CO (<i>J</i>= 2–1) Line Observations of the Galactic Center Molecular Cloud Complex. II Dynamical Structure and Physical Conditions

Oka, Tomoharu; Hasegawa, Tetsuo; Hayashi, Masahiko; Handa, Toshihiro; Sakamoto, Seiichi

doi:10.1086/305133

Cited by 140 publications

(160 citation statements)

References 49 publications

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“…This was seen first toward the Galactic Center (e.g. Oka et al, 1998;Strong et al, 2004), and has been noted in other nearby galactic nuclei as well . This effect was perhaps most famously pointed out by Downes & Solomon (1998), who showed that using a typical Milky Way X-factor in nearby galaxy mergers and starbursts would cause the inferred gas mass to exceed the dynamical mass.…”

Section: Deriving H 2 Gas Masses From High-redshift Galaxiessupporting

confidence: 63%

Dusty star-forming galaxies at high redshift

2014

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Far-infrared and submillimeter wavelength surveys have now established the important role of dusty, star-forming galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe. The brightest of these galaxies have infrared luminosities in excess of 10 13 L with implied star-formation rates of thousands of solar masses per year. They represent the most intense starbursts in the Universe, yet many are completely optically obscured. Their easy detection at submm wavelengths is due to dust heated by ultraviolet radiation of newly forming stars. When summed up, all of the dusty, star-forming galaxies in the Universe produce an infrared radiation field that has an equal energy density as the direct starlight emission from all galaxies visible at ultraviolet and optical wavelengths. The bulk of this infrared extragalactic background light emanates from galaxies as diverse as gas-rich disks to mergers of intense starbursting galaxies. Major advances in far-infrared instrumentation in recent years, both spacebased and ground-based, has led to the detection of nearly a million DSFGs, yet our understanding of the underlying astrophysics that govern the start and end of the dusty starburst phase is still in nascent stage. This review is aimed at summarizing the current status of DSFG studies, focusing especially on the detailed characterization of the bestunderstood subset (submillimeter galaxies, who were summarized in the last review of this field over a decade ago, Blain et al. 2002), but also the selection and characterization of more recently discovered DSFG populations. We review DSFG population statistics, their physical properties including dust, gas and stellar contents, their environments, and current theoretical models related to the formation and evolution of these galaxies.

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Section: Deriving H 2 Gas Masses From High-redshift Galaxiessupporting

confidence: 63%

Dusty star-forming galaxies at high redshift

2014

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“…Sakamoto et al 1995, who derive a mean value of 0.66 ± 0.01). A similar study conducted by Oka et al (1998) in the Taurus and the Orion A Molecular Clouds, including star-forming sites, lead to mean values of 0.53 ± 0.01 and 0.75 ± 0.01 respectively.…”

Section: Line Intensities and Velocity Structuresupporting

confidence: 64%

Radio-millimetre investigation of galactic infrared dark clouds

Teyssier

Hennebelle

Pérault

2002

A&A

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Abstract. We present follow-up observations of the mid-Infrared dark clouds selected from the ISOGAL inner Galaxy sample. On-the-fly maps of 13 CO, C 18 O and the 1.2 mm continuum emission were conducted at the IRAM 30-m telescope, showing spectacular correlation with the mid-IR absorption. The dark clouds are distributed as far as the prominent molecular ring at a distance of 3 to 7 kpc from the Sun. The clouds exhibit shapes ranging from globules to thin filaments down to < ∼ 1 pc in size. The on-the-fly images obtained in 13 CO and C 18 O confirmed that the cores are dense, compact molecular emitters, significantly more massive than local dark clouds (more than 1000 M ) and lie within low activity Giant Molecular Clouds (GMC's). Ratios of the emission in the J = (2−1) and (1−0) transitions of 13 CO and C 18 O show a remarkable uniformity within each cloud, with a significant portion of the sample represented well by a ratio of 0.67 ± 0.12. Preliminary analysis of temperature and density measurements reveals that most of the cores have densities above 10 5 cm −3 and temperatures between 8 and 25 K, these latter clouds being associated with young embedded stars. Despite the high extinction inferred from mid-IR (Av > 50, Hennebelle et al. 2001), the molecular lines are surprisingly weak, indicating likely depletion onto cold grains.

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“…The average intrinsic line ratio in molecular clouds of our Galaxy varies between 0.5 and 0.8 (Oka et al 1998), being higher at low galactic latitudes. In external galaxies intrinsic ratios are as low as 0.3 or as high as 2 (e.g.…”

Section: Uniform Intrinsic Line Ratiomentioning

confidence: 84%

On the nature of faint mid-infrared sources in M 33

Corbelli

Giovanardi

Palla

et al. 2011

A&A

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Aims. We investigate the nature of 24 μm sources in M 33 that have weak or no associated Hα emission. Both bright evolved stars and embedded star-forming regions are visible as compact infrared sources in the 8 and 24 μm Spitzer maps of M 33 and contribute to the more diffuse and faint emission in these bands. Can we distinguish the two populations? Methods. We carry out deep CO J = 2-1 and J = 1-0 line searches at the location of 18 compact mid-IR sources and two optically selected ones to unveil an ongoing star formation process throughout the disk of M 33. In the absence of high-resolution CO maps we use different assumptions to estimate cloud masses from pointed observations. We also analyze if the spectral energy distribution and mid-IR colors can be used to discriminate between evolved stars and star-forming regions.Results. Molecular emission is detected at the location of 17 sources at the level of 0.3 K km s −1 or higher in at least one of the CO rotational lines. Even though the number of giant molecular clouds drops beyond 4 kpc in M 33, our deep observations reveal that clouds of smaller mass are common out to 6.8 kpc. Estimated cloud masses range between 10 4 and 10 5 M , assuming likely values of the CO-to-H 2 conversion factor and virial equilibrium. Sources that are known to be evolved variable stars show weaker or undetectable CO lines. Evolved stars occupy a well defined region of the IRAC color-color diagrams. Star-forming regions are scattered throughout a larger area, even though the bulk of the distribution has different IRAC colors than evolved variable stars. We estimate that about half of the 24 μm sources without an Hα counterpart are genuine embedded star-forming regions. Sources with faint but compact Hα emission have an incomplete Initial Mass Function (IMF) at the high-mass end and are compatible with a population of young clusters with a stochastically sampled, universal IMF.

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CO (J= 2–1) Line Observations of the Galactic Center Molecular Cloud Complex. II Dynamical Structure and Physical Conditions

Cited by 140 publications

References 49 publications

Dusty star-forming galaxies at high redshift

Dusty star-forming galaxies at high redshift

Radio-millimetre investigation of galactic infrared dark clouds

On the nature of faint mid-infrared sources in M 33

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