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arXiv 1909.01549astro-ph.GA
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M83环核上的化学演化

Chemical evolution along the circumnuclear ring of M83

Nanase Harada, Kazushi Sakamoto, Sergio Martin, Yoshimasa Watanabe, Rebeca Aladro, Denise Riquelme, Akihiko Hirota

摘要:

本文报道了对棒旋星系M83中心星际分子云演化及其恒星形成的天体化学研究。我们使用阿塔卡马大型毫米/亚毫米阵列(ALMA)对指示激波的分子种类(SiO,CH $_3$ OH)、致密核心(N $_2$ H $^+$)和光解离区域(CN和CCH)以及追踪活跃恒星形成区域的射电复合线(H41 $α$)进行成像。M83有一个环绕核的气体环,它在两个区域由来自棒上前缘气体通道的气流连接。我们在其中一个轨道交叉区域发现了激波和致密核示踪物的丰度升高,并在下游发现了CN和H41 $α$的峰值。在另一个轨道交叉区域,我们发现了类似的激波示踪物的增强,但其他示踪物的变化较小,并且没有活跃的恒星形成的迹象。我们建议,所观察到的化学变化或缺乏它是由于存在或不存在碰撞引起的分子云演化和诱导恒星形成。由于ALMA的分辨率和灵敏度,这项工作提出了棒星系环核环化学演化的最清晰的案例。

英文摘要:

We report an astrochemical study on the evolution of interstellar molecular clouds and consequent star formation in the center of the barred spiral galaxy M83. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to image molecular species indicative of shocks (SiO, CH$_3$OH), dense cores (N$_2$H$^+$), and photodissociation regions (CN and CCH), as well as a radio recombination line (H41$α$) tracing active star-forming regions. M83 has a circumnuclear gas ring that is joined at two areas by gas streams from the leading-edge gas lanes on the bar. We found elevated abundances of the shock and dense-core tracers in one of the orbit-intersecting areas, and found peaks of CN and H41$α$ downstream. At the other orbit-intersection area, we found similar enhancement of the shock tracers, but less variation of other tracers, and no sign of active star formation in the stream. We propose that the observed chemical variation or lack of it is due to the presence or absence of collision-induced evolution of molecular clouds and induced star formation. This work presents the most clear case of the chemical evolution in the circumnuclear rings of barred galaxies, thanks to the ALMA resolution and sensitivity.

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