A comparison of CO(J = 1 yields 0) and CO(J = 2 yields 1) emission in the Milky Way molecular ring

Chiar, J. E.; Kutner, Marc L.; Verter, Frances; Leous, James

doi:10.1086/174517

Cited by 20 publications

(6 citation statements)

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“…Even in the molecular-rich inner Galaxy, there are substantial contributions of diffuse molecular emission, suggesting the existence of small clouds. (Polk et al 1988;Chiar et al 1994). It seems natural to assume that inter-arm molecular clouds are dominated by the small molecular clouds.…”

Section: Evolution Of Gmc In the Spiral Armmentioning

confidence: 99%

“…An investigation of the dynamical properties of GMCs is important in discussing the formation and evolution processes of GMCs. Recent molecular cloud studies in the Galaxy indicated that GMCs which lack associated star formation activity are not as unusual as once thought (e.g., Chiar et al 1994). A comparison of cloud properties between star-forming GMCs and quiescent GMCs is important in addressing what really controls the star formation activity in GMCs.…”

Section: Introductionmentioning

confidence: 97%

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Giant Molecular Clouds in the Spiral Arm of Ic 342

Hirota

Kuno

Sato

et al. 2011

ApJ

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We present results of 12 CO (1-0) and 13 CO (1-0) observations of the northeastern spiral arm segment of IC 342 with a ∼ 50pc resolution carried out with the Nobeyama Millimeter Array. Zerospacing components were recovered by combining with the existing data taken with the Nobeyama 45m telescope. The objective of this study is to investigate the variation of cloud properties across the spiral arm with a resolution comparable to the size of giant molecular clouds (GMCs). The observations cover a 1 kpc × 1.5 kpc region located ∼ 2 kpc away from the galactic center, where a giant molecular association is located at trailing side and associated star forming regions at leading side. The spiral arm segment was resolved into a number of clouds whose size, temperature and surface mass density are comparable to typical GMCs in the Galaxy. Twenty-six clouds were identified from the combined data cube and the identified clouds followed the line width-size relation of the Galactic GMCs. The identified GMCs were divided into two categories according to whether they are associated with star formation activity or not. Comparison between both categories indicated that the active GMCs are more massive, have smaller line width, and are closer to virial equilibrium compared to the quiescent GMCs. These variations of the GMC properties suggest that dissipation of excess kinetic energy of GMC is a required condition for the onset of massive star formation.

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Section: Evolution Of Gmc In the Spiral Armmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Giant Molecular Clouds in the Spiral Arm of Ic 342

Hirota

Kuno

Sato

et al. 2011

ApJ

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“…Different choices of the density and temperature within the range n(H 2 ) ¼ 10 2 -10 3 cm À3 and T k ¼ 10-20 K do not alter this conclusion. Large-scale CO surveys implies that a significant amount of 12 CO emission in the Galactic plane is produced by molecular gas with a lower opacity than that of giant molecular clouds (Polk et al 1988;Chiar et al 1994). The [C i] emission in the Galactic plane is also produced by such ''translucent'' molecular clouds.…”

Section: Lvg Analysesmentioning

confidence: 99%

Atomic Carbon in the Southern Milky Way

Oka

Kamegai

Hayashida

et al. 2005

ApJ

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We present a coarsely sampled longitude-velocity (l-V ) map of the region l ¼ 300 -354 , b ¼ 0 in the 492 GHz fine-structure transition of neutral atomic carbon (C 0 3 P 1 -3 P 0 ; [C i]), observed with the Portable 18 cm Submillimeter-wave Telescope (POST18). The l-V distribution of the [C i] emission resembles closely that of the CO J ¼ 1 0 emission, showing a widespread distribution of atomic carbon on the Galactic scale. The ratio of the antenna temperatures, R C i = CO , concentrates on the narrow range from 0.05 to 0.3. A large velocity gradient (LVG) analysis shows that the [C i] emission from the Galactic disk is dominated by a population of neutral gas with high C 0 /CO abundance ratios and moderate column densities, which can be categorized as diffuse translucent clouds. The ratio of bulk emissivity, J C i / J CO , shows a systematic trend, suggesting the bulk C 0 /CO abundance ratio increasing with the Galactic radius. A mechanism related to kiloparsec-scale structure of the Galaxy may control the bulk C 0 /CO abundance ratio in the Galactic disk. Two groups of high-ratio (R C i = CO > 0:3) areas reside in the l-V loci several degrees inside of tangential points of the Galactic spiral arms. These could be gas condensations just accumulated in the potential well of spiral arms and be in the early stages of molecular cloud formation.

