Publication Search Results

ID: 159434
Type: article
Authors: Law, Charles J.; Zhang, Qizhou; Öberg, Karin I.; Galván-Madrid, Roberto; Keto, Eric; Liu, Hauyu Baobab; Ho, Paul T. P.
Abstract: Massive star-forming regions exhibit an extremely rich and diverse chemistry, which in principle provides a wealth of molecular probes, as well as laboratories for interstellar prebiotic chemistry. Since the chemical structure of these sources displays substantial spatial variation among species on small scales (≲10⁴ au), high-angular-resolution observations are needed to connect chemical structures to local environments and inform astrochemical models of massive star formation. To address this, we present ALMA 1.3 mm observations toward OB cluster-forming region G10.6-0.4 (hereafter "G10.6") at a resolution of 0"14 (700 au). We find highly structured emission from complex organic molecules (COMs) throughout the central 20,000 au, including two hot molecular cores and several shells or filaments. We present spatially resolved maps of rotational temperature and column density for a large sample of COMs and warm gas tracers. These maps reveal a range of gas substructure in both O- and N-bearing species. We identify several spatial correlations that can be explained by existing models for the formation of COMs, including NH₂CHO/HNCO and CH₃OCHO/CH₃OCH₃, but also observe unexpected distributions and correlations that suggest that our current understanding of COM formation is far from complete. Importantly, complex chemistry is observed throughout G10.6, rather than being confined to hot cores. The COM composition appears to be different in the cores compared to the more extended structures, which illustrates the importance of high-spatial-resolution observations of molecular gas in elucidating the physical and chemical processes associated with massive star formation.

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: 159261
Type: article
Authors: Walker, Daniel L.; Longmore, Steven N.; Bally, John; Ginsburg, Adam; Kruijssen, J. M. Diederik; Zhang, Qizhou; Henshaw, Jonathan D.; Lu, Xing; Alves, João; Barnes, Ashley T.; Battersby, Cara; Beuther, Henrik; Contreras, Yanett A.; Gómez, Laura; Ho, Luis C.; Jackson, James M.; Kauffmann, Jens; Mills, Elisabeth A. C.; Pillai, Thushara
Abstract: G0.253+0.016, aka 'the Brick', is one of the most massive (>10⁵ M_⊙) and dense (>10⁴ cm^-3) molecular clouds in the Milky Way's Central Molecular Zone. Previous observations have detected tentative signs of active star formation, most notably a water maser that is associated with a dust continuum source. We present ALMA Band 6 observations with an angular resolution of 0.13 arcsec (1000 AU) towards this 'maser core' and report unambiguous evidence of active star formation within G0.253+0.016. We detect a population of eighteen continuum sources (median mass ∼2 M_⊙), nine of which are driving bi-polar molecular outflows as seen via SiO (5-4) emission. At the location of the water maser, we find evidence for a protostellar binary/multiple with multidirectional outflow emission. Despite the high density of G0.253+0.016, we find no evidence for high-mass protostars in our ALMA field. The observed sources are instead consistent with a cluster of low-to-intermediate-mass protostars. However, the measured outflow properties are consistent with those expected for intermediate-to-high-mass star formation. We conclude that the sources are young and rapidly accreting, and may potentially form intermediate- and high-mass stars in the future. The masses and projected spatial distribution of the cores are generally consistent with thermal fragmentation, suggesting that the large-scale turbulence and strong magnetic field in the cloud do not dominate on these scales, and that star formation on the scale of individual protostars is similar to that in Galactic disc environments.

