The ALMA Band 9 receiver

Abstract

Aims. We describe the design, construction, and characterization of the Band 9 heterodyne receivers (600-720 GHz) for the Atacama Large Millimeter/submillimeter Array (ALMA). First-light Band 9 data, obtained during ALMA commissioning and science verification phases, are presented as well. Methods. The ALMA Band 9 receiver units (so-called "cartridges"), which are installed in the telescope's front end, have been designed to detect and down-convert two orthogonal linear polarization components of the light collected by the ALMA antennas. The light entering the front end is refocused with a compact arrangement of mirrors, which is fully contained within the cartridge. The arrangement contains a grid to separate the polarizations and two beam splitters to combine each resulting beam with a local oscillator signal. The combined beams are fed into independent double-sideband mixers, each with a corrugated feedhorn coupling the radiation by way of a waveguide with backshort cavity into an impedance-tuned superconductor-insulator-superconductor (SIS) junction that performs the heterodyne down-conversion. Finally, the generated intermediate frequency (IF) signals are amplified by cryogenic and room-temperature HEMT amplifiers and exported to the telescope's IF back end for further processing and, finally, correlation. Results. The receivers have been constructed and tested in the laboratory and they show an excellent performance, complying with ALMA requirements. Performance statistics on all 73 Band 9 receivers are reported. Importantly, two different tunnel-barrier technologies (necessitating different tuning circuits) for the SIS junctions have been used, namely conventional AlO x barriers and the more recent high-current-density AlN barriers. On-sky characterization and tests of the performance of the Band 9 cartridges are presented using commissioning data. Continuum and line images of the low-mass protobinary IRAS 16293-2422 are presented which were obtained as part of the ALMA science verification program. An 8 GHz wide Band 9 spectrum extracted over a 0.3 × 0.3 region near source B, containing more than 100 emission lines, illustrates the quality of the data.

Ingredients for solar-like systems: protostar IRAS 16293-2422 B versus comet 67P/Churyumov–Gerasimenko

“…CH3OH was detected on envelope scales in the infrared with the Herschel/HIFI guaranteed time CHESS key program ). CH3OH and 13 CH3OH have been observed towards the two protostars individually , even at spatial resolution superseding that of PILS -lines of CH3OH, 13 CH3OH, CH2DOH have been labelled in Baryshev et al (2015) and Martín-Doménech et al (2016). Towards source B, CH3OH emission displays inverse P Cygni profiles, indicating infall (Zapata et al 2013).…”

“…It also traces the outflows from the system (Walker et al 1988;Mizuno et al 1990), as also solidified by the detection of CO + in ISO/LWS data (Ceccarelli et al 1998c, although still remaining to be verified with ALMA observations). Most recently, studies with spatial resolution superseding that of PILS have been used to study the shocks and outflows stemming from source A as traced by carbon monoxide emission (Kristensen et al 2013, based on the line labelled in Baryshev et al 2015;Girart et al 2014;Favre et al 2014;van der Wiel et al 2019). Unfortunately, estimates of the column density are not provided in those works as too few lines are targeted at a time.…”

“…Formaldehyde has also been shown to be associated with larger scale shocked regions (Castets et al 2001), although it is significantly more abundant in the warm inner regions around the protostars . Individual lines of D2CO and HDCO have been labelled in high spatial resolution observations of Baryshev et al (2015) and Martín-Doménech et al (2016). Estimates of the column densities towards A and B have been provided in Rivilla et al (2019); however, corrections for optically thick emission have not been carried out.…”

The ALMA Protostellar Interferometric Line Survey (PILS)

“…The chemical richness (and differentiations) of the gas toward IRAS16293, seen in the 6-8 element interferometric data, made it an obvious target for science verification observations with ALMA at 220 GHz or 1.4 mm (Pineda et al 2012;Jør-gensen et al 2012) and at 690 GHz or 0.43 mm (Baryshev et al 2015). These early observations were already more than an order of magnitude more sensitive than the previous interferometric data and, as mentioned above, showed the first discovery of a prebiotic molecule, glycolaldehyde, toward a solar-type protostar (Jørgensen et al 2012).…”

“…Instead we extract the spectra at positions half a beam and one beam southeast of the continuum peak (see Fig. 7 as well as higher angular resolution Band 9 data of Baryshev et al 2015;their Fig. 13).…”