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Register a new userMultiple outflows in the high-mass cluster forming region, G25.82-0.17
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We present results of continuum and spectral line observations with ALMA and 22 GHz water (H$_2$O) maser observations using KaVA and VERA toward a high-mass star-forming region, G25.82-0.17. Multiple 1.3 mm continuum sources are revealed, indicating the presence of young stellar objects (YSOs) at different evolutionary stages, namely an ultra-compact HII region, G25.82-E, a high-mass young stellar object (HM-YSO), G25.82-W1, and starless cores, G25.82-W2 and G25.82-W3. Two SiO outflows, at N-S and SE-NW orientations, are identified. The CH$_3$OH 8$_{-1}$-7$_{0}$ E line, known to be a class I CH$_3$OH maser at 229 GHz is also detected showing a mixture of thermal and maser emission. Moreover, the H$_2$O masers are distributed in a region ~0.25 shifted from G25.82-W1. The CH$_3$OH 22$_{4}$-21$_{5}$ E line shows a compact ring-like structure at the position of G25.82-W1 with a velocity gradient, indicating a rotating disk or envelope. Assuming Keplerian rotation, the dynamical mass of G25.82-W1 is estimated to be $>$25 M$_{odot}$ and the total mass of 20 M$_odot$-84 M$_odot$ is derived from the 1.3 mm continuum emission. The driving source of the N-S SiO outflow is G25.82-W1 while that of the SE-NW SiO outflow is uncertain. Detection of multiple high-mass starless$/$protostellar cores and candidates without low-mass cores implies that HM-YSOs could form in individual high-mass cores as predicted by the turbulent core accretion model. If this is the case, the high-mass star formation process in G25.82 would be consistent with a scaled-up version of low-mass star formation.
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The abundance of deuterated molecules in a star-forming region is sensitive to the environment in which they are formed. Deuteration fractions therefore provide a powerful tool for studying the physical and chemical evolution of a star-forming system. While local low-mass star-forming regions show very high deuteration ratios, much lower fractions are observed towards Orion and the Galactic Centre. We derive methanol deuteration fractions at a number of locations towards the high-mass star-forming region NGC 6334I, located at a mean distance of 1.3 kpc, and discuss how these can shed light on the conditions prevailing during its formation. We use high sensitivity, high spatial and spectral resolution observations obtained with ALMA to study transitions of the less abundant, optically thin, methanol-isotopologues: (13)CH3OH, CH3(18)OH, CH2DOH and CH3OD, detected towards NGC 6334I. Assuming LTE and excitation temperatures of 120-330 K, we derive column densities for each of the species and use these to infer CH2DOH/CH3OH and CH3OD/CH3OH fractions. Interestingly, the column densities of CH3OD are consistently higher than those of CH2DOH throughout the region. All regions studied in this work show CH2DOH/CH3OH as well as CH2DOH/CH3OD ratios that are considerably lower than those derived towards low-mass star-forming regions and slightly lower than those derived for the high-mass star-forming regions in Orion and the Galactic Centre. The low ratios indicate a grain surface temperature during formation ~30 K, for which the efficiency of the formation of deuterated species is significantly reduced.
We have conducted mapping observations toward the n3 and n5 positions in the NGC,2264-D cluster-forming region with the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3. Observations with 10000 au scale beam reveal the chemical composition at the clump scale. The spatial distributions of the observed low upper-state-energy lines of CH$_{3}$OH are similar to those of CS and SO, and the HC$_{3}$N emission seems to be predominantly associated with clumps containing young stellar objects. The turbulent gas induced by the star formation activities produces large-scale shock regions in NGC,2264-D, which are traced by the CH$_{3}$OH, CS and SO emissions. We derive the HC$_{3}$N, CH$_{3}$CN, and CH$_{3}$CHO abundances with respect to CH$_{3}$OH. Compared to the n5 field, the n3 field is farther (in projected apparent distance) from the neighboring NGC,2264-C, yet the chemical composition in the n3 field tends to be similar to that of the protostellar candidate CMM3 in NGC,2264-C. The HC$_{3}$N/CH$_{3}$OH ratios in the n3 field are higher than those in the n5 field. We find an anti-correlation between the HC$_{3}$N/CH$_{3}$OH ratio and their excitation temperatures. The low HC$_{3}$N/CH$_{3}$OH abundance ratio at the n5 field implies that the n5 field is an environment with more active star formation compared with the n3 field.
