The first analytical expression to estimate photometric redshifts suggested by a machine

Abstract

We report the first analytical expression purely constructed by a machine to determine photometric redshifts (Zphot) of galaxies. A simple and reliable functional form is derived using 41 214 galaxies from the Sloan Digital Sky Survey Data Release 10 (SDSS-DR10) spectroscopic sample. The method automatically dropped the u and z bands, relying only on g, r and i for the final solution. Applying this expression to other 1417 181 SDSS-DR10 galaxies, with measured spectroscopic redshifts (Zspec), we achieved a mean 〈 (Zphot - Zspec)/(1 + Zspec)〉 ≲ 0.0086 and a scatter σ(Zphot-Zspec)/(1+Zspec) ≲ 0.045 when averaged up to z ≲ 1.0. The method was also applied to the PHAT0 data set, confirming the competitiveness of our results when faced with other methods from the literature. This is the first use of symbolic regression in cosmology, representing a leap forward in astronomy-data-mining connection. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.