Constraints on the velocity dispersion function of early-type galaxies from the statistics of strong gravitational lensing

We use the distribution of gravitationally lensed image separations observed in the Cosmic Lens All-Sky Survey ( CLASS) and the PMN-NVSS Extragalactic Lens Survey ( PANELS), which are ( nearly) complete for the image separation range 03 <= Delta theta <= 6, to constrain a model velocity dispersion function (VF) of early-type galaxies. Assuming a current concordance cosmological model and adopting a singular isothermal ellipsoid ( SIE) model for galactic potentials, we consider constraining both a characteristic velocity dispersion ( parameter sigma(*)) and the shape of the function ( parameters alpha and beta; from Sheth et al.) for 0: 3 less than or similar to z less than or similar to 1. If all three parameters are allowed to vary, then none of the parameters can be tightly constrained by the lensing data because of the small size of the sample. If we fix the shape of the function by either the SDSS local stellar VF or an inferred local stellar VF based on the SSRS2 galaxy sample, then the constrained values of sigma(*) are nearly equal to the corresponding stellar values; we have f(SIE/center)( sigma(*), SIE/sigma(*); center) 0: 90 +/- 0: 18 ( SDSS) or 1: 04 +/- 0: 19 ( SSRS2), assuming nonevolution of the function between the present epoch and z similar to 0:6. Finally, using only the CLASS statistical sample ( from Browne et al.), and thus including an absolute multiple-imaging probability, we find that the SDSS stellar VF may have significantly underestimated the abundance of morphologically early-type galaxies.