Initial mass function effects on the colour evolution of disk galaxies^*

Astronomical Institute. Department of Physics and Astronomy, University of Basel, Venusstr. 7, 4102 Binningen, Switzerland e-mail: [westera;buser]@astro.unibas.ch

Received: 17 July 2006
Accepted: 21 December 2006

Abstract

Aims.In this work, we want to find out if the IMF can be determined from colour images, integrated colours, or mass-to-light ratios, especially at high redshift, where galaxies cannot be resolved into individual stars, which would enable us to investigate dependencies of the IMF on cosmological epoch.

Methods.We use chemo-dynamical models to investigate the influence of the Initial Mass Function (IMF) on the evolution of a Milky Way-type disk galaxy, in particular of its colours.

Results.We find that the effect of the IMF on the internal gas absorption is larger than its effect on the light from the stellar content. However, the two effects work in the opposite sense: An IMF with more high mass stars leads to brighter and bluer star-light, but also to more interstellar dust and thus to more absorption, causing a kind of “IMF degeneracy”. The most likely wavelength region in which to detect IMF effects is the infrared (i.e., JHK). We also provide photometric absorption and inclination corrections in the SDSS ugriz and the HST WFPC2 and NICMOS systems.