ID: 159435
Type: article
Authors: Yue, Nan-Nan; Li, Di; Zhang, Qi-Zhou; Zhu, Lei; Henshaw, Jonathan; Mardones, Diego; Ren, Zhi-Yuan
Abstract: We report here Atacama Large Millimeter/submillimeter Array (ALMA) N₂H⁺ (1-0) images of the Orion Molecular Cloud 2 and 3 (OMC-2/3) with high angular resolution (3″ or 1200 au) and high spatial dynamic range. Combining a dataset from the ALMA main array, Atacama Compact Array (ACA), Nobeyama 45-m Telescope and Very Large Array (VLA) (providing temperature measurement on matching scales), we find that most of the dense gas in OMC-2/3 is subsonic (σ_NT / C_s = 0.62) with a mean line width (Δυ) of 0.39 km s^-1 full width at half maximum (FWHM). This is markedly different from the majority of previous observations of massive star-forming regions. In contrast, line widths from the Nobeyama Telescope are transonic at 0.69 km s^-1 (σ_NT / C_s = 1.08). We demonstrated that the larger line widths obtained by the single-dish telescope arose from unresolved sub-structures within their respective beams. The dispersions from larger scales σ_ls (as traced by the Nobeyama Telescope) can be decomposed into three components such that ${\sigma }_{{\rm{ls}}}^{2}={\sigma }_{{\rm{ss}}}^{2}+{\sigma }_{{\rm{bm}}}^{2}+{\sigma }_{{\rm{rd}}}^{2}$ , where small-scale σ_ss is the line dispersion of each ALMA beam, bulk motion σ_bm is dispersion between peak velocity of each ALMA beam and σ_rd is the residual dispersion. Such decomposition, though purely empirical, appears to be robust throughout our data cubes. Apparent supersonic line widths, commonly found in massive molecular clouds, are thus likely due to the effect of poor spatial resolution. The observed non-thermal line dispersion (sometimes referred to as 'turbulence') transits from supersonic to subsonic at ∼ 0.05 pc scales in the OMC-2/3 region. Such transition could be commonly found with sufficient spatial (not just angular) resolution, even in regions with massive young clusters, such as the Orion molecular clouds studied here.

ID: 158648
Type: article
Authors: Añez-López, N.; Busquet, G.; Koch, P. M.; Girart, J. M.; Liu, H. B.; Santos, F.; Chapman, N. L.; Novak, G.; Palau, A.; Ho, P. T. P.; Zhang, Qizhou
Abstract: Context. Magnetic fields are predicted to play a significant role in the formation of filamentary structures and their fragmentation to form stars and star clusters.
Aims: We aim to investigate the role of the magnetic field in the process of core fragmentation toward the two hub-filament systems in the infrared dark cloud G14.225-0.506, which present different levels of fragmentation.
Methods: We performed observations of the thermal dust polarization at 350 µm using the Caltech Submillimeter Observatory (CSO) with an angular resolution of 10" toward the two hubs (Hub-N and Hub-S) in the infrared dark cloud G14.225-0.506. We additionally applied the polarization-intensity-gradient method to estimate the significance of the magnetic field over the gravitational force.
Results: The sky-projected magnetic field in Hub-N shows a rather uniform structure along the east-west orientation, which is roughly perpendicular to the major axis of the hub-filament system. The intensity gradient in Hub-N displays a single local minimum coinciding with the dust core MM1a detected with interferometric observations. Such a prevailing magnetic field orientation is slightly perturbed when approaching the dust core. Unlike the northern Hub, Hub-S shows two local minima, reflecting the bimodal distribution of the magnetic field. In Hub-N, both east and west of the hub-filament system, the intensity gradient and the magnetic field are parallel whereas they tend to be perpendicular when penetrating the dense filaments and hub. Analysis of the |d|- and S_B-maps indicates that, in general, the magnetic field cannot prevent gravitational collapse, both east and west, suggesting that the magnetic field is initially dragged by the infalling motion and aligned with it, or is channeling material toward the central ridge from both sides. Values of S_B ? 1 are found toward a north-south ridge encompassing the dust emission peak, indicating that in this region magnetic field dominates over gravity force, or that with the current angular resolution we cannot resolve a hypothetically more complex structure. We estimated the magnetic field strength, the mass-to-flux ratio, and the Alfvén Mach number, and found differences between the two hubs.
Conclusions: The different levels of fragmentation observed in these two hubs could arise from differences in the properties of the magnetic field rather than from differences in the intensity of the gravitational field because the density in the two hubs is similar. However, environmental effects could also play a role.

