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We report Submillimeter Array (SMA) observations of polarized 0.88 mm thermal dust emission and various molecular line transitions toward the early B-type (L" ~ 2 × 103 L☉) star-forming region G192.16-3.84 (IRAS 05553+1631). The peak of the continuum Stokes-I emission coincides with a hot rotating disk/envelope (SO2 rotational temperature T SO2 rot ~ 84+18 -13 K), with a north-south velocity gradient. Joint analysis of the rotation curve traced by HCO+ 4-3 and SO2 191,19-180,18 suggests that the dense molecular gas is undergoing a spinning-up rotation, marginally bound by the gravitational force of an enclosed massM"+gas+dust ~11.2-25.2M☉. Perpendicular to the rotational plane, a≳100/cos(i) kms-1 (i ~ 63°) high velocity molecular jet and a~15-20 km s-1 expanding biconical cavity were revealed in the CO 3-2 emission. The polarization percentage of the 0.88 mm continuum emission decreases toward the central rotating disk/envelope. The polarization angle in the inner ~2" (0.015 pc) disk/envelope is perpendicular to the plane of the rotation. The magnetic field lines, which are predominantly in the toroidal direction along the disk plane, are likely to be dragged by the gravitationally accelerated rotation. [ABSTRACT FROM AUTHOR]

Metals are thought to have profound effects on the internal structures of the molecular clouds in which stars are born. The absence of metals is expected to prevent gas from efficient cooling and fragmentation in theory. However, this effect has not yet been observed in low-metallicity environments, such as in the early universe and local dwarf galaxies, because of the lack of high-spatial-resolution maps of gas. We carried out Atacama Large Millimeter/submillimeter Array observations of the carbon monoxide (CO) J = 2–1 emission line at 1.4 parsec resolutions of a molecular cloud in DDO 70 at 7% solar metallicity, the most metal-poor galaxy currently known with a CO detection. In total, five clumps have been identified and they are found to more or less follow Larson’s law. Since the CO emission exists in regions with visual extinction AV around 1.0, we converted this AV to the gas-mass surface density using a gas-to-dust ratio of 4594 ± 2848 for DDO 70. We found that the CO clumps in DDO 70 exhibit significantly larger (on average four times) sizes than those at the same gas-mass surface densities in the massive star formation regions of the Milky Way. The existence of such large clumps appears to be consistent with theoretical expectations that gas fragmentation in low-metallicity clouds is suppressed. While our observation is only for one cloud in the galaxy, if it is representative, the above result implies suppressed gas fragmentation during the cloud collapse and star formation in the early universe. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present Submillimeter Array (SMA) observations in the CO J = 3–2, SiO J = 5–4 and 8–7, and SO 98–87 lines, as well as Atacama Pathfinder EXperiment observations in the CO J = 6–5 line, of an extremely high-velocity and jet-like outflow in high-mass star-forming region HH 80–81. The outflow is known to contain two prominent molecular bullets, namely B1 and B2, discovered from our previous SMA CO J = 2–1 observations. While B1 is detected in all the CO, SiO, and SO lines, B2 is only detected in CO lines. The CO 3–2/2–1 line ratio in B1 is clearly greater than that in B2. We perform a large velocity gradient analysis of the CO lines and derive a temperature of 70–210 K for B1 and 20–50 K for B2. Taking into account the differences in the velocity, distance from the central source, excitation conditions, and chemistry between the two bullets, we suggest that the bullets are better explained by direct ejections from the innermost vicinity of the central high-mass protostar, and that we are more likely observing the molecular component of a primary wind rather than entrained or swept-up material from the ambient cloud. These findings further support our previous suggestions that the molecular bullets indicate an episodic, disk-mediated accretion in the high-mass star formation process. [ABSTRACT FROM AUTHOR]

