Empirical ugri-UBVRc Transformations for Galaxies

TL;DR

This paper develops empirical color transformations between SDSS ugri and Johnson-Cousins UBVRc filters specifically for nearby galaxies, addressing limitations of previous models by reducing systematic offsets and better matching observed galaxy colors.

Contribution

It provides new galaxy-specific transformations that improve accuracy over previous star-based or model-based methods.

Findings

Previous transformations show significant color scatter and systematic offsets.

LVL-based transformations eliminate systematic offsets and match observed color trends.

Transformations are tailored for non-starbursting, nearby galaxies.

Abstract

We present empirical color 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 colors are described by previous transformations derived from standard calibration stars and model-based galaxy templates. We find significant galaxy color scatter around most of the previous transformation relationships. In addition, the previous transformations show systematic offsets between transformed and observed galaxy colors which are visible in observed color-color trends. The LVL-based $galaxy$ transformations show no systematic color offsets and reproduce the observed color-color galaxy trends.