SHORT-LIVED STAR-FORMING GIANT CLUMPS IN COSMOLOGICAL SIMULATIONS OF z≈ 2 DISKS

Abstract

Many observed massive star-forming z ≈ 2 galaxies are large disks that exhibit irregular morphologies, with ≈1 kpc, ≈10 8 –10 10 M ⊙ clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M * ≈ 10 10.5 M ⊙ galaxies in ≈10 12 M ⊙ halos at z ≈ 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions ( f g ≈ 50%), and high specific star formation rates (≳1 Gyr −1 ). In accord with recent models, giant clumps ( M clump ≈ (5 × 10 8 –10 9 )M ⊙ ) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside–out formation of the disks rather than inward clump migration.