We present the POL-2 850 μm linear polarization map of the Barnard 1 clump in the Perseus molecular cloud complex from the B-fields In STar-forming Region Observations survey at the James Clerk Maxwell Telescope. We find a trend of decreasing polarization fraction as a function of total intensity, which we link to depolarization effects toward higher-density regions of the cloud. We then use the polarization data at 850 μm to infer the plane-of-sky orientation of the large-scale magnetic field in Barnard 1. This magnetic field runs north–south across most of the cloud, with the exception of B1-c, where it turns more east–west. From the dispersion of polarization angles, we calculate a turbulence correlation length of 5.0 ± 2.″5 (1500 au) and a turbulent-to-total magnetic energy ratio of 0.5 ± 0.3 inside the cloud. We combine this turbulent-to-total magnetic energy ratio with observations of NH3 molecular lines from the Green Bank Ammonia Survey to estimate the strength of the plane-of-sky component of the magnetic field through the Davis–Chandrasekhar–Fermi method. With a plane-of-sky amplitude of 120 ± 60 μG and a criticality criterion λc = 3.0 ± 1.5, we find that Barnard 1 is a supercritical molecular cloud with a magnetic field nearly dominated by its turbulent component. [ABSTRACT FROM AUTHOR]

Reaching a length of 10 pc projected in the plane of the sky, the radio jet associated with Herbig–Haro (HH) objects 80 and 81 (HH 80–81) is known to be the largest and best collimated protostellar jet in our Galaxy. The nature of the molecular outflow associated with this extraordinary jet remains an unsolved question, and is of great interest for our understanding of the relationship between jets and outflows in high-mass star formation. Here we present Atacama Pathfinder EXperiment CO (6–5) and (7–6), James Clerk Maxwell Telescope CO (3–2), Caltech Submillimeter Observatory CO (2–1), and Submillimeter Array CO and 13CO (2–1) mapping observations of the outflow. We report on the detection of a two-component outflow consisting of a collimated component along the jet path and a wide-angle component with an opening angle of about 30°. The gas velocity structure suggests that each of the two components traces part of a primary wind. From large velocity gradient calculations of the CO lines, the outflowing gas has a temperature around 88 K, indicating that it is being heated by shocks. Based on the CO (6–5) data, the outflow mass is estimated to be a few M⊙, dominated by the wide-angle component. A comparison between the HH 80–81 outflow and other well shaped massive outflows suggests that the opening angle of massive outflows continues to increase over time. Therefore, the mass-loss process in the formation of early-B stars seems to be similar to that in low-mass star formation, except that a jet component would disappear as the central source evolved to an ultracompact H ii region. [ABSTRACT FROM AUTHOR]

We report Submillimeter Array molecular line observations in the 345 GHz band of five massive dense cores, Cyg-N38, Cyg-N43, Cyg-N48, Cyg-N51, and Cyg-N53 in the DR21 filament. The molecular line data reveal several dynamical features of the cores: (1) prominent outflows in all cores seen in the CO and SiO lines, (2) significant velocity gradients in Cyg-N43 and Cyg-N48 seen in the H13CN and H13CO+ lines suggesting 0.1 pc scale rotational motions, and (3) possible infalls in Cyg-N48 found in the SiO and SO lines. Comparing the molecular line data and our dust polarization data in Ching et al., we find that the gradients of line-of-sight velocities appear to be randomly oriented relative to the plane-of-sky magnetic fields. Our simulations suggest that this random alignment implies parallel or random alignment between the velocity gradients and magnetic fields in the three-dimensional space. The linewidths of H13CN emission are consistently wider than those of H13CO+ emission in the 3″–10″ detectable scales, which can be explained by the existence of ambipolar diffusion with maximum plane-of-the-sky magnetic field strengths of 1.9 mG and 5.1 mG in Cyg-N38 and Cyg-N48, respectively. Our results suggest that the gas dynamics may distort the magnetic fields of the cores of into complex structures and ambipolar diffusion could be important in dissipating the magnetic energies of the cores. [ABSTRACT FROM AUTHOR]

