PAHs in star-forming regions

The PAH fraction, the abundance of PAHs relative to total dust mass, is a key parameter in ISM physics. Using JWST and MUSE observations of 42 galaxies from the PHANGS survey, we analyze the PAH fraction in over 17000 HII regions spanning a gas-phase oxygen abundance of 12+log(O/H)=8.0-8.8 (Z~0.2-1.3Z_{sun}_), and ~400 isolated supernova remnants (SNRs).

We find a significantly lower PAH fraction toward HII regions compared to a reference sample of diffuse ISM areas at matched metallicity. At 12+log(O/H)>8.2, the PAH fraction toward HII regions is strongly anti-correlated with the local ionization parameter, suggesting that PAH destruction is correlated with ionized gas and/or hydrogen-ionizing UV radiation. At lower metallicities, the PAH fraction declines steeply in both HII regions and the diffuse ISM, likely reflecting less efficient PAH formation in metal-poor environments.