The Star Formation Rates in Ultra-Massive z > 2 Galaxies

Abstract

Understanding the assembly of the most massive galaxies is one of the most important problems in astronomy today. It is now feasible to identify the most massive galaxies out to z 2.5, yet we have just begun to probe their evolution. To address this, we propose to obtain deep NIRI NIR long-slit spectroscopy of a sample of 15 ultra-massive galaxies (M_* > 10^11 M_0) at 1.8 < z < 2.6 with large MIPS 24 um and UV fluxes, for which we have unique, deep imaging with HST/NICMOS. With NIRI spectroscopy we will measure: H-alpha SFRs, combine SFRs with NICMOS-derived sizes to calculate the surface star formation density and to derive estimates of cold gas masses. This will be the first systematic study of these properties within ultra-massive galaxies at this redshift. With this new data, we will investigate how gas supplies, star formation activity, and AGN feedback mechanisms influence the early formation of massive galaxies at z 2.