ISO LWS Spectroscopy of M82: A Unified Evolutionary Model
CALIFORNIA UNIV LOS ANGELES CA DEPT OF PHYSICS AND ASTRONOMY
Pagination or Media Count:
We present the first complete far-infrared spectrum 43-197 micrometers of M82, the brightest infrared galaxy in the sky, taken with the Long Wavelength Spectrometer of the Infrared Space Observatory ISO. We detected seven fine structure emission lines, O I 63 and 145 micrometers, O III 52 and 88 micrometers , N II 122 micrometers, N III 57 micrometers, and C II 158 micrometers, and fitted their ratios to a combination starburst and photodissociation region PDR model. The best fit is obtained with H II regions with n250cu cm, an ionization parameter of 10exp -3.5, and PDRs with n10exp 3.3cu cm and a far-ultraviolet flux of Go10exp 2.8. We applied both continuous and instantaneous starburst models, with our best fit being a 3-5 Myr old instantaneous burst model with a 100 M sun cutoff. We also detected the ground-state rotational line of OH in absorption at 119.4 micrometers. No excited level OH transitions are apparent, indicating that the OH is almost entirely in its ground state with a column density 4x10exp 14 sq cm. The spectral energy distribution over the long-wavelength spectrometer wavelength range is well fitted with a 48 K dust temperature and an optical depth, Tausub Dust proportional to varies as gamma exp -1.