基于叠加的河外星系中性氢(HI)谱线数据处理方法  

Extragalactic HI spectra data processing method based on Stacking

作　　者：郭元旗 朱明[1,2] 艾美[1,2] GUO YuanQi;ZHU Ming;AI Mei(National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China;CAS Key Laboratory of FAST,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院国家天文台,北京100012 [2]中国科学院FAST重点实验室,北京100012 [3]中国科学院大学,北京100049

出　　处：《中国科学：物理学、力学、天文学》2018年第11期100-110,共11页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家重点基础研究发展计划(编号：2017YFA0402600)和国家自然科学基金(批准号：U153124-6)资助项目

摘　　要：中性氢(HI)巡天是探测宇宙气体大尺度结构的重要手段.在对河外星系进行HI巡天的过程中,由于信号本身非常弱,再加上望远镜灵敏度的限制,导致观测数据中大量星系的HI谱线信号被湮没在噪声之中,无法直接观测到.但是利用谱线叠加技术就可以通过叠加一些已知光学红移和位置的星系来提高谱线的信噪比.本文所要介绍的就是将一个星系群中所有成员星系的HI谱线进行叠加得到合成HI谱线的方法.通过这种方法获得的叠加谱线就是该星系群中总的HI辐射.叠加后的谱线由于rms水平的降低而获得比单一成员星系的谱线更高的信噪比,从而使一些在原来单条谱线中并不明显的HI信号在叠加后的合成谱线中显现出来,达到S/N> 4.5的水平.谱线叠加过程涉及了大量数据的批量处理,因此我们开发了相关的自动化软件,用来处理美国Arecibo望远镜ALFALFA中性氢巡天观测的数据,成功得到了80多个选自SDSS观测星表的星系群样本的叠加谱线.预计未来我国的FAST望远镜巡天将产生大量的中性氢谱线数据,这一软件将会在大批量处理FAST河外星系HI谱线叠加方面发挥重要作用.Blind HI survey is a powerful tool for exploring the HI universe. During the extragalactic HI survey, due to the weakness of HI signal and the limitation of telescope sensibility, most HI emissions from galaxies are overwhelmed by noise signals and cannot be directly detected. However, using the technique of spectral stacking, we can increase the the signal-to-noise ratio （SNR） by co-adding a set of spectra if the optical redshifts and position are known. This paper presents a method to derive the integrated HI emission in a galaxy group by stacking all the HI spectra of the member galaxies in the group. This method can generate a stacked spectrum representing the total HI emission of the group. The s-acked spectrum have a lower rms noise level and thus higher S/N ratio than that of the individual member galaxies, i-tt＇some cases, the integrated HI emission shows clear detection （S/N〉4.5） in the stacked spectrum even though no detection is visible in the spectrum of individual member galaxy in the group. We have also developed a software code to automatically handle the stacking of large amount spectra in galaxy groups. As an example, we use this software to derive the stacked HI spectra of 80 galaxy groups selected from the SDSS galaxy group catalog, of which the HI data are from the ALFALFA HI survey. Such software will be a valuable tool to process the stacking of large mount of HI spectra from the future extragalactic HI survey with the Five hundred meter Aperture Spherical radio Telescope （FAST）.

关 键 词：中性氢 谱线 叠加 河外星系 

分 类 号：P15[天文地球—天文学] P148