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$_{\ast}$ $\sim$ 10$^{10}$ M$_\odot$) IRAC- and MIPS 24$\mu$m-detected Lyman
Break Galaxies (LBGs) with spectroscopic redshifts z$\sim$3 in the GOODS-North
field (L$_{\rm UV}$$>1.8\times$L$^{\ast}_{z=3}$). For LBGs without individual
24$\mu$m detections, we employ stacking techniques at 24$\mu$m, 1.1mm and
1.4GHz, to construct the average UV-to-radio spectral energy distribution and
find it to be consistent with that of a Luminous Infrared Galaxy (LIRG) with
L$\rm_{IR}$=4.5$^{+1.1}_{-2.3}$$\times 10^{11}$ L$_{\odot}$ and a specific star
formation rate (SSFR) of 4.3 Gyr$^{-1}$ that corresponds to a mass doubling
time $\sim$230 Myrs. On the other hand, when considering the 24$\mu$m-detected
LBGs we find among them galaxies with L$\rm_{IR}> 10^{12}$ L$_{\odot}$,
indicating that the space density of $z\sim$3 UV-selected Ultra-luminous
Infrared Galaxies (ULIRGs) is $\sim$(1.5$\pm$0.5)$\times 10^{-5}$ Mpc$^{-3}$.
We compare measurements of star formation rates (SFRs) from data at different
wavelengths and find that there is tight correlation (Kendall's $\tau >$ 99.7%)
and excellent agreement between the values derived from dust-corrected UV,
mid-IR, mm and radio data for the whole range of L$\rm_{IR}$ up to L$\rm_{IR}$
$\sim$ 10$^{13}$ L$_{\odot}$. This range is greater than that for which the
correlation is known to hold at z$\sim$2, possibly due to the lack of
significant contribution from PAHs to the 24$\mu$m flux at $z\sim$3. The fact
that this agreement is observed for galaxies with L$\rm_{IR}$ $>$ 10$^{12}$
L$_{\odot}$ 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
$z=2$.
