Surface Brightness Profiles of Dwarf Galaxies: II. Color Trends and Mass Profiles

TL;DR

This study analyzes radial color and mass density profiles of 141 dwarf galaxies, revealing diverse surface brightness profile types and their relation to stellar mass density, with implications for galaxy evolution.

Contribution

It provides a detailed classification of dwarf galaxy surface brightness profiles and links color trends and mass density features to galaxy type and luminosity.

Findings

Type I dwarfs generally redden with radius, unlike spirals.

Type II dwarfs show six color trend variations, including 'U' shapes.

Type III dwarfs exhibit 'S'-shaped color profiles similar to spirals.

Abstract

In this second paper of a series, we explore the B-V, U-B, and FUV-NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies. Like spirals, dwarf galaxies have three types of radial surface brightness profiles: (I) single exponential throughout the observed extent (the minority), (II) down-bending (the majority), and (III) up-bending. We find that colors of (1) Type I dwarfs generally become redder with increasing radius unlike spirals that have a blueing trend that flattens beyond ~1.5 disk scale lengths, (2) Type II dwarfs come in six different "flavors," one of which mimics the "U" shape of spirals, and (3) Type III dwarfs have a stretched "S" shape where central colors are flattish, become steeply redder to the surface brightness break, then remain roughly constant beyond, similar to spiral TypeIII color profiles, but without the central outward bluing. Faint (-9 > M_B > -14) Type II dwarfs tend to have continuously red or "U" shaped colors and steeper color slopes than bright (-14 > M_B > -19) Type II dwarfs, which additionally have colors that become bluer or remain constant with increasing radius. Sm dwarfs and BCDs tend to have at least some blue and red radial color trend, respectively. Additionally, we determine stellar surface mass density (Sigma) profiles and use them to show that the break in Sigma generally remains in Type II dwarfs (unlike Type II spirals) but generally disappears in Type III dwarfs (unlike Type III spirals). Moreover, the break in Sigma is strong, intermediate, and weak in faint dwarfs, bright dwarfs, and spirals, respectively, indicating that Sigma may straighten with increasing galaxy mass. Lastly, the average stellar surface mass density at the surface brightness break is roughly 1-2 M_S/pc^2 for Type II dwarfs but higher at 5.9 M_S/pc^2 or 27 M_S/pc^2 for Type III BCDs and dIms, respectively.