Early science with the Large Millimeter Telescope: a 1.1 mm AzTEC survey of red-Herschel dusty star-forming galaxies

We present Large Millimeter Telescope (LMT)/AzTEC 1.1 mm observations of ∼100 luminous high-redshift dusty star-forming galaxy candidates from the ∼600 sq.deg Herschel-ATLAS survey, selected on the basis of their SPIRE red far-infrared colours and with S500μm=35−80 mJy. With an effective θFWHM ≈ 9.5arcsec angular resolution, our observations reveal that at least 9 per cent of the targets break into multiple systems with signal-to-noise ratio ≥4 members. The fraction of multiple systems increases to ∼23 per cent (or more) if some non-detected targets are considered multiples, as suggested by the data. Combining the new AzTEC and deblended Herschel photometry, we derive photometric redshifts, infrared luminosities, and star formation rates. While the median redshifts of the multiple and single systems are similar (zmed ≈ 3.6), the redshift distribution of the latter is skewed towards higher redshifts. Of the AzTEC sources, ∼85 per cent lie at zphot > 3 while ∼33 per cent are at zphot > 4. This corresponds to a lower limit on the space density of ultrared sources at 4 4 galaxies.