Giant molecular clouds in the Galaxy. I - The axisymmetric distribution of H2

Sanders, D. B.; Solomon, P. M.; Scoville, N. Z.

doi:10.1086/161602

Cited by 309 publications

(201 citation statements)

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“…At last, we share Solomon & Barrett (1991) point of view: "CO to H 2 conversion factor is fairly robust -robust but not perfect". Chaty et al (1996) used X CO = 3.6 × 10 20 K −1 km −1 s cm −2 (Sanders et al 1984) and T * A instead of T mb . We calculated the integrated antenna temperature in the 12 CO(J = 1−0) line for each molecular cloud for which we considered 25 percent uncertainty of the estimated value.…”

Section: Methodsmentioning

confidence: 99%

On the optical extinction and distance of GRS 1915+105

Chapuis

Corbel

2004

A&A

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Abstract. Based on new millimeter and radio observations, we reevaluate the total hydrogen column density along the line of sight to the microquasar GRS 1915+105 to N H = (3.5±0.3)×10 22 cm −2 . Our value is consistent with the one derived from X-ray measurements, namely (3.8 ± 0.3) × 10 22 cm −2 (Ebisawa et al. 1998). Using the empirical law between the visual extinction and the total column density of hydrogen, A v is found to 19.6 ± 1.7 mag. This result is ∼7 mag lower than previously thought, and therefore, a reevaluation of infrared fluxes after derredening is needed. The revisited kinematic study allows to give a lower limit to the distance of GRS 1915+105 , namely 6.0 kpc. Taking into account the most accurate upper limit of distance inferred from radio data (11.2 ± 0.8 kpc, Fender et al. 1999) as well as this lower limit, this implies a distance of 9.0 ± 3.0 kpc.

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Section: Methodsmentioning

confidence: 99%

On the optical extinction and distance of GRS 1915+105

Chapuis

Corbel

2004

A&A

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“…Deciding how to disentangle between the near and far distance has been a major difficulty in estimating the properties of Galactic molecular gas. Different methods have been used to circumvent this difficulty: (1) association with objects at known distance, such as H ii regions (Kolpak et al 2003); (2) 21 cm absorption (Roman-Duval et al 2009); (3) the cloud mass-size relationship (Roman-Duval et al 2010); (4) Galactic axial symmetry (Scoville & Solomon 1975;Gordon & Burton 1976;Sanders et al 1984;Bronfman et al 1988); and (5) two Gaussian latitude profiles (Clemens et al 1988;Nakanishi & Sofue 2006).…”

Section: Cloud Angular Radiusmentioning

confidence: 99%

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

Miville-Deschênes¹,

Murray²,

Lee³

2017

ApJ

359

303

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This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the 12 CO emission observed within b ± 5• . The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame et al. data. The total H 2 mass in the catalog is 1.2 × 10 9 M , in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is R ∼ 30 pc. We find that M ∝ R 2.2±0.2 , with no correlation between the cloud surface density, Σ, and R. In contrast with the general idea, we find a rather large range of values of Σ, from 2 to 300 M pc −2 , and a systematic decrease with increasing Galactic radius, R gal . The cloud velocity dispersion and the normalization σ 0 = σ v /R 1/2 both decrease systematically with R gal . When studied over the whole Galactic disk, there is a large dispersion in the line width-size relation, and a significantly better correlation between σ v and Σ R. The normalization of this correlation is constant to better than a factor of two for R gal < 20 kpc. This relation is used to disentangle the ambiguity between near and far kinematic distances. We report a strong variation of the turbulent energy injection rate. In the outer Galaxy it may be maintained by accretion through the disk and/or onto the clouds, but neither source can drive the 100 times higher cloud-averaged injection rate in the inner Galaxy.

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“…Here, the CO(2−1) beam is 12 ∼ 40 pc on the major axis, however, the inclination of the plane limits the resolution. Typically, gaseous discs in the centre of galaxies have a characteristic scaleheight of 50 pc, as determined in the Milky Way (e.g., Sanders et al 1984). The inclined line of sight across the disc of M 31 encompasses a region of size = tan(77 • ) × 50 pc = 216 pc in the direction parallel to the minor axis (while it is the size of the beam, 40 pc, in the perpendicular direction).…”

Section: Special Case Of M 31mentioning

confidence: 99%

Molecular gas in the inner 0.7 kpc-radius ring of M 31

Melchior

Combes

2011

A&A

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The study of the gas kinematic in the central 1.5 kpc × 1.5 kpc region of M 31 has revealed several surprises. The starting point of this investigation was the detection at the IRAM-30 m telescope of molecular gas with very large line splittings up to 260 km s −1 within the beam (∼40 pc). In this region, which is known for its low gas content, we also detect an ionised gas outflow in the circumnuclear region (within 75 pc from the centre) extending to the whole area in X-ray. Relying on atomic, ionised, and molecular gas, we account for most observables with a scenario that assumes that a few hundreds Myr ago, M 31 underwent a frontal collision with M 32, which triggered some star-formation activity in the centre, and this collision explains the special configuration of M 31 with two rings observed at 0.7 kpc and 10 kpc. The inner disc (whose rotation is detected in HI and ionised gas ([NII])) has thus been tilted (inclination: 43 deg, PA: 70 deg) with respect to the main disc (inclination: 77 deg, PA: 35 deg). One of the CO velocity components is compatible with this inner disc, while the second one comes from a tilted ring-like material with 40 deg inclination and PA = −35 deg. The relic star formation estimated by previous works to have occurred more than 100 Myr ago could have been triggered by the collision and could be linked to the outflow detected in the ionised gas. Last, we demonstrate that the amplitude of the line splittings detected in CO centred on the systemic velocity with a relatively high spatial resolution (40 pc) cannot be accounted for by a possible weak bar that is roughly aligned along the minor axis. Although M 31 has a triaxial bulge, there are no bar indicators in the gas component (photometry, no strong skewness of the isovelocities, etc.).

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Giant molecular clouds in the Galaxy. I - The axisymmetric distribution of H2

Cited by 309 publications

References 0 publications

On the optical extinction and distance of GRS 1915+105

On the optical extinction and distance of GRS 1915+105

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

Molecular gas in the inner 0.7 kpc-radius ring of M 31

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