Analysis of the spatially-resolved $V$-3.6$mu$m colors and dust extinction in 257 nearby NGC and IC galaxies. (arXiv:1901.00565v2 [astro-ph.GA] UPDATED)

Analysis of the spatially-resolved $V$-3.6$mu$m colors and dust extinction in 257 nearby NGC and IC galaxies. (arXiv:1901.00565v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Kim_D/0/1/0/all/0/1">Duho Kim</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jansen_R/0/1/0/all/0/1">Rolf A. Jansen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Windhorst_R/0/1/0/all/0/1">Rogier A. Windhorst</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cohen_S/0/1/0/all/0/1">Seth H. Cohen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McCabe_T/0/1/0/all/0/1">Tyler McCabe</a>

We present and analyze spatially-resolved maps for the observed $V$- and
$g$-band to 3.6$mu$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 PSF-matched mosaics of SDSS $g$- and $r$-band images and
Spitzer/IRAC 3.6$mu$m mosaics, with all pixels contaminated by foreground
stars or background objects masked out. By applying the $beta_V$ method
(Tamura et al. 2009, 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-$sigma$ scatter in
$beta_V$ around the average, both within a galaxy and in each morphological
type bin, is $sim$20%. Combined, these result in a $sim$0.4 mag scatter in
$A_V$. The spatial resolution effect levels out at $zgtrsim$0.02, where the
pixel size becomes larger than the typical size of giant molecular clouds
($sim$200pc). We find noticeably redder $V$$-$3.6$mu$m colors in the center
of star-forming galaxies and galaxies with a weak AGN. The derived intrinsic
$V$$-$3.6$mu$m colors for each Hubble type are generally consistent with the
model predictions of Kim et al. (2017). Finally, we discuss the applicability
of the $beta_V$ dust-correction method to more distant galaxies, for which
well-matched HST rest-frame visible and JWST rest-frame $sim$3.5$mu$m images
will become available in the near-future.

We present and analyze spatially-resolved maps for the observed $V$- and
$g$-band to 3.6$mu$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 PSF-matched mosaics of SDSS $g$- and $r$-band images and
Spitzer/IRAC 3.6$mu$m mosaics, with all pixels contaminated by foreground
stars or background objects masked out. By applying the $beta_V$ method
(Tamura et al. 2009, 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-$sigma$ scatter in
$beta_V$ around the average, both within a galaxy and in each morphological
type bin, is $sim$20%. Combined, these result in a $sim$0.4 mag scatter in
$A_V$. The spatial resolution effect levels out at $zgtrsim$0.02, where the
pixel size becomes larger than the typical size of giant molecular clouds
($sim$200pc). We find noticeably redder $V$$-$3.6$mu$m colors in the center
of star-forming galaxies and galaxies with a weak AGN. The derived intrinsic
$V$$-$3.6$mu$m colors for each Hubble type are generally consistent with the
model predictions of Kim et al. (2017). Finally, we discuss the applicability
of the $beta_V$ dust-correction method to more distant galaxies, for which
well-matched HST rest-frame visible and JWST rest-frame $sim$3.5$mu$m images
will become available in the near-future.

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