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“…Observational programs such as large area surveys probing radio continuum and recombination line emission have supplied much of our present knowledge on the gas photoionized by massive stars (Lockman 1989;Helfand et al 1992;Whiteoak 1992;Becker et al 1989;Kuchar & Bania 1992;McClure-Griffiths 2001;Kolpak et al 2003), and on the nonthermal emission due to recent supernovae in the inner Galaxy (Leahy & Wu 1989;Green 1991Green , 2001). Molecular line emission surveys have provided an overall picture of the distribution and physical conditions of giant molecular clouds (Dame et al 1987(Dame et al , 2001Chiar et al 1994;Bronfman et al 1996Bronfman et al , 2000McQuinn et al 2002), while mid-infrared surveys such as that carried out by IRAS have revealed a wealth of star forming sites (Wood & Churchwell 1989;Hughes & MacLeod 1989;Codella et al 1995;Comerón & Torra 1996;Egan et al 1998). Recent near-infrared surveys like DENIS (Ruphy et al 1997;López-Corredoira et al 2001;Van Loon et al 2003), 2MASS (Alard 2001;Ojha 2001;López-Corredoira et al 2002) or TMGS (López-Corredoira et al 1999Picaud et al 2003) are yielding extensive lists of stellar objects suitable for studies of galactic structure.…”

Section: Introductionmentioning

confidence: 99%

A search for late-type supergiants in the inner regions of the Milky Way

Comerón

Torra

Chiappini

et al. 2004

A&A

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Abstract. We present the results of a narrow-band infrared imaging survey of a narrow strip (12 wide) around the Galactic equator between 6• and 21• of galactic longitude aimed at detecting field stars with strong CO absorption, mainly late-type giants and supergiants. Our observations include follow-up low resolution spectroscopy (R = 980) of 191 selected candidates in the H and K bands. Most of these objects have photometric and spectroscopic characteristics consistent with their being red giants, and some display broad, strong absorption wings due to water vapor absorption between the H and K bands. We also identify in our sample 18 good supergiant candidates characterized by their lack of noticeable water absorption, strong CO bands in the H and K windows, and HK S photometry suggestive of high intrinsic luminosity and extinction reaching up to A V 40 mag. Another 9 candidates share the same features except for weak H 2 O absorption, which is also observed among some M supergiants in the solar neighbourhood. Interesting differences are noticed when comparing our stars with a local sample of late-type giants and supergiants, as well as with a sample of red giants in globular clusters of moderately subsolar metallicity and to a sample of bulge stars. A large fraction of the stars in our sample have CaI and NaI features markedly stronger than those typical in the local reference sample (both giants and supergiants), whereas the equivalent widths of the CO bands are similar or weaker. In this regard, our stars in the inner Milky Way disk display differences very similar to those identified by other authors between cool giants and supergiants near the galactic center and their counterparts in the solar neighbourhood. We propose that the systematic spectroscopic differences of our inner Galaxy stars are due to their higher metallicities that cause deeper mixing in their mantles, resulting in lower surface abundances of C and O and higher abundances of CN, which contribute to the strength of the CaI and NaI features at low resolution. Our results stress the limitations of using local stars as templates for the study of composite cool stellar populations such as central starbursts in galaxies.

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A comparison of CO(J = 1 yields 0) and CO(J = 2 yields 1) emission in the Milky Way molecular ring

Cited by 20 publications

References 0 publications

Giant Molecular Clouds in the Spiral Arm of Ic 342

Giant Molecular Clouds in the Spiral Arm of Ic 342

Atomic Carbon in the Southern Milky Way

A search for late-type supergiants in the inner regions of the Milky Way

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