2024/10/30 by Xiangyu Zhang, Brandon S. Hensley, Zhang, Xiangyu +3
Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Gravitation Theories #FOS: Physical sciences #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2410.23171
openalex publication_date 2024/10/30 · openalex created_date 2024/11/14 · openalex updated_date 2026/07/28
The first all-sky, high-resolution, 3D map of the optical extinction curve of the Milky Way (Zhang & Green 2024) revealed an unexpected steepening of the extinction curve in the moderate-density, "translucent" interstellar medium (ISM). We argue that this trend is driven by growth of polycyclic aromatic hydrocarbons (PAHs) through gas-phase accretion. We find a strong anti-correlation between the slope of the optical extinction curve -- parameterized by R(V) -- and maps of PAH abundance -- parameterized by q\rm PAH -- derived from infrared emission. The range of observed q\rm PAH indicates PAH growth by a factor of ∼2 between AV ≃ 1 and 3. This implies a factor-of-two stronger 2175 Angstrom feature, which is sufficient to lower R(V) by the observed amount. This level of PAH growth is possible given rapid accretion timescales and the depletion of carbon in the translucent ISM. Spectral observations by JWST would provide a definitive test of this proposed explanation of R(V) variation.