Galaxies: The Long Wavelength View
NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
Pagination or Media Count:
Far-infrared spectroscopy obtained with the ISO LWS has shown that there is strong variation more than 2 orders of magnitude in the C IIFIR ratios in galaxies extending from blue compact dwarfs, to normal and starburst galaxies, down to elliptical and ultraluminous galaxies ULICs. The variation in the relative C 11158 micrometer line strength has been attributed to low metallicity in blue compact dwarfs, high Gon for normal galaxies and ULIGs, soft radiation fields in ellipticals, and extinction or enhanced abundance of dust in ionized regions in ULIGs. Full ISOLWS far-infrared 43 - 197 micrometer spectra of six nearby IR-bright galaxies reveal a dramatic progression of decreasing fine-structure line emission from ionized species to molecular OH and H2O absorption line dominated. The archetypical ULIC, Arp 220, lies at the absorption line dominated end of this sequence. For Arp 220, radiative transfer models indicate that it is optically thick in the FIR and that the water molecules observed in absorption are radiatively excited. If extinction plays a role in the sequence it appears from this analysis that the affected regions are heavily obscured even in the far-infrared, while the detected line emission is not more obscured in ULIGs than in starbursts. Linear correlation between polycyclic aromatic hydrocarbon PAH 6.2 micrometer feature strength and the C II158 micrometer line strength in starbursts and ULIGs suggests a similar effect for these emitting species, and that the detected PAR emission is not more obscured in ULIGs than in lower luminosity starbursts.
- Atomic and Molecular Physics and Spectroscopy