Staveley-Smith et al. present spectral-line results from the new cryogenic phased array feed (cryoPAF) on Murriyang, the Parkes radiotelescope. The cryoPAF offers a significant improvement in field of view, aperture efficiency, bandwidth, chromaticity and survey speed compared with conventional horn-fed receivers. This is demonstrated with measurements of sky calibrators and observations of 21-cm neutral hydrogen (HI) in the Large Magellanic Cloud (LMC) and the nearby galaxy NGC 6744.

CryoPAF commissioning data for this paper were taken on 2024 November 18 for the Large Magellanic Cloud (LMC). The LMC data consist of 66 minutes of azimuth-elevation tracks of 49 discrete pointing centres with all 72 beams, i.e. ∼80 sec per pointing. A 230 MHz bandwidth between 1300 to 1530 MHz was used with a frequency resolution of 4.4 kHz. Within that band, a zoom band covering 1417.5 ± 7.5 MHz was used for the LMC, with a zoom band frequency resolution of 0.55 kHz (0.12 km/s).

The image above shows a comparison of HI spectra at a similar position within the LMC. The red spectrum is a 5 second archival multibeam spectrum from 1998. The blue spectrum is 10 s of data from cryoPAF beam 19 from 2024 November, smoothed to a similar resolution as the multibeam data (3.9 kHz). Both are Stokes I (total intensity) spectra. No bandpass calibration or baseline fitting has been applied to either spectrum — illustrating the intrinsic flatness of the cryoPAF spectrum (owing to the absence of any narrow-band analogue bandpass filter). The cryoPAF brightness temperature and barycentric frequency scales are approximately correct. The multibeam spectrum has an arbitrary temperature scale, with no barycentric correction applied. The comparison of cryoPAF data with previous multibeam observations (which have a higher rms noise level despite a factor of 30 times longer on-source integration time) shows excellent temperature agreement.