Submillimeter Observations of [ITAL]Midcourse Space Experiment[/ITAL] Galactic Infrared-Dark Clouds

Carey, Sean; Feldman, P. A.; Redman, R. O.; Egan, M. P.; MacLeod, J. M.; Price, S. D.

doi:10.1086/317270

Cited by 175 publications

(240 citation statements)

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“…Our results are thus in line with earlier findings (e.g. Carey et al 2000;Simon et al 2006a;Teyssier et al 2002), which see many IRDCs as an intrinsic part of a larger molecular cloud.…”

Section: Resultssupporting

confidence: 94%

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Understanding star formation in molecular clouds

Schneider

Csengeri

Klessen

et al. 2015

A&A

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We analyse column density and temperature maps derived from Herschel dust continuum observations of a sample of prominent, massive infrared dark clouds (IRDCs) i.e. G11.11-0.12, G18.82-0.28, G28.37+0.07, and G28.53-0.25. We disentangle the velocity structure of the clouds using 13 CO 1→0 and 12 CO 3→2 data, showing that these IRDCs are the densest regions in massive giant molecular clouds (GMCs) and not isolated features. The probability distribution function (PDF) of column densities for all clouds have a power-law distribution over all (high) column densities, regardless of the evolutionary stage of the cloud: G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain (proto)-stars, while G28.53-0.25 shows no signs of star formation. This is in contrast to the purely log-normal PDFs reported for near and/or mid-IR extinction maps. We only find a log-normal distribution for lower column densities, if we perform PDFs of the column density maps of the whole GMC in which the IRDCs are embedded. By comparing the PDF slope and the radial column density profile of three of our clouds, we attribute the power law to the effect of large-scale gravitational collapse and to local free-fall collapse of pre-and protostellar cores for the highest column densities. A significant impact on the cloud properties from radiative feedback is unlikely because the clouds are mostly devoid of star formation. Independent from the PDF analysis, we find infall signatures in the spectral profiles of 12 CO for G28.37+0.07 and G11.11-0.12, supporting the scenario of gravitational collapse. Our results are in line with earlier interpretations that see massive IRDCs as the densest regions within GMCs, which may be the progenitors of massive stars or clusters. At least some of the IRDCs are probably the same features as ridges (high column density regions with N > 10 23 cm −2 over small areas), which were defined for nearby IR-bright GMCs. Because IRDCs are only confined to the densest (gravity dominated) cloud regions, the PDF constructed from this kind of a clipped image does not represent the (turbulence dominated) low column density regime of the cloud.

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“…Our results are thus in line with earlier findings (e.g. Carey et al 2000;Simon et al 2006a;Teyssier et al 2002), which see many IRDCs as an intrinsic part of a larger molecular cloud.…”

Section: Resultssupporting

confidence: 94%

“…On the other hand, an increasing number of studies (e.g. Carey et al 2000;Rathborne et al 2011;Sakai et al 2013) now reveal that many of the massive IRDCs show signatures of active and ongoing (massive) star formation such as hot core and outflow emission and IR hot spots. A&A 578, A29 (2015) Notes.…”

Section: Introductionmentioning

confidence: 99%

Understanding star formation in molecular clouds

Schneider

Csengeri

Klessen

et al. 2015

A&A

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“…When a core shows the polycyclic aromatic hy-E-mail: liuxiaolan10@mails.gucas.ac.cn drocarbon (PAH) emission at 8 µm, it is considered to be in the finally red core stage. Furthermore, these detected cores have the strong dust emission from millimetre and submillimetre bands (Lis & Carlstrom 1994;Carey et al 2000;Redman et al 2003;Rathborne et al 2005;Beuther et al 2005;Rathborne et al 2005Rathborne et al , 2006 and only some cores have embedded protostars, indicating that the IRDCs may represent the earliest observable stage of high-mass star formation. Thus, IRDCs can provide us with an opportunity to study the physical and chemical conditions of massive star-forming processes in the earliest stage.…”

Section: Introductionmentioning

confidence: 94%

“…Previous researchers suggested that IRDCs were the cold (T < 25 K) and dense (10 5 cm −3 ) regions, with a scale of 1∼10 pc and a mass of 10 2 ∼ 10 5 M Carey et al 1998Carey et al , 2000Rathborne et al 2006). Chambers et al (2009) proposed that the cores within the IRDCs may be in different phase, from a quiescent to an active, and finally into a red core.…”

