The GALEX/S4G Surface Brightness and Color Profiles Catalog - I. Surface Photometry and Color Gradients of Galaxies

TL;DR

This paper provides a comprehensive catalog of surface brightness and color profiles for nearly 2000 nearby galaxies, analyzing their structure, star formation activity, and evolutionary states using multi-wavelength photometry.

Contribution

It introduces a new dataset combining GALEX and Spitzer data, enabling detailed analysis of galaxy surface brightness, color gradients, and bulge-disk separation with comparisons to evolutionary models.

Findings

Exponential disk components can be isolated using specific surface brightness and mass density thresholds.

Distributions of galaxy spin and circular velocity are consistent within a factor of two with kinematic measurements.

Many Green Valley galaxies show a radial decline in star formation rate, indicating outside-in quenching mechanisms.

Abstract

We present new, spatially resolved, surface photometry in FUV and NUV from images obtained by the $\textit{Galaxy Evolution Explorer}$ (GALEX), and IRAC1 (3.6 $\mu$m) photometry from the $\textit{Spitzer Survey of Stellar Structure in Galaxies}$ (S$^{4}$G) (Sheth et al. 2010). We analyze the radial surface brightness profiles $\mu_{FUV}$, $\mu_{NUV}$, and $\mu_{[3.6]}$, as well as the radial profiles of (FUV $-$ NUV), (NUV $-$ [3.6]), and (FUV $-$ [3.6]) colors in 1931 nearby galaxies (z $<$ 0.01). The analysis of the 3.6 $\mu$m surface brightness profiles also allows us to separate the bulge and disk components in a quasi-automatic way, and to compare their light and color distribution with those predicted by the chemo-spectrophotometric models for the evolution of galaxy disks of Boissier & Prantzos (2000). The exponential disk component is best isolated by setting an inner radial cutoff and an upper surface brightness limit in stellar mass surface density. The best-fitting models to the measured scale length and central surface brightness values yield distributions of spin and circular velocity within a factor of two to those obtained via direct kinematic measurements. We find that at a surface brightness fainter than $\mu_{[3.6]}=20.89$ mag arcsec$^{-2}$, or below $3\times 10^{8}$ $M_{\odot}$ kpc$^{-2}$ in stellar mass surface density, the average specific star formation rate for star forming and quiescent galaxies remains relatively flat with radius. However, a large fraction of GALEX Green Valley galaxies (defined in Bouquin et al. 2015) shows a radial decrease in specific star formation rate. This behavior suggests that an outside-in damping mechanism, possibly related to environmental effects, could be testimony of an early evolution of galaxies from the blue sequence of star forming galaxies towards the red sequence of quiescent galaxies.