1. The Polycyclic Aromatic Hydrocarbon Mass Fraction on a 10 pc Scale in the Magellanic Clouds
- Author
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Karl D. Gordon, Caroline Bot, Jérémy Chastenet, Yasuo Fukui, Adam K. Leroy, Dyas Utomo, Kisetsu Tsuge, Karin Sandstrom, I-Da Chiang, B. T. Draine, and Toshikazu Onishi
- Subjects
010504 meteorology & atmospheric sciences ,Milky Way ,Metallicity ,FOS: Physical sciences ,Polycyclic aromatic hydrocarbon ,Astrophysics ,01 natural sciences ,SPITZER LEGACY PROGRAM ,INFRARED-EMISSION BANDS ,WARM IONIZED MEDIUM ,PHOTOMETRIC SURVEY ,0103 physical sciences ,Magellanic Clouds ,GALAXY EVOLUTION SAGE ,polycyclic compounds ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Cosmic dust ,abundances [ISM] ,POINT-SOURCE CLASSIFICATION ,Physics ,chemistry.chemical_classification ,extinction ,Radiation field ,Astronomy and Astrophysics ,Plasma ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Chemistry ,Physics and Astronomy ,chemistry ,13. Climate action ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,MILKY-WAY ,dust ,MU-M PAH ,Mass fraction ,LOW-METALLICITY ENVIRONMENTS ,INTERSTELLAR DUST - Abstract
We present maps of the dust properties in the Small and Large Magellanic Clouds (SMC, LMC) from fitting Spitzer and Herschel observations with the \citet{DL07} dust model. We derive the abundance of the small carbonaceous grain (or polycyclic aromatic hydrocarbon; PAH) component. The global PAH fraction (q_pah, the fraction of the dust mass in the form of PAHs) is smaller in the SMC (1.0$^{+0.3}_{-0.3}$%) than in the LMC (3.3$^{+1.4}_{-1.3}$%). We measure the PAH fraction in different gas phases (H II regions, ionized gas outside of H II regions, molecular gas, and diffuse neutral gas). H II regions appear as distinctive holes in the spatial distribution of the PAH fraction. In both galaxies, the PAH fraction in the diffuse neutral medium is higher than in the ionized gas, but similar to the molecular gas. Even at equal radiation field intensity, the PAH fraction is lower in the ionized gas than in the diffuse neutral gas. We investigate the PAH life-cycle as a function of metallicity between the two galaxies. The PAH fraction in the diffuse neutral medium of the LMC is similar to that of the Milky Way ($\sim4.6$%), while it is significantly lower in the SMC. Plausible explanations for the higher PAH fraction in the diffuse neutral medium of the LMC compared to the SMC include: a more effective PAH production by fragmentation of large grains at higher metallicity, and/or the growth of PAHs in molecular gas., Comment: Accepted for publication in ApJ
- Published
- 2019