Identification of z > or ~ 2 Herschel 500 μm sources using color deconfusion

We present a new method to search for candidate z greater than or similar to 2. Herschel. 500 mu m sources in the Great Observatories Origins Deep Survey-North field using a S-500 mu m/S-24 mu m "color deconfusion" technique. Potential high-z sources are selected against low-redshift ones from their large 500 to 24 mu m flux density ratios. By effectively reducing the contribution from low-redshift populations to the observed 500 mu m emission, we are able to identify counterparts to high-z 500 mu m sources whose 24 mu m fluxes are relatively faint. The recovery of known z greater than or similar to 4 starbursts confirms the efficiency of this approach in selecting high-z. Herschel. sources. The resulting sample consists of 34 dusty star-forming galaxies at z greater than or similar to 2. The inferred infrared luminosities are in the range 1.5 x 10(12)-1.8 x 10(13) L-circle dot, corresponding to dust-obscured star formation rates (SFRs) of similar to 260-3100 M-circle dot yr(-1) for a Salpeter initial mass function. Comparison with previous SCUBA 850 mu m-selected galaxy samples shows that our method is more efficient at selecting high-z dusty galaxies, with a median redshift of z = 3.07 +/- 0.83 and with 10 of the sources at z greater than or similar to 4. We find that at a fixed luminosity, the dust temperature is similar to 5 K cooler than that expected from theT(d) -L-IR relation at z less than or similar to 1, though different temperature selection effects should be taken into account. The radio-detected subsample (excluding three strong active galactic nucleus) follows the far-infrared (far-IR)/radio correlation at lower redshifts, and no evolution with redshift is observed out to z similar to 5, suggesting that the far-IR emission is star formation dominated. The contribution of the high-z. Herschel 500 mu m sources to the cosmic SFR density is comparable to that of (sub)millimeter galaxy populations at z similar to 2.5 and at least 40% of the extinction-corrected UV samples at z similar to 4. Further investigation into the nature of these high-z dusty galaxies will be crucial for our understanding of the star formation histories and the buildup of stellar mass at the earliest cosmic epochs.