Molecular Clouds

Goldreich, Peter; Kwan, John

doi:10.1086/152821

Cited by 560 publications

(402 citation statements)

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“…In the opposite case, scenario ii (grey dot-dashed curve), the observed ratio is reached only for very low excitation temperatures. However, this optically thin CO scenario can be ruled out because both the 12 CO to 13 CO ratios and the low-J 12 CO line ratios in the SPT sample imply that CO is moderately optically thick with τ CO(1-0) = 1 − 10 (Spilker et al 2014), similar to what is seen in our own galaxy (Penzias et al 1972;Goldreich & Kwan 1974). Scenario iii, where the [CII] and CO(1-0) optical depths are in the same regime is thus the only one that can fit the observed ratios, but only for excitation temperatures 180 K. While we cannot distinguish mathematically between low and high optical depth, the known τ CO(1-0) = 1 − 10 and the equality of both the excitation temperatures and opacities would imply that also [CII] would need to be (nearly or fully) optically thick.…”

Section: Same [Cii] and Co Excitation Temperaturessupporting

confidence: 71%

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

Gullberg

Breuck

Vieira

et al. 2015

Monthly Notices of the Royal Astronomical Society

152

224

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We present [CII] observations of 20 strongly lensed dusty star forming galaxies at 2.1 < z < 5.7 using APEX and Herschel. The sources were selected on their 1.4 mm flux (S 1.4 mm > 20 mJy) from the South Pole Telescope survey, with far-infrared (FIR) luminosities determined from extensive photometric data. The [CII] line is robustly detected in 17 sources, all but one being spectrally resolved. Eleven out of 20 sources observed in [CII] also have low-J CO detections from ATCA. A comparison with midand high-J CO lines from ALMA reveals consistent [CII] and CO velocity profiles, suggesting that there is little differential lensing between these species. The [CII], low-J CO and FIR data allow us to constrain the properties of the interstellar medium. We find [CII] to CO(1-0) luminosity ratios in the SPT sample of 5200 ± 1800, with significantly less scatter than in other samples. This line ratio can be best described by a medium of [CII] and CO emitting gas with a higher [CII] than CO excitation temperature, high CO optical depth τ CO (1-0) 1, and low to moderate [CII] optical depth τ [CII] 1. The geometric structure of photodissociation regions allows for such conditions.

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Section: Same [Cii] and Co Excitation Temperaturessupporting

confidence: 71%

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

Gullberg

Breuck

Vieira

et al. 2015

Monthly Notices of the Royal Astronomical Society

152

224

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“…Thermal equilibrium between the dust and the H 2 is theoretically expected to occur at gas densities n H 2 > 10 4 cm −3 (Goldreich & Kwan 1974). Indeed, the dust colour temperature in KL is ∼60 K, i.e., similar to the gas kinetic temperature determined from the CO line brightness temperature.…”

Section: Observed Properties Of Molecular Gasmentioning

confidence: 66%

“…The escape probability formalism used to treat this optically thick situation was first applied to molecular clouds by Scoville & Solomon (1974) and Goldreich & Kwan (1974) and is now routinely used to analyse interstellar molecule excitation (often called large velocity gradient [LVG], non-thermal equilibrium [non-LTE] analysis; see, e.g., van der Tak et al (2007) and their publicly available RADEX code) † . One of the biggest advantages of the LVG formalism is that it permits treatment of the coupled radiative transfer and molecular excitation as a local problem -a fact probably not fully appreciated by current routine users of these codes.…”

Section: Molecular Excitationmentioning

confidence: 99%

“…In the photon trapping regime, the spontaneous decay rates (A) used in analysing the equilibrium molecular excitation are reduced by a factor β equal to the effective probability for escape of line photons from the emission region (Scoville & Solomon 1974;Goldreich & Kwan 1974). Thus, the critical density for thermalisation of the levels is reduced by the same factor β.…”

Section: Molecular Excitationmentioning

confidence: 99%

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Evolution of star formation and gas

Scoville¹

2013

Secular Evolution of Galaxies

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In these lectures I review observations of star-forming molecular clouds in our Galaxy and nearby galaxies to develop a physical intuition for understanding star formation in the local and high-redshift Universe. A lot of this material is drawn from early work in the field since much of the work was done two decades ago and this background is not generally available in the present literature. I also attempt to synthesise our welldeveloped understanding of star formation in low-redshift galaxies with constraints from theory and observations at high redshift to develop an intuitive model for the evolution of galaxy mass and luminosity functions in the early Universe.The overall goal of this contribution is to provide students with background helpful for analysis of far-infrared (FIR) observations from Herschel and millimetre/submillimetre (mm/submm) imaging with ALMA (the Atacama Large Millimetre/submillimetre Array).These two instruments will revolutionise our understanding of the interstellar medium (ISM) and associated star formation and galaxy evolution, both locally and in the distant Universe. To facilitate interpreting the FIR spectra of Galactic star-forming regions and high-redshift sources, I develop a model for the dust heating and radiative transfer in order to elucidate the observed infrared (IR) emissions. I do this because I am not aware of a similar coherent discussion in the literature. Star-forming molecular cloudsHere, I provide an overview of the observations and physics of star-forming molecular clouds in the Galaxy and nearby normal galaxies. The motivation is to develop the intuitive background for analysis of observations at high 1 arXiv:1210.6990v2 [astro-ph.CO] 1 Nov 2012

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“…Both molecules are btype asymmetric oblate rotors, having two distinct species, ortho and para. With the aim to determine the physical conditions required for occurring the anomalous absorption against the cosmic 2.7 K background, we performed NLTE radiative transfer calculations for cyclopropenylidene (C 3 H 2 ), and ethylene oxide (C 2 H 4 O), using a large velocity gradient (LVG) code (Cox et al 1987;Rausch et al 1996; de Jong et al 1975;Goldreich & Kwan 1974), where the physical model is that of a homogeneous collapsing cloud.…”

Section: Formulation Of the Problemmentioning

confidence: 99%

Absorption Against the Cosmic 2.7 K Background

Chandra

Kegel²,

Sharma

2001

First Steps in the Origin of Life in the Universe

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Abstract. Two interstellar lines, 110 → 111 of formaldehyde at 4.831 GHz, and 220 → 211 of cyclopropenylidene at 21.590 GHz, have so far been observed in absorption against the cosmic 2.7 K background. Observation of an interstellar line in absorption against the cosmic 2.7 K background is an unusual phenomenon, and can only be possible under rather peculiar conditions developed in the molecule, generating the line. We predict that two more lines, 330 → 321 at 27.100 GHz, and 331 → 322 at 59.550 GHz of cyclopropenylidene, and three lines, 220 → 211 at 15.600 GHz, 330 → 321 at 23.100 GHz, and 331 → 322 at 39.700 GHz of ethylene oxide, may show absorption against the cosmic 2.7 K background. We speculate that such peculiar conditions are characteristic for b-type asymmetrical top molecules. -The observation of these lines may be used to place upper bounds to the density in the absorbing region.

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Molecular Clouds

Cited by 560 publications

References 0 publications

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

Evolution of star formation and gas

Absorption Against the Cosmic 2.7 K Background

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