[论文解读] A Survey of HC3N in Extragalactic Sources - Is HC3N a Tracer of Activity in ULIRGs?

J. E. Lindberg, S. Aalto+4 more|arXiv (Cornell University)|Jan 10, 2011

Astrophysics and Star Formation Studies参考文献 56被引用 19

一句话总结

本研究首次对河外星系中的HC3N进行了调查，发现高HC3N/HCN线亮度比与超亮红外星系（ULIRGs）及巨脉泽活动强烈相关，表明HC3N可追踪尘埃包裹核区的早期嵌入式恒星形成。该分子的存活与温暖、受屏蔽的环境有关，具有高尘埃温度和硅酸盐吸收特征，表明其在高度遮蔽星系中具有作为核活动示踪剂的潜力。

ABSTRACT

Context. HC3N is a molecule that is mainly associated with Galactic star-forming regions, but it has also been detected in extragalactic environments. Aims. To present the first extragalactic survey of HC3N, when combining earlier data from the literature with six new single-dish detections, and to compare HC3N with other molecular tracers (HCN, HNC), as well as other properties (silicate absorption strength, IR flux density ratios, C II flux, and megamaser activity). Methods. We present mm IRAM 30 m, OSO 20 m, and SEST observations of HC3N rotational lines (mainly the J = 10-9 transition) and of the J = 1-0 transitions of HCN and HNC. Our combined HC3N data account for 13 galaxies (excluding the upper limits reported for the non-detections), while we have HCN and HNC data for more than 20 galaxies. Results. A preliminary definition "HC3N-luminous galaxy" is made based upon the HC3N/HCN ratio. Most (~80 %) HC3N-luminous galaxies seem to be deeply obscured galaxies and (U)LIRGs. A majority (~60 % or more) of the HC3N-luminous galaxies in the sample present OH mega- or strong kilomaser activity. A possible explanation is that both HC3N and OH megamasers need warm dust for their excitation. Alternatively, the dust that excites the OH megamaser offers protection against UV destruction of HC3N. A high silicate absorption strength is also found in several of the HC3N-luminous objects, which may help the HC3N to survive. Finally, we find that a high HC3N/HCN ratio is related to a high dust temperature and a low C II flux.

研究动机与目标

• 对河外源中的HC3N开展首次全面调查，结合新观测数据与文献数据。
• 探究HC3N是否可作为深度遮蔽星系（特别是ULIRGs）中核活动的可靠示踪剂。
• 探索HC3N发射与其它分子示踪剂（HCN、HNC）、尘埃特性（硅酸盐吸收）及活动指标（巨脉泽、CII通量）之间的相关性。
• 评估尘埃温度与屏蔽在极端环境中HC3N的存活与激发中的作用。
• 评估HC3N/HCN线亮度比作为识别活跃星系中早期嵌入式恒星形成诊断工具的潜力。

提出的方法

• 利用IRAM 30 m、OSO 20 m和SEST望远镜进行毫米波单镜面观测，探测HC3N的转动跃迁，主要为J=10-9跃迁。
• 在同一星系中同步观测HCN和HNC的J=1-0跃迁，以实现线亮度比的比较。
• 将新检测结果与现有文献数据结合，形成一个包含13个确认HC3N发射的星系样本。
• 采用辐射转移与激发建模方法解释线强度，同时考虑HC3N的转动与振动激发。
• 将HC3N/HCN线亮度比与尘埃温度（来自红外SED）、硅酸盐吸收强度、CII通量及巨脉泽活动进行相关分析。
• 应用统计分析识别HC3N丰度指标与核活动诊断参数之间的趋势。

实验结果

研究问题

• RQ1 HC3N是否是ULIRGs及其他遮蔽星系中核活动的可靠示踪剂？
• RQ2 HC3N发射与河外源中巨脉泽活动之间存在何种关系？
• RQ3 尘埃温度与硅酸盐吸收如何影响星系核区HC3N的可探测性与存活率？
• RQ4 HC3N/HCN线亮度比在多大程度上与恒星形成或AGN活动的其他指标相关？
• RQ5 HC3N的振动激发能否提供关于被遮蔽红外源强度与温度结构的见解？

主要发现

• 样本中约80%的HC3N高 luminosity 星系被归类为ULIRGs或深度遮蔽的星暴星系。
• 约60%或更多的HC3N高 luminosity 星系表现出OH巨脉泽或强千脉泽活动，表明其激发机制可能涉及温暖尘埃。
• 高HC3N/HCN线亮度比与高尘埃温度及低CII/FIR通量比强烈相关，表明C+可能在HC3N破坏中起作用。
• HC3N高 luminosity 源表现出增强的硅酸盐吸收（A_9.7μm > 1），表明尘埃屏蔽可保护HC3N免受紫外辐射破坏。
• HC3N/HCN与HNC/HCN线亮度比之间存在显著相关性，暗示这些分子物种在致密、受屏蔽区域中的共同演化。
• 在若干源（如NGC 4418、Arp 220、IC 860）中检测到HC3N的振动激发，证实红外泵浦在激发过程中的重要性。