Inclination- and dust-corrected galaxy parameters: Bulge-to-disc ratios and size-luminosity relations

TL;DR

This paper develops methods to correct galaxy parameters for dust and inclination effects, providing intrinsic measurements of bulge and disc properties, and analyzes their relations across galaxy types.

Contribution

It introduces simple correction equations for dust and inclination effects on galaxy parameters and compiles intrinsic bulge and disc properties across galaxy types.

Findings

Derived dust-corrected galaxy parameters in multiple passbands.

Provided intrinsic bulge-to-disc flux ratios as a function of galaxy type.

Revealed non-linear luminosity-size relation for elliptical galaxies.

Abstract

While galactic bulges may contain no significant dust of their own, the dust within galaxy discs can strongly attenuate the light from their embedded bulges. Furthermore, such dust inhibits the ability of observationally-determined inclination corrections to recover intrinsic (i.e. dust free) galaxy parameters. Using the sophisticated 3D radiative transfer model of Popescu et al. and Tuffs et al., together with Driver et al.'s recent determination of the average face-on opacity in nearby disc galaxies, we provide simple equations to correct (observed) disc central surface brightnesses and scalelengths for the effects of both inclination and dust in the B, V, I, J and K passband. We then collate and homogenise various literature data sets and determine the typical intrinsic scalelengths, central surface brightnesses and magnitudes of galaxy discs as a function of morphological type. All galaxies have been carefully modelled in their respective papers with a Sersic bulge plus an exponential disc. Using the bulge magnitude corrections from Driver et al., we additionally derive the average, dust-corrected, bulge-to-disc flux ratio as a function of galaxy type. With values typically less than 1/3, this places somewhat uncomfortable constraints on some current semi-analytic simulations. Typical bulge sizes, profile shapes, surface brightnesses and deprojected densities are provided. Finally, given the two-component nature of disc galaxies, we present luminosity-size and (surface brightness)-size diagrams for discs and bulges. We also show that the distribution of elliptical galaxies in the luminosity-size diagram is not linear but strongly curved.