Section: Introductionmentioning

confidence: 99%

A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

Liu

Wang

2013

Monthly Notices of the Royal Astronomical Society

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We have studied 14 southern infrared dark clouds (IRDCs) using the data taken from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey and the GLIMPSE and MIPSGAL mid-infrared survey of the inner Galaxy. The physical and chemical characteristics of the 14 IRDCs are investigated using N 2 H + (1-0), HNC(1-0), HCO + (1-0), and HCN(1-0) molecular lines. We find that the 14 IRDCs are in different evolutionary stages from the "starless" to the sources with an UCHII region. Three IRDCs are detected to have the star forming activities. The integrated intensity ratios I HCO + /HCN , I N2H + /HCN , and I HNC/HCN are all about 1.5, which is different from the previous measurements, suggesting that the integrated intensity ratios may be affected by the cloud environments. The integrated intensities of HNC, HCO + and HCN show a tight correlation for the 14 IRDCs, implying a close link to the chemical evolution of these three species in the IRDCs. The derived excitation temperature for each IRDC is less than 25 K. We estimate the abundances of the four molecules from 10 −11 to 10 −9 , and the average abundance ratios N HNC /N HCN = 1.47 ± 0.50, N HNC /N HCO + = 1.74 ± 0.22, N HCN /N HCO + = 1.21 ± 0.41.

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“…These clouds are observed in silhouette against the bright infrared background emission of the galactic plane. IRDCs are typically cold (<25 K) and dense (∼10 5 cm −3 ) with masses ranging from ∼100−10 5 M Carey et al 1998Carey et al , 2000 and they are located at larger distances (>1 kpc) compared to wellstudied low-mass star forming regions. A recently published catalog of dark clouds extracted from the GLIMPSE Survey by Peretto & Fuller (2009) shows that most IRDCs have column densities below N(H 2 ) ≈ 5 × 10 22 cm −2 , with some extreme objects reaching N(H 2 ) > 10 23 cm −2 .…”

Section: Introductionmentioning

confidence: 99%

Searching for dark clouds in the outer galactic plane

Frieswijk¹,

Shipman

2010

A&A

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Context.Most of what is known about clustered star formation to date comes from well studied star forming regions located relatively nearby, such as Rho-Ophiuchus, Serpens and Perseus. However, the recent discovery of infrared dark clouds may give new insights in our understanding of this dominant mode of star formation in the Galaxy. Though the exact role of infrared dark clouds in the formation process is still somewhat unclear, they seem to provide useful laboratories to study the very early stages of clustered star formation. Infrared dark clouds have been identified predominantly toward the bright inner parts of the galactic plane. The low background emission makes it more difficult to identify similar objects in mid-infrared absorption in the outer parts. This is unfortunate, because the outer Galaxy represents the only nearby region where we can study effects of different (external) conditions on the star formation process. Aims. The aim of this paper is to identify extended red regions in the outer galactic plane based on reddening of stars in the nearinfrared. We argue that these regions appear reddened mainly due to extinction caused by molecular clouds and young stellar objects. The work presented here is used as a basis for identifying star forming regions and in particular the very early stages. An accompanying paper describes the cross-identification of the identified regions with existing data, uncovering more on the nature of the reddening. Methods. We use the Mann-Whitney U-test, in combination with a friends-of-friends algorithm, to identify extended reddened regions in the 2MASS all-sky JHK survey. We process the data on a regular grid using two different resolutions, 60 and 90 . The two resolutions have been chosen because the stellar surface density varies between the crowded spiral arm regions and the sparsely populated galactic anti-center region. Results. We identify 1320 extended red regions at the higher resolution and 1589 in the lower resolution run. The linear extent of the identified regions ranges from a few arc-minutes to about a degree. Conclusions. The majority of extended red regions are associated with major molecular cloud complexes, supporting our hypothesis that the reddening is mostly due to foreground clouds and embedded objects. The reliability of the identified regions is >99.9%. Because we choose to identify object with a high reliability we can not quantify the completeness of the list of regions.

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Submillimeter Observations of [ITAL]Midcourse Space Experiment[/ITAL] Galactic Infrared-Dark Clouds

Cited by 175 publications

References 12 publications

Understanding star formation in molecular clouds

Understanding star formation in molecular clouds

A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

Searching for dark clouds in the outer galactic plane

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