Radiation-Driven Implosion and Triggered Star Formation

Bisbas, Thomas G.; Wünsch, Richard; Whitworth, Anthony Peter; Hubber, D. A.; Walch, Stefanie

doi:10.1088/0004-637x/736/2/142

Cited by 130 publications

(149 citation statements)

References 40 publications

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“…Numerical simulations show that photo-ionisation from massive stars inside molecular clouds generally leads to a slight decrease in the global star formation efficiency, with gas expulsion partly compensated for by triggered star formation (e.g., Dale et al 2012a,b). Nevertheless, they show that triggered star formation does occur, and amounts to a few% of the total cloud mass (see also Walch et al 2011). Dale et al (2012b) find that the association of young stars with gas structures such as shells or pillars, as occurs in NGC 6357, is a good but not conclusive indication of triggered star formation.…”

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

confidence: 99%

“…The elephant trunk with IRS 4 at the tip inside G353.2+0.9 suggests that the so-called "radiation-driven implosion" (see Bisbas et al 2011 and references therein) may be under way. When an ionisation front crosses a dense clump, it generates a shock which compresses the clump making it collapse under some conditions.…”

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 We used new deep JHK s photometry, along with unpublished deep Spitzer/IRAC mid-infrared photometry, complemented with optical HST/WFPC2 high spatial resolution photometry and X-ray Chandra observations, to constrain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: From Gas To Starsmentioning

confidence: 99%

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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“…It was shown that under zero ionizing flux, a prolate cloud in interstellar background radiation field either collapsed to a spindle or dispersed into space, depending on its initial conditions (Nelson & Langer 1998). The recent work by Bisbas et al (2011) proved that ionizing flux between 10 9 and 10 11 cm −2 s −1 can trigger star formation in a molecular cloud while a weak or high ionizing flux would erode or disperse a molecular cloud of initial condition as a Bonnor-Ebert sphere (Bonnor 1956) The initial temperature of the prolate cloud was set as 60 K, considering the warm nature of the surroundings of stars, similar to that used in the previous RDI simulations for the formation of different types of BRCs (Miao et al 2006(Miao et al , 2009(Miao et al , 2010 and collapse of molecular cloud in FUV radiation field (Nelson & Langer 1999).…”

Section: Ionizing Radiation Flux and The Initial Temperaturementioning

confidence: 99%

Triggered Star Formation in a Bright-Rimmed Cloud (Brc 5) of Ic 1805

Fukuda

Miao

Sugitani

et al. 2013

ApJ

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We report recent optical, near-infrared (NIR), and millimeter observations which have revealed some new features of the bright-rimmed cloud BRC 5 associated with W4. With slitless spectroscopy, we detected 17 Hα emission stars around the cloud; 4 are near the surface of the cloud, and 1 is toward IRAS 02252+6120. NIR photometry shows that the central Hα emission star, together with one bright infrared source, has large NIR excesses and Class I spectral energy distributions. These two Class I objects are associated with the 2.9 mm continuum peaks and with a bipolar outflow, and are in between two separate, elongated C 18 O(J = 1-0) cores. The C 18 O cores and the two Class I sources are aligned along a line at position angle ∼240 • , somewhat less than perpendicular to the direction of UV radiation from the OB stars. Most of the detected Hα emission stars, all T Tauri candidates, are located within ∼3 of the cloud on the exciting star side. An estimate of the age of the stars based on a color-magnitude diagram suggests that these T Tauri candidates have ages of ∼1 Myr or less, but are more evolved objects than the central young stellar objects. This age sequence suggests sequential star formation within the BRC 5 cloud. The 13 CO(J = 1-0) emission shows three elongated structures, which indicates the asymmetric structure toward the UV incident axis. We present our exploratory simulation results by using a smoothed particle hydrodynamic code that suggests that the asymmetrical BRC 5 structure could possibly result from the evolution of a preexisting prolate molecular cloud subject to radiation-driven implosion (RDI). Our best-fit prolate cloud has an initial mass of ∼400 M , an axial ratio of ∼1.7, and a semi-major axis of ∼1.6 pc, pointing away from the ionization flux by an angle of 15 • . The simulated cloud structure not only closely matches the observed asymmetric morphological structure of BRC 5, but also reveals the possibility of the development of two major cores at the head of BRC 5. For the first time, the possibility of forming two stars by an RDI mechanism in a BRC is investigated.

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“…It allows us to study how the shell resulting from the collect and collapse scenario may be perturbed. The possibility to have localized density gradients has been extensively studied with the radiation-driven-implosion scenario (Mackey & Lim 2010;Bisbas et al 2011;Gritschneder et al 2009) and more recently within a turbulent media (Gritschneder et al 2010). In this work, we first want to focus on more simple and schematic situations in which the physical processes at work can be identified and studied more easily.…”

Section: Forming Pillarsmentioning

confidence: 99%

“…This scenario has been studied in detail with numerical simulations for years (see Lefloch & Lazareff 1994;Williams et al 2001;KesselDeynet & Burkert 2003). Recently, Bisbas et al (2011) and Gritschneder et al (2009) looked at the implosion of isothermal spherical clouds with smoothed particle hydrodynamics (SPH) codes. Using a grid code, Mackey & Lim (2010) produced elongated structures from dense spherical clumps using the shadowing effects of these structures.…”

Section: Introductionmentioning

confidence: 99%

3D simulations of pillar formation around HII regions: the importance of shock curvature

Tremblin

Audit

Minier

et al. 2012

A&A

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Aims. Radiative feedback from massive stars is a key process for understanding how HII regions enhance or inhibit star formation in pillars and globules at the interface with molecular clouds. We aim to contribute by modelling the interactions between ionization and gas clouds to better understand the processes at work. We study in detail the impact of modulations on the cloud-HII region interface and density modulations inside the cloud. Methods. We ran 3D hydrodynamical simulations based on Euler equations coupled with gravity using the HERACLES code. We implemented a method to solve ionization/recombination equations and took into account typical heating and cooling processes at work in the interstellar medium that are caused by ionization/recombination physics. Results. UV radiation creates a dense shell compressed between an ionization front and a shock ahead. Interface modulations produce a curved shock that collapses on itself, which leads to stable growing pillar-like structures. The narrower the initial interface modulation, the longer the resulting pillar. We interpret pillars resulting from density modulations in terms of the ability of these density modulations to curve the shock ahead of the ionization front. Conclusions. The shock curvature is a key process for understanding the formation of structures at the edge of HII regions. Interface and density modulations at the edge of the cloud have a direct impact on the morphology of the dense shell during its formation. Deeper inside the cloud, structures have less influence because of the high densities reached by the shell during its expansion.

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Radiation-Driven Implosion and Triggered Star Formation

Cited by 130 publications

References 40 publications

Young open clusters in the Galactic star forming region NGC 6357

Young open clusters in the Galactic star forming region NGC 6357

Triggered Star Formation in a Bright-Rimmed Cloud (Brc 5) of Ic 1805

3D simulations of pillar formation around HII regions: the importance of shock curvature

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