基于多分辨率融合距离的低质量星系光谱红移测量方法

A New Redshift Measuring Method for Low-Quality Galaxy Spectra Based on Multi Resolution Fusion Distance

星系光谱红移测量是大规模天体光谱巡天项目中的一个重要研究内容,其目的是从在光谱中测量出对应星系由于多普勒效应引起的红移。随着银河系外巡天项目的开展,观测目标距离(红移)越来越远,其星等越来越暗,光谱的质量也随之越来越差,如何能够有效准确地从这些低质量的光谱测量出红移是河外巡天面临的一个重要问题。基于此问题,充分考虑到低质量星系光谱的特点及数据特征,新定义了一种针对低质量巡天光谱数据的多分辨率融合距离,以此为基础提出一种针对低质量星系光谱的红移测量方法。该方法充分结合不同分辨率下光谱的特征,计算距离时首先将模板光谱和待测光谱同时降到多个相同分辨率下,该分辨率下所有波长采样点都计算一个偏差进而得到一个距离,然后将多个分辨率下得到的距离通过加权得到一个融合距离。基于多分辨率融合距离提出的星系红移测量方法,能够有效的解决低质量星系光谱的红移无法准确测量的问题。研究了不同信噪比下红移测量的精度,在信噪比大于5之后,该方法测量准确率可以达到90%以上。大量实验表明,提出的方法在星系光谱质量较低的情况可以非常准确地从中测量出红移,测量误差和红移大小无关,可以很好地应用于大规模巡天数据的星系光谱红移测量中。

The redshift measurement of galaxy spectrum is a key issue in large astronomical spectral survey.Its goal is to extract the redshift from spectrum,which is caused the Doppler Effect.With the development of the extragalactic sky survey project,the distance（redshift）of the observed targets is becoming further.As a result,the magnitude of the observed objects becomes darker and the spectral quality becomes poorer.Therefore,how to effectively and accurately measure the redshift from these low quality spectra is becoming an important problem in the extragalactic survey.Considering the spectral features and the data character,a new definition of multi-resolution fusion distance for low quality spectra is proposed.In this paper,we put forward a redshift measuring method for low quality galaxy spectra.This method combines the spectral features with different resolutions.The template spectrum and the spectrum to measure are reduced to the resolution and then a distance is computed by combining the offset of the above two spectra in different wavelengths.Then,a fusion distance is weighted averaged from the distances with different resolutions.In this paper,the effect of signal-to-noise ratio（SNR）on the measuring accuracy of the proposed method is discussed.The measuring accuracy is larger than 90% when the SNR is larger than 5.A large number of experiments show that the method proposedin this paper is very efficient in measuring the redshift of the low-quality galaxy spectra and the measuring error has nothing to do with the redshift value.The proposed method can be applied in redshift measurement of galaxies for the large-scale survey data.