A face-on view of the first galactic quadrant in molecular clouds

Solomon, P. M.; Rivolo, A. R.

doi:10.1086/167345

Cited by 69 publications

(68 citation statements)

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“…Nevertheless, our own survey looks at a region in the vicinity of the Galactic center for which both Rosolowsky et al (2010) and Beuther et al (2012) found that more dense gas is located within the inner l < 30 • of the Galactic plane. While most gas is concentrated within a molecular ring around the Galactic center at 4 kpc < R < 8 kpc (Solomon & Rivolo 1989), the ring does not seem homogeneous and the outer regions of that ring seem to contain less gas. This might indicate that the extrapolated numbers for the entire Galaxy might be higher than average and therefore require a higher SFR.…”

Section: Discussion Of the Lifetimesmentioning

confidence: 99%

“…Figure 7 shows the locations of the starless clumps within the Milky Way Galaxy. One notes a clear gap between 5 kpc and 11 kpc in the source distribution, which can be explained in several ways: (1) the elliptical orbits in the bulge of the Milky Way randomize its clouds' velocities and the rotation curve places them at random distances; (2) circular orbits close to the tangent point have very large d(dist) dv , hence small errors in the velocities propagate into large distance offsets; (3) the majority of the cold gas is homogeneously distributed in a molecular ring around the Galactic center with 4 kpc < R GC < 8 kpc (Solomon & Rivolo 1989). Therefore, no clumps are expected outside that region.…”

Section: Distancesmentioning

confidence: 99%

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Search for starless clumps in the ATLASGAL survey

Tackenberg

Beuther

Henning

et al. 2012

A&A

100

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Context. Understanding massive star formation requires comprehensive knowledge about the initial conditions of this process. The cradles of massive stars are believed to be located in dense and massive molecular clumps. Aims. In this study, we present an unbiased sample of the earliest stages of massive star formation across 20 deg 2 of the sky. Methods. Within the region 10 • < l < 20 • and |b| < 1 • , we search the ATLASGAL survey at 870 μm for dense gas condensations. These clumps are carefully examined for indications of ongoing star formation using YSOs from the GLIMPSE source catalog as well as sources in the 24 μm MIPSGAL images, to search for starless clumps. We calculate the column densities as well as the kinematic distances and masses for sources where the v lsr is known from spectroscopic observations. Results. Within the given region, we identify 210 starless clumps with peak column densities >1 × 10 23 cm −2 . In particular, we identify potential starless clumps on the other side of the Galaxy. The sizes of the clumps range between 0.1 pc and 3 pc with masses between a few tens of M up to several ten thousands of M . Most of them may form massive stars, but in the 20 deg 2 area we only find 14 regions massive enough to form stars more massive than 20 M and 3 regions with the potential to form stars more massive than 40 M . The slope of the high-mass tail of the clump mass function for clumps on the near side of the Galaxy is α = 2.2 and, therefore, Salpeter-like. We estimate the lifetime of the most massive starless clumps to be (6 ± 5) × 10 4 yr. Conclusions. The sample offers a uniform selection of starless clumps. In the large area surveyed, we only find a few potential precursors of stars in the excess of 40 M . It appears that the lifetime of these clumps is somewhat shorter than their free-fall times, although both values agree within the errors. In addition, these are ideal objects for detailed studies and follow-up observations.

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Section: Discussion Of the Lifetimesmentioning

confidence: 99%

Section: Distancesmentioning

confidence: 99%

Search for starless clumps in the ATLASGAL survey

Tackenberg

Beuther

Henning

et al. 2012

A&A

100

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“…Examining Figure 2 in this light, the most salient question becomes: why do GRB DLAs exhibit a preponderance of N H i > 10 22 cm À2 measurements? Indeed, the gas mass required to average N H i ¼ 10 22 cm À2 at 100 pc along random sight lines is M H i ¼ 10 7 M ; this exceeds the masses of even the largest molecular clouds in the Milky Way (Solomon & Rivolo 1989;Blitz 1993). It seems unlikely, therefore, that the observed H i gas corresponds to the circumstellar medium that hosted the GRB.…”

Section: Hydrogen Column Densitiesmentioning

confidence: 99%

Probing the Interstellar Medium near Star‐forming Regions with Gamma‐Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust

Prochaska

Chen

Dessauges‐Zavadsky

et al. 2007

ApJ

220

306

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We study the chemical abundances of the interstellar medium surrounding high-z gamma-ray bursts (GRBs) through analysis of the damped Ly systems ( DLAs) identified in afterglow spectra. These GRB DLAs are characterized by large H i column densities N H i and metallicities [M/H] spanning 1/100 to nearly solar, with median ½M/H > À1 dex. The majority of GRB DLAs have [M/H] values exceeding the cosmic mean metallicity of atomic gas at z > 2; i.e., if anything, the GRB DLAs are biased to larger metallicity. We also observe (1) large [Zn/Fe] values (> +0.6 dex) and subsolar Ti/Fe ratios, which imply substantial differential depletion; (2) large /Fe ratios, suggesting nucleosynthetic enrichment by massive stars; and (3) low C 0 /C + ratios (<10 À4 ). Quantitatively, the observed depletion levels and C 0 /C + ratios of the gas are not characteristic of cold, dense H i clouds in the Galactic interstellar medium (ISM). We argue that the GRB DLA represents the ISM near the GRB but not gas directly local to the GRB (e.g., its molecular cloud or circumstellar material). We compare these observations with DLAs intervening in background quasars (QSO DLAs). The GRB DLAs exhibit larger N H i values, higher /Fe and Zn/Fe ratios, and higher metallicity than the QSO DLAs. Although these differences are statistically significant, the offsets are relatively modest (N H i excepted). We argue that the differences result primarily from galactocentric radius-dependent differences in the ISM: GRB DLAs preferentially probe denser, more depleted, higher metallicity gas located in the inner few kiloparsecs, whereas QSO DLAs are more likely to intersect the less dense, less enriched, outer regions of the galaxy. Finally, we investigate whether dust obscuration may exclude GRB DLA sight lines from QSO DLA samples; we find that the majority of GRB DLAs would be recovered, which implies little observational bias against large N H i systems.

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“…Rice et al (2016) identified clouds using a dendrogram technique. However, previous studies that identified clouds from CO data managed to include at most 40% of the CO emission in their clouds (Solomon et al 1987;Solomon & Rivolo 1989;Rice et al 2016).…”

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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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A face-on view of the first galactic quadrant in molecular clouds

Cited by 69 publications

References 0 publications

Search for starless clumps in the ATLASGAL survey

Search for starless clumps in the ATLASGAL survey

Probing the Interstellar Medium near Star‐forming Regions with Gamma‐Ray Burst Afterglow Spectroscopy: Gas, Metals, and Dust

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

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