The size distribution of galaxies in the Sloan Digital Sky Survey

Accepted........ Received.......; in original form....... We use a complete sample of about 140,000 galaxies from the Sloan Digital Sky Survey (SDSS) to study the size distribution of galaxies and its dependence on their luminosity, stellar mass, and morphological type. The large SDSS database provides statistics of unprecedented accuracy. For each type of galaxy, the size distribution at given luminosity (or stellar mass) is well described by a log-normal function, characterized by its median ¯ R and dispersion σln R. For late-type galaxies, there is a characteristic luminosity at Mr,0 ∼ −20.5 (assuming h = 0.7) corresponding to a stellar mass M0 ∼ 10 10.6 M⊙. Galaxies more massive than M0 have ¯ R ∝ M 0.4 and σln R ∼ 0.3, while less massive galaxies have ¯ R ∝ M 0.15 and σln R ∼ 0.5. For early-type galaxies, the ¯ R- M relation is significantly steeper, ¯ R ∝ M 0.55, but the σln R- M relation is similar to that of late-type galaxies. Faint red galaxies have sizes quite independent of their luminosities. We use simple theoretical