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Modelling the spectral energy distribution of galaxies
I. Radiation fields and grain heating in the edge-on spiral NGC 891
C.C. Popescu * 1,
A. Misiriotis 2,3,
N.D. Kylafis 2,4,
R.J. Tuffs 1 and
J. Fischera 1
Received 27 June 2000 / Accepted 26 July 2000
We describe a new tool for the analysis of the UV to the sub-millimeter (sub-mm) spectral energy distribution (SED) of spiral galaxies. We use a consistent treatment of grain heating and emission, solve the radiation transfer problem for a finite disk and bulge, and self-consistently calculate the stochastic heating of grains placed in the resulting radiation field.
We use this tool to analyse the well-studied nearby edge-on spiral galaxy NGC 891. First we investigate whether the old stellar population in NGC 891, along with a reasonable assumption about the young stellar population, can account for the heating of the dust and the observed far-infrared and sub-mm emission. The dust distribution is taken from the model of Xilouris et al. (1999), who used only optical and near-infrared observations to determine it. We have found that such a simple model cannot reproduce the SED of NGC 891, especially in the sub-mm range. It underestimates by a factor of 2-4 the observed sub-mm flux.
A number of possible explanations exist for the missing sub-mm flux. We investigate a few of them and demonstrate that one can reproduce the observed SED in the far-infrared and the sub-mm quite well, as well as the observed radial profile at m.
For the models calculated we give the relative proportion of the dust radiation powered by the old and young stellar populations as a function of FIR/sub-mm wavelength. In all models we find that the dust is predominantly heated by the young stellar population.
Key words: ISM: dust, extinction galaxies: individual: NGC 891 galaxies: spiral galaxies: stellar content infrared: galaxies submillimeter
Send offprint requests to: C.C. Popescu (Cristina.Popescu@mpi-hd.mpg.de)
Online publication: October 30, 19100