Abstract
We describe the redmonster automated redshift measurement and spectral
classification software designed for the extended Baryon Oscillation
Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV). We
describe the algorithms, the template standard and requirements, and the newly
developed galaxy templates to be used on eBOSS spectra. We present results from
testing on early data from eBOSS, where we have found a 90.5% automated
redshift and spectral classification success rate for the luminous red galaxy
sample (redshifts 0.6 $łesssim$ $z$ $łesssim$ 1.0). The redmonster
performance meets the eBOSS cosmology requirements for redshift classification
and catastrophic failures, and represents a significant improvement over the
previous pipeline. We describe the empirical processes used to determine the
optimum number of additive polynomial terms in our models and an acceptable
$\Delta\chi_r^2$ threshold for declaring statistical confidence. Statistical
errors on redshift measurement due to photon shot noise are assessed, and we
find typical values of a few tens of km s$^-1$. An investigation of redshift
differences in repeat observations scaled by error estimates yields a
distribution with a Gaussian mean and standard deviation of $\mu\sim$ 0.01 and
$\sigma\sim$ 0.65, respectively, suggesting the accuracy of the statistical
redshift errors estimates are over-estimated by $\sim$ 54%. We assess the
effects of object magnitude, signal-to-noise ratio, fiber number, and fiber
head location on the pipeline's redshift success rate. Finally, we describe
directions of ongoing development.
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