DEPENDENCE ON LUMINOSITY OF PHOTOMETRIC PROPERTIES OF DISK GALAXIES - SURFACE BRIGHTNESS, SIZE, AND INTERNAL EXTINCTION

A sample of more than 1700 galaxies for which I band CCD images, redshifts, and H I lines velocity widths are available is used to study the dependence on luminosity of the main photometric parameters of spiral disks. For some derivations, the sample is complemented by other data in the public domain. The impact of sample selection criteria on the distribution function of observed parameters is monitored vis-a-vis sample visibility functions and by inspecting the properties of Monte Carlo simulations of the data. Significant dependences on luminosity are found for the disk central surface brightness and for the relations that convert isophotal radii, scale lengths, and magnitudes to the edge-on perspective. These dependences are tightly wedded to the extinction processes that operate in disks. The amount of internal extinction at I band depends both on disk inclination and galaxy luminosity: more luminous edge-on galaxies appear to be dimmed more than less luminous ones. Corrections of the isophotal radius at mu(I)=23.5 mag arcsec(-2) to the face-on perspective are larger for intrinsically faint galaxies. At that isophote, the less luminous galaxies appear to be completely transparent while the photometric profiles of highly inclined, luminous objects may still be affected by extinction. The relative amount of internal extinction suggests that the ratio of scale heights for the stellar and dust components of the disk decreases with increasing luminosity. Adoption of inadequate extinction laws that do not take into account the luminosity dependence can affect the slope of the Tully-Fisher relation and may introduce nonlinearity, resulting in both a luminosity bias and an inclination bias in the predicted galaxy distances. (C) 1995 American Astronomical Society.