Empirical ugr i-UBV Rc transformations for galaxies

Abstract

We present empirical colour transformations between Sloan Digital Sky Survey ugri and Johnson-Cousins UBVRc photometry for nearby galaxies (D < 11 Mpc). We use the Local Volume Legacy (LVL) galaxy sample where there are 90 galaxies with overlapping observational coverage for these two filter sets. The LVL galaxy sample consists of normal, non-starbursting galaxies. We also examine how well the LVL galaxy colours are described by previous transformations derived from standard calibration stars and model-based galaxy templates. We find significant galaxy colour scatter around most of the previous transformation relationships. In addition, the previous transformations show systematic offsets between transformed and observed galaxy colours which are visible in observed colour-colour trends. The LVL-based galaxy transformations show no systematic colour offsets and reproduce the observed colour-colour galaxy trends.