The Fraction of Dust Mass in the Form of PAHs on 10-50 pc Scales in Nearby Galaxies
arxiv(2024)
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are a ubiquitous component of the
interstellar medium (ISM) in z 0 massive, star-forming galaxies and play key
roles in ISM energy balance, chemistry, and shielding. Wide field of view, high
resolution mid-infrared (MIR) images from JWST provides the ability to map the
fraction of dust in the form of PAHs and the properties of these key dust
grains at 10-50 pc resolution in galaxies outside the Local Group. We use MIR
JWST photometric observations of a sample of 19 nearby galaxies from the
"Physics at High Angular Resolution in Nearby GalaxieS" (PHANGS) survey to
investigate the variations of the PAH fraction. By comparison to lower
resolution far-IR mapping, we show that a combination of the MIRI filters
(R_PAH = [F770W+F1130W]/F2100W) traces the fraction of dust by mass in
the form of PAHs (i.e., the PAH fraction, or q_PAH). Mapping
R_PAH across the 19 PHANGS galaxies, we find that the PAH fraction
steeply decreases in HII regions, revealing the destruction of these small
grains in regions of ionized gas. Outside HII regions, we find R_PAH
is constant across the PHANGS sample with an average value of 3.43±0.98,
which, for an illuminating radiation field of intensity 2-5 times that of the
radiation field in the solar neighborhood, corresponds to q_PAH values
of 3-6
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