THE SIZE-VIRIAL RADIUS RELATION OF GALAXIES

I use the abundance matching ansatz, which has proven to be successful in reproducing galaxy clustering and other statistics, to derive estimates of the virial radius, R-200, for galaxies of different morphological types and a wide range of stellar masses. I show that over eight orders of magnitude in stellar mass galaxies of all morphological types follow an approximately linear relation between half-mass radius of their stellar distribution, r(1/2), and virial radius, r(1/2) approximate to 0.015 R-200, with scatter of approximate to 0.2 dex. Such scaling is in remarkable agreement with the expectation of models that assume that galaxy sizes are controlled by halo angular momentum, r(1/2) alpha lambda R-200, where lambda is the spin of galaxy parent halo. The scatter about the relation is comparable with the scatter expected from the distribution of lambda. Moreover, I show that when the stellar and gas surface density profiles of galaxies of different morphological types are rescaled by the radius r(n) = 0.015 R-200, the rescaled profiles follow approximately universal exponential (for late types) and de Vaucouleurs (for early types) form with scatter of only approximate to 30%-50% at R approximate to 1-3r(n). Remarkably, both late-and early-type galaxies have similar mean stellar surface density profiles at R greater than or similar to 1r(n). The main difference between their stellar distributions is thus at R < r(n). The results of this study imply that galaxy sizes and radial distribution of baryons are shaped primarily by properties of their parent halos and that the sizes of both late-type disks and early-type spheroids are controlled by halo angular momentum.