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Polycyclic aromatic hydrocarbons in HII regions: correlation with metallicity
PAHs are the smallest components of dust. They are observed mainly near the bright UV objects heating them. Unlike large particles just a single UV-photon is needed to heat and excite the PAHs (stochasting heating mechanism). The PAHs are concentrated generally to HII regions in spiral and irregular galaxies. We have perfomed the aperture photometry of HII regions using infrared images from telescopes Spitzer and Herschel at passbands 3.6, 4.5, 5.8, 8.0, 24, 70 and 160 μm. Emission of PAHs are observed at passbands 3.6 - 8.0 μm, 24 μm is emission likely of hot small particles and finally large particles are responsible for emission at 70 and 160 μm. We determine abundances of PAHs using model of Draine & Li (2007) . Comparing metallicities of HII regions and abundances of PAHs we get a correlation between these parameteres. There is a lack of PAHs in low metallicity regions, and conversely an excess of PAHs in high metallicity regions. This result is illustrated in Fig. 1. However 24 mkm emission do not correlate with metallicity (Fig. 2). Results of this work are in this paper .
Fig.1		Fig.2
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