Subsonic islands within a high-mass star-forming infrared dark cloud

High-mass star forming regions are typically thought to be dominated by supersonic motions. We present combined Very Large Array and Green Bank Telescope (VLA+GBT) observations of NH3 (1,1) and (2,2) in the infrared dark cloud (IRDC) G035.39-00.33, tracing cold and dense gas down to scales of 0.07 pc. We find that, in contrast to previous, similar studies of IRDCs, more than a third of the fitted ammonia spectra show subsonic non-thermal motions (mean line width of 0.71 km s−1), and sonic Mach number distribution peaks around ℳ = 1. As possible observational and instrumental biases would only broaden the line profiles, our results provide strong upper limits to the actual value of ℳ, further strengthening our findings of narrow line widths. This finding calls for a re-evaluation of the role of turbulent dissipation and subsonic regions in massive-star and cluster formation. Based on our findings in G035.39, we further speculate that the coarser spectral resolution used in the previous VLA NH3 studies may have inhibited the detection of subsonic turbulence in IRDCs. The reduced turbulent support suggests that dynamically important magnetic fields of the 1 mG order would be required to support against possible gravitational collapse. Our results offer valuable input into the theories and simulations that aim to recreate the initial conditions of high-mass star and cluster formation.

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On the size of the CO-depletion radius in the IRDC G351.77−0.51

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2818 ◽

2019 ◽

Vol 490 (4) ◽

pp. 4489-4501 ◽

Cited By ~ 3

Author(s):

G Sabatini ◽

A Giannetti ◽

S Bovino ◽

J Brand ◽

S Leurini ◽

...

Keyword(s):

Large Scale ◽

Spatial Scales ◽

High Mass ◽

Mass Star ◽

Number Density ◽

Dark Cloud ◽

Star Forming ◽

Dark Clouds ◽

Physical Conditions ◽

Star Forming Regions

ABSTRACT An estimate of the degree of CO-depletion (fD) provides information on the physical conditions occurring in the innermost and densest regions of molecular clouds. A key parameter in these studies is the size of the depletion radius, i.e. the radius within which the C-bearing species, and in particular CO, are largely frozen on to dust grains. A strong depletion state (i.e. fD > 10, as assumed in our models) is highly favoured in the innermost regions of dark clouds, where the temperature is <20 K and the number density of molecular hydrogen exceeds a few × 104 cm−3. In this work, we estimate the size of the depleted region by studying the Infrared Dark Cloud (IRDC) G351.77−0.51. Continuum observations performed with the Herschel Space Observatory and the LArge APEX BOlometer CAmera, together with APEX C18O and C17O J = 2→1 line observations, allowed us to recover the large-scale beam- and line-of-sight-averaged depletion map of the cloud. We built a simple model to investigate the depletion in the inner regions of the clumps in the filament and the filament itself. The model suggests that the depletion radius ranges from 0.02 to 0.15 pc, comparable with the typical filament width (i.e. ∼0.1 pc). At these radii, the number density of H2 reaches values between 0.2 and 5.5 × 105 cm−3. These results provide information on the approximate spatial scales on which different chemical processes operate in high-mass star-forming regions and also suggest caution when using CO for kinematical studies in IRDCs.

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Laboratory rotational spectrum and astronomical search for methoxyacetaldehyde

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833773 ◽

2018 ◽

Vol 619 ◽

pp. A67 ◽

Cited By ~ 4

Author(s):

L. Kolesniková ◽

I. Peña ◽

E. R. Alonso ◽

B. Tercero ◽

J. Cernicharo ◽

...

Keyword(s):

Millimeter Wave ◽

Ethyl Formate ◽

High Mass ◽

Spectroscopic Constants ◽

Mass Star ◽

Rotational Spectrum ◽

Stable Conformer ◽

Dark Cloud ◽

Star Forming ◽

Star Forming Regions

Context. Methoxyacetaldehyde belongs to a group of structural isomers with the general formula C3H6O2, of which methyl acetate and ethyl formate are known interstellar molecules. Rotational data available for methoxyacetaldehyde are limited to 40 GHz, which makes predictions at higher frequencies rather uncertain.Aims. The aim of this work is to provide accurate experimental frequencies of methoxyacetaldehyde in the millimeter-wave region to support its detection in the interstellar medium.Methods. The rotational spectrum of methoxyacetaldehyde was recorded at room-temperature from 75 to 120 GHz and from 170 to 310 GHz using the millimeter-wave spectrometer in Valladolid. Additional measurements were also performed at conditions of supersonic expansion from 6 to 18 GHz. The assigned rotational transitions were analyzed using theS-reduced semirigid-rotor Hamiltonian.Results. We newly assigned over 1000 lines for the most stable conformer of methoxyacetaldehyde in its ground state and five lowest excited vibrational states, and precise sets of spectroscopic constants were obtained. We searched for spectral features of methoxyacetaldehyde in the high-mass star-forming regions Orion KL and Sagittarius B2, as well as in the cold dark cloud Barnard 1 (B1-b). No lines belonging to methoxyacetaldehyde were detected above the detection limit of our data. We provide upper limits to the methoxyacetaldehyde colum density in these sources.

