REVEALING THE PHYSICAL PROPERTIES OF MOLECULAR GAS IN ORION WITH A LARGE-SCALE SURVEY IN
 J
 = 2-1 LINES OF
 12
 CO,
 13
 CO, AND C
 18
 O

Nishimura, Atsushi; Tokuda, Kazuki; Kimura, Kouji; Muraoka, Kazuyuki; Maezawa, Hiroyuki; Ogawa, Hideo; Dobashi, Kazuhito; Shimoikura, Tomomi; Mizuno, Akira; Fukui, Y.; Onishi, Toshikazu

doi:10.1088/0067-0049/216/1/18

Cited by 145 publications

(173 citation statements)

References 71 publications

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“…The HCN/HCO+ line ratio is compatible with the average ratio computed for M31's disc by Brouillet et al (2005). Again, the Galactic clouds of Nishimura et al (2015) lie on the right hand side of this figure and are difficult to compare with M31 measurements. Our measurements are not compatible with Seyfert galaxies, which makes sense because there is no sign of active galactic nuclei (AGN) in M31 (Li et al 2011).…”

Section: Observed Line Ratiossupporting

confidence: 61%

“…As a result of very different cloud geometries, it is difficult to compare our 13 CO/ 12 CO(2-1) line ratio measurements in M31 with studies performed in Galactic regions. For instance, Orion regions observed by Nishimura et al (2015) or Planck cold dust clumps (Wu et al 2012) exhibits relatively low 12 CO/ 13 CO line ratio (∼2-3) because the dense clouds fill the beam and 12 CO is very optically thick. Figure 10 shows the HCN/HCO+(1-0) and 13 CO/ 12 CO(2-1) ratios we measured in the components approaching us in the north-western positions and the south-east stacking .…”

Section: Observed Line Ratiosmentioning

confidence: 99%

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Dense gas tracing the collisional past of Andromeda

Melchior

Combes

2015

A&A

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The central kiloparsec region of the Andromeda galaxy is relatively gas poor, while the interstellar medium appears to be concentrated in a ring-like structure at about 10 kpc radius. The central gas depletion has been attributed to a possible head-on collision 200 Myr ago, supported by the existence of an offset inner ring of warm dust. We present new IRAM 30 m radio telescope observations of the molecular gas in the central region, and the detection of CO and its isotopes 13 CO(2−1) and C 18 O(2−1), together with the dense gas tracers, HCN(1−0) and HCO+(1−0). A systematic study of the observed peak temperatures with non-local thermal equilibrium simulations shows that the detected lines trace dense regions with n H 2 in the range 2.5 × 10 4 −5.6 × 10 5 cm −3 , while the gas is very clumpy with a beam filling factor of 0.5−2 × 10 −2 . This is compatible with the dust mass derived from the far-infrared emission, assuming a dust-to-gas mass ratio of 0.01 with a typical clump size of 2 pc. We also show that the gas is optically thin in all lines except for 12 CO(1-0) and 12 CO(2-1), CO lines are close to their thermal equilibrium condition at 17-20 K, the molecular hydrogen density is larger than critical, and HCN and HCO+ lines have a subthermal excitation temperature of 9 K with a density smaller than critical. The average 12 CO/ 13 CO line ratio is high (∼21), and close to the 12 CO/C 18 O ratio (∼30) that was measured in the north-western region and estimated in the south-east stacking. The fact that the optically thin 13 CO and C 18 O lines have comparable intensities means that the secondary element 13 C is depleted with respect to the primary 12 C, as is expected just after a recent star formation. This suggests that there has been a recent starburst in the central region, supporting the head-on collision scenario.

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Section: Observed Line Ratiossupporting

confidence: 61%

Section: Observed Line Ratiosmentioning

confidence: 99%

Dense gas tracing the collisional past of Andromeda

Melchior

Combes

2015

A&A

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“…The radial density structure of the ISF is proportional to r −13/8 (Stutz & Gould 2016). The CO line emission from the ISF shows linewidths around 3-4 km s −1 and the C 18 O emission around 1 km s −1 when averaged over a threearcminute beam (Nishimura et al 2015); this indicates strong non-thermal motions given the typical temperatures of ∼20 K (e.g., Stutz & Kainulainen 2015). The Zeeman-splitting measurements suggest that the filament is wrapped in a helical magnetic field (Heiles 1997, see also discussion in Stutz & Gould 2016).…”

Section: Applicability Of Gravitational Fragmentation Modelsmentioning

confidence: 95%

Resolving the fragmentation of high line-mass filaments with ALMA: the integral shaped filament in Orion A

