Surface Photometry and Radial Color Gradients of Nearby Luminous Early-type Galaxies in SDSS Stripe 82

TL;DR

This study uses SDSS Stripe 82 images to analyze surface brightness profiles and color gradients in nearby early-type galaxies, revealing complex radial color behaviors influenced by low-surface-brightness regions and merger histories.

Contribution

It provides detailed analysis of LSB areas in ETGs, showing their impact on profile fitting and color gradients, and highlights the importance of double-Sersic models for accurate characterization.

Findings

Majority of ETGs have negative color gradients within 1.5Re

LSB areas cause deviations from standard Sersic profiles

Many ETGs show opposite color gradients in inner and outer regions

Abstract

We make use of the images from the Sloan Digital Sky Survey Stripe 82 to present an analysis of r band surface brightness profiles and radial color gradients (g - r, u - r) in 111 nearby early-type galaxies (ETGs). With Stripe 82 images, we are able to pay special attentions to the low-surface-brightness areas (LSB areas) of the galaxies. The LSB areas make a difference to the Sersic fittings and concentration indices, making both the indices less than the typical values for ETGs. There are about 60% negative color gradients (red-core) within 1.5Re , much more than the approximately 10% positive ones (blue-core) within the same radius. However, taking into account of the LSB areas, we find that the color gradients are not necessarily monotonic: about one third of the red-core (or blue-core) galaxies have positive (or negative) color gradients in the outer areas. So LSB areas not only make ETGs' Sersic profiles deviate from de Vaucouleur ones and shift to the disk end, but also reveal that quite a number of ETGs have opposite color gradients in inner and outer areas. These outcomes remind us the necessity of double-Sersic fitting. These LSB phenomena may be interpreted by mergers and thus different metallicity in the outer areas. Isophotal parameters are also discussed briefly in this paper: more disky nearby ETGs are spotted than boxy ones.