou; Silva, Andrea; Chen, Huei-Ru Vivien; Li, Shanghuo; Ohashi, Satoshi; Nakamura, Fumitaka; Sakai, Takeshi; Wu, Benjamin
Abstract: We observed the high-mass star-forming region G335.579-0.292 with the Atacama Large Millimeter/submillimeter Array (ALMA) at 226 GHz with an angular resolution of 0"3 (∼1000 au resolution at the source distance). G335.579-0.292 hosts one of the most massive cores in the Galaxy (G335-MM1). The continuum emission shows that G335-MM1 fragments into at least five sources, while molecular line emission is detected in two of the continuum sources (ALMA1 and ALMA3). We found evidence of large- and small-scale infall in ALMA1 revealed by an inverse P-Cygni profile and the presence of a blueshifted spot at the center of the first moment map of the CH₃CN emission. In addition, hot gas expansion in the innermost region is unveiled by a redshifted spot in the first moment map of HDCO and (CH₃)₂CO (both with E_u > 1100 K). Our modeling reveals that this expansion motion originates close to the central source, likely due to reversal of the accretion flow induced by the expansion of the H II region, while infall and rotation motions originate in the outer regions. ALMA3 shows clear signs of rotation, with a rotation axis inclination with respect to the line of sight close to 90°, and a system mass (disk + star) in the range of 10-30 M_☉.

ID: 159351
Type: article
Authors: Sahu, Dipen; Liu, Sheng-Yuan; Liu, Tie; Evans, Neal J.,II; Hirano, Naomi; Tatematsu, Ken'ichi; Lee, Chin-Fei; Kim, Kee-Tae; Dutta, Somnath; Alina, Dana; Bronfman, Leonardo; Cunningham, Maria; Eden, David J.; Garay, Guido; Goldsmith, Paul F.; He, JinHua; Hsu, Shih-Ying; Jhan, Kai-Syun; Johnstone, Doug; Juvela, Mika; Kim, Gwanjeong; Kuan, Yi-Jehng; Kwon, Woojin; Lee, Chang Won; Lee, Jeong-Eun; Li, Di; Li, Pak Shing; Li, Shanghuo; Luo, Qiu-Yi; Montillaud, Julien; Moraghan, Anthony; Pelkonen, Veli-Matti; Qin, Sheng-Li; Ristorcelli, Isabelle; Sanhueza, Patricio; Shang, Hsien; Shen, Zhi-Qiang; Soam, Archana; Wu, Yuefang; Zhang, Qizhou; Zhou, Jianjun
Abstract: Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars are born. They are expected, at the stage of transitioning to the protostellar phase, to harbor centrally concentrated dense (sub)structures that will seed the formation of a new star or the binary/multiple stellar systems. Characterizing this critical stage of evolution is key to our understanding of star formation. In this work, we report the detection of high-density (sub)structures on the thousand-astronomical-unit (au) scale in a sample of dense prestellar cores. Through our recent ALMA observations toward the Orion Planck Galactic Cold Clumps, we have found five extremely dense prestellar cores, which have centrally concentrated regions of ∼2000 au in size, and several 10⁷ cm^-3 in average density. Masses of these centrally dense regions are in the range of 0.30 to 6.89 M_⊙. For the first time, our higher resolution observations (0.8″ ∼ 320 au) further reveal that one of the cores shows clear signatures of fragmentation; such individual substructures/fragments have sizes of 800-1700 au, masses of 0.08 to 0.84 M_⊙, densities of 2 - 8 × 10⁷ cm^-3, and separations of ∼1200 au. The substructures are massive enough (≳0.1 M_⊙) to form young stellar objects and are likely examples of the earliest stage of stellar embryos that can lead to widely (∼1200 au) separated multiple systems.

