Citizen Science with the LOFAR Surveys

Our main Citizen Science platform is Radio Galaxy Zoo (LOFAR) — we use this to analyse the complex radio images we find and to match them up with optical host galaxies. Below you can find some updates on its progress.

Update 24/12/20

As I write it's Christmas Eve and we're just approaching the 600,000th classification on the project, which has been running for almost exactly ten months. The usual plot of our progress on the sky is below (click to enlarge).

I've been working over the past couple of weeks on the processing of the results for the WEAVE-LOFAR project that I mentioned in my last update. In the image you can see the two fields that we're working on for LoTSS's second data release, DR2, which we call the 13-hour field (the middle of the image) and the 0-hour field (the left and right-hand edges of the image). Specifically we're trying to finish off a stripe around declination 60 to 65 degrees in the north of the 13h field, and all of the 0h field below a declination of about 35 degrees (which is where the Legacy Survey optical data that we're using runs out). We have almost all the Zooniverse views we need for all of this, apart from some small regions on the north edge of the 0h field that are now our top priority and will be appearing for you to classify over the holiday period. For this reason other parts of the sky appear as 'Paused' and we'll get back to them when the 0h field is done.

You might be wondering what happens in between your clicks on the website and the final optical catalogue that we'll be using for science and sending off to WEAVE. It's complicated, and for the details of similar things we've done for other fields you can have a look at some of the papers the team have written (like this one and this one). But basically, the process is this:

  • your associations and identifications are amalgamated and treated as votes to get a consensus view on each LOFAR object;
  • your clicks on optical objects are matched with a catalogue of known galaxies;
  • we merge your associations and optical IDs together with the ones for simple sources that are generated by our automated cross-matching;
  • team members visually inspect everything that was tagged by volunteers as 'too zoomed in' or 'blend', or are ambiguous in volunteers' classifications, using special interactive workflows;
  • we check all extended sources without optical IDs after this process using a newly developed algorithm that can identify plausible host galaxies using the radio morphology — which is why it's important to associate extended sources even if you can't see an ID;
  • Finally we cross-match the optical positions from these four different routes with a catalogue of known optical and infra-red objects to ensure consistency — and it's this catalogue that will go off to be observed by WEAVE in early 2021.

It's taken a huge amount of work to get us to this point but citizen scientists' efforts are finally paying off in a tangible way as we ready the first WEAVE-LOFAR target list — and optimistically, looking at the relatively small sky areas left to do, we may hope to see optical identifications in the DR2 data release scheduled for 2021.

If you've read this far, let me finish by thanking you for being involved in the project over the past ten months in what have been difficult times around the world, and by wishing you a very happy festive season and New Year.

Martin Hardcastle
Radio Galaxy Zoo (LOFAR) Project Scientist

Update 07/08/20

See blog post by Martin Hardcastle here.

Update 20/03/20

See blog post by Erik Osinga here.