Influence of the environment on polycyclic aromatic hydrocarbon emission in star-forming regions

Lebouteiller, V.; Bernard-Salas, J.; Whelan, D. G.; Brandl, B.; Galliano, F.; Charmandaris, V.; Madden, S. and Kunth, D. (2011). Influence of the environment on polycyclic aromatic hydrocarbon emission in star-forming regions. The Astrophysical Journal, 728(1), article no. 45.

DOI: https://doi.org/10.1088/0004-637X/728/1/45

Abstract

We investigate the emission properties of polycyclic aromatic hydrocarbons (PAHs) in various metallicity environments with the Infrared Spectrograph on board Spitzer. Local giant H II regions are used as references as they enable access to the distinct interstellar medium components that contribute to the mid-infrared spectrum of star-forming galaxies: photodissociation regions (PDRs), photoionized gas, stellar clusters, and embedded regions. Three objects are considered: NGC 3603 in the Milky Way, 30 Doradus in the Large Magellanic Cloud, and N 66 in the Small Magellanic Cloud. From the variations of the PAH/14 μm ratio, we find that PAHs are destroyed in the ionized gas for a radiation field such that [Ne iii]/[Ne ii] >_~ 3. From the variations of the PAH/Huα ratio, we find that the PAH emission sources in the giant H II regions follow the same photodestruction law regardless of metallicity. We then compare these results with observations of starburst galaxies, Hii galaxies, and blue compact dwarf galaxies (BCDs). While the integrated mid-infrared spectra of BCDs are reminiscent of a warm dusty ionized gas, we observe a significant contribution to the PAH emission in starburst galaxies that is not arising from PDRs.

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