We have obtained deep 1 and 3 mm spectral-line scans towards a candidate z ≳ 5 ALMA-identified AzTEC submillimetre galaxy (SMG) in the Subaru/XMM-Newton Deep Field (or UKIDSS UDS), ASXDF1100.053.1, using the NOrthern Extended Millimeter Array (NOEMA), aiming to obtain its spectroscopic redshift. ASXDF1100.053.1 is an unlensed optically dark millimetre-bright SMG with S 1100 μ m = 3:5 mJy and KAB > 25:7 (2s), which was expected to lie at z = 5-7 based on its radio-submillimetre photometric redshift. Our NOEMA spectral scan detected line emission due to 12CO(J = 5-4) and (J = 6-5), providing a robust spectroscopic redshift, zCO = 5:2383 ± 0:0005. Energy-coupled spectral energy distribution modelling from optical to radio wavelengths indicates an infrared luminosity LIR = 8:3+1:5-1:4 × 1012 L, a star formation rate SFR = 630+-260 380 M yr-1, a dust mass Md = 4:4+-0 0:4 3 × 108 M, a stellar mass Mstellar = 3:5+3:6-1:4 × 1011 M, and a dust temperature Td = 37:4+-2 1:3 8 K. The CO luminosity allows us to estimate a gas mass M gas = 3:1 ± 0:3 × 1010 M, suggesting a gas-to-dust mass ratio of around 70, fairly typical for z ∼ 2 SMGs. ASXDF1100.053.1 has ALMA continuum size Re = 1:0+0:2-0:1 kpc, so its surface infrared luminosity density SIR is 1:2+-0 0:1 2 × 1012 L kpc-2. These physical properties indicate that ASXDF1100.053.1 is a massive dusty star-forming galaxy with an unusually compact starburst. It lies close to the star-forming main sequence at z ∼ 5, with low Mgas/Mstellar = 0:09, SFR/SFRMS(RSB) = 0:6, and a gas-depletion time tdep of 50 Myr, modulo assumptions about the stellar initial mass function in such objects. ASXDF1100.053.1 has extreme values of M gas=Mstellar, RSB, and tdep compared to SMGs at z ∼ 2-4, and those of ASXDF1100.053.1 are the smallest among SMGs at z > 5. ASXDF1100.053.1 is likely a late-stage dusty starburst prior to passivisation. The number of z = 5:1-5.3 unlensed SMGs now suggests a number density dN=dz = 30:4 ± 19:0 deg-2, barely consistent with the latest cosmological simulations.

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We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter bank and microwave kinetic inductance detector (MKID) to investigate dusty starburst galaxies in the distant universe at millimeter and submillimeter wavelengths. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV 0.4–3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of 1σ=4%, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array.@en

Ultra-wideband, three-dimensional (3D) imaging spectrometry in the millimeter–submillimeter (mm–submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution^1–3. However, it is challenging to scale up conventional coherent heterodyne receivers⁴ or free-space diffraction techniques⁵ to sufficient bandwidths (≥1 octave) and numbers of spatial pixels^2,3 (>10²). Here, we present the design and astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer⁶, which covers 332–377 GHz with a spectral resolution of F/ΔF ~ 380. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs)⁷ with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on-sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to ~1.1 THz. The miniature chip footprint of a few cm² allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large-volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible^1–3.

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