Kainulainen

Stutz

Stanke³

et al. 2017

A&A

112

151

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We study the fragmentation of the nearest high line-mass filament, the integral shaped filament (ISF, line-mass ∼ 400 M ⊙ pc −1 ) in the Orion A molecular cloud. We have observed a 1.6 pc long section of the ISF with the Atacama Large Millimetre/submillimeter Array (ALMA) at 3 mm continuum emission, at a resolution of ∼3 ′′ (1 200 AU). We identify from the region 43 dense cores with masses about a solar mass. 60% of the ALMA cores are protostellar and 40% are starless. The nearest neighbour separations of the cores do not show a preferred fragmentation scale; the frequency of short separations increases down to 1 200 AU. We apply a twopoint correlation analysis on the dense core separations and show that the ALMA cores are significantly grouped at separations below ∼17 000 AU and strongly grouped below ∼6 000 AU. The protostellar and starless cores are grouped differently: only the starless cores group strongly below ∼6 000 AU. In addition, the spatial distribution of the cores indicates periodic grouping of the cores into groups of ∼30 000 AU in size, separated by ∼50 000 AU. The groups coincide with dust column density peaks detected by Herschel. These results show hierarchical, two-mode fragmentation in which the maternal filament periodically fragments into groups of dense cores. Critically, our results indicate that the fragmentation models for lower line-mass filaments (∼ 16 M ⊙ pc −1 ) fail to capture the observed properties of the ISF. We also find that the protostars identified with Spitzer and Herschel in the ISF are grouped at separations below ∼17 000 AU. In contrast, young stars with disks do not show significant grouping. This suggests that the grouping of dense cores is partially retained over the protostar lifetime, but not over the lifetime of stars with disks. This is in agreement with a scenario where protostars are ejected from the maternal filament by the slingshot mechanism, a model recently proposed for the ISF by Stutz & Gould. The separation distributions of the dense cores and protostars may also provide an evolutionary tracer of filament fragmentation.

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“…We use 13 CO as an alternative mass tracer assuming that 12 CO and 13 CO are in local thermodynamic equilibrium (LTE) at a common excitation temperature (e.g., Nishimura et al 2015). We assume the 12 CO (2-1) line is optically thick at line center and not subject to beam dilution, so that for a given line of sight the excitation temperature is uniform and given by T ex [K] = 11.06 ln 1 + 11.06 T 12,pk + 0.187…”

Section: Comparison With 13 Co-based Massesmentioning

confidence: 99%

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

Wong

Hughes

Tokuda

et al. 2017

ApJ

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We present high-resolution (sub-parsec) observations of a giant molecular cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band 6 observations trace the bulk of the molecular gas in 12 CO(2-1) and high column density regions in 13 CO(2-1). Our target is a quiescent cloud (PGCC G282.98−32.40, which we refer to as the "Planck cold cloud" or PCC) in the southern outskirts of the galaxy where star-formation activity is very low and largely confined to one location. We decompose the cloud into structures using a dendrogram and apply an identical analysis to matched-resolution cubes of the 30 Doradus molecular cloud (located near intense star formation) for comparison. Structures in the PCC exhibit roughly 10 times lower surface density and 5 times lower velocity dispersion than comparably sized structures in 30 Dor, underscoring the non-universality of molecular cloud properties. In both clouds, structures with relatively higher surface density lie closer to simple virial equilibrium, whereas lower surface density structures tend to exhibit super-virial line widths. In the PCC, relatively high line widths are found in the vicinity of an infrared source whose properties are consistent with a luminous young stellar object. More generally, we find that the smallest resolved structures ("leaves") of the dendrogram span close to the full range of line widths observed across all scales. As a result, while the bulk of the kinetic energy is found on the largest scales, the smallscale energetics tend to be dominated by only a few structures, leading to substantial scatter in observed size-linewidth relationships.

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REVEALING THE PHYSICAL PROPERTIES OF MOLECULAR GAS IN ORION WITH A LARGE-SCALE SURVEY IN J = 2-1 LINES OF ¹² CO, ¹³ CO, AND C ¹⁸ O

Cited by 145 publications

References 71 publications

Dense gas tracing the collisional past of Andromeda

Dense gas tracing the collisional past of Andromeda

Resolving the fragmentation of high line-mass filaments with ALMA: the integral shaped filament in Orion A

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

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REVEALING THE PHYSICAL PROPERTIES OF MOLECULAR GAS IN ORION WITH A LARGE-SCALE SURVEY IN J = 2-1 LINES OF 12 CO, 13 CO, AND C 18 O

Cited by 145 publications

References 71 publications

Dense gas tracing the collisional past of Andromeda

Dense gas tracing the collisional past of Andromeda

Resolving the fragmentation of high line-mass filaments with ALMA: the integral shaped filament in Orion A

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

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Product

Resources

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REVEALING THE PHYSICAL PROPERTIES OF MOLECULAR GAS IN ORION WITH A LARGE-SCALE SURVEY IN J = 2-1 LINES OF ¹² CO, ¹³ CO, AND C ¹⁸ O