NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-17 T16:29:37 PDT
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For refcode 2014MNRAS.444..757K:
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NED Abstract

Copyright by Royal Astronomical Society. 2014MNRAS.444..757K Optical and infrared emission of H II complexes as a clue to the PAH life cycle Khramtsova, M. S.; Wiebe, D. S.; Lozinskaya, T. A.; Egorov, O. V. Abstract. We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 H II complexes in nine galaxies. Spectra obtained with the 6-m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied H II complexes. Physical properties (age, radiation field parameters, metallicity) are related to the F_8_/F_24_ ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in H II complexes. The well-known correlation between the F_8_/F_24_ ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [O III]lambda5007/Hbeta ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [O III]lambda5007/Hbeta and metallicity. In separate metallicity bins, the F_8_/F_24_ ratio is found to correlate with an age of an H II complex, which is estimated from the equivalent width of Hbeta line. The correlation is positive for low-metallicity complexes and negative for high-metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within H II complexes, but this is not necessarily due to their destruction. If PAHs can also form in H II complexes due to some processes like aromatization, photodestruction, shattering and sputtering of very small grains, the net F_8_/F_24_ ratio is determined by a balance between all these processes that can be different at different metallicities. Key words: galaxies: ISM, infrared: galaxies, infrared: ISM
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