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Cloud–cloud collisions and triggered star formation

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa103 ◽

2020 ◽

Author(s):

Yasuo Fukui ◽

Asao Habe ◽

Tsuyoshi Inoue ◽

Rei Enokiya ◽

Kengo Tachihara

Keyword(s):

Star Formation ◽

Cluster Formation ◽

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Ngc 6334 ◽

Almost All ◽

Massive Cluster

Abstract Star formation is a fundamental process for galactic evolution. One issue over the last several decades has been determining whether star formation is induced by external triggers or self-regulated in a closed system. The role of an external trigger, which can effectively collect mass in a small volume, has attracted particular attention in connection with the formation of massive stellar clusters, which in extreme cases may lead to starbursts. Recent observations have revealed massive cluster formation triggered by cloud–cloud collisions in nearby interacting galaxies, including the Magellanic system and the Antennae Galaxies as well as almost all well-known high-mass star-forming regions in the Milky Way, such as RCW 120, M 20, M 42, NGC 6334, etc. Theoretical efforts are going into the foundation for the mass compression that causes massive cluster/star formation. Here, we review the recent progress on cloud–cloud collisions and the triggered star-cluster formation, and discuss future prospects for this area of study.

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Quiescent high mass cores in Orion region

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307002761 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 488-488

Author(s):

T. Velusamy ◽

D. Li ◽

P. F. Goldsmith ◽

W. D. Langer

Keyword(s):

Initial Conditions ◽

High Mass ◽

Mass Star ◽

Core Mass ◽

Star Forming ◽

Star Forming Regions ◽

Starting Point ◽

Order Of Magnitude ◽

Mass Size ◽

Low Mass

Our goal is to study relatively quiescent dense gas cores, isolated from disruptive stars, to understand the initial conditions of massive star formation. Determining their mass, size, dynamical status, and core mass distribution is a starting point to understand the mechanisms for formation, collapse, and the origin of their IMF. We obtained CSO 350 μm, images of quiescent regions in Orion and detected 51 resolved or nearly resolved molecular cores with masses ranging from 0.1 M to 46 M (Li et al. 2006). The mean mass is 9.8 M, which is one order of magnitude higher than that of the resolved cores in low mass star forming regions, such as Taurus. Our sample includes largely thermally unstable cores, which implies that the cores are supported neither by thermal pressure nor by turbulence, and are probably supercritical. They are likely precursors of protostars.

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Looking for outflow and infall signatures in high-mass star-forming regions

Astronomy and Astrophysics ◽

10.1051/0004-6361/201118350 ◽

2012 ◽

Vol 538 ◽

pp. A140 ◽

Cited By ~ 16

Author(s):

P. D. Klaassen ◽

L. Testi ◽

H. Beuther

Keyword(s):

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions

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Nitrogen and hydrogen fractionation in high-mass star-forming cores from observations of HCN and HNC

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730576 ◽

2018 ◽

Vol 609 ◽

pp. A129 ◽

Cited By ~ 12

Author(s):

L. Colzi ◽

F. Fontani ◽

P. Caselli ◽

C. Ceccarelli ◽

P. Hily-Blant ◽

...

Keyword(s):

Solar System ◽

Solar Nebula ◽

Rotational Transition ◽

High Mass ◽

Evolutionary Stage ◽

Mass Star ◽

Stellar Cluster ◽

Star Forming ◽

Star Forming Regions ◽

Dense Cores

The ratio between the two stable isotopes of nitrogen, 14N and 15N, is well measured in the terrestrial atmosphere (~272), and for the pre-solar nebula (~441, deduced from the solar wind). Interestingly, some pristine solar system materials show enrichments in 15N with respect to the pre-solar nebula value. However, it is not yet clear if and how these enrichments are linked to the past chemical history because we have only a limited number of measurements in dense star-forming regions. In this respect, dense cores, which are believed to be the precursors of clusters and also contain intermediate- and high-mass stars, are important targets because the solar system was probably born within a rich stellar cluster, and such clusters are formed in high-mass star-forming regions. The number of observations in such high-mass dense cores has remained limited so far. In this work, we show the results of IRAM-30 m observations of the J = 1−0 rotational transition of the molecules HCN and HNC and their 15N-bearing counterparts towards 27 intermediate- and high-mass dense cores that are divided almost equally into three evolutionary categories: high-mass starless cores, high-mass protostellar objects, and ultra-compact Hii regions. We have also observed the DNC(2–1) rotational transition in order to search for a relation between the isotopic ratios D/H and 14N/15N. We derive average 14N/15N ratios of 359 ± 16 in HCN and of 438 ± 21 in HNC, with a dispersion of about 150–200. We find no trend of the 14N/15N ratio with evolutionary stage. This result agrees with what has been found for N2H+ and its isotopologues in the same sources, although the 14N/15N ratios from N2H+ show a higher dispersion than in HCN/HNC, and on average, their uncertainties are larger as well. Moreover, we have found no correlation between D/H and 14N/15N in HNC. These findings indicate that (1) the chemical evolution does not seem to play a role in the fractionation of nitrogen, and that (2) the fractionation of hydrogen and nitrogen in these objects is not related.

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Deuteration in High-Mass Star Forming Regions

The Labyrinth of Star Formation - Astrophysics and Space Science Proceedings ◽

10.1007/978-3-319-03041-8_85 ◽

2014 ◽

pp. 425-427

Author(s):

Javier A. Rodón ◽

Henrik Beuther ◽

Qizhou Zhang

Keyword(s):

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions

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ATLASGAL – Ammonia observations towards the southern Galactic plane

Astronomy and Astrophysics ◽

10.1051/0004-6361/201526384 ◽

2018 ◽

Vol 609 ◽

pp. A125 ◽

Cited By ~ 8

Author(s):

M. Wienen ◽

F. Wyrowski ◽

K. M. Menten ◽

J. S. Urquhart ◽

C. M. Walmsley ◽

...

Keyword(s):

Standard Deviation ◽

Hyperfine Structure ◽

Optical Depth ◽

Line Width ◽

Rotational Temperature ◽

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

Low Mass

Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subsample of 289 sources, the N2H+ (1–0) line was measured with the Mopra telescope. Results. We measured a median NH3 (1, 1) line width of ~ 2 km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 × 10-6 to 10-8. For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1.

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