EDP Sciences
Free access
Volume 440, Number 1, September II 2005
Page(s) 67 - 71
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041913

A&A 440, 67-71 (2005)
DOI: 10.1051/0004-6361:20041913

Can rotation curves reveal the opacity of spiral galaxies?

A. Misiriotis

University of Crete, Physics Department, PO Box 2208, 710 03 Heraklion, Crete, Greece
    e-mail: angmis@physics.uoc.gr

(Received 16 August 2004 / Accepted 21 April 2005)

The observed anti-correlation between the inclination and the slope of the innermost part of the rotation curve can be attributed to dust extinction. However, the implied central face-on opacity of $\tau=2{-}4$ for the most luminous galaxies is embarrassingly high compared with studies of edge-on galaxies, which yield central face-on opacities equal to at most $\tau=1$ in the optical band. I show that the controversy can be resolved by adopting a model that includes the velocity dispersion of the emitters. Through the use of such a model, I reproduce the correlation between galaxy inclination and the slope of its inner rotation curve without having to resort to excessively high optical depth.

Key words: dust, extinction -- galaxies: kinematics and dynamics -- galaxies: spiral

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