Driving conditions of protostellar outflows in different star-forming environments. Issue 3 (17th April 2019)

• Record Type: Journal Article
• Authors: Higuchi, Koki; Machida, Masahiro N; Susa, Hajime
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 486:Issue 3(2019)
• Page Start: 3741
• Page End: 3754
• Publication Date: 2019-04-17
• Subjects: MHD -- stars: magnetic field -- stars: Population II -- stars: Population III; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz1079
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: The evolution of collapsing clouds embedded in different star-forming environments is investigated using three-dimensional non-ideal magnetohydrodynamics simulations considering different cloud metallicities ($\mathrm{\mathit{ Z}}/\, \mathrm{Z}_\odot$ = 0, 10 −5, 10 −4, 10 −3, 10 −2, 10 −1, and 1) and ionization strengths ( C ζ = 0, 0.01, 1, and 10, where C ζ is a coefficient controlling the ionization intensity and C ζ = 1 corresponds to the ionization strength of nearby star-forming regions). With all combinations of these considered values of$\mathrm{\mathit{ Z}}/\, \mathrm{Z}_\odot$ and C ζ, 28 different star-forming environments are prepared and simulated. The cloud evolution in each environment is calculated until the central density reaches$n\approx 10^{16}\, {\rm cm}^{-3}$ just before protostar formation, and the outflow driving conditions are derived. An outflow appears when the (first) adiabatic core forms in a magnetically active region where the magnetic field is well coupled with the neutral gas. In cases where outflows are driven, their momentum fluxes are always comparable to the observations of nearby star-forming regions. Thus, these outflows should control the mass growth of the protostars as in the local universe. Roughly, an outflow appears when$\mathrm{\mathit{ Z}}/\, \mathrm{Z}_\odot \gt 10^{-4}$ and C ζ ≥ 0.01. It is expected that the transition of the star formation mode from massive stars to normal solar-type stars occurs when the cloud metallicity is enhanced to the range of$\mathrm{\mathit{ Z}}/\, \mathrm{Z}_\odot \approx 10^{-4}$ –10 −3, above which relatively low-mass stars would preferentially appear as a result of strong mass ejection.