ID: 157805
Type: article
Authors: Battersby, Cara; Keto, Eric; Walker, Daniel; Barnes, Ashley; Callanan, Daniel; Ginsburg, Adam; Hatchfield, H. Perry; Henshaw, Jonathan; Kauffmann, Jens; Kruijssen, J. M. Diederik; Longmore, Steven N.; Lu, Xing; Mills, Elisabeth A. C.; Pillai, Thushara; Zhang, Qizhou; Bally, John; Butterfield, Natalie; Contreras, Yanett A.; Ho, Luis C.; Ott, Jürgen; Patel, Nimesh; Tolls, Volker
Abstract: We present an overview of the CMZoom survey and its first data release. CMZoom is the first blind, high-resolution survey of the Central Molecular Zone (CMZ; the inner 500 pc of the Milky Way) at wavelengths sensitive to the pre-cursors of high-mass stars. CMZoom is a 550 hr Large Program on the Submillimeter Array that mapped at 1.3 mm all of the gas and dust in the CMZ above a molecular hydrogen column density of 10²³ cm^-2 at a resolution of ∼3″ (0.1 pc). In this paper, we focus on the 1.3 mm dust continuum and its data release, but also describe CMZoom spectral line data which will be released in a forthcoming publication. While CMZoom detected many regions with rich and complex substructure, its key result is an overall deficit in compact substructures on 0.1-2 pc scales (the compact dense gas fraction: CDGF). In comparison with clouds in the Galactic disk, the CDGF in the CMZ is substantially lower, despite having much higher average column densities. CMZ clouds with high CDGFs are well-known sites of active star formation. The inability of most gas in the CMZ to form compact substructures is likely responsible for the dearth of star formation in the CMZ, surprising considering its high density. The factors responsible for the low CDGF are not yet understood but are plausibly due to the extreme environment of the CMZ, having far-reaching ramifications for our understanding of the star formation process across the cosmos.

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: 158658
Type: article
Authors: Benac, Peyton; Matrà, Luca; Wilner, David J.; Jimènez-Donaire, Marìa J.; Monnier, J. D.; Harries, Tim J.; Laws, Anna; Rich, Evan A.; Zhang, Qizhou
Abstract: Millimeter observations of disks around young stars reveal substructures indicative of gas pressure traps that may aid grain growth and planet formation. We present Submillimeter Array observations of HD 34700: two Herbig Ae stars in a close binary system (Aa/Ab, ˜0.25 au), surrounded by a disk presenting a large cavity and spiral arms seen in scattered light, and two distant, lower-mass companions. These observations include 1.3 mm continuum emission and the ¹²CO 2-1 line at ˜0"5 (178 au) resolution. They resolve a prominent azimuthal asymmetry in the continuum and Keplerian rotation of a circumbinary disk in the ¹²CO line. The asymmetry is located at a radius of 155⁺¹¹_-7 au, consistent with the edge of the scattered-light cavity, being resolved in both radius (72 ⁺¹⁴_-15 au) and azimuth (FWHM = 64^°+8_-7). The strong asymmetry in millimeter continuum emission could be evidence for a dust trap, together with the more symmetric morphology of ¹²CO emission and small grains. We hypothesize an unseen circumbinary companion responsible for the cavity in scattered light and creating a vortex at the cavity edge that manifests in dust trapping. The disk mass has limitations imposed by the detection of ¹²CO and nondetection of ¹³CO. We discuss its consequences for the potential past gravitational instability of this system, likely accounting for the rapid formation of a circumbinary companion. We also report the discovery of resolved continuum emission associated with HD 34700B (projected separation ˜1850 au), which we explain through a circumstellar disk.

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: 157596
Type: article
Authors: Feng, S.; Li, D.; Caselli, P.; Du, F.; Lin, Y.; Sipilä, O.; Beuther, H.; Sanhueza, Patricio; Tatematsu, K.; Liu, S. Y.; Zhang, Qizhou; Wang, Y.; Hogge, T.; Jimenez-Serra, I.; Lu, X.; Liu, T.; Wang, K.; Zhang, Z. Y.; Zahorecz, S.; Li, G.; Liu, H. B.; Yuan, J.
Abstract: The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 μm-dArk and bright clOuds (MIAO). At a linear resolution of 0.1-0.5 pc, this work presents a detailed study of parsec-scale CO depletion and HCO⁺ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each source with T deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each source with T _H ∼ 10⁴-10⁵ cm^-3, we compared pairs of neighboring 70 μm bright and dark clumps and found that (1) the H₂ column density and dust temperature of each source show strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue lines and dense gas tracers, such as 1-0 lines of H¹³CO⁺ and DCO⁺, are anticorrelated; (3) the abundance ratio between C¹⁸O and DCO⁺ shows a strong correlation with the source temperature; (4) both the C¹⁸O depletion factor and D-fraction of HCO⁺ show a robust decrease from younger clumps to more evolved clumps by a factor of more than 3; and (5) preliminary chemical modeling indicates that chemical ages of our sources are ∼8 × 10⁴ yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young.