H2D+ is a primary ion which dominates the gas-phase chemistry of cold dense gas. Therefore it is hailed as a unique tool in probing the earliest, prestellar phase of star formation. Observationally, its abundance and distribution is however just beginning to be understood in low-mass prestellar and cluster-forming cores. In high mass star forming regions, H2D+ has been detected only in two cores, and its spatial distribution remains unknown. Here we present the first map of the 372 GHz ortho-H2D+ and N2H+ 4-3 transition in the DR21 filament of Cygnus-X with the JCMT, and N2D+ 3--2 and dust continuum with the SMA. We have discovered five very extended (<= 34000 AU diameter) weak structures in H2D+ in the vicinity of, but distinctly offset from embedded protostars. More surprisingly, the H2D+ peak is not associated with either a dust continuum or N2D+ peak. We have therefore uncovered extended massive cold dense gas that was undetected with previous molecular line and dust continuum surveys of the region. This work also shows that our picture of the structure of cores is too simplistic for cluster forming cores and needs to be refined: neither dust continuum with existing capabilities, nor emission in tracers like N2D+ can provide a complete census of the total prestellar gas in such regions. Sensitive H2D+ mapping of the entire DR21 filament is likely to discover more of such cold quiescent gas reservoirs in an otherwise active high mass star-forming region.
We study the core mass function (CMF) of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3~mm continuum emission at a resolution of 1.0arcsec (2500~au). We have mapped a field of 5.3arcmin$times$5.3arcmin centered on the protocluster clump. We measure the CMF in the central region, exploring various core detection algorithms, which give source numbers ranging from 60 to 125, depending on parameter selection. We estimate completeness corrections due to imperfect flux recovery and core identification via artificial core insertion experiments. For masses $Mgtrsim1:M_odot$, the fiducial dendrogram-identified CMF can be fit with a power law of the form ${rm{d}}N/{rm{d}}{rm{log}}Mpropto{M}^{-alpha}$ with $alpha simeq1.24pm0.17$, slightly shallower than, but still consistent with, the index of the Salpeter stellar initial mass function of 1.35. Clumpfind-identified CMFs are significantly shallower with $alphasimeq0.64pm0.13$. While raw CMFs show a peak near $1:M_odot$, completeness-corrected CMFs are consistent with a single power law extending down to $sim 0.5:M_odot$, with only a tentative indication of a shallowing of the slope around $sim1:M_odot$. We discuss the implications of these results for star and star cluster formation theories.
Theoretical models suggest that massive stars form via disk-mediated accretion, with bipolar outflows playing a fundamental role. A recent study toward massive molecular outflows has revealed a decrease of the SiO line intensity as the object evolves. The present study aims at characterizing the variation of the molecular outflow properties with time, and at studying the SiO excitation conditions in outflows associated with massive YSOs. We used the IRAM30m telescope to map 14 massive star-forming regions in the SiO(2-1), SiO(5-4) and HCO+(1-0) outflow lines, and in several dense gas and hot core tracers. Hi-GAL data was used to improve the spectral energy distributions and the L/M ratio, which is believed to be a good indicator of the evolutionary stage of the YSO. We detect SiO and HCO+ outflow emission in all the sources, and bipolar structures in six of them. The outflow parameters are similar to those found toward other massive YSOs. We find an increase of the HCO+ outflow energetics as the object evolve, and a decrease of the SiO abundance with time, from 10^(-8) to 10^(-9). The SiO(5-4) to (2-1) line ratio is found to be low at the ambient gas velocity, and increases as we move to high velocities, indicating that the excitation conditions of the SiO change with the velocity of the gas (with larger densities and/or temperatures for the high-velocity gas component). The properties of the SiO and HCO+ outflow emission suggest a scenario in which SiO is largely enhanced in the first evolutionary stages, probably due to strong shocks produced by the protostellar jet. As the object evolves, the power of the jet would decrease and so does the SiO abundance. During this process, however, the material surrounding the protostar would have been been swept up by the jet, and the outflow activity, traced by entrained molecular material (HCO+), would increase with time.
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