ID: 158744
Type: article
Authors: Dutta, Somnath; Lee, Chin-Fei; Liu, Tie; Hirano, Naomi; Liu, Sheng-Yuan; Tatematsu, Ken'ichi; Kim, Kee-Tae; Shang, Hsien; Sahu, Dipen; Kim, Gwanjeong; Moraghan, Anthony; Jhan, Kai-Syun; Hsu, Shih-Ying; Evans, Neal J.; Johnstone, Doug; Ward-Thompson, Derek; Kuan, Yi-Jehng; Lee, Chang Won; Lee, Jeong-Eun; Traficante, Alessio; Juvela, Mika; Vastel, Charlotte; Zhang, Qizhou; Sanhueza, Patricio; Soam, Archana; Kwon, Woojin; Bronfman, Leonardo; Eden, David; Goldsmith, Paul F.; He, JinHua; Wu, Yuefang; Pelkonen, Veli-Matti; Qin, Sheng-Li; Li, Shanghuo; Li, Di
Abstract: Planck Galactic Cold Clumps (PGCCs) are considered to be the ideal targets to probe the early phases of star formation. We have conducted a survey of 72 young dense cores inside PGCCs in the Orion complex with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm (band 6) using three different configurations (resolutions ˜0"35, 1"0, and 7"0) to statistically investigate their evolutionary stages and substructures. We have obtained images of the 1.3 mm continuum and molecular line emission (¹²CO, and SiO) at an angular resolution of ˜0"35 (˜140 au) with the combined arrays. We find 70 substructures within 48 detected dense cores with median dust mass ˜0.093 M_? and deconvolved size ˜0"27. Dense substructures are clearly detected within the central 1000 au of four candidate prestellar cores. The sizes and masses of the substructures in continuum emission are found to be significantly reduced with protostellar evolution from Class 0 to Class I. We also study the evolutionary change in the outflow characteristics through the course of protostellar mass accretion. A total of 37 sources exhibit CO outflows, and 20 (>50%) show high-velocity jets in SiO. The CO velocity extents (?Vs) span from 4 to 110 km s^-1 with outflow cavity opening angle width at 400 au ranging from [T_obs]₄₀₀ ˜ 0"6-3"9, which corresponds to 33°4-125°7. For the majority of the outflow sources, the ?Vs show a positive correlation with [T_obs]₄₀₀, suggesting that as protostars undergo gravitational collapse, the cavity opening of a protostellar outflow widens and the protostars possibly generate more energetic outflows.

ID: 158208
Type: article
Authors: Li, Fei; Wang, Junzhi; Fang, Min; Tan, Qing-Hua; Zhang, Zhi-Yu; Gao, Yu; Li, Shanghuo
Abstract: We present observations of HCN 3-2 emissions towards 37 local galaxies using the 10 m Submillimeter Telescope. HCN 3-2 emission is detected in 23 galaxies. The correlation of infrared luminosity (L_IR) and the luminosity of HCN 3-2 line emission measured in our sample is fitted with a slope of 1.11 and correlation coefficient of 0.91, which follows the linear correlation found in other dense gas tracers in the literature. Although molecular gas above a certain volume density threshold (i.e., $n_{\rm H_2}\ge 10^4\:$ cm^-3) statistically gave a similar relation with infrared luminosity, the large scatter of HCN 3-2/HCN 1-0 ratios for galaxies with different L_IR indicates that dense gas masses estimated from the line luminosities of only one transition of dense gas tracers should be treated with caution for individual galaxies.

