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 µm 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 PSF-matched mosaics of SDSS gand r-band images and Spitzer/IRAC 3.6 µm mosaics, with all pixels contaminated by foreground stars or background objects masked out. By applying the β V method (Tamura et al. 2009(Tamura et al. , 2010, which was recently calibrated as a function of redshift and morphological type by Kim, Jansen, & Windhorst (2017), 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 µm colors in the center of star-forming galaxies and galaxies with a weak AGN. The derived intrinsic V −3.6 µm colors for each Hubble type are generally consistent with the model predictions of Kim et al. (2017). Finally, we discuss the applicability of the β V dust-correction method to more distant galaxies, for which well-matched HST rest-frame visible and JWST rest-frame ∼3.5µm images will become available in the near-future.

A Spatially Resolved Analysis of Star Formation Burstiness by Comparing UV and Hα in Galaxies at z ∼ 1 with UVCANDELS

“…Before being interpreted as star formation indicators, both rest-UV and Hα emission need to be corrected for attenuation due to the presence of dust in the host galaxy itself. Since the main goal of this work is to compare the rest-UV and Hα emission from galaxies as a function of their positions inside the galaxy, it is imperative to make an effort to address the fact that dust absorption may itself vary inside a galaxy (e.g., Kim et al 2019). Hence, we compute a resolved dust map for each galaxy to correct for dust attenuation, while preserving the morphological detail.…”

JWST NIRCam Photometry: A Study of Globular Clusters Surrounding Bright Elliptical Galaxy VV 191a at z = 0.0513

“…Bonatto et al (2013) found extinction in 66 GCs with mean values ranging from 〈δE(B − v) 〉 ≈ 0.018 (NGC 6981) to 〈δE(B − v) 〉 ≈ 0.016 (Palomar 2), and therefore an implied A V ∼ 0.05 mag, consistent with the above value. More recent work by Kim et al (2019) made a pixel-to-pixel analysis of a large sample of nearby ellipticals with ground-based and Spitzer 3.6 μm images and found that the radial extinction profiles in the elliptical centers have on average A V  0.1 mag and generally do not exceed A V = 0.2 mag in their central reddening values.…”