Ultraviolet escape fractions from giant molecular clouds during early cluster formation

• Verfasst von: Howard, Corey S. [VerfasserIn]
• Verfasst von: Pudritz, Ralph E. [VerfasserIn]
• Verfasst von: Klessen, Ralf S. [VerfasserIn]
• Titel: Ultraviolet escape fractions from giant molecular clouds during early cluster formation
• Verf.angabe: Corey Howard, Ralph Pudritz, and Ralf Klessen
• E-Jahr: 2017
• Jahr: 2017 January 1
• Umfang: 9 S.
• Fussnoten: Gesehen am 26.10.2017
• Titel Quelle: Enthalten in: The astrophysical journal / 1
• Ort Quelle: London : Institute of Physics Publ., 1996
• Jahr Quelle: 2017
• Band/Heft Quelle: 834(2017,1) Artikel-Nummer 40, 9 Seiten
• ISSN Quelle: 1538-4357
• DOI: doi:10.3847/1538-4357/834/1/40
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1564804062

Abstract

The UV photon escape fraction from molecular clouds is a key parameter for understanding the ionization of the interstellar medium and extragalactic processes such as cosmic reionization. We present the ionizing photon flux and the corresponding photon escape fraction ( f esc ) arising as a consequence of star cluster formation in a turbulent, 10 6 M ⊙ giant molecular cloud, simulated using the code FLASH. We make use of sink particles to represent young, star-forming clusters coupled with a radiative transfer scheme to calculate the emergent UV flux. We find that the ionizing photon flux across the cloud boundary is highly variable in time and space due to the turbulent nature of the intervening gas. The escaping photon fraction remains at ∼5% for the first 2.5 Myr, followed by two pronounced peaks at 3.25 and 3.8 Myr with a maximum f esc of 30% and 37%, respectively. These peaks are due to the formation of large H ii regions that expand into regions of lower density, some of which reaching the cloud surface. However, these phases are short-lived, and f esc drops sharply as the H ii regions are quenched by the central cluster passing through high-density material due to the turbulent nature of the cloud. We find an average f esc of 15% with factor of two variations over 1 Myr timescales. Our results suggest that assuming a single value for f esc from a molecular cloud is in general a poor approximation, and that the dynamical evolution of the system leads to large temporal variation.