Submillimeter Galaxies as Tracers of Mass Assembly at Large M

Abstract

Deep imaging in the rest-frame UV has constrained both the evolution of the cosmic star formation rate density [1] and its time integral, the growth of the cosmic stellar mass density [2]. Short-wavelength studies give an incomplete picture, however, since an important population of high-redshift galaxies is heavily dust-obscured. The strength of the extragalactic mid- and far-IR/submillimeter background indicates that about half of the cosmic energy density comes from dusty luminous and ultra-luminous infrared galaxies (LIRGs/ULIRGs: L_IR ~ 10^11.5 to 10^13.5 L_⊙) at z ≥ 1 [3,4]. Because the brightest of these submillimeter galaxies (SMGs; see [5] and references therein) tend to lack strong X-ray emission [6], their large IR luminosities probably correspond to high star formation rates [7]. As the strikingly different appearances of the Hubble Deep Field at 0.83 μm [8] and 850 μm [9] exemplify, SMGs are rarer and forming stars much more intensely than typical optically selected systems [8,9]. Here we discuss new observations that shed light on the importance of SMGs in the history of galaxy mass assembly (all numbers assuming a flat Ω _Λ = 0.7 cosmology with H₀ = 70 km s^–1 Mpc^–1).