Molecular Clouds and Star Formation in the Southern H II Regions

Yamaguchi, Ryuichi; Saito, Hiro; Mizuno, N.; Mine, Yoshihiro; Mizuno, Akira; Ogawa, Hideo; Fukui, Y.

doi:10.1093/pasj/51.6.791

Cited by 69 publications

(109 citation statements)

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“…Yamaguchi et al (1999) Shock speeds derived from observations are similar. White et al (1999) and Thompson et al (2004) derived shock velocities from pressure in pre-and post-shock regions.…”

Section: Comparison With Observationsmentioning

confidence: 80%

A radiation driven implosion model for the enhanced luminosity of protostars near HII regions

Motoyama

Umemoto

Shang

2007

A&A

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Context. Molecular clouds near H ii regions tend to harbor more luminous protostars.Aims. We investigate whether a radiation-driven implosion mechanism enhances the luminosity of protostars near regions of high ionizing fluxes. Methods. We performed numerical simulations to model collapse of cores exposed to UV radiation from O stars. We investigated the dependence of mass loss rates on the initial density profiles of cores and variation of UV fluxes. We derived simple analytic estimates of accretion rates and final masses of protostars. Results. The radiation-driven implosion mechanism can increase accretion rates of protostars by 1-2 orders of magnitude. On the other hand, mass loss due to photo-evaporation is not high enough to have a significant impact on the luminosity. The increase in accretion rate results in luminosity 1-2 orders of magnitude higher than those of protostars that form without external triggering.Conclusions. Radiation-driven implosion can help explain the observed higher luminosity of protostars in molecular clouds near H ii regions.

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Section: Comparison With Observationsmentioning

confidence: 80%

A radiation driven implosion model for the enhanced luminosity of protostars near HII regions

Motoyama

Umemoto

Shang

2007

A&A

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“…Molecular line observations toward RCW 38 are very limited. Yamaguchi et al (1999) observed a large area of RCW 38 in the 13 CO J = 1-0 emission with NANTEN and found a molecular cloud at 2-3 km s −1 that coincides with IRS 2, although detailed structures including the ring-like component were not resolved due to a relatively coarse resolution. On the other hand, Zinchenko et al (1995) observed the central region of RCW 38 at a half-power beam width (HPBW) of ∼1′ in the CS emission to resolve the ring shape surrounding IRS 2.…”

Section: Rcw 38 As the Youngest Super Star Cluster In The Milky Waymentioning

confidence: 99%

The Two Molecular Clouds in RCW 38: Evidence for the Formation of the Youngest Super Star Cluster in the Milky Way Triggered by Cloud–cloud Collision

Fukui

Torii

Ohama

et al. 2016

ApJ

124

148

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We present distributions of two molecular clouds having velocities of 2 and 14 km s −1 toward RCW 38, the youngest super star cluster in the Milky Way, in the 12 CO J = 1-0 and 3-2 and 13 CO J = 1-0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3-2 emission to the J = 1-0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s −1 cloud. We suggest that the collision is currently continuing toward part of the 2 km s −1 cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud-cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.

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“…The HII regions, their ionising star(s), heliocentric distances and associated BRCs are listed in Table 1. The ionising star(s), spectral types and assumed distances are drawn from Yamaguchi et al (1999) and Thompson et al (2004b) and references therein, apart from σ Sco where the spectral type and assumed distance are taken from Eggen (1998). The spectral types of HD 305938, CCDM J16212−2536AB, HD 326286 and HD 152245 have been drawn from SIMBAD.…”

Section: Southern Catalogue Of Brcsmentioning

confidence: 99%

“…The Gum Nebula is located at a heliocentric distance of ∼450 pc and covers a region of 30 • × 30 • (Sugitani & Ogura 1994 and references therein). It is excited by two stars, ζ Pup and γ 2 Vel, which have spectral types O4 If and WC 8+O8 III respectively (Yamaguchi et al 1999). There are six BRCs associated with Gum nebula (SFO 46,48,(50)(51)(52)(53), only one of which is located within the MSX survey region (SFO 51).…”

Section: The Gum Nebulamentioning

confidence: 99%

Observational study of sites of triggered star formation

Urquhart

Morgan

Thompson

2009

A&A

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Context. Bright-rimmed clouds (BRCs) are isolated molecular clouds located on the edges of evolved HII regions. Star formation within these clouds may have been triggered through the propagation of photoionisation-induced shocks driven by the expansion of the HII region. Aims. The main focus of this paper is to investigate the current level of star formation within a sample of southern hemisphere BRCs and evaluate to what extent, if any, star formation may have been triggered. Methods. In this paper we present the results of a programme of position-switched CO observations towards 45 southern BRCs. The 12 CO, 13 CO and C 18 O J = 1−0 rotational transitions were simultaneously observed using the 22-m Mopra telescope. We complement these observations with archival mid-infrared data obtained from the MSX and Spitzer, as well as submillimetre and radio data previously reported in the literature. Combining all of the available data with the observations presented here allows us to build up a comprehensive picture of the current level of star formation activity within a significant number of BRCs. Results. Analysis of the CO, mid-infrared and radio data result in the clouds being divided into three distinct groups: a) clouds that appear to be relatively unaffected by the photoionisation from the nearby OB star(s); b) clouds that show evidence of significant interaction between the molecular material and the HII regions; c) clouds towards which no CO emission is detected, but are associated with strong ionisation fronts; these are thought to be examples of clouds undergoing an ionisation flash. We refer to these groups as spontaneous, triggered, and zapped clouds, respectively. Comparing the physical parameters of spontaneous and triggered samples we find striking differences in luminosity, surface temperature and column density with all three quantities significantly enhanced for the clouds considered to have been triggered. Furthermore, we find strong evidence for star formation within the triggered sample by way of methanol and H 2 O masers, embedded mid-infrared point sources and CO wings, however, we find evidence of ongoing star formation within only two of the spontaneous sample. Conclusions. We have used CO, mid-infrared and radio data to identify 24 of the 45 southern BRCs that are undergoing a strong interaction with their HII region. We can therefore exclude the other 21 sources (∼50%) from future studies of triggered star formation. Fourteen of the 24 interacting BRCs are found to be associated with embedded mid-infrared point sources and we find strong evidence that these clouds are forming stars. The absence of mid-infrared sources towards the remaining ten clouds and the lack of any other evidence of star formation within these clouds leads us to conclude that these represent an earlier evolutionary stage of star formation.

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Molecular Clouds and Star Formation in the Southern H II Regions

Cited by 69 publications

References 0 publications

A radiation driven implosion model for the enhanced luminosity of protostars near HII regions

A radiation driven implosion model for the enhanced luminosity of protostars near HII regions

The Two Molecular Clouds in RCW 38: Evidence for the Formation of the Youngest Super Star Cluster in the Milky Way Triggered by Cloud–cloud Collision

Observational study of sites of triggered star formation

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