Multiwavelength Constraints on the Cosmic Star Formation History from Spectroscopy: The Rest‐Frame Ultraviolet, Hα, and Infrared Luminosity Functions at Redshifts 1.9 ≲z≲ 3.4

Abstract

We use a sample of rest-frame UV-selected and spectroscopically observed galaxies at redshifts 1.9 ⩽ z < 3.4, combined with ground-based spectroscopic Hα and Spitzer MIPS 24 μm data, to derive the most robust measurements of the rest-frame UV, Hα, and infrared (IR) luminosity functions (LFs) at these redshifts. Our sample is by far the largest of its kind, with over 2000 spectroscopic redshifts in the range 1.9 ⩽ z < 3.4 and ~15,000 photometric candidates in 29 independent fields covering a total area of almost a square degree. Our method for computing the LFs takes into account a number of systematic effects, including photometric scatter, Lyα line perturbations to the observed optical colors of galaxies, and contaminants. Taking into account the latter, we find no evidence for an excess of UV-bright galaxies over what was inferred in early z ∼ 3 LBG studies. The UV LF appears to undergo little evolution between z ∼ 4 and z ∼ 2. Corrected for extinction, the UV luminosity density (LD) at z ∼ 2 is at least as large as the value at z ∼ 3 and a factor of ~9 larger than the value at z ∼ 6, primarily reflecting an increase in the number density of bright galaxies between z ∼ 6 and z ∼ 2. Our analysis yields the first constraints anchored by extensive spectroscopy on the infrared and bolometric LFs for faint and moderately luminous ( L bol ≲ 10 12 L ☉ ) galaxies. Adding the IR to the emergent UV luminosity, incorporating independent measurements of the LD from ULIRGs, and assuming realistic dust attenuation values for UV-faint galaxies, indicates that galaxies with L bol < 10 12 L ☉ account for ≈80% of the bolometric LD and SFRD at z ∼ 2–3. This suggests that previous estimates of the faint end of the L bol LF may have underestimated the steepness of the faint-end slope at L bol < 10 12 L ☉ . Our multiwavelength constraints on the global SFRD indicate that approximately one-third of the present-day stellar mass density was formed in subultraluminous galaxies between redshifts z = 1.9–3.4.