Fast Automatic Redshift Determination Using Absorption Lines Recognition

To precisely measure the redshifts of non-ELGs (ELGs: emission-line galaxies), weaker-ELGs and galaxies with only one emission line that is clearly visible in the optical band, a fast automatic redshift determination algorithm (FRA) is proposed, which is different from the widely used cross-correlation method. The algorithm has higher speed because it determines the redshift by extracting and recognizing two pairs of prominent absorption lines in the blue band of a spectrum, G-band $\lambda$ 4306 and H ${\gamma}$ $\lambda$ 4342 (vacuum wavelength), H ${\beta}$ $\lambda$ 4863 and Mg $\lambda$ 5177, rather than through matching an observational galaxy spectrum with the complete galaxy templates. Moreover, a wide range of redshift measurements from 0 to 0.65 and relatively high success rates can be reached by FRA. For spectra with a relatively wide wavelength range and with a resolution above $R$ $=$ 1000, FRA is an efficient automatic algorithm that can be used in spectra redshift surveys with large amounts of data.