ISO-LWS Spectroscopy of Centaurus A: Extended Star Formation
Abstract
We present the first full FIR spectrum of Centaurus A (NGC 5128) from 43 - 196.7 micrometers. The data was obtained with the ISO Long Wavelength Spectrometer (LWS). We conclude that the FIR emission in a 70" beam centred on the nucleus is dominated by star formation rather than active galactic nucleus (AGN) activity. The flux in the far-infrared lines is ~1% of the total FIR: the [C II] line flux is ~0.4% FIR and the [O I] line is ~0.2%, with the remainder arising from [O III], [N II] and [N III] lines. These are typical values for starburst galaxies. The ratio of the [N III] / [N II] line intensities from the HII regions in the dust lane corresponds to an effective temperature, Teff ~35,500 K, implying that the tip of the main sequence is headed by O8.5 stars and that the starburst is ~6 x 10(exp 6) years old. This suggests that the galaxy underwent either a recent merger or a merger which triggered a series of bursts. The N/O abundance ratio is consistent with the range of ~0.2 - 0.3 found for Galactic HII regions. We estimate that < 5% of the observed [C II] arises in the cold neutral medium (CNM) and that ~10% arises in the warm ionized medium (WIM). The main contributors to the [C II] emission are the PDRs, which are located throughout the dust lane and in regions beyond where the bulk of the molecular material lies. On scales of ~1 kpc the average physical properties of the PDRs are modelled with a gas density, II ~10(exp 3) cu cm, an incident far-UV field, G ~10(exp 2) times the local Galactic field, and a gas temperature of ~250 K.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2000
- Accession Number
- ADA464795
Entities
People
- G. J. Stacey
- H. A. Smith
- Jordan Fisher
- M. Greenhouse
- M. L. Luhman
- P. E. Clegg
- Peter Timothy Cox
- S. D. Lord
- S. J. Unger
- S. Satyapal
Organizations
- Queen Mary University of London