Optical and infrared emission of H II complexes as a clue to the PAH life cycle

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 SAO RAS 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]$\lambda 5007/\mathrm{H}\beta$ 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]$\lambda 5007/\mathrm{H}\beta$ 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 $\mathrm{H}\beta$ 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 aromatisation, 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.

Accepted to MNRAS

References in corpus (15)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• The ACS Nearby Galaxy Survey Treasury
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point
• The Behavior of the Aromatic Features in M101 HII Regions: Evidence for Dust Processing
• Stellar Evolutionary Effects on the Abundances of PAH and SN-Condensed Dust in Galaxies
• Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: II. Control of the \HII Region Parameters
• GHASP : An Halpha kinematic survey of 203 spiral and irregular galaxies - VII. Revisiting the analysis of Halpha data cubes for 97 galaxies
• A self-consistent model of Galactic stellar and dust infrared emission and the abundance of polycyclic aromatic hydrocarbons
• The Arecibo Legacy Fast ALFA Survey: V. HI Source Catalog of the Anti-Virgo Region at dec=27 degrees
• The Effects of Metallicity and AGN Activity on the Mid-Infrared Dust Emission of Galaxies
• Oxygen and nitrogen abundances of HII regions in six spiral galaxies
• Dust Evolution in the Dwarf Galaxy Holmberg II
• Spectroscopy of H II Regions in the Late-Type Spiral Galaxy NGC 6946
• Polycyclic aromatic hydrocarbons in the dwarf galaxy IC 10

Cited by in corpus (6)

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• Revealing Efficient Dust-Formation at Low Metallicity in Extragalactic Carbon-Rich Wolf-Rayet Binaries
• Restructuring and destruction of hydrocarbon dust in the interstellar medium
• Relation between parameters of dust and parameters of molecular and atomic gas in extragalactic star-forming regions
• The evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust
• CO-to-H${}_2$ conversion factor and grain size distribution through the analysis of ${\alpha }_{\mathrm{CO}}$-$q_{\mathrm{PAH}}$ relation