Dispersal of molecular clouds by ionizing radiation

By Stefanie Walch, A. Whitworth, T. Bisbas, R. Wunsch, David Hubber. 2012

176 citations recorded by the source corpus.

Feedback from massive stars is believed to be a key element in the evolution of molecular clouds. We use high-resolution 3D smoothed particle hydrodynamics simulations to explore the dynamical effects of a single O7 star-emitting ionizing photons at 1049 s−1 and located at the centre of a molecular cloud with mass 104 M⊙ and radius 6.4 pc; we also perform comparison simulations in which the ionizing star is removed. The initial internal structure of the cloud is characterized by its fractal dimension, which we vary between and 2.8, and the standard deviation of the approximately log-normal initial density PDF, which is σ10 = 0.38 for all clouds. (i) As regards star formation, in the short term ionizing feedback is positive, in the sense that star formation occurs much more quickly (than in the comparison simulations), in gas that is compressed by the high pressure of the ionized gas. However, in the long term ionizing feedback is negative, in the sense that most of the cloud is dispersed with an outflow rate of up to ∼10−2 M⊙yr−1, on a time-scale comparable with the sound-crossing time for the ionized gas (), and triggered star formation is therefore limited to a few per cent of the cloud's mass. We will describe in greater detail the statistics of the triggered star formation in a companion paper. (ii) As regards the morphology of the ionization fronts (IFs) bounding the H ii region and the systematics of outflowing gas, we distinguish two regimes. For low , the initial cloud is dominated by large-scale structures, so the neutral gas tends to be swept up into a few extended coherent shells, and the ionized gas blows out through a few large holes between these shells; we term these H ii regions shell dominated. Conversely, for high , the initial cloud is dominated by small-scale structures, and these are quickly overrun by the advancing IF, thereby producing neutral pillars protruding into the H ii region, whilst the ionized gas blows out through a large number of small holes between the pillars; we term these H ii regions pillar dominated. (iii) As regards the injection of bulk kinetic energy, by ∼1 Myr, the expansion of the H ii region has delivered a mass-weighted rms velocity of ∼6 km s−1; this represents less than 0.1 per cent of the total energy radiated by the O7 star.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ae3f33055607fa4de15647629685de5d5915451f

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Radiative feedback and the low efficiency of galaxy formation in low-mass haloes at high redshift (2013, background): “These HII regions expand due to a combination of photoionization and photoheating processes, as well as radiation pressure by the photons emitted from massive stars in young star clusters (Matzner 2002; Krumholz & Matzner 2009; Pellegrini et al. 2011; Walch et al. 2012).”
The SILCC (SImulating the LifeCycle of molecular Clouds) project – I. Chemical evolution of the supernova-driven ISM (2014, background): “…many of these clouds and exert strong feedback on the surrounding gas, in the form of UV radiation (Dale et al. 2005; Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013), stellar winds (Toalá & Arthur 2011; Rogers & Pittard 2013), and supernova (SN) explosions (Hill et al. 2012; Gatto et al.…”
The SILCC (SImulating the LifeCycle of molecular Clouds) project - II. Dynamical evolution of the supernova-driven ISM and the launching of outflows (2015, unknown): “Numerical studies support this paradigm and show efficient heating of the surroundings by OB stars (Dale et al. 2005; Peters et al. 2010; Arthur et al. 2011; Walch et al. 2012; Dale et al. 2014; Geen et al. 2015).”
TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS (2012, background): “…there is also plenty of evidence that dense star forming regions are destroyed by their HII regions, driven by ionization at low cluster masses (Walch et al. 2012) and radiation pressure, i.e. momentum transfer from radiation emitted by young massive stars to gas and dust (Murray et al. 2005),…”
ESCAPE FRACTION OF IONIZING PHOTONS DURING REIONIZATION: EFFECTS DUE TO SUPERNOVA FEEDBACK AND RUNAWAY OB STARS (2014, background): “Walch et al.(2012) claims that a 104M⊙ molecular cloud of the radius 6.4 pc can be dispersed on a 1-2 Myr timescale by the overpressure of HII regions.”
Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, background): “This creates an over-pressurised HII bubble that lowers the density of the ambient medium and drives winds with velocities up to 10 km s−1 (e.g. Krumholz et al. 2007; Walch et al. 2012; Dale et al. 2014).”
The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae (2016, background): “…ionizing radiation (e.g. Peters et al. 2010, 2011; ⋆ E-mail: walch@ph1.uni-koeln.de (SW); naab@mpa-garching.mpg.de (TN) Dale, Ercolano & Bonnell 2012; Walch et al. 2012, 2013; Dale et al. 2014; Geen et al. 2015), radiation pressure (e.g. Krumholz & Matzner 2009; Murray, Quataert & Thompson 2010;…”
The Formation and Destruction of Molecular Clouds and Galactic Star Formation (2015, background): “…al. (2012, 2013) have done extensive three dimensional simulations ofstar cluster formation with ionization or stellar wind feedbackand shown that the effects of photo-ionization and stellar winds are limited in quenching the star formation in massive molecular clouds (see also Walch et al. 2012).”
Before the first supernova: combined effects of H II regions and winds on molecular clouds (2014, unknown): “These results are similar to those obtained by Walch et al. (2012), who modelled the influence of photoionization on fractal clouds.”
Theoretical Challenges in Galaxy Formation (2016, background): “…clouds on short time-scales (Krumholz, Matzner & McKee 2006; Walch et al. 2012), however, over-dense regions of the surrounding ISM will also be compressed into clumps and pillars (Dale, Bonnell & Whitworth 2007; Gritschneder et al. 2010; Walch et al. 2012) making further coupling more difficult.”
Physical Processes in the Interstellar Medium (2014, background): “They can also influence the molecular cloud material that surrounds Ralf Klessen & Simon Glover 89 the young star cluster (e.g. Dale et al., 2005; Dale & Bonnell, 2011; Walch et al., 2012, 2013).”
Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “Similar structures have also been seen in previous numerical simulations of expanding H II regions in a turbulent medium (e.g., Mellema et al. 2006; Gritschneder et al. 2009, 2010; Walch et al. 2012).”