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A kinematic analysis of the CO clouds toward a reflection nebula NGC 2023 observed using the Nobeyama 45 m telescope: Further evidence for a cloud–cloud collision in the Orion region
Publications of the Astronomical Society of Japan ( IF 2.2 ) Pub Date : 2021-05-18 , DOI: 10.1093/pasj/psab050
Rin I Yamada 1 , Rei Enokiya 1, 2 , Hidetoshi Sano 1, 3 , Shinji Fujita 1, 4 , Mikito Kohno 1, 5 , Daichi Tsutsumi 1 , Atsushi Nishimura 4, 6 , Kengo Tachihara 1 , Yasuo Fukui 1, 7
Affiliation  

We performed fully sampled J = 1–0 line observations of 12CO and 13CO toward the reflection nebula NGC 2023 using the Nobeyama 45 m telescope. It covered the entire NGC 2023 region with angular and velocity resolutions of 19″ corresponding to 0.04 pc and 0.33 km s−1, respectively. We analyzed the data focusing on gas dynamics and revealed two velocity components, each with a mass of $\sim\! 3000 \mbox{$\, {M}_\odot $}$, at radial velocities of 10 and 12 km s−1. These components show spatially complementary distributions and are connected in velocity, both of which are the typical signatures of cloud–cloud collision (CCC). Although previous studies favored a scheme of triggering by the H ii region of IC 434, our results show that the effect of the H ii region is limited only to the surface of the molecular cloud, and does not contribute to the entire gas compression and the overall star formation. Comparing the present results with those for neighboring NGC 2024, we find that their active star formation can be explained by a single CCC event. We suggest that the 10 and 12 km s−1 clouds collided ∼0.4 Myr ago, which is common to the regions, but triggered the B1.5V-type star HD 37903 as well as ∼20 low-mass stars in NGC 2023, and ∼20 OB stars in NGC 2024. The column density in NGC 2023 is two to three times lower than that of NGC 2024, which may result in the different star formation activity suggested by the trend of ∼50 other CCC-triggered star-forming regions in the literature.

中文翻译:

使用 Nobeyama 45 m 望远镜观测到的对反射星云 NGC 2023 的 CO 云的运动学分析:猎户座地区云-云碰撞的进一步证据

我们使用 Nobeyama 45 m 望远镜对反射星云 NGC 2023 进行了完全采样的 J = 1-0 线观测。它覆盖了整个 NGC 2023 区域,角和速度分辨率为 19 英寸,分别对应于 0.04 pc 和 0.33 km s-1。我们分析了侧重于气体动力学的数据并揭示了两个速度分量,每个分量的质量为 $\sim\! 3000 \mbox{$\, {M}_\odot $}$,径向速度为 10 和 12 km s-1。这些分量显示出空间互补分布并在速度上相互关联,这两者都是云-云碰撞 (CCC) 的典型特征。虽然之前的研究支持由 IC 434 的 H ii 区域触发的方案,但我们的结果表明,H ii 区域的影响仅限于分子云的表面,并且对整个气体压缩和整个恒星形成没有贡献。将目前的结果与邻近 NGC 2024 的结果进行比较,我们发现它们的活跃恒星形成可以通过单个 CCC 事件来解释。我们认为 10 和 12 km s−1 的云在 ∼0.4 Myr 前发生碰撞,这在该地区很常见,但触发了 B1.5V 型恒星 HD 37903 以及 NGC 2023 中的 20 颗低质量恒星,并且NGC 2024中有~20个OB星。NGC 2023中的柱密度比NGC 2024低两到三倍,这可能导致其他~50个CCC触发的恒星形成区域的趋势所暗示的不同恒星形成活动在文献中。我们发现它们活跃的恒星形成可以用一个 CCC 事件来解释。我们认为 10 和 12 km s−1 的云在 ∼0.4 Myr 前发生碰撞,这在该地区很常见,但触发了 B1.5V 型恒星 HD 37903 以及 NGC 2023 中的 20 颗低质量恒星,并且NGC 2024中有~20个OB星。NGC 2023中的柱密度比NGC 2024低两到三倍,这可能导致其他~50个CCC触发的恒星形成区域的趋势所暗示的不同恒星形成活动在文献中。我们发现它们活跃的恒星形成可以用一个 CCC 事件来解释。我们认为 10 和 12 km s−1 的云在 ∼0.4 Myr 前发生碰撞,这在该地区很常见,但触发了 B1.5V 型恒星 HD 37903 以及 NGC 2023 中的 20 颗低质量恒星,并且NGC 2024中有~20个OB星。NGC 2023中的柱密度比NGC 2024低两到三倍,这可能导致其他~50个CCC触发的恒星形成区域的趋势所暗示的不同恒星形成活动在文献中。
更新日期:2021-05-18
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