FROM RINGS TO BULGES: EVIDENCE FOR RAPID SECULAR GALAXY EVOLUTION AT z ∼ 2 FROM INTEGRAL FIELD SPECTROSCOPY IN THE SINS SURVEY

We present H alpha integral field spectroscopy of well-resolved, UV/optically selected z similar to 2 star-forming galaxies as part of the SINS survey with SINFONI on the ESO VLT. Our laser guide star adaptive optics and good seeing data show the presence of turbulent rotating star-forming outer rings/disks, plus central bulge/inner disk components, whose mass fractions relative to the total dynamical mass appear to scale with the [N II]/H alpha flux ratio and the star formation age. We propose that the buildup of the central disks and bulges of massive galaxies at z similar to 2 can be driven by the early secular evolution of gas-rich proto-disks. High-redshift disks exhibit large random motions. This turbulence may in part be stirred up by the release of gravitational energy in the rapid cold accretion flows along the filaments of the cosmic web. As a result, dynamical friction and viscous processes proceed on a timescale of < 1 Gyr, at least an order of magnitude faster than in z similar to 0 disk galaxies. Early secular evolution thus drives gas and stars into the central regions and can build up exponential disks and massive bulges, even without major mergers. Secular evolution along with increased efficiency of star formation at high surface densities may also help to account for the short timescales of the stellar buildup observed in massive galaxies at z similar to 2.