Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

Carlhoff, P.; Luong, Q. Nguyên; Schilke, P.; Motte, F.; Schneider, N.; Beuther, H.; Bontemps, Sylvain; Heitsch, Fabian; Hill, T.; Krämer, C.; Ossenkopf, V.; Schüller, F.; Simon, R.; Wyrowski, F.

doi:10.1051/0004-6361/201321592

Cited by 63 publications

(89 citation statements)

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“…As the dust observations have no velocity resolution, we see all the dust and thus gas along the line of sight. Carlhoff et al (2013) showed that the Herschel dust data are similar within the uncertainties to the CO data at the velocity range of W43 (v LSR = 60−120 km s −1 ). Hence, the Herschel dust observations are dominated by the emission from W43 and the contributions of other regions along the line of sight can be neglected.…”

Section: H 2 Column Densitymentioning

confidence: 57%

“…This region is situated at the intersection of the Galactic bar and the first spiral arm (Scutum-Centaurus Galactic arm, Nguyen Luong et al 2011;Carlhoff et al 2013), leading to complex kinematic structures and possibly high star formation activity. The complex W43 is referred to as a Galactic mini-starburst region (Motte et al 2003;Bally et al 2010) and shows a star formation rate of ∼0.1 M yr −1 (Nguyen Luong et al 2011) or 5−10% of the star formation rate in the entire Milky Way.…”

Section: Introductionmentioning

confidence: 99%

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THOR: The H i, OH, Recombination line survey of the Milky Way

Bihr

Beuther

Ott

et al. 2015

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To study the atomic, molecular, and ionized emission of giant molecular clouds (GMCs) in the Milky Way, we initiated a large program with the Karl G. Jansky Very Large Array (VLA): "THOR: The H , OH, Recombination line survey of the Milky Way". We map the 21 cm H  line, 4 OH lines, up to 19 Hα recombination lines and the continuum from 1 to 2 GHz of a significant fraction of the Milky Way (l = 15• −67• , |b| ≤ 1 • ) at an angular resolution of ∼20 . Starting in 2012, as a pilot study we mapped 4 square degrees of the GMC associated with the W43 star formation complex. The rest of the THOR survey area was observed during 2013 and 2014. In this paper, we focus on the H  emission from the W43 GMC complex. Classically, the H  21 cm line is treated as optically thin with properties such as the column density calculated under this assumption.This approach might yield reasonable results for regions of low-mass star formation, however, it is not sufficient to describe GMCs. We analyzed strong continuum sources to measure the optical depth along the line of sight, and thus correct the H  21 cm emission for optical depth effects and weak diffuse continuum emission. Hence, we are able to measure the H  mass of this region more accurately and our analysis reveals a lower limit for the H  mass of M = 6.6 −1.8 × 10 6 M (v LSR = 60−120 km s −1 ), which is a factor of 2.4 larger than the mass estimated with the assumption of optically thin emission. The H  column densities are as high as N H  ∼ 150 M pc −2 ≈ 1.9 × 10 22 cm −2 , which is an order of magnitude higher than for low-mass star formation regions. This result challenges theoretical models that predict a threshold for the H  column density of ∼10 M pc −2 , at which the formation of molecular hydrogen should set in. By assuming an elliptical layered structure for W43, we estimate the particle density profile. For the atomic gas particle density, we find a linear decrease toward the center of W43 with values decreasing from n H  = 20 cm −3 near the cloud edge to almost 0 cm −3 at its center. On the other hand, the molecular hydrogen, traced via dust observations with the Herschel Space Observatory, shows an exponential increase toward the center with densities increasing to n H 2 > 200 cm −3 , averaged over a region of ∼10 pc. While atomic and molecular hydrogen are well mixed at the cloud edge, the center of the cloud is strongly dominated by H 2 emission. We do not identify a sharp transition between hydrogen in atomic and molecular form. Our results, which challenge current theoretical models, are an important characterization of the atomic to molecular hydrogen transition in an extreme environment.

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Section: H 2 Column Densitymentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

THOR: The H i, OH, Recombination line survey of the Milky Way

Bihr

Beuther

Ott

et al. 2015

A&A

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“…Probability distribution functions of CO (Goldsmith et al 2008;Goodman et al 2009) are clipped at higher column densities owing to a high optical depth. Only recently has a special method been developed to obtain an H 2 map from 13 CO and C 18 O observations in W43 that suffers less from a cut-off at high column densities (Carlhoff et al 2013). However, all methods are still subject to other uncertainties, such as the variable CO/H 2 conversion factor or the variation in excitation temperature T ex (see Fig.…”

Section: Line-of-sight Confusion In Continuum Mapsmentioning

confidence: 99%

“…However, all methods are still subject to other uncertainties, such as the variable CO/H 2 conversion factor or the variation in excitation temperature T ex (see Fig. 11 in Carlhoff et al 2013 that shows how the PDF shifts by changing only a few Kelvin T ex ).…”