ID: 158747
Type: article
Authors: Li, Shanghuo; Sanhueza, Patricio; Zhang, Qizhou; Nakamura, Fumitaka; Lu, Xing; Wang, Junzhi; Liu, Tie; Tatematsu, Ken'ichi; Jackson, James M.; Silva, Andrea; Guzmán, Andrés E.; Sakai, Takeshi; Izumi, Natsuko; Tafoya, Daniel; Li, Fei; Contreras, Yanett; Morii, Kaho; Kim, Kee-Tae
Abstract: We present a study of outflows at extremely early stages of high-mass star formation obtained from the ALMA Survey of 70 µm dark High-mass clumps in Early Stages (ASHES). Twelve massive 3.6-70 µm dark prestellar clump candidates were observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6. Forty-three outflows are identified toward 41 out of 301 dense cores using the CO and SiO emission lines, yielding a detection rate of 14%. We discover six episodic molecular outflows associated with low- to high-mass cores, indicating that episodic outflows (and therefore episodic accretion) begin at extremely early stages of protostellar evolution for a range of core masses. The time span between consecutive ejection events is much smaller than those found in more evolved stages, which indicates that the ejection episodicity timescale is likely not constant over time. The estimated outflow dynamical timescale appears to increase with core masses, which likely indicates that more massive cores have longer accretion timescales than less massive cores. The lower accretion rates in these 70 µm dark objects compared to the more evolved protostars indicate that the accretion rates increase with time. The total outflow energy rate is smaller than the turbulent energy dissipation rate, which suggests that outflow-induced turbulence cannot sustain the internal clump turbulence at the current epoch. We often detect thermal SiO emission within these 70 µm dark clumps that is unrelated to CO outflows. This SiO emission could be produced by collisions, intersection flows, undetected protostars, or other motions.

ID: 157483
Type: article
Authors: Li, Shanghuo; Zhang, Qizhou; Liu, Hauyu Baobab; Beuther, Henrik; Palau, Aina; Girart, Josep Miquel; Smith, Howard A.; Hora, Joseph L.; Lin, Yuxing; Qiu, Keping; Strom, Shaye; Wang, Junzhi; Li, Fei; Yue, Nannan
Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (JVLA) observations of the massive infrared dark cloud NGC 6334S (also known as IRDC G350.56+0.44), located at the southwestern end of the NGC 6334 molecular cloud complex. The H¹³CO⁺ and NH₂D lines covered by the ALMA observations at a ∼3″ angular resolution (∼0.02 pc) reveal that the spatially unresolved nonthermal motions are predominantly subsonic and transonic, a condition analogous to that found in low-mass star-forming molecular clouds. The observed supersonic nonthermal velocity dispersions in massive star-forming regions, often reported in the literature, might be significantly biased by poor spatial resolutions that broaden the observed line widths owing to unresolved motions within the telescope beam. Our 3 mm continuum image resolves 49 dense cores, whose masses range from 0.17 to 14 M_☉. The majority of them are resolved with multiple velocity components. Our analyses of these gas velocity components find an anticorrelation between the gas mass and the virial parameter. This implies that the more massive structures tend to be more gravitationally unstable. Finally, we find that the external pressure in the NGC 6334S cloud is important in confining these dense structures and may play a role in the formation of dense cores and, subsequently, the embedded young stars.

ID: 152925
Type: article
Authors: Li, Shanghuo; Wang, Junzhi; Fang, Min; Zhang, Qizhou; Li, Fei; Zhang, Zhi-Yu; Li, Juan; Zhu, Qingfeng; Zeng, Shaoshan
Abstract: We performed a survey in the SiO J = 5 → 4 line toward a sample of 199 Galactic massive star-forming regions at different evolutionary stages with the Submillimeter Telescope (SMT) 10 m and Caltech Submillimeter Observatory (CSO) 10.4 m telescopes. The sample consists of 44 infrared dark clouds (IRDCs), 86 protostellar candidates, and 69 young H II regions. We detected SiO J = 5 → 4 line emission in 102 sources, with a detection rate of 57%, 37%, and 65% for IRDCs, protostellar candidates, and young H II regions, respectively. We find both broad line emissions with full widths at zero power >20 km s^‑1 and narrow line emissions of SiO in objects at various evolutionary stages, likely associated with high-velocity shocks and low-velocity shocks, respectively. The SiO luminosities do not show apparent differences among various evolutionary stages in our sample. We find no correlation between the SiO abundance and the luminosity-to-mass ratio, indicating that the SiO abundance does not vary significantly in regions at different evolutionary stages of star formation.

