text:   21cm intensity mapping experiments",7,"['Paper alert (with a delay due to holiday season!) -- in <LINK> led by @CunningtonSD  we studied the degeneracy between primordial non-gaussianity (PNG) and foreground removal systematics for intensity mapping experiments [thread].', 'Foreground removal methods remove some signal (unless one is very conservative, but then the error budget becomes much larger due to the residuals), especially on the large scales, where PNG signatures are expected to lie!', 'With simulated data and MCMC we studied the effects of this on the precision accuracy with which we can probe the f_NL local parameter with a large SKA1-MID @SKA_telescope survey, using FG removal methods that are currently used in real data analyses.', 'If we ignore the possibility of FG removal effects on the signal, we get *extremely biased* (wrong) estimates of f_NL, as shown in the purple contour where our fiducial f_NL = 0. The other contours correspond to the unrealistic cases where FG removal is 0 or perfectly known. https://t.co/Dugeg7WHzB', 'To add some realism, we devised a model with 1 free, nuisance parameter, which is marginalised over to account for FG removal properly. We found that it works well, and that we can recover unbiased estimates (but the f_NL uncertainties increase a lot!). https://t.co/QIxyRc9uyP', 'This result has implications also for cross-correlations and multi-tracer methods, and it means that further work is required to get the precision we need to be competitive. We are thinking about solutions -- more, hopefully, soon!', ""As an aside, note that we have made suites of simulated data and power spectrum and MCMC codes available at our group's repository https://t.co/FCvccjqwAy -- @CunningtonSD @psahds also see https://t.co/aoXY9jEffy""]",20,07,1659