The color gradients of spiral disks in the Sloan Digital Sky Survey

TL;DR

This study analyzes the radial color gradients in about 20,000 face-on spiral galaxies from SDSS, revealing that most have negative color gradients independent of morphology, but dependent on surface brightness, offering constraints for galaxy evolution models.

Contribution

It provides the first large-scale statistical analysis of disk color gradients, linking them to surface brightness and offering new observational constraints for galaxy formation theories.

Findings

Most galaxies show negative color gradients.

Color gradients depend on surface brightness, not morphology.

Quantified correlations between color gradients and surface brightness.

Abstract

We investigate the radial color gradients of galactic disks using a sample of about 20,000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentration, size and luminosity to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3 kpc), almost all galaxies show negative disk color gradients with mean g-r gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}=-0.018 mag kpc^{-1}. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness \mu_{d}, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as G_{gr}=-0.011\mu_{d}+0.233 and G_{rz}=-0.015\mu_{d}+0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.