| الملخص: |
Mid-infrared spectra of almost all astronomical objects reveal a rich array of emission features largely attributed to the IR florescence of polycyclic aromatic hydrocarbons (PAHs). These features can account for a significant portion of the total infrared luminosity but exhibit a dependence on their local environment, including metalicity, that is not yet well understood. We present deep 5 to 38 um spectroscopic data taken with the SL and LL IRS instrument of the Spitzer space telescope of three high radial abundance gradient nearby galaxies: NGC5457, NGC0628, and NGC2403. Available data are subdivided into 13" extraction regions in order to maximize the resolution of our analysis while still presenting a reasonable signal to noise. We measure the strength of the PAH features in each sub-region by performing a multi-dimensional fit of the underlying continuum due to aggregate dust temperatures, PAH features, and electronic transitions using the IDL routine PAHFIT. We also present Herschel PACS 70,100,160, GALEX FUV and NUV data on our targeted regions. We show for the first time that the well known correlation of total PAH intensity to total Infrared intensity and oxygen abundance on galactic scales also hold on sub kpc scales within these galaxies. We examine the impact that the local abundance, intensity and hardness of the radiation field has on PAH intensity and the physical conditions implied by PAH band ratios and that all play a significant role. |
