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We have observed the HN13C J = 1-0 and DNC J = 1-0 lines toward 18 massive clumps, including infrared dark clouds (IRDCs) and high-mass protostellar objects (HMPOs), by using the Nobeyama Radio Observatory 45 m telescope. We have found that the HN13C emission is stronger than the DNC emission toward all of the observed sources. The averaged DNC/HNC ratio is indeed lower toward the observed high-mass sources (0.009 ± 0.005) than toward the low-mass starless and star-forming cores (0.06). The kinetic temperature derived from the NH3 (J, K) = (1, 1) and (2, 2) line intensities is higher toward the observed high-mass sources than toward the low-mass cores. However, the DNC/HNC ratio of some IRDCs involving the Spitzer 24μm sources is found to be lower than that of HMPOs, although the kinetic temperature of the IRDCs is lower than that of the HMPOs. This implies that the DNC/HNC ratio does not depend only on the current kinetic temperature. With the aid of chemical model simulations, we discuss how the DNC/HNC ratio decreases after the birth of protostars. We suggest that the DNC/HNC ratio in star-forming cores depends on the physical conditions and history in their starless-core phase, such as its duration time and the gas kinetic temperature. [ABSTRACT FROM AUTHOR]

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 ), 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 (<1 ) cores and no high-mass (>30 ) prestellar cores (maximum mass 11 ). 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. [ABSTRACT FROM AUTHOR]

We observed the Class I protostellar source Elias 29 with the Atacama Large Millimeter/submillimeter Array. We detected CS, SO, 34SO, SO2, and SiO line emissions in a compact component concentrated near the protostar, and a ridge component separated from the protostar by 4″ (∼500 au). The former component is abundant in SO and SO2, but deficient in CS. The abundance ratio SO/CS is as high as at the protostar, which is even higher than that in the outflow-shocked region of L1157 B1. However, organic molecules (HCOOCH3, CH3OCH3, CCH, and c-C3H2) are deficient in Elias 29. We attribute this deficiency in organic molecules and richness in SO and SO2 to the evolved nature of the source or the relatively high dust temperature (≳20 K) in the parent cloud of Elias 29. The SO and SO2 emissions trace rotation around the protostar. Assuming a highly inclined configuration (i ≥ 65°; 0° for a face-on configuration) and Keplerian motion for simplicity, the protostellar mass is estimated to be (0.8–1.0) . The 34SO and SO2 emissions are asymmetric in their spectra; the blueshifted components are weaker than the redshifted ones. Although this may be attributed to the asymmetric molecular distribution, other possibilities are also discussed. [ABSTRACT FROM AUTHOR]

A survey observation of the DNC (J = 1−0 and J = 3−2) and HN13C (J = 1−0 and J = 3−2) emission toward 34 Class 0 and I protostellar sources in the Perseus molecular cloud has been conducted with the NRO 45 m and IRAM 30 m telescopes to explore how the deuterium ratio of the neutral species changes after the birth of a protostar. We have detected the J = 1−0 and J = 3−2 lines of DNC toward 32 sources and the J = 1−0 and J = 3−2 lines of HN13C toward 31 and 26 sources, respectively. A mean deuterium ratio of HNC, which is defined as RD(HNC) = N(DNC)/N(HNC), is found to be 0.049–0.056. We compare RD(HNC) with physical parameters of the sources, and find a negative correlation between RD(HNC) and the bolometric temperature. This result suggests that RD(HNC) decreases as a protostar evolves. Compared with the deuterium ratio of the molecular ion , RD(HNC) seems to decrease slowly with the protostellar evolution. [ABSTRACT FROM AUTHOR]

We report molecular line observations of the NGC 1333 IRAS 4C outflow in the Perseus Molecular Cloud with the Atacama Large Millimeter/Submillimeter Array. The CCH and CS emission reveal an outflow cavity structure with clear signatures of rotation with respect to the outflow axis. The rotation is detected from about 120 au up to about 1400 au above the envelope/disk midplane. As the distance to the central source increases, the rotation velocity of the outflow decreases while the outflow radius increases, which gives a flat specific angular momentum distribution along the outflow. The mean specific angular momentum of the outflow is about 100 . On the basis of reasonable assumptions on the outward velocity of the outflow and the protostar mass, we estimate the range of outflow-launching radii to be 5–15 au. Such a launching radius rules out that this outflow is launched as an X-wind, but rather, it is more consistent to be a slow disk wind launched from relatively large radii on the disk. The radius of the centrifugal barrier is roughly estimated, and the role of the centrifugal barrier in the outflow launching is discussed. [ABSTRACT FROM AUTHOR]