ID: 158745
Type: article
Authors: Galametz, Maud; Maury, Anaëlle; Girart, Josep M.; Rao, Ramprasad; Zhang, Qizhou; Gaudel, Mathilde; Valdivia, Valeska; Hennebelle, Patrick; Cabedo-Soto, Victoria; Keto, Eric; Lai, Shih-Ping
Abstract:
Aims: The main goal of the following analysis is to assess the potential role of magnetic fields in regulating the envelope rotation, the formation of disks and the fragmentation of Class 0 protostars in multiple systems.
Methods: We use the Submillimeter Array to carry out observations of the dust polarized emission at 0.87 mm, in the envelopes of a large sample of 20 Class 0 protostars. We estimate the mean magnetic field orientation over the central 1000 au envelope scales to characterize the orientation of the main component of the organized magnetic field at the envelope scales in these embedded protostars. This direction is compared to that of the protostellar outflow in order to study the relation between their misalignment and the kinematics of the circumstellar gas. The latter is traced via velocity gradient observed in the molecular line emission (mainly N₂H⁺) of the gas at intermediate envelope scales.
Results: We discover a strong relationship between the misalignment of the magnetic field orientation with the outflow and the amount of angular momentum observed at similar scales in the protostellar envelope, revealing a potential link between the kinetic and the magnetic energy at envelope scales. The relation could be driven by favored B-misalignments in more dynamical envelopes or a dependence of the envelope dynamics with the large-scale B initial configuration. Comparing the trend with the presence of fragmentation, we observe that single sources are mostly associated with conditions of low angular momentum in the inner envelope and good alignment of the magnetic field with protostellar outflows, at intermediate scales. Our results suggest that the properties of the magnetic field in protostellar envelopes bear a tight relationship with the rotating-infalling gas directly involved in the star and disk formation: we find that it may not only influence the fragmentation of protostellar cores into multiple stellar systems, but also set the conditions establishing the pristine properties of planet-forming disks.

ID: 158764
Type: article
Authors: Goddi, C.; Ginsburg, A.; Maud, L. T.; Zhang, Qizhou; Zapata, Luis A.
Abstract: We observed the W51 high-mass star-forming complex with the Atacama Large Millimeter/submillimeter Array's longest-baseline configurations, achieving an angular resolution of ˜20 mas, corresponding to a linear resolution of ˜100 au at D_W51 = 5.4 kpc. The observed region contains three high-mass protostars in which the dust continuum emission at 1.3 mm is optically thick up to a radius ?1000 au and has brightness temperatures ?200 K. The high luminosity (?10⁴ L_?) in the absence of free-free emission suggests the presence of massive stars (M ? 20 M_?) at the earliest stages of their formation. Our continuum images reveal remarkably complex and filamentary structures arising from compact cores. Molecular emission shows no clear signs of rotation or infall on scales from 150 to 2000 au; we do not detect disks. The central sources drive young (t_dyn ˜ 100 yr), fast (v ˜ 100 km s^-1), powerful ( $\dot{M}\gt {10}^{-4}$ M_? yr^-1), collimated outflows. These outflows provide indirect evidence of accretion disks on scales r ? 100-500 au (depending on the object). The active outflows are connected to fossil flows that have different orientations on larger spatial scales, implying that the orientations of these small disks change over time. These results together support a variant of an accretion model for high-mass star formation in which massive protostars do not form a large, stable Keplerian disk during their early stages but instead accrete material from multiple massive flows with different angular momentum vectors. This scenario therefore contrasts with the simplified classic paradigm of a stable disk+jet system, which is the standard model for low-mass star formation, and provides experimental confirmation of a multidirectional and unsteady accretion model for massive star formation.

ID: 158746
Type: article
Authors: Hatchfield, H. Perry; Battersby, Cara; Keto, Eric; Walker, Daniel; Barnes, Ashley; Callanan, Daniel; Ginsburg, Adam; Henshaw, Jonathan D.; Kauffmann, Jens; Kruijssen, J. M. Diederik; Longmore, Steve N.; Lu, Xing; Mills, Elisabeth A. C.; Pillai, Thushara; Zhang, Qizhou; Bally, John; Butterfield, Natalie; Contreras, Yanett A.; Ho, Luis C.; Ott, Jürgen; Patel, Nimesh; Tolls, Volker
Abstract: In this paper we present the CMZoom survey's catalog of compact sources (₂) = 10²³ cm^-2) of the innermost 500 pc of the Galaxy in the 1.3 mm dust continuum. We generate both a robust catalog designed to reduce spurious source detections, and a second catalog with higher completeness, both generated using a pruned dendrogram. In the robust catalog, we report 285 compact sources, or 816 in the high-completeness catalog. These sources have effective radii between 0.04 and 0.4 pc, and are the potential progenitors of star clusters. The masses for both catalogs are dominated by the Sagittarius B2 cloud complex, where masses are likely unreliable due to free-free contamination, uncertain dust temperatures, and line-of-sight confusion. Given the survey selection and completeness, we predict that our robust catalog accounts for more than ˜99% of compact substructure capable of forming high-mass stars in the CMZ. This catalog provides a crucial foundation for future studies of high-mass star formation in the Galactic Center.

