The gravitationally-lensed galaxy A1689-zD1 is one of the most distant spectroscopically confirmed sources (z=7.5). It is the earliest known galaxy where the interstellar medium (ISM) has been detected; dust emission was detected with the Atacama Large Millimetre Array (ALMA). A1689-zD1 is also unusual among high-redshift dust emitters as it is a sub-L* galaxy and is therefore a good prospect for the detection of gaseous ISM in a more typical galaxy at this redshift. We observed A1689-zD1 with ALMA in bands 6 and 7 and with the Green Bank Telescope (GBT) in band Q. To study the structure of A1689-zD1, we map the mm thermal dust emission and find two spatial components with sizes about 0.4−1.7\,kpc (lensing-corrected). The rough spatial morphology is similar to what is observed in the near-infrared with {\it HST} and points to a perturbed dynamical state, perhaps indicative of a major merger or a disc in early formation. The ALMA photometry is used to constrain the far-infrared spectral energy distribution, yielding a dust temperature (Tdust∼35--45\,K for β=1.5−2). We do not detect the CO(3-2) line in the GBT data with a 95\% upper limit of 0.3\,mJy observed. We find a slight excess emission in ALMA band~6 at 220.9\,GHz. If this excess is real, it is likely due to emission from the [CII] 158.8\,μm line at z[CII]=7.603. The stringent upper limits on the [CII]/LFIR luminosity ratio suggest a [CII] deficit similar to several bright quasars and massive starbursts.
@article{arxiv.1603.03222,
title = {A merger in the dusty, $z=7.5$ galaxy A1689-zD1?},
author = {Kirsten K. Knudsen and Darach Watson and David Frayer and Lise Christensen and Anna Gallazzi and Michal J. Michalowski and Johan Richard and Jesus Zavala},
journal= {arXiv preprint arXiv:1603.03222},
year = {2017}
}