(I continue my ongoing quest to provoke outrage on Twitter without actually being on Twitter. One of these days I'll succeed.)
Anyway, this paper finally uses FAST to do something useful and look at HI in galaxies like a respectable radio telescope. Annoyingly, they cite just about every HI survey of any importance apart from AGES. This annoys me. Especially as they focus on the importance of sensitivity and looking to higher redshifts, both of which AGES does pretty well (though to be fair we haven't published any of the higher redshift detections yet).
It's a bit of an odd paper. Normally in a first-results paper there's tonnes of stuff about the instrumental capabilities and the technical specifications, but this is almost entirely absent. Basically they looked at four galaxies doing a totally standard observing mode and detected three of them. One of them is nicely consistent with a previous ALFALFA HI measurement, another shows a similar HI and CO profile, while the third shows a bit of a difference. Since the CO and HI line widths are similar, they infer that both components probe the flat part of the rotation curve. This is entirely reasonable but there's just not much more you can do with a sample of three. They also estimate the dynamical masses, although quite honestly I have absolutely no idea why.
There are two other oddities. One is the comment that you can use gravitational magnification to boost sensitivity, which is true but they then list surveys as examples which, as far as I know, do not make use of this. The other is where all their time went. They were allocated a total of 10 hours, or or an average of 2.5 hours of observing time per source. The galaxy previously detected by ALFALFA required 48s of integration time in the earlier survey, while FAST used a 5 minute scan. They say the sensitivity level would have been about the same, correcting for the difference in observing time. All well and good, but what did they do with the rest of the observing time ?
In practise 5 minutes on-source typically means 15 minutes of actual observing time - you also need 5 minutes off-source to calibrate and a generous 5 minutes for slewing and whatnot. So a typical complete scan is 0.25 hours. Since they were given a total of 10 hours, so that amounts to 40 scans, or 10 scans per source. But they say they used 3-8 scans per source. If there were three scans for one source and eight for the others, then that's only 27 scans out of a possible 40 ! That's several hours of time unaccounted for. Do they have extremely slow slew times ? Does the data reduction take a long time ?
I dunno. It's all just a bit strange. And given that they go for sensitivity, I would have expected some discussion on what their results indicate for future surveys, but there isn't any - they discuss science instead, which there's bugger all you can do with four galaxies. Surely it would have been better to accept a modest drop in sensitivity and go for 40 targets instead of four !
Anyway, good news that FAST is finally starting to do proper science. Even with all the oddities and strange fixation on pulsars, I'm sure it will be a valuable addition to the arsenal of telescopes pointed at the HI sky.
The atomic gas of star-forming galaxies at z$\sim$0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope
We report new HI observations of four z$\sim$0.05 star-forming galaxies undertaken during the commissioning phase of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). FAST is the largest single-dish telescope with a 500 meter aperture and a 19-Beam receiver.
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