ID: 154518
Type: article
Authors: Li, Shanghuo; Zhang, Qizhou; Pillai, Thushara; Stephens, Ian W.; Wang, Junzhi; Li, Fei
Abstract: We present Submillimeter Array observations of seven massive molecular clumps that are dark in the far-infrared for wavelengths up to 70 μm. Our 1.3 mm continuum images reveal 44 dense cores, with gas masses ranging from 1.4 to 77.1 M _☉. Twenty-nine dense cores have masses greater than 8 M _☉ and the other 15 dense cores have masses between 1.4 and 7.5 M _☉. Assuming the core density follows a power law in radius ρ ∝ r ^−b , the index b is found to be between 0.6 and 2.1, with a mean value of 1.3. The virial analysis reveals that the dense cores are not in virial equilibrium. CO outflow emission was detected toward six out of seven molecular clumps and associated with 17 dense cores. For five of these cores, CO emissions appear to have line wings at velocities of greater than 30 km s⁻¹ with respect to the source systemic velocity, which indicates that most of the clumps harbor protostars and thus are not quiescent in star formation. The estimated outflow timescale increases with core mass, which likely indicates that massive cores have longer accretion timescales than less massive ones. The fragmentation analysis shows that the masses of low-mass and massive cores are roughly consistent with thermal and turbulent Jeans masses, respectively.

ID: 154557
Type: article
Authors: Sanhueza, Patricio; Contreras, Yanett; Wu, Benjamin; Jackson, James M.; Guzmán, Andrés E.; Zhang, Qizhou; Li, Shanghuo; Lu, Xing; Silva, Andrea; Izumi, Natsuko; Liu, Tie; Miura, Rie E.; Tatematsu, Ken'ichi; Sakai, Takeshi; Beuther, Henrik; Garay, Guido; Ohashi, Satoshi; Saito, Masao; Nakamura, Fumitaka; Saigo, Kazuya; Veena, V. S.; Nguyen-Luong, Quang; Tafoya, Daniel
Abstract: The ALMA Survey of 70 μm dark High-mass clumps in Early Stages (ASHES) is designed to systematically characterize the earliest stages and constrain theories of high-mass star formation. Twelve massive (>500 {M}_ȯ ), cold (≤15 K), 3.6─70 μm dark prestellar clump candidates, embedded in infrared dark clouds, were carefully selected in the pilot survey to be observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We have mosaicked each clump (∼1 arcmin²) in continuum and line emission with the 12 m, 7 m, and Total Power (TP) arrays at 224 GHz (1.34 mm), resulting in ∼1.″2 resolution (∼4800 au, at the average source distance). As the first paper in the series, we concentrate on the continuum emission to reveal clump fragmentation. We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or "warm core" line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass () in continuum and line emission with the 12 m, 7 m, and Total Power (TP) arrays at 224 GHz (1.34 mm), resulting in ∼1.″2 resolution (∼4800 au, at the average source distance). As the first paper in the series, we concentrate on the continuum emission to reveal clump fragmentation. We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or "warm core" line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass (_ȯ ) cores and no high-mass (>30 {M}_ȯ ) prestellar cores (maximum mass 11 {M}_ȯ ). From the prestellar core mass function, we derive a power-law index of 1.17 ± 0.10, which is slightly shallower than Salpeter. We used the minimum spanning tree (MST) technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and separations detected in the sample, the mean separation and mass per clump are well explained by thermal Jeans fragmentation and are inconsistent with turbulent Jeans fragmentation. Core spatial distribution is well described by hierarchical subclustering rather than centrally peaked clustering. There is no conclusive evidence of mass segregation. We test several theoretical conditions and conclude that overall, competitive accretion and global hierarchical collapse scenarios are favored over the turbulent core accretion scenario.