[论文解读] Towards DIB mapping in galaxies beyond 100 Mpc A radial profile of the lambda 5780.5 diffuse interstellar band in AM1353-272 B

A. Monreal‐Ibero, Peter M. Weilbacher+6 more|arXiv (Cornell University)|Nov 7, 2018

Astrophysics and Star Formation Studies参考文献 31被引用 10

一句话总结

本研究利用MUSE积分场光谱仪对距离159 Mpc的星系AM 1353-272B进行观测，首次在本星系群以外的星系中实现了对λ5780.5弥散星际带（DIB）的空间分辨检测。结果揭示了DIB等效宽度随径向减小，并与星际消光呈相关性，首次在外部盘状星系中证实了全局DIB-消光关系。

ABSTRACT

Context. Diffuse interstellar bands (DIBs) are non-stellar weak absorption features of unknown origin found in the spectra of stars viewed through one or several clouds of the interstellar medium (ISM). Research of DIBs outside the Milky Way is currently very limited. In particular, spatially resolved investigations of DIBs outside of the Local Group are, to our knowledge, inexistent. Aims. In this contribution, we explore the capability of the high-sensitivity integral field spectrograph, MUSE, as a tool for mapping diffuse interstellar bands at distances larger than 100 Mpc. Methods. We used MUSE commissioning data for AM1353-272 B, the member with the highest extinction of the Dentist's Chair, an interacting system of two spiral galaxies. High signal-to-noise spectra were created by co-adding the signal of many spatial elements distributed in a geometry of concentric elliptical half-rings. Results. We derived decreasing radial profiles for the equivalent width of the lambda 5780.5 DIB both in the receding and approaching side of the companion galaxy up to distances of similar to 4.6 kpc from the centre of the galaxy. The interstellar extinction as derived from the Ha/H beta line ratio displays a similar trend, with decreasing values towards the external parts. This translates into an intrinsic correlation between the strength of the DIB and the extinction within AM1353-272 B, consistent with the currently existing global trend between these quantities when using measurements for Galactic and extragalactic sightlines. Conclusions. It seems feasible to map the DIB strength in the Local Universe, which has up to now only been performed for the Milky Way. This offers a new approach to studying the relationship between DIBs and other characteristics and species of the ISM in addition to using galaxies in the Local Group or sightlines towards very bright targets outside the Local Group.

研究动机与目标

• 展示利用高灵敏度积分场光谱仪在100 Mpc以外的星系中实现空间分辨DIB测绘的可行性。
• 调查在星际介质（ISM）条件不同的星系中，银河系内观测到的DIB-消光相关性是否依然成立。
• 探索MUSE及类似仪器在具有空间分辨信息的河外环境中探测DIB的潜力。
• 评估金属丰度、辐射场和尘气比等星系参数对河外星系中DIB强度的影响。
• 为未来在本地宇宙范围内对星系开展2D DIB测绘奠定基础，推动超越银河系的ISM比较研究。

提出的方法

• 利用MUSE在AM 1353-272B（一个距离159 Mpc的低光度、高消光螺旋星系）的调试数据。
• 通过将分布在同心椭圆半环上的568个空间单元信号进行叠加，生成高信噪比光谱。
• 在距离星系中心约4.6 kpc以内的六个不同径向位置测量了λ5780.5 DIB的等效宽度（EW）。
• 通过Hα/Hβ线对的比值推导出星际消光，以与星系内DIB强度进行比较。
• 采用标准MUSE数据处理流程（偏置减除、平场校准、波长定标、通量校准），使用标准恒星和暮光平场进行处理。
• 构建了DIB等效宽度与消光的径向分布曲线，评估其在星系盘面内的相关性。

实验结果

研究问题

• RQ1 能否利用当前的积分场光谱仪在本星系群以外的星系中实现DIB的空间分辨测绘？
• RQ2 在星际介质条件各异的外部盘状星系中，银河系内观测到的DIB强度与星际消光之间的相关性是否依然存在？
• RQ3 在AM 1353-272B这类高消光、受星暴影响的星系中，DIB强度如何随星系不同区域变化？
• RQ4 金属丰度、辐射场和尘气比等星系参数在多大程度上调节河外星系中DIB-消光关系？
• RQ5 在河外星系中开展2D DIB测绘，是否能通过探测多样化的星际介质环境，有助于约束DIB载体的物理本质？

主要发现

• AM 1353-272B中λ5780.5 DIB的等效宽度从星系中心向外呈现径向减小趋势，在约4.6 kpc范围内，退行侧与蓝移侧均表现出一致的分布特征。
• 由Hα/Hβ线对比测得的星际消光也随向外区域而减小，与DIB变化趋势一致。
• 在AM 1353-272B内，DIB等效宽度与消光（E(B−V)）之间存在显著且内在的强相关性，其比值在整个星系范围内保持恒定，误差范围内无显著变化。
• AM 1353-272B中的DIB-消光关系与银河系、M31及其他河外视线观测到的全局趋势一致，尤其在螺旋星系的分辨研究中表现明显。
• AM 1353-272B的数据将DIB-消光关系延伸至更高的等效宽度和E(B−V)值，与本地星系群内大型螺旋星系的观测行为一致。
• 本研究证实，借助MUSE等高灵敏度仪器，对本星系群以外星系开展2D DIB测绘是可行的，为河外ISM研究开辟了新途径。