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Astron. Astrophys. 331, 894-900 (1998)


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Optical and NIR modelling of NGC 891

E.M. Xilouris 1, 3, P.B. Alton 4, J.I. Davies 4, N.D. Kylafis 2, 3, J. Papamastorakis 2, 3 and M. Trewhella 4

1 University of Athens, Department of Physics, Section of Astrophysics, Astronomy & Mechanics, GR-157 83 Athens, Greece
2 University of Crete, Physics Department, P.O. Box 2208, GR-710 03 Heraklion, Crete, Greece
3 Foundation for Research and Technology-Hellas, P.O. Box 1527, GR-711 10 Heraklion, Crete, Greece
4 Department of Physics and Astronomy, University of Wales, Cardiff, P.O. Box 913, Cardiff CF2 3YB, UK

Received 12 September 1997 / Accepted 13 November 1997

Abstract

We compare B, V, I, J, K surface photometry of the edge-on spiral galaxy NGC 891 with corresponding surface photometry calculated from a realistic model of spiral galaxies, taking into account both absorption and scattering by dust. For the stars and the dust in the disk, we use exponential distributions in both directions, radially and perpendicular to the plane of the disk. For the bulge we use the emissivity distribution given by the Hubble profile. Apart from the exponential main stellar disk, it was found necessary to include also a second stellar disk, describing the young stellar population in this galaxy. This disk has a scaleheight about three times less than that of the main disk and its emissivity is constant in the radial direction with a cut off at the visual end of the galaxy. The young stars are detected only in the B and V bands, indicating that in these bands they contribute significantly to the light near the major axis. For this galaxy we have found a face-on central optical depth of less than one in all bands, indicating that if the galaxy were seen face-on, it would be transparent in the optical and near infrared region of the spectrum. The total dust mass is calculated from the model parameters and the gas to dust ratio is found to be very similar to that of our Galaxy. The ratios [FORMULA] of the extinction values are computed for the five bands and compare quite well with the values given for our Galaxy.

Key words: galaxies: photometry – galaxies: spiral – galaxies: individual: NGC 891 – galaxies: ISM – dust, extinction – galaxies: structure

Send offprint requests to: xilouris@physics.uch.gr

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998
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