中红外低分辨光谱红移的自动测量
Automated measurement of redshift from mid-infrared low resolution spectroscopy
摘要：
我们提出了一个新的SED拟合为基础的例行红移测定，优化中红外（MIR）低分辨率光谱。其灵活的模板缩放增加了对光谱中斜率变化和小尺度特征的敏感性，而与标准最大似然（ML）方法相比，称为最大组合伪似然（MCPL）的新选择算法提供了更高的准确性和更少的离群值。与ML不同，MCPL搜索“伪似然”（PL）函数的局部（而不是绝对）最大值，并结合库中所有模板获得的结果，以消除虚假的红移解决方案。通过将其结果与常规ML的结果以及来自0<z<3.7的源的491个Spitzer/IRS光谱的光谱红移进行比较，证明了MCPL的能力。MCPL对样本中78%的星系实现了dz/（1+z）<0.005的红移精度，而ML为68%。异常值率（dz/（1+z）>0.02）对于MCPL为14%，对于ML为22%。ML解的卡方2值与光谱的信噪比相关，但与红移精度无关。相比之下，归一化的组合PL（伽马）的峰值被发现提供了一个很好的指示MCPL解决方案的可靠性，为个别来源。红移的准确性和可靠性在很大程度上取决于MIR SED。与活动星系核连续体主导的源相比，具有显著多环芳烃排放的源获得了更好的结果。然而，对于一个给定的伽玛的准确的解决方案和离群值的频率在很大程度上是独立于他们的SED类型。MCPL解决方案的可靠性指标允许选择具有高度可靠红移的子样本。特别地，gamma>0.15阈值保留了79%的dz/（1+z）<0.005的源，同时将离群值率降低到3.8%（删节）。
英文摘要：
We present a new SED-fitting based routine for redshift determination that is optimised for mid-infrared (MIR) low-resolution spectroscopy. Its flexible template scaling increases the sensitivity to slope changes and small scale features in the spectrum, while a new selection algorithm called Maximum Combined Pseudo-Likelihood (MCPL) provides increased accuracy and a lower number of outliers compared to the standard maximum-likelihood (ML) approach. Unlike ML, MCPL searches for local (instead of absolute) maxima of a 'pseudo-likelihood' (PL) function, and combines results obtained for all the templates in the library to weed out spurious redshift solutions. The capabilities of MCPL are demonstrated by comparing its results to those of regular ML and to the optical spectroscopic redshifts of a sample of 491 Spitzer/IRS spectra from sources at 0<z<3.7. MCPL achieves a redshift accuracy dz/(1+z)<0.005 for 78% of the galaxies in the sample compared to 68% for ML. The rate of outliers (dz/(1+z)>0.02) is 14% for MCPL and 22% for ML. chi^2 values for ML solutions are found to correlate with the SNR of the spectra, but not with redshift accuracy. By contrast, the peak value of the normalised combined PL (gamma) is found to provide a good indication on the reliability of the MCPL solution for individual sources. The accuracy and reliability of the redshifts depends strongly on the MIR SED. Sources with significant polycyclic aromatic hydrocarbon emission obtain much better results compared to sources dominated by AGN continuum. Nevertheless, for a given gamma the frequency of accurate solutions and outliers is largely independent on their SED type. This reliability indicator for MCPL solutions allows to select subsamples with highly reliable redshifts. In particular, a gamma>0.15 threshold retains 79% of the sources with dz/(1+z)<0.005 while reducing the outlier rate to 3.8% (abridged).
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