Analysis of the Spatially Resolved V−3.6 μm Colors and Dust Extinction in 257 Nearby NGC and IC Galaxies

Abstract

We present and analyze spatially resolved maps for the observed V - and g -band to 3.6 μ m flux ratios and the inferred dust-extinction values, A V , for a sample of 257 nearby NGC and IC galaxies. Flux ratio maps are constructed using point-spread function-matched mosaics of Sloan Digital Sky Survey g - and r -band images and Spitzer /InfraRed Array Camera 3.6 μ m mosaics, with all pixels contaminated by foreground stars or background objects masked out. By applying the β V method, which was recently calibrated as a function of redshift and morphological type by Kim et al., dust-extinction maps were created for each galaxy. The typical 1 σ scatter in β V around the average, both within a galaxy and in each morphological type bin, is ∼20%. Combined, these result in a ∼0.4 mag scatter in A V . β V becomes insensitive to small-scale variations in stellar populations once resolution elements subtend an angle larger than that of a typical giant molecular cloud (∼200 pc). We find noticeably redder V −3.6 μ m colors in the center of star-forming galaxies and galaxies with a weak active galactic nucleus. The derived intrinsic V −3.6 μ m colors for each Hubble type are generally consistent with the model predictions of Kim et al. Finally, we discuss the applicability of the β V dust-correction method to more distant galaxies, for which well-matched Hubble Space Telescope rest-frame visible and James Webb Space Telescope rest-frame ∼3.5 μ m images will become available in the near-future.