A multi-wavelength view of the star formation activity at z ∼ 3

We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M _* ∼ 10¹⁰ M _⊙) IRAC- and MIPS 24 μm detected Lyman break galaxies (LBGs) with spectroscopic redshifts z 3 in the GOODS-North field. For LBGs without individual 24 μm detections, we employ stacking techniques at 24 μm, 1.1mm, and 1.4GHz to construct the average UV-to-radio spectral energy distribution and find it to be consistent with that of a luminous infrared galaxy with L _IR = 4.5 ^+1.1 _-2.3 × 10¹¹ L _⊙ and a specific star formation rate of 4.3 Gyr^-1 that corresponds to a mass doubling time 230 Myr. On the other hand, when considering the 24 μm detected LBGs we find among them galaxies with L _IR>10 ¹² L _⊙, indicating that the space density of z 3 UV-selected ultra-luminous infrared galaxies (ULIRGs) is (1.5 0.5) × 10^-5 Mpc^-3. We compare measurements of star formation rates from data at different wavelengths and find that there is tight correlation (Kendall's τ>99.7%) and excellent agreement between the values derived from dust-corrected UV, mid-IR, millimeter, and radio data for the whole range of L _IR up to L _IR 10¹³ L _⊙. This range is greater than that for which the correlation is known to hold at z ∼ 2, possibly due to the lack of significant contribution from polycyclic aromatic hydrocarbons to the 24 μm flux at z ∼ 3. The fact that this agreement is observed for galaxies with L _IR> 10¹² L _⊙ suggests that star formation in UV-selected ULIRGs, as well as the bulk of star formation activity at this redshift, is not embedded in optically thick regions as seen in local ULIRGs and submillimeter-selected galaxies at z = 2.