Section: Line-of-sight Confusion In Continuum Mapsmentioning

confidence: 99%

Understanding star formation in molecular clouds

Schneider

Ossenkopf

Csengeri

et al. 2015

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134

203

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Column-density maps of molecular clouds are one of the most important observables in the context of molecular cloud-and starformation (SF) studies. With the Herschel satellite it is now possible to precisely determine the column density from dust emission, which is the best tracer of the bulk of material in molecular clouds. However, line-of-sight (LOS) contamination from fore-or background clouds can lead to overestimating the dust emission of molecular clouds, in particular for distant clouds. This implies values that are too high for column density and mass, which can potentially lead to an incorrect physical interpretation of the column density probability distribution function (PDF). In this paper, we use observations and simulations to demonstrate how LOS contamination affects the PDF. We apply a first-order approximation (removing a constant level) to the molecular clouds of Auriga and Maddalena (low-mass star-forming), and Carina and NGC 3603 (both high-mass SF regions). In perfect agreement with the simulations, we find that the PDFs become broader, the peak shifts to lower column densities, and the power-law tail of the PDF for higher column densities flattens after correction. All corrected PDFs have a lognormal part for low column densities with a peak at A v ∼ 2 mag, a deviation point (DP) from the lognormal at A v (DP) ∼ 4−5 mag, and a power-law tail for higher column densities. Assuming an equivalent spherical density distribution ρ ∝ r −α , the slopes of the power-law tails correspond to α PDF = 1.8, 1.75, and 2.5 for Auriga, Carina, and NGC 3603. These numbers agree within the uncertainties with the values of α ≈ 1.5, 1.8, and 2.5 determined from the slope γ (with α = 1 − γ) obtained from the radial column density profiles (N ∝ r γ ). While α ∼ 1.5−2 is consistent with a structure dominated by collapse (local free-fall collapse of individual cores and clumps and global collapse), the higher value of α > 2 for NGC 3603 requires a physical process that leads to additional compression (e.g., expanding ionization fronts). From the small sample of our study, we find that clouds forming only low-mass stars and those also forming high-mass stars have slightly different values for their average column density (1.8 × 10 21 cm −2 vs. 3.0 × 10 21 cm −2 ), and they display differences in the overall column density structure. Massive clouds assemble more gas in smaller cloud volumes than low-mass SF ones. However, for both cloud types, the transition of the PDF from lognormal shape into power-law tail is found at the same column density (at A v ∼ 4−5 mag). Low-mass and high-mass SF clouds then have the same low column density distribution, most likely dominated by supersonic turbulence. At higher column densities, collapse and external pressure can form the power-law tail. The relative importance of the two processes can vary between clouds and thus lead to the observed differences in PDF and column density structure.

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“…The Herschel key program HOBYS (see Motte et al 2010Motte et al , 2012 identifies ridges as high-density filaments, above 10 23 cm −2 in colFinal IRAM/PdBI FITS cube is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A15 umn density, which is favorable to the formation of high-mass (OB-type, ≥8 M ) stars (see Hill et al 2011;Nguyen Luong et al 2011a;Hennemann et al 2012). The most extreme of these ridges, W43-MM1, lies in the massive, highly concentrated and very dynamic W43 molecular complex located at 6 kpc (Nguyen Luong et al 2011b;Carlhoff et al 2013). In its central region, W43-MM1 is thought to be experiencing a cloud collision , causing a remarkably efficient burst of high-mass star formation (Motte et al 2003).…”

Section: Introductionmentioning

confidence: 99%

The W43-MM1 mini-starburst ridge, a test for star formation efficiency models

Louvet¹,

Motte²,

Hennebelle³

et al. 2014

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106

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Context. Star formation efficiency (SFE) theories are currently based on statistical distributions of turbulent cloud structures and a simple model of star formation from cores. They remain poorly tested, especially at the highest densities. Aims. We investigate the effects of gas density on the SFE through measurements of the core formation efficiency (CFE). With a total mass of ∼2 × 10 4 M , the W43-MM1 ridge is one of the most convincing candidate precursors of Galactic starburst clusters and thus one of the best places to investigate star formation. Methods. We used high-angular resolution maps obtained at 3 mm and 1 mm within the W43-MM1 ridge with the IRAM Plateau de Bure Interferometer to reveal a cluster of 11 massive dense cores, and, one of the most massive protostellar cores known. A Herschel column density image provided the mass distribution of the cloud gas. We then measured the "instantaneous" CFE and estimated the SFE and the star formation rate (SFR) within subregions of the W43-MM1 ridge. Results. The high SFE found in the ridge (∼6% enclosed in ∼8 pc 3 ) confirms its ability to form a starburst cluster. There is, however, a clear lack of dense cores in the eastern part of the ridge, which may be currently assembling. The CFE and the SFE are observed to increase with volume gas density, while the SFR per free fall time steeply decreases with the virial parameter, α vir . Statistical models of the SFR may describe the outskirts of the W43-MM1 ridge well, but struggle to reproduce its inner part, which corresponds to measurements at low α vir . It may be that ridges do not follow the log-normal density distribution, Larson relations, and stationary conditions forced in the statistical SFR models.

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Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

Cited by 63 publications

References 64 publications

THOR: The H i, OH, Recombination line survey of the Milky Way

THOR: The H i, OH, Recombination line survey of the Milky Way

Understanding star formation in molecular clouds

The W43-MM1 mini-starburst ridge, a test for star formation efficiency models

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