IDENTIFICATION OF z ≳ 2 Herschel 500 μm SOURCES USING COLOR DECONFUSION

Abstract

ABSTRACT We present a new method to search for candidate z ≳ 2 Herschel 500 μm sources in the Great Observatories Origins Deep Survey-North field using a S 500 μm/S 24 μm “color deconfusion” technique. Potential high-z sources are selected against low-redshift ones from their large 500 to 24 μm flux density ratios. By effectively reducing the contribution from low-redshift populations to the observed 500 μm emission, we are able to identify counterparts to high-z 500 μm sources whose 24 μm fluxes are relatively faint. The recovery of known z ≳ 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 ≳ 2. The inferred infrared luminosities are in the range 1.5 × 1012–1.8 × 1013 L ⊙, corresponding to dust-obscured star formation rates (SFRs) of ∼260–3100 M ⊙ yr−1 for a Salpeter initial mass function. Comparison with previous SCUBA 850 &mgr; 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 ≳ 4. We find that at a fixed luminosity, the dust temperature is ∼5 K cooler than that expected from the T d − L IR ?> relation at z ≲ ?> 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 ∼ 5 ?> , suggesting that the far-IR emission is star formation dominated. The contribution of the high-z Herschel 500 μm sources to the cosmic SFR density is comparable to that of (sub)millimeter galaxy populations at z ∼ 2.5 ?> and at least 40% of the extinction-corrected UV samples at z ∼ 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.