Neutral hydrogen (HI) is one of the fundamental components of the Galactic interstellar medium. The HI gas is the raw material for star formation and plays an important role in galaxy evolution. Observing the emission line of the Galactic HI gas can reveal the structure and dynamics of the Galaxy over a much extended region in the Galactic disk even in the very far side of the Galaxy. Both single dish radio telescopes and interferometers have been used to observe the Galactic HI gas.
During observations of the Galactic Plane Pulsar Snapshot (GPPS) survey, a set of independent spectrum digital backends are connected to the 19-beam L-band receivers, and the four polarization products of spectral line data of 1024k channels covering the frequency band of 1000 - 1500 MHz are simultaneously recorded. The huge collecting area of FAST and the 5-minute long integration time for each beam make the GPPS piggyback spectral data the most sensitive survey of Galactic HI emission/absorption by far (Fig.1).
We have processed the piggyback HI data for the region of the Galactic longitude from 33 to 55 degree and the Galactic latitude within ± 2 degree (Fig.2). The initial released HI data product has a velocity resolution of 0.1 km/s in the range of -300 km/s to +300 km/s. It can be used to detect exquisite interstellar HI structures and improve our understanding of the interstellar medium.
The FAST GPPS survey piggyback HI data product:
(v1.0 in a fits file) is released here.
Since data in some observations have much more RFIs, we will be continuously improving the data processing for the piggyback spectra of the FAST GPPS survey, e.g. on baseline fitting, RFIs cleaning etc, and will update the data product and release new version of the fits file.
You are welcome to use this most updated version of fits file.
If you find any problem or have any comments and suggestions, please contact us.