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تسجيل مستخدم جديدA merger in the dusty, $z=7.5$ galaxy A1689-zD1?
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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 ($T_{rm dust} sim 35$--$45$,K for $beta = 1.5-2$). 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,$mu$m line at $z_{rm [CII]} = 7.603$. The stringent upper limits on the [CII]/$L_{rm FIR}$ luminosity ratio suggest a [CII] deficit similar to several bright quasars and massive starbursts.
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