Early Science with the Large Millimeter Telescope: a 1.1 mm AzTEC Survey of Red-$Herschel$ dusty star-forming galaxies

Abstract

We present LMT/AzTEC 1.1mm observations of $\sim 100$ luminous high-redshift dusty star-forming galaxy candidates from the $\sim 600$sq.deg $Herschel$-ATLAS survey, selected on the basis of their SPIRE red far-infrared colours and with $S_{500\mu \mathrm{m}}=35-80$ mJy. With an effective ${\theta }_{\mathrm{FWHM}}\approx 9.5$ arcsec angular resolution, our observations reveal that at least 9 per cent of the targets break into multiple systems with SNR $\ge 4$ members. The fraction of multiple systems increases to $\sim 23$ 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, IR luminosities, and star formation rates. While the median redshifts of the multiple and single systems are similar $(z_{\mathrm{med}}\approx 3.6)$, the redshift distribution of the latter is skewed towards higher redshifts. Of the AzTEC sources $\sim 85$ per cent lie at $z_{\mathrm{phot}}>3$ while $\sim 33$ per cent are at $z_{\mathrm{phot}}>4$. This corresponds to a lower limit on the space density of ultra-red sources at $4<z<6$ of $\sim 3\times 10^{-7}{\text{Mpc}}^{-3}$ with a contribution to the obscured star-formation of $\gtrsim 8\times 10^{-4}{\text{M}}_{\odot }{\text{yr}}^{-1}{\text{Mpc}}^{-3}$. Some of the multiple systems have members with photometric redshifts consistent among them suggesting possible physical associations. Given their angular separations, these systems are most likely galaxy over-densities and/or early-stage pre-coalescence mergers. Finally, we present 3mm LMT/RSR spectroscopic redshifts of six red-$Herschel$ galaxies at $z_{\mathrm{spec}}=3.85-6.03$, two of them (at $z\sim 4.7$) representing new redshift confirmations. Here we release the AzTEC and deblended $Herschel$ photometry as well as catalogues of the most promising interacting systems and $z>4$ galaxies.

Accepted for publication in Monthly Notices of the Royal Astronomical Society. 23 pages, 18 figures

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