CENTRAL STELLAR MASS DEFICITS IN THE BULGES OF LOCAL LENTICULAR GALAXIES, AND THE CONNECTION WITH COMPACT z ∼ 1.5 GALAXIES

We have used the full radial extent of images from the Hubble Space Telescope's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to extract surface brightness profiles from a sample of six, local lenticular galaxy candidates. We have modeled these profiles using a core-Sérsic bulge plus an exponential disk model. Our fast rotating lenticular disk galaxies with bulge magnitudes MV ∼< –21.30 mag have central stellar deficits, suggesting that these bulges may have formed from ''dry'' merger events involving supermassive black holes (BHs) while their surrounding disk was subsequently built up, perhaps via cold gas accretion scenarios. The central stellar mass deficits Mdef are roughly 0.5-2 MBH (BH mass), rather than ∼10-20 MBH as claimed from some past studies, which is in accord with core-Sérsic model mass deficit measurements in elliptical galaxies. Furthermore, these bulges have Sérsic indices n ∼3, half-light radii Re < 2 kpc and masses >1011 M☉, and therefore appear to be descendants of the compact galaxies reported at z ∼ 1.5-2. Past studies which have searched for these local counterparts by using single-component galaxy models to provide the z ∼ 0 size comparisons have overlooked these dense, compact, and massive bulges in today's early-type disk galaxies. This evolutionary scenario not only accounts for what are today generally old bulges—which must be present in z ∼ 1.5 images—residing in what are generally young disks, but it eliminates the uncomfortable suggestion of a factor of three to five growth in size for the compact, z ∼ 1.5 galaxies that are known to possess infant disks.