We present Atacama Pathfinder EXperiment (APEX) observations toward the massive star-forming region G240.31+0.07 in the CO J = 3–2, 6–5, and 7–6 lines. We detect a parsec-sized, bipolar, and high-velocity outflow in all the lines, which allow us, in combination with the existing CO J = 2–1 data, to perform a multi-line analysis of physical conditions of the outflowing gas. The CO 7–6/6–5, 6–5/3–2, and 6–5/2–1 ratios are found to be nearly constant over a velocity range of ∼5–25 km s−1 for both blueshifted and redshifted lobes. We carry out rotation diagram and large velocity gradient calculations of the four lines and find that the outflow is approximately isothermal with a gas temperature of ∼50 K and that the CO column density clearly decreases with the outflow velocity. If the CO abundance and the velocity gradient do not vary much, the decreasing CO column density indicates a decline in the outflow gas density with velocity. By comparing with theoretical models of outflow driving mechanisms, our observations and calculations suggest that the massive outflow in G240.31+0.07 is being driven by a wide-angle wind and further support a disk-mediated accretion at play for the formation of the central high-mass star. [ABSTRACT FROM AUTHOR]

We report Submillimeter Array dust continuum and molecular spectral line observations toward the Orion Bar photon-dominated region (PDR). The 1.2 mm continuum map reveals, for the first time, a total of nine compact (r < 0.01 pc) dust condensations located within a distance of ∼0.03 pc from the dissociation front of the PDR. Part of the dust condensations are also seen in spectral line emissions of CS (5–4) and H2CS (71,7–61,6), though the CS map also reveals dense gas further away from the dissociation front. We also detect compact emissions in H2CS (60,6–50,5), (62,4–52,3) and C34S, C33S (4–3) toward bright dust condensations. The line ratio of H2CS (60,6–50,5)/(62,4–52,3) suggests a temperature of 73 ± 58 K. A nonthermal velocity dispersion of ∼0.25–0.50 km s−1 is derived from the high spectral resolution C34S data and indicates a subsonic to transonic turbulence in the condensations. The masses of the condensations are estimated from the dust emission, and range from 0.03 to 0.3 M⊙, all significantly lower than any critical mass that is required for self-gravity to play a crucial role. Thus the condensations are not gravitationally bound, and could not collapse to form stars. In cooperating with recent high-resolution observations of the compressed surface layers of the molecular cloud in the Bar, we speculate that the condensations are produced as a high-pressure wave induced by the expansion of the H ii region compresses and enters the cloud. A velocity gradient along a direction perpendicular to the major axis of the Bar is seen in H2CS (71,7–61,6), and is consistent with the scenario that the molecular gas behind the dissociation front is being compressed. [ABSTRACT FROM AUTHOR]

We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as ∝ , which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with down to 10−5 yr−1 kpc−2, which are outliers of both the Kennicutt–Schmidt and Silk–Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt–Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments. [ABSTRACT FROM AUTHOR]

We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s−1, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity. [ABSTRACT FROM AUTHOR]

We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey’s aims and objectives. We describe the rationale behind the survey, and the questions that the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous “integral filament” in the densest regions of that filament. Furthermore, we see an “hourglass” magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments. [ABSTRACT FROM AUTHOR]

We present Submillimeter Array 880 μm dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores and the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields a plane-of-sky magnetic field strength of 0.4–1.7 mG for the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that the gravitational energy in the filament dominates magnetic and kinematic energies, while the kinematic energy dominates in the cores. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores. [ABSTRACT FROM AUTHOR]

We present a Submillimeter Array (SMA) observation toward the young massive double-core system G350.69-0.49. This system consists of a northeast (NE) diffuse gas bubble and a southwest (SW) massive young stellar object (MYSO), both clearly seen in the Spitzer images. The SMA observations reveal a gas flow between the NE bubble and the SW MYSO in a broad velocity range from 5 to 30 km s−1 with respect to the system velocity. The gas flow is well confined within the interval between the two objects and traces a significant mass transfer from the NE gas bubble to the SW massive core. The transfer flow can supply the material accreted onto the SW MYSO at a rate of 4.2 × 10−4M⊙ yr−1. The whole system therefore suggests a mode for the mass growth in the MYSO from a gas transfer flow launched from its companion gas clump, despite the driving mechanism of the transfer flow not being fully determined from the current data. [ABSTRACT FROM AUTHOR]

We present observations toward a high-mass (), low-luminosity () 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 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 relative to the quiescent cloud, these lobes clearly indicate the presence of a strong bipolar outflow from this 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 , 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 ) 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. [ABSTRACT FROM AUTHOR]