| 1. |
- Bisbas, T.G., et al.
(author)
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GMC Collisions as Triggers of Star Formation. V. Observational Signatures
- 2017
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In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 850:1, s. 23-32
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Journal article (peer-reviewed)abstract
- © 2017. The American Astronomical Society. All rights reserved.. We present calculations of molecular, atomic, and ionic line emission from simulations of giant molecular cloud (GMC) collisions. We post-process snapshots of the magnetohydrodynamical simulations presented in an earlier paper in this series by Wu et al. of colliding and non-colliding GMCs. Using photodissociation region (PDR) chemistry and radiative transfer, we calculate the level populations and emission properties of the transitions of 12 CO J = 1-0, [C i] at 609 μm, [C ii] 158 μm, and [O i] at 63 μm. From emission maps of integrated intensity and position-velocity diagrams, we find that fine-structure lines, particularly [C ii] 158 μm, can be used as a diagnostic tracer for cloud-cloud collision activity. These results hold even in more evolved systems in which the collision signature in molecular lines has been diminished.
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| 2. |
- Tanaka, K.E.I., et al.
(author)
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Outflow-confined H II Regions. II. The Early Break-out Phase
- 2017
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In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 849:2, s. 133-141
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Journal article (peer-reviewed)abstract
- © 2017. The American Astronomical Society. All rights reserved. In this series of papers, we model the formation and evolution of the photoionized region and its observational signatures during massive star formation. Here, we focus on the early breakout of the photoionized region into the outflow cavity. Using results of 3D magnetohydrodynamic-outflow simulations and protostellar evolution calculations, we perform a post-processing radiative transfer. The photoionized region first appears at a protostellar mass of m∗ = 10 M ⊙ in our fiducial model and is confined to within 10-100 au by the dense inner outflow, which is similar to some of the observed very small hypercompact H II regions. Since the ionizing luminosity of the massive protostar increases dramatically as the Kelvin-Helmholtz (KH) contraction proceeds, the photoionized region breaks out to the entire outflow region in ≲10,000 year. Accordingly, the radio free-free emission brightens significantly in this stage. In our fiducial model, the radio luminosity at 10 GHz changes from 0.1 mJy kpc 2 at m∗ = 11 M ⊙ to 100 mJy kpc 2 at m∗ = 16 M ⊙ , while the infrared luminosity increases by less than a factor of two. The radio spectral index also changes in the break-out phase from the optically thick value of ∼2 to the partially optically thin value of ∼0.6. Additionally, we demonstrate that short-timescale variation in the free-free flux would be induced by an accretion burst. The outflow density is enhanced in the accretion burst phase, which leads to a smaller ionized region and weaker free-free emission. The radio luminosity may decrease by one order of magnitude during such bursts, while the infrared luminosity is much less affected because internal protostellar luminosity dominates over accretion luminosity after the KH contraction starts. Such a variability may be observable on timescales as short 10-100 year if accretion bursts are driven by disk instabilities.
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