ID: 158090
Type: article
Authors: Hsu, Shih-Ying; Liu, Sheng-Yuan; Liu, Tie; Sahu, Dipen; Hirano, Naomi; Lee, Chin-Fei; Tatematsu, Ken'ichi; Kim, Gwanjeong; Juvela, Mika; Sanhueza, Patricio; He, JinHua; Johnstone, Doug; Qin, Sheng-Li; Bronfman, Leonardo; Chen, Huei-Ru Vivien; Dutta, Somnath; Eden, David J.; Jhan, Kai-Syun; Kim, Kee-Tae; Kuan, Yi-Jehng; Kwon, Woojin; Lee, Chang Won; Lee, Jeong-Eun; Moraghan, Anthony; Rawlings, M. G.; Shang, Hsien; Soam, Archana; Thompson, M. A.; Traficante, Alessio; Wu, Yuefang; Yang, Yao-Lun; Zhang, Qizhou
Abstract: We report the detection of four new hot corino sources, G211.47-19.27S, G208.68-19.20N1, G210.49-19.79W, and G192.12-11.10, from a survey study of Planck Galactic Cold Clumps in the Orion Molecular Cloud Complex with the Atacama Compact Array. Three sources had been identified as low-mass Class 0 protostars in the Herschel Orion Protostar Survey. One source in the λ Orionis region is first reported as a protostellar core. We have observed abundant complex organic molecules (COMs), primarily methanol but also other oxygen-bearing COMs (in G211.47-19.27S and G208.68-19.20N1) and the molecule of prebiotic interest NH₂CHO (in G211.47-19.27S), signifying the presence of hot corinos. While our spatial resolution is not sufficient to resolve most of the molecular emission structure, the large line width and high rotational temperature of COMs suggest that they likely reside in the hotter and innermost region immediately surrounding the protostar. In G211.47-19.27S, the D/H ratio of methanol ([CH₂DOH]/[CH₃OH]) and the ¹²C/¹³C ratio of methanol ([CH₃OH]/[¹³CH₃OH]) are comparable to those of other hot corinos. Hydrocarbons and long-carbon-chain molecules such as c-C₃H₂ and HCCCN are also detected in the four sources, likely tracing the outer and cooler molecular envelopes.

ID: 157482
Type: article
Authors: Jiménez-Serra, Izaskun; Báez-Rubio, Alejandro; Martín-Pintado, Jesús; Zhang, Qizhou; Rivilla, Víctor M.
Abstract: Theories of massive star formation predict that massive protostars accrete gas through circumstellar disks. Although several cases have been found already thanks to high angular-resolution interferometry, the internal physical structure of these disks remains unknown, in particular whether they present warps or internal holes, as observed in low-mass protoplanetary disks. Here, we report very high angular-resolution observations of the H21α radio recombination line carried out in Band 9 with the Atacama Large Millimeter/submillimeter Array (beam of 80 mas × 60 mas, or 70 au × 50 au) toward the IRS2 massive young stellar object in the Monoceros R2 star-forming cluster. The H21α line shows maser amplification, which allows us to study the kinematics and physical structure of the ionized gas around the massive protostar down to spatial scales of ∼1-2 au. Our ALMA images and 3D radiative transfer modeling reveal that the ionized gas around IRS2 is distributed in a Keplerian circumstellar disk and an expanding wind. The H21α emission centroids at velocities between -10 and 20 km s^-1 deviate from the disk plane, suggesting a warping for the disk. This could be explained by the presence of a secondary object (a stellar companion or a massive planet) within the system. The ionized wind seems to be launched from the disk surface at distances ∼11 au from the central star, consistent with magnetically-regulated disk wind models. This suggests a similar wind-launching mechanism to that recently found for evolved massive stars such as MWC349A and MWC922.

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: 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.