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Astron. Astrophys. 338, 795-806 (1998)

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Near-infrared observations of galaxies in Pisces-Perseus

II. Extinction effects and disk opacity

G. Moriondo 1, 2, R. Giovanelli 2 and M.P. Haynes 2

1 Dipartimento di Astronomia e Scienza dello spazio, Universita' di Firenze, L. E. Fermi 5, I-50125 Firenze, Italy
2 Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853, USA

Received 28 April 1998 / Accepted 28 May 1998


We study the correlations with inclination of H-band disk and bulge structural parameters and [FORMULA] colour profiles for a sample of 154 spiral galaxies, in order to detect possible effects due to internal extinction by dust. The selection of the sample assures that galaxies at different inclinations are not intrinsically different, so that the observed correlations represent the real behaviour of the parameter considered. All the parameters are derived from a bi-dimensional fitting of the galaxy image. We find that extinction, though small at near infrared wavelengths, is sufficient to produce observable effects. In particular the observed increase of the average disk scalelength and the reddening of the disk [FORMULA] colour at high inclinations are clear signatures of the presence of dust. The total H-band disk luminosity depends little on inclination; on the other hand significant corrections to the face-on aspect are derived for the H-band central disk brightness and the disk scalelength. The bulge parameters exhibit little or no dependence on inclination. Simulations carried out with a simple model for an internally-extincted galaxy show that these results imply a central H-band optical depth between 0.3 and 0.5.

Key words: galaxies: photometry – structure – ISM – infrared: galaxies

Send offprint requests to: G. Moriondo

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998