paper

A Multi-wavelength View of the Star Formation Activity at z~3

arXiv:1003.5773 · doi:10.1088/0004-637X/714/2/1740

Abstract

We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M $_{*}$ $\sim$ 10 $^{10}$ M $_{⊙}$ ) IRAC- and MIPS 24 $I^¼$ m-detected Lyman Break Galaxies (LBGs) with spectroscopic redshifts z $\sim$ 3 in the GOODS-North field (L $_{UV}$ $> 1.8 \times$ L $_{z = 3}^{*}$ ). For LBGs without individual 24 $I^¼$ m detections, we employ stacking techniques at 24 $I^¼$ 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 $_{IR}$ =4.5 $_{- 2.3}^{+ 1.1}$ $\times 1 0^{11}$ L $_{⊙}$ 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 $I^¼$ m-detected LBGs we find among them galaxies with L $_{IR} > 1 0^{12}$ L $_{⊙}$ , indicating that the space density of $z \sim$ 3 UV-selected Ultra-luminous Infrared Galaxies (ULIRGs) is $\sim$ (1.5 $\pm$ 0.5) $\times 1 0^{- 5}$ Mpc $^{- 3}$ . We compare measurements of star formation rates (SFRs) from data at different wavelengths and find that there is tight correlation (Kendall's $I ¨ >$ 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 $_{IR}$ up to L $_{IR}$ $\sim$ 10 $^{13}$ L $_{⊙}$ . 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 $I^¼$ m flux at $z \sim$ 3. The fact that this agreement is observed for galaxies with L $_{IR}$ $>$ 10 $^{12}$ 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 $z = 2$ .

Accepted for publication in ApJ