Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.200h&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Other
Scientific paper
We are studying the properties of the polycyclic aromatic emission features in a wide variety of environments across the Large Magellanic Clouds, in order to characterise the band ratio variations. The different PAH band ratios are known to vary in galaxies from source to source reflecting variations in local galactic environments. The strength of the PAH emission bands compared to other IR components also varies, reflecting variations in dust processing and illumination conditions. From a laboratory point of view there are several competing effects that determine the band ratios. These include the charge state of the molecules as well as possible local variations of chemical make-up of the PAH family effecting the shape of the bands. Sage-SPEC is a Spitzer/IRS mid-infrared spectroscopic study providing the unique possibility to study the environmental influence on the PAH emission features. In this study we present spectroscopic maps of HII regions, diffuse regions and molecular cloud regions covering a wide range of targets from relatively quiescent environments to the most actively star forming regions in the LMC. We have applied an advanced spatial rebinning scheme to be able main the maximum possible spatial resolution in bright regions, while averaging fainter regions in order to meet the required signal-to-noise-ratio. The main PAH band strengths have been obtained by fitting detailed model PAH feature profiles plus underlying continuum contribution to the observed spectra. The model profiles are derived high resolution mid-IR spectra and give better residuals than using Lorentzian profiles. We see ratios of the 7.7/11.3 um bands, for example, which span a range of a factor of 4 of the LMC. We see no effects of the band ratios as a function of radiation field hardness. The range of band ratios of diffuse regions clusters at the lower end of the band ratio range, while the HII regions tend to show higher 7.7/11.3 um band ratios, suggesting that variations of the band ratios are controlled by ionisation effects. We compare the range of band ratios seen within the LMC with the wide range of PAH band ratios seen in other galaxies to be able to lend more comprehensive interpretation on the use of the band ratios to trace radiation field density and other physical parameters.
Hony Sacha
SAGE-Spec Team
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