PHANGS–JWST First Results: Variations in PAH Fraction as a Function of ISM Phase and Metallicity

Media type: E-Article
Title: PHANGS–JWST First Results: Variations in PAH Fraction as a Function of ISM Phase and Metallicity
Contributor: Chastenet, Jérémy; Sutter, Jessica; Sandstrom, Karin; Belfiore, Francesco; Egorov, Oleg V.; Larson, Kirsten L.; Leroy, Adam K.; Liu, Daizhong; Rosolowsky, Erik; Thilker, David A.; Watkins, Elizabeth J.; Williams, Thomas G.; Barnes, Ashley. T.; Bigiel, Frank; Boquien, Médéric; Chevance, Mélanie; Chiang 江, I-Da 宜達; Dale, Daniel A.; Kruijssen, J. M. Diederik; Emsellem, Eric; Grasha, Kathryn; Groves, Brent; Hassani, Hamid; Hughes, Annie; [...]
imprint: American Astronomical Society, 2023
Published in: The Astrophysical Journal Letters
Language: Not determined
DOI: 10.3847/2041-8213/acadd7
ISSN: 2041-8205; 2041-8213
Keywords: Space and Planetary Science ; Astronomy and Astrophysics
Origination:
Footnote:
Description: <jats:title>Abstract</jats:title> <jats:p>We present maps tracing the fraction of dust in the form of polycyclic aromatic hydrocarbons (PAHs) in IC 5332, NGC 628, NGC 1365, and NGC 7496 from JWST/MIRI observations. We trace the PAH fraction by combining the F770W (7.7 <jats:italic>μ</jats:italic>m) and F1130W (11.3 <jats:italic>μ</jats:italic>m) filters to track ionized and neutral PAH emission, respectively, and comparing the PAH emission to F2100W, which traces small, hot dust grains. We find the average <jats:italic>R</jats:italic> <jats:sub>PAH</jats:sub> = (F770W + F1130W)/F2100W values of 3.3, 4.7, 5.1, and 3.6 in IC 5332, NGC 628, NGC 1365, and NGC 7496, respectively. We find that H <jats:sc>ii</jats:sc> regions traced by MUSE H<jats:italic>α</jats:italic> show a systematically low PAH fraction. The PAH fraction remains relatively constant across other galactic environments, with slight variations. We use CO+H<jats:sc>i</jats:sc> +H<jats:italic>α</jats:italic> to trace the interstellar gas phase and find that the PAH fraction decreases above a value of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{I}}}_{{\rm{H}}\alpha }/{{\rm{\Sigma }}}_{{\rm{H}}{\rm\small{I}}+{{\rm{H}}}_{2}}\sim {10}^{37.5}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{kpc}}^{-2}\,{({M}_{\odot }\,{\mathrm{pc}}^{-2})}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">I</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathsize="small" mathvariant="normal">I</mml:mi> <mml:mo>+</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>37.5</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:mi>erg</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>kpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi>pc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlacadd7ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in all four galaxies. Radial profiles also show a decreasing PAH fraction with increasing radius, correlated with lower metallicity, in line with previous results showing a strong metallicity dependence to the PAH fraction. Our results suggest that the process of PAH destruction in ionized gas operates similarly across the four targets.</jats:p>
Access State: Open Access

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