Molecular clouds under the influence of massive stars in the Galactic Hii region G353.2+0.9

Giannetti, A.; Brand, J.; Massi, F.; Tieftrunk, A. R.; Beltrán, M. T.

doi:10.1051/0004-6361/201116774

Cited by 12 publications

(33 citation statements)

References 20 publications

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“…8 and Table 5) represent real substructures or are rather the effect of variable extinction. Although the bulk of molecular gas lies in the SofI northern field, a few molecular clumps have been found projected towards the core (e.g., CO clumps E, F, and G of Massi et al 1997, and CS clump D3 of Giannetti et al 2012). However, some of these clumps appear red-shifted and those authors suggested that this is because these may lie in the rear part of the complex, accelerated away by rocket effect.…”

Section: Star Formation On the Smaller Scale: Substructures In Pismis 24mentioning

confidence: 97%

“…As discussed in Appendix F, this region hosts less massive stars than subcluster core C which may be an effect of photo-ionisation (Dale et al 2012b). Giannetti et al (2012) found that many of the gas clumps in the north are virialised and/or exhibit possible compression from outside, which may lead to further star formation.…”

Section: Star Formation On the Smaller Scale: From Gas To Starsmentioning

confidence: 99%

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Young open clusters in the Galactic star forming region NGC 6357

Massi

Giannetti

Carlo

et al. 2014

A&A

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Context. NGC 6357 is an active star forming region with very young massive open clusters. These clusters contain some of the most massive stars in the Galaxy and strongly interact with nearby giant molecular clouds. Aims. We study the young stellar populations of the region and of the open cluster Pismis 24, focusing on their relationship with the nearby giant molecular clouds. We seek evidence of triggered star formation "propagating" from the clusters. Methods. We used new deep JHK s photometry, along with unpublished deep Spitzer/IRAC mid-infrared photometry, complemented with optical HST/WFPC2 high spatial resolution photometry and X-ray Chandra observations, to constrain age, initial mass function, and star formation modes in progress. We carefully examine and discuss all sources of bias (saturation, confusion, different sensitivities, extinction). Results. NGC 6357 hosts three large young stellar clusters, of which Pismis 24 is the most prominent. We found that Pismis 24 is a very young (∼1-3 Myr) open cluster with a Salpeter-like initial mass function and a few thousand members. A comparison between optical and infrared photometry indicates that the fraction of members with a near-infrared excess (i.e., with a circumstellar disk) is in the range 0.3-0.6, consistent with its photometrically derived age. We also find that Pismis 24 is likely subdivided into a few different subclusters, one of which contains almost all the massive members. There are indications of current star formation triggered by these massive stars, but clear age trends could not be derived (although the fraction of stars with a near-infrared excess does increase towards the Hii region associated with the cluster). The gas out of which Pismis 24 formed must have been distributed in dense clumps within a cloud of less dense gas ∼1 pc in radius. Conclusions. Our findings provide some new insight into how young stellar populations and massive stars emerge, and evolve in the first few Myr after birth, from a giant molecular cloud complex.

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Section: Star Formation On the Smaller Scale: Substructures In Pismis 24mentioning

confidence: 97%

Section: Star Formation On the Smaller Scale: From Gas To Starsmentioning

confidence: 99%

Young open clusters in the Galactic star forming region NGC 6357

Massi

Giannetti

Carlo

et al. 2014

A&A

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“…For CS, there is a large scatter in observed values for highmass star-forming regions with [CS]/[H 2 ] = 10 −9 to a few times 10 −10 (Gianetti et al 2012;Li et al 2015;Neufeld et al 2015). Low-mass cores have typical values of a few times 10 −9 (e.g.…”

Section: The Pdfs From Cs and N 2 H +mentioning

confidence: 99%

Understanding star formation in molecular clouds

Schneider

Bontemps

Motte

et al. 2016

A&A

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The probability distribution function of column density (N-PDF) serves as a powerful tool to characterise the various physical processes that influence the structure of molecular clouds. Studies that use extinction maps or H 2 column-density maps (N) that are derived from dust show that star-forming clouds can best be characterised by lognormal PDFs for the lower N range and a power-law tail for higher N, which is commonly attributed to turbulence and self-gravity and/or pressure, respectively. While PDFs from dust cover a large dynamic range (typically N ∼ 10 20−24 cm −2 or A v ∼ 0.1−1000), PDFs obtained from molecular lines -converted into H 2 column density -potentially trace more selectively different regimes of (column) densities and temperatures. They also enable us to distinguish different clouds along the line of sight through using the velocity information. We report here on PDFs that were obtained from observations of 12 CO, 13 CO, C 18 O, CS, and N 2 H + in the Cygnus X North region, and make a comparison to a PDF that was derived from dust observations with the Herschel satellite. The PDF of 12 CO is lognormal for A v ∼ 1-30, but is cut for higher A v because of optical depth effects. The PDFs of C 18 O and 13 CO are mostly lognormal up to A v ∼ 1-15, followed by excess up to A v ∼ 40. Above that value, all CO PDFs drop, which is most likely due to depletion. The high density tracers CS and N 2 H + exhibit only a power law distribution between A v ∼ 15 and 400, respectively. The PDF from dust is lognormal for A v ∼ 3-15 and has a power-law tail up to A v ∼ 500. Absolute values for the molecular line column densities are, however, rather uncertain because of abundance and excitation temperature variations. If we take the dust PDF at face value, we "calibrate" the molecular line PDF of CS to that of the dust and determine an abundance [CS]/[H 2 ] of 10 −9 . The slopes of the power-law tails of the CS, N 2 H + , and dust PDFs are −1.6, −1.4, and −2.3, respectively, and are thus consistent with free-fall collapse of filaments and clumps. A quasi static configuration of filaments and clumps can also possibly account for the observed N-PDFs, providing they have a sufficiently condensed density structure and external ram pressure by gas accretion is provided. The somehow flatter slopes of N 2 H + and CS can reflect an abundance change and/or subthermal excitation at low column densities.

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“…A shell of fragmented molecular gas was also identified in CO emission (e.g. Massi et al 1997) and Giannetti et al (2012) show the presence of a velocity gradient in the region suggesting that the expansion of the ionised gas is pushing the molecular gas. In addition, at least four other H II regions (see Fig.…”

Section: Introductionmentioning

confidence: 92%

Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357

Russeil

Figueira

Zavagno

et al. 2019

A&A

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Aims. To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) that are able to form high-mass star(s). This is one of the purposes of the Herschel/HOBYS key programme. Here, we carry out the census and characterise of the properties of the MDCs population of the NGC 6357 H II region. Methods. Our study is based on the Herschel/PACS and SPIRE 70−500 μm images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract ~0.1 pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. Results. We obtain a complete census of 23 massive dense cores, amongst which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we have considered their evolutionary status, and suggest that only five of them are likely to form a high-mass star. Conclusions. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge or hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.

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Molecular clouds under the influence of massive stars in the Galactic Hii region G353.2+0.9

Cited by 12 publications

References 20 publications

Young open clusters in the Galactic star forming region NGC 6357

Young open clusters in the Galactic star forming region NGC 6357

Understanding star formation in molecular clouds

Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357

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