http://arxiv.org/abs/1706.05664
We carried out a molecular line study toward the high-mass star forming regions with reflection nebulae, NGC2068 and NGC2071, in Orion with NANTEN2 in the $^{13} \rm CO (\it J\rm=2-1)$transition. The $^{13} \rm CO$ distribution shows that there are two velocity components at $8.25$ km s$^{-1}$ and $11.5$ km s$^{-1}$. The blue-shifted \textcolor{blue}{component} is in the northeast associated with NGC2071, and the red-shifted \textcolor{blue}{component} is in the southwest associated with NGC2068. The two clouds have a gap of $\sim 1$ pc in total intensity distribution, suggesting that they are detached at present. A detailed spatial comparison between them indicates that the two show complementary distribution, the blue-shifted \textcolor{blue}{component} lies toward an intensity depression in the northwest of the red-shifted \textcolor{blue}{component}, where we find that a displacement of \textcolor{red}{$0.6$} pc nearly along the Galactic plane makes the two clouds fit well with each other. Based on these results we hypothesize that the two components collided with each other at a projected relative velocity $2.5$ km s$^{-1}$. The timescale of the collision is estimated to be $4 \times10^5$ yrs for an assumed angle 45 deg of the relative motion to the line of sight. We assume that the two most massive early B–type stars in the cloud, illuminating stars of the two reflection nebulae, were formed by the collisional triggering at the \textcolor{red}{interfaces} between the two clouds. Along with the other young high-mass star forming regions, M42, M43, and NGC2024 (Fukui et al. (2017) , Ohama et al. 2017 in prep), it seems possible that collisional triggering is independently working to form O–type and early B–type stars in Orion in the last Myr over a projected distance of $\sim 80$ pc.
D. Tsutsumi, A. Ohama, K. Okawa, et. al.
Tue, 20 Jun 17
51/72
Comments: 17peges, 6 figures
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