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arXiv 1801.05941astro-ph.GA
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夜光并合星NGC 3256的ALMA天体化学观测

ALMA Astrochemical Observations of the Infrared-Luminous Merger NGC 3256

Nanase Harada, Kazushi Sakamoto, Sergio Martin, Susanne Aalto, Rebeca Aladro, Kazimierz Sliwa

摘要:

在外部星系中,分子组成可能会受到极端环境的影响,如恒星爆发和星系合并。为了研究这样的分子化学,我们使用阿塔卡玛大型毫米/亚毫米阵列观测了发光红外星系和合并的NGC 3256。我们覆盖了大部分的3毫米和1.3毫米波段的多物种,多过渡分析。我们首先分析了选定的线,如HCN/HCO $^+$,这表明没有增强活动星系核的强度比地图。然后,我们比较了NGC 3256内的两个原子核,潮汐臂和位置的化学成分与银河系外流的影响。我们发现最大的变化在SiO和CH $_3$ OH,物种可能会被增强的冲击。接下来,我们比较了NGC 3256、NGC 253和Arp 220星系核的化学成分;这些星系核具有不同的恒星形成效率。Arp 220的SiO和HC $_3$ N丰度高于NGC 3256和NGC 253。大多数物种的丰度与恒星形成效率没有很强的相关性,但CH $_3$ CCH丰度似乎与恒星形成效率有弱的正相关性。最后,将NGC 3256的旋臂位置与银河系分子云复合体W 51的旋臂位置进行了比较,发现NGC 3256中激波示踪物的丰度比W 51高,致密气体的丰度也可能比W 51高。

英文摘要:

In external galaxies, molecular composition may be influenced by extreme environments such as starbursts and galaxy mergers. To study such molecular chemistry, we observed the luminous-infrared galaxy and merger NGC 3256 using the Atacama Large Millimeter/sub-millimeter Array. We covered most of the 3-mm and 1.3-mm bands for a multi-species, multi-transition analysis. We first analyzed intensity ratio maps of selected lines such as HCN/HCO$^+$, which shows no enhancement at an AGN. We then compared the chemical compositions within NGC 3256 at the two nuclei, tidal arms, and positions with influence from galactic outflows. We found the largest variation in SiO and CH$_3$OH, species that are likely to be enhanced by shocks. Next, we compared the chemical compositions in the nuclei of NGC 3256, NGC 253, and Arp 220; these galactic nuclei have varying star formation efficiencies. Arp 220 shows higher abundances of SiO and HC$_3$N than NGC 3256 and NGC 253. Abundances of most species do not show strong correlation with the star formation efficiencies, although the CH$_3$CCH abundance seems to have a weak positive correlation with the star formation efficiency. Lastly, the chemistry of spiral arm positions in NGC 3256 is compared with that of W 51, a Galactic molecular cloud complex in a spiral arm. We found higher fractional abundances of shock tracers, and possibly also higher dense gas fraction in NGC 3256 compared with W 51.

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