SURFACE DENSITY DISTRIBUTION OF HOT AND COLD DUST IN A COMPLETE SAMPLE OF FACE-ON SPIRAL GALAXIES. PART 1.

spiral galaxies exhibit a large range in properties such as scalelength, surface brightness, gas surface density and star formation (sf) history. a recent study by of one of us (de jong 1994) shows that low surface brightness (lsb) galaxies are about as numerous as high surface brightness galaxies. this means that a very numerous class of galaxies is hardly studied. in order to reach this important we obtained surface photometry in the b, v, r, i, h and k bands of 86 faceon spiral galaxies. this is the only statistically complete sample of galaxies with surface photometry in such a wide range in passbands and easily correctable for selection effects. further study of this sample shows that most galaxy parameters are independent of scale size, but depend on surface brightness. especially colors show a strong dependence on surface brightness, all galaxies become bluer going radially outward and lsb galaxies are bluer than hsb galaxies by the same amount. two explanations are the most obvious; a change in stellar populations or reddening caused by dust extinction. at the moment our data is insufficient to distinguish between the two possibilities. to limit our evolution models it is imperative to have radial information on both the current sf rate and the distribution of dust. we propose to image a statistically complete subsample of virgul35 galaxies from the previous mentioned sample with isocam using lw3. this will give us detailed information on the distribution of hot dust and the current sf. to measure the cold dust content we will scan all galaxies at 180 micron using isophot. this method gives us accurate background subtraction and information on the spatial extent of the cold dust for 34 large galaxies. as we already have the optical and nearir data we can ensure that our sample is complete in hubble type (sasm), surface brightness and color range. these observations enable us to distingu tru [truncated!, Please see actual data for full text]