The Engineering Development Array ( EDA ) is a single test station for Square Kilometre Array ( SKA ) precursor technology .
We have used the EDA to detect low-frequency radio recombination lines ( RRLs ) from the Galactic Centre region .
Low-frequency RRLs are an area of interest for future low-frequency SKA work as these lines provide important information on the physical properties of the cold neutral medium .
In this project we investigate the EDA , its bandpass and the radio frequency interference environment for low-frequency spectroscopy .
We present line spectra from 30 to 325 MHz for the Galactic Centre region .
The decrease in sensitivity for the EDA at the low end of the receiver prevents carbon and hydrogen RRLs to be detected below 40 and 60 MHz respectively .
RFI strongly affects frequencies in the range 276–292 , 234–270 , 131–138 , 95–102 and below 33 MHz .
Cn \alpha RRLs were detected in absorption for quantum levels n = 378 to 550 ( 39 – 121 MHz ) and in emission for n = 272 to 306 ( 228 – 325 MHz ) .
Cn \beta lines were detected in absorption for n = 387 to 696 ( 39 – 225 MHz .
Hn \alpha RRLs were detected in emission for n = 272 to 480 ( 59 – 325 MHz ) .
Hn \beta lines were detected for n = 387 to 453 ( 141 – 225 MHz ) .
The stacked Hn \alpha detection at 63 MHz is the lowest frequency detection made for hydrogen RRLs and shows that a cold ( partially ) ionized medium exists along the line of sight to the Galactic Centre region .
The size and velocity of this cold H ^ { + } gas indicates that it is likely associated with the nearby Riegel-Crutcher cloud .