2004MNRAS.354..779G

We present a deep, new 1200-µm survey of the ELAISN2 and Lockman Hole fields using the Max-Planck Millimeter Bolometer array (MAMBO). The areas surveyed are 160 arcmin² in ELAISN2 and 197 arcmin² in the Lockman Hole, covering the entire Submillimetre Common User Bolometer Array (SCUBA) 8-mJy survey. In total, 27 (44) sources have been detected at a significance ≥4.0σ (≥3.5σ). The primary goals of the survey were to investigate the reliability of (sub)millimetre galaxy (SMG) samples, to analyse SMGs using flux ratios sensitive to redshift at z > 3, and to search for `SCUBA drop-outs', i.e. galaxies at z≫ 3. We present the 1200-µm number counts and find tentative evidence of a fall at bright flux levels. Employing parametric models for the evolution of the local 60-µm IRAS luminosity function, we are able to account simultaneously for the 1200- and 850-µm counts, suggesting that the MAMBO and SCUBA sources trace the same underlying population of high-redshift, dust-enshrouded galaxies. From a nearest-neighbour clustering analysis, we find tentative evidence that the most significant MAMBO sources come in pairs, typically separated by ∼23 arcsec. Our MAMBO observations unambiguously confirm around half of the SCUBA sources. In a robust subsample of 13 SMGs detected by both MAMBO and SCUBA at a significance ≥3.5σ, only one has no radio counterpart. Furthermore, the distribution of 850/1200-µm flux density ratios for this subsample is consistent with the spectroscopic redshift distribution of radio-detected SMGs. Finally, we have searched for evidence of a high-redshift tail of SMGs amongst the 18 MAMBO sources that are not detected by SCUBA. Although we cannot rule out that some of them are SCUBA drop-outs at z≫ 3, their overall 850-to-1200 µm flux distribution is statistically indistinguishable from that of the 13 SMGS which were robustly identified by both MAMBO and SCUBA.