Giant clumps in the FIRE simulations: a case study of a massive high-redshift galaxy

The morphology of massive star-forming galaxies at high redshift is often dominated by giant clumps of mass similar to 10(8)-10(9) M-circle dot and size similar to 100-1000 pc. Previous studies have proposed that giant clumps might have an important role in the evolution of their host galaxy, particularly in building the central bulge. However, this depends on whether clumps live long enough to migrate from their original location in the disc or whether they get disrupted by their own stellar feedback before reaching the centre of the galaxy. We use cosmological hydrodynamical simulations from the FIRE (Feedback in Realistic Environments) project which implement explicit treatments of stellar feedback and interstellar medium physics to study the properties of these clumps. We follow the evolution of giant clumps in a massive ( M-* similar to 10(10.8) M-circle dot at z = 1), discy, gas-rich galaxy from redshift z greater than or similar to 2 to z = 1. Even though the clumpy phase of this galaxy lasts over a gigayear, individual gas clumps are short-lived, with mean lifetime of massive clumps of similar to 20 Myr. During that time, they turn between 0.1 per cent and 20 per cent of their gas into stars before being disrupted, similar to local giant molecular clouds. Clumps with M greater than or similar to 10(7) M-circle dot account for similar to 20 per cent of the total star formation in the galaxy during the clumpy phase, producing similar to 10(10) M-circle dot of stars. We do not find evidence for net inward migration of clumps within the galaxy. The number of giant clumps and their mass decrease at lower redshifts, following the decrease in the overall gas fraction and star formation rate.