Implications of the ISO LWS Spectrum of the Prototypical Ultraluminous Galaxy: ARP 220
Abstract
We present a low resolution (R =lamba / Delta lamba ~200) far-infrared (43-197 micrometer) spectrum of the ultraluminous galaxy Arp 220, obtained from deep full-range scans using the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory (ISO). The spectrum is vastly different from the spectra of less luminous IR bright galaxies: the fine-structure lines that are typical of IR bright galaxies are weak or absent and the spectrum is dominated by absorption lines of OH, H2O, CH, NH3 and [0 I]. From the 43-197 micrometer continuum fit we derive that the optical depth of the thermal dust emission, Tau (sub dust), is about unity at 150 micrometer. From our continuum fit we derive a Lyman continuum production rate of Q=9 x 10(exp 54) sec(exp -1) and our simple spherical radiative transfer solution indicates a cool central source. The upper limits on the FIR fine-structure lines indicate a softer radiation field in Arp 220 than in starburst galaxies such as M82 or in AGN. The low L(sub CII) 158 / L(sub FIR) ratio in Arp 220 cannot be easily explained by dust obscuration or saturation effects. These results may be explained by a starburst model with a low upper mass cutoff or by unusually high dust absorption of UV photons within the ionized regions of a starburst or AGN.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1997
- Accession Number
- ADA464643
Entities
People
- G. J. Stacey
- G. Melnick
- H. A. Smith
- J. Cernicharo
- John Fischer
- M. A. Greenhouse
- M. L. Luhman
- Peter Timothy Cox
- S. D. Lord
- S. Satyapal
Organizations
- United States Naval Research Laboratory