Using Galactic Plane surveys, we have selected a massive (1200 M⊙), cold (14 K) 3.6–70 μm dark IRDC, G331.372-00.116. This infrared dark cloud (IRDC) has the potential to form high-mass stars, and given the absence of current star formation signatures, it seems to represent the earliest stages of high-mass star formation. We have mapped the whole IRDC with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.1 and 1.3 mm in dust continuum and line emission. The dust continuum reveals 22 cores distributed across the IRDC. In this work, we analyze the physical properties of the most massive core, ALMA1, which has no molecular outflows detected in the CO (2–1), SiO (5–4), and H2CO (3–2) lines. This core is relatively massive (M = 17.6 M⊙), subvirialized (virial parameter αvir = Mvir/M = 0.14), and is barely affected by turbulence (transonic Mach number of 1.2). Using the HCO+ (3–2) line, we find the first detection of infall signatures in a relatively massive, prestellar core (ALMA1) with the potential to form a high-mass star. We estimate an infall speed of 1.54 km s−1 and a high accretion rate of 1.96 × 10−3M⊙ yr−1. ALMA1 is rapidly collapsing, out of virial equilibrium, which is more consistent with competitive accretion scenarios rather than the turbulent core accretion model. On the other hand, ALMA1 has a mass ∼6 times larger than the clumps Jeans mass, as it is in an intermediate mass regime (MJ = 2.7 < M ≲ 30 M⊙), contrary to what both the competitive accretion and turbulent core accretion theories predict. [ABSTRACT FROM AUTHOR]

We have observed complex organic molecules (COMs) and deuterated species toward a hot core/corino (HC) associated with the infrared dark cloud clump G34.43+00.24 MM3 with the Atacama Large Millimeter/submillimeter Array. We have detected six normal-COMs (CH3OH, CH3CHO, CH3CH2CN, CH3OCH3, HCOOCH3, and NH2CHO), one deuterated-COM (CH2DCN), and two deuterated fundamental molecules (D2CO and DNC) toward G34.43+00.24 MM3 HC. None of these lines, except for CH3OH, are detected toward the shocked regions in our data, which suggests that COMs do not originate in shocks. The abundance of the COMs relative to CH3OH in G34.43+00.24 MM3 HC is found to be similar to those in high-mass hot cores, rather than those in hot corinos in low-mass star-forming regions. This result suggests that the physical conditions of the warm-up phase of G34.43+00.24 MM3 HC are similar to those of high-mass sources. On the other hand, the D2CO abundance relative to CH3OH in G34.43+00.24 MM3 HC is higher than that of other hot cores, and seems to be comparable to that of hot corinos. The relatively high D2CO/CH3OH ratio of G34.43+00.24 MM3 HC implies a long cold starless phase of G34.43+00.24 MM3 HC. [ABSTRACT FROM AUTHOR]

We have conducted an interferometric line survey in the 0.8 mm band toward the young high-mass protostar candidate NGC 2264 CMM3 with ALMA. CMM3 is resolved into the two continuum peaks, CMM3A and CMM3B, at an angular separation of . Thus, CMM3 is found to be a binary system candidate. We have detected molecular outflows associated with CMM3A and CMM3B each, indicating active star formation. In addition to the two peaks, six faint continuum peaks are detected around CMM3A and CMM3B, most of which are thought to be evolved low-mass protostars. CMM3A is found to be rich in molecular line emission including complex organic molecules such as HCOOCH3 and CH3OCH3. The emission of complex organic molecules is distributed within a compact region around the continuum peak of CMM3A. Hence, CMM3A apparently harbors a hot core. On the other hand, CMM3B is deficient in molecular line emission, although its continuum flux is almost comparable to that of CMM3A. Possible origins of the striking difference between CMM3A and CMM3B are discussed. [ABSTRACT FROM AUTHOR]

The Class 0 protostar, L483, has been observed in various molecular lines in the 1.2 mm band at a subarcsecond resolution with ALMA. An infalling–rotating envelope is traced by the CS line, while a very compact component with a broad velocity width is observed for the CS, SO, HNCO, NH2CHO, and HCOOCH3 lines. Although this source is regarded as the warm carbon-chain chemistry (WCCC) candidate source at a 1000 au scale, complex organic molecules characteristic of hot corinos such as NH2CHO and HCOOCH3 are detected in the vicinity of the protostar. Thus, both hot corino chemistry and WCCC are seen in L483. Although such a mixed chemical character source has been recognized as an intermediate source in previous single-dish observations, we here report the first spatially resolved detection. A kinematic structure of the infalling–rotating envelope is roughly explained by a simple ballistic model with a protostellar mass of 0.1–0.2 and a radius of the centrifugal barrier (half of the centrifugal radius) of 30–200 au, assuming an inclination angle of 80° (0° for face-on). The broad-line emission observed in the above molecules most likely comes from the disk component inside the centrifugal barrier. Thus, a drastic chemical change is seen around the centrifugal barrier. [ABSTRACT FROM AUTHOR]

We study deuterium fractionation in two massive starless/early-stage cores, C1-N and C1-S, in Infrared Dark Cloud G028.37+00.07, which was first identified by Tan et al. with ALMA. Line emission from multiple transitions of N2H+ and N2D+ were observed with the ALMA, CARMA, SMA, JCMT, NRO 45 m, and IRAM 30 m telescopes. By simultaneously fitting the spectra, we estimate the excitation conditions and deuterium fraction, , with values of ≃ 0.2–0.7, several orders of magnitude above the cosmic [D]/[H] ratio. Additional observations of o-H2D+ are also presented that help constrain the ortho-to-para ratio of H2, which is a key quantity affecting the degree of deuteration. We then present chemodynamical modeling of the two cores, especially exploring the implications for the collapse rate relative to free-fall, αff. In order to reach the high level of observed deuteration of , we find that the most likely evolutionary history of the cores involves collapse at a relatively slow rate, ≲ one-tenth of free-fall. [ABSTRACT FROM AUTHOR]

Spectral line survey observations are conducted toward the high-mass protostar candidate NGC 2264 CMM3 in the 4, 3, and 0.8 mm bands with the Nobeyama 45 m telescope and the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope. In total, 265 emission lines are detected in the 4 and 3 mm bands, and 74 emission lines in the 0.8 mm band. As a result, 36 molecular species and 30 isotopologues are identified. In addition to the fundamental molecular species, many emission lines of carbon-chain molecules such as HC5N, C4H, CCS, and C3S are detected in the 4 and 3 mm bands. Deuterated molecular species are also detected with relatively strong intensities. On the other hand, emission lines of complex organic molecules such as HCOOCH3 and CH3OCH3 are found to be weak. For the molecules for which multiple transitions are detected, rotation temperatures are derived to be 7–33 K except for CH3OH. Emission lines with high upper-state energies (Eu > 150 K) are detected for CH3OH, indicating the existence of a hot core. In comparison with the chemical composition of the Orion KL, carbon-chain molecules and deuterated molecules are found to be abundant in NGC 2264 CMM3, while sulfur-bearing species and complex organic molecules are deficient. These characteristics indicate the chemical youth of NGC 2264 CMM3 in spite of its location at the center of the cluster forming core, NGC 2264 C. [ABSTRACT FROM AUTHOR]

We have observed the clump G34.43+00.24 MM3 associated with an infrared dark cloud in DNC J = 3–2, HN13C J = 3–2, and N2H+J = 3–2 with the Atacama Large Millimeter/submillimeter Array (ALMA). The N2H+ emission is found to be relatively weak near the hot core and the outflows, and its distribution is clearly anti-correlated with the CS emission. This result indicates that a young outflow is interacting with cold ambient gas. The HN13C emission is compact and mostly emanates from the hot core, whereas the DNC emission is extended around the hot core. Thus, the DNC and HN13C emission traces warm regions near the protostar differently. The DNC emission is stronger than the HN13C emission toward most parts of this clump. The DNC/HNC abundance ratio averaged within a 15 × 15 area around the phase center is higher than 0.06. This ratio is much higher than the value obtained by the previous single-dish observations of DNC and HN13C J = 1–0 (∼0.003). It seems likely that the DNC and HNC emission observed with the single-dish telescope traces lower density envelopes, while that observed with ALMA traces higher density and highly deuterated regions. We have compared the observational results with chemical-model results in order to investigate the behavior of DNC and HNC in the dense cores. Taking these results into account, we suggest that the low DNC/HNC ratio in the high-mass sources obtained by the single-dish observations are at least partly due to the low filling factor of the high density regions. [ABSTRACT FROM AUTHOR]