Bonjour Heratics, I talked to Saleem and Leon quite a bit in Paris (supposedly, all the talks were filmed <http://ilp.upmc.fr/firstlight/program.php>, but only the first two days have been posted and that doesn't include either talk or mine). Some interesting tidbits and clarifications:
- The key improvement over previous results is that they now use only the long baselines to calibrate (especially the direction-dependent calibration). Before using short baselines in the direciton-dependent calibration caused a loss of all diffuse structure, which got absorbed into their inferred beams. That calibration is done on every 10 seconds of data. - The LOFAR analysis strategy has been repeated iterations of refining a source model, calibrating to it, and rerunning all their analysis. They've done this ~10 times so far. They say it'll get a lot faster now, since they just bought a big new analysis cluster. On the other hand, the analysis scales with the amount of data used and this limit comes from ~150 hours out of the ~2000 they have in the can (about 4 petabytes). - The power spectrum error bars (e.g. on slide 25 of Ger's talk) are 2 sigma. The power spectra really are inconsistent with noise at all k, though they only go up the a relatively modest k corresponding to a 0.4 MHz binned channel width. - Saleem showed variance statistic plots as a function of frequency, both for Stokes I and Stokes V. Stokes V look at the 10ish mK level, I at the 50ish mK level. Those numbers are hard to interpret, since the variance statistic (both data and theory) depend on the smoothing scale in frequency. He also showed a "cross RMS" which came from correlating neighboring channels (on roughly the 100 kHz scale), which gave slightly better results (40ish mK). This is a harder statistic to interpret, since the correlation of EoR structure between channels on that scale is not 100%. It seems strange to me that they wouldn't look at interleaved channels, since they have so much spectral resolution at the outset, but they must have to bin too coarsely in frequency at some intermediate stage for that to work. - Saleem said that LOFAR didn't see the wedge in their final result, referring to the same slide as Ger's slide 24. Whatever their systematics, they must mix k_perp modes. After his talk, Saleem showed me some power spectra with less foreground subtraction that he said had "wedge structure" in them. It was really hard to tell how "wedge-like" they were, in part because they were small and over a limited k range, and in part because they used those contours plots that are so hard to read. -Josh On Wed, Dec 9, 2015 at 11:36 PM, Saul Kohn <[email protected]> wrote: > This is published online (no login required; the conference website), so I > think it's kosher to share. Check out slides 23-25. > http://lwa.phys.unm.edu/abq2015/talks/deBruyn.pdf > > Saul > > On Thu, Dec 3, 2015 at 9:12 AM, Adrian Liu <[email protected]> wrote: > >> Absolutely, it’s complementary and valuable. It’s definitely a result >> that’s not just line-of-sight, and relies on foreground subtraction at low >> k’s. The foregrounds were removed using the GMCA algorithm, with 6 >> components, though (understandably) during the talk they didn’t go into too >> much detail about it. (I had to talk to Ger afterwards to get the number 6). >> >> Ger will unfortunately not be here on Friday, which is why he had to >> present yesterday even though all the other EoR talks are on Friday. >> >> > On Dec 3, 2015, at 6:50 AM, Chris Carilli <[email protected]> wrote: >> > >> > well, yes and no. the number may not be much different, but, if they are >> > doing this in the image domain as well as line of sight, it shows that >> > progress can be made in 3D. that is, if the result is believable? I >> would >> > assume so, given they are presenting in public, but need to see paper. >> and >> > maybe they are focusing on LoS PS? mantra: 'multiple approaches and >> > experiments are good...' >> > >> > I will be talking about PAPER and HERA at New Mexico Tech physics dept >> > today at 4PM, for those in ABQ who might be bored and want to take the >> > drive... >> > >> > I will be in ABQ friday and will try to get some info from Ger. >> > >> > cc >> > >> > >> > >> >> as i mentioned earlier, saleem said that the limits were "PAPER-like", >> so >> >> nothing revolutionarily new... he also mentioned moving back to the >> power >> >> spectrum statistic, in lieu of the variance, since the foregrounds were >> >> easier to deal with... >> >> >> >>> On 03.12.2015., at 14.30, Adam Beardsley <[email protected]> >> >>> wrote: >> >>> >> >>> mK >> >>>> On Thu, Dec 3, 2015 at 6:30 AM Jonathan Pober >> >>>> <[email protected]> wrote: >> >>>> 20 or 30 mK or mK^2? >> >>>> >> >>>>> On Wed, Dec 2, 2015 at 11:47 PM, Adrian Liu <[email protected]> >> >>>>> wrote: >> >>>>> Yes. They have both P(kperp,kpara) limits as well as P(k) limits. No >> >>>>> mention of the variance method today. >> >>>>> >> >>>>>> On Dec 2, 2015, at 9:42 PM, danny jacobs <[email protected]> >> >>>>>> wrote: >> >>>>>> >> >>>>>> But this is a power spectrum limit rather than with the variance >> >>>>>> method? >> >>>>>> >> >>>>>>> On Wednesday, December 2, 2015, Saul Kohn <[email protected] >> > >> >>>>>>> wrote: >> >>>>>>> Hi all, >> >>>>>>> >> >>>>>>> To follow this up, Ger made a LOFAR EoR project overview >> >>>>>>> presentation (probably the same one as Dave was mentioning) in >> >>>>>>> Albuquerque this afternoon. >> >>>>>>> >> >>>>>>> They were hazy on the details of power spectrum estimation from >> >>>>>>> their images, but he quoted *preliminary* limits of between 20 and >> >>>>>>> 30mK for redshifts 7.5 to 10, k~0.05 Mpc^-1 using 155 hours of >> data. >> >>>>>>> Their estimate on systematics comes from Stokes V, which was at >> >>>>>>> levels ~ 10mK, so intersecting with the higher-power EoR models. >> On >> >>>>>>> the slide it quoted "Zaroubi et al. 2016", so I guess we can >> expect >> >>>>>>> to see something official next year. >> >>>>>>> >> >>>>>>> Saul >> >>>>>>> >> >>>>>>>> On Wed, Nov 11, 2015 at 5:06 PM, DAVID DEBOER >> >>>>>>>> <[email protected]> wrote: >> >>>>>>>> To clarify a bit, I’m not sure that Michiel’s statement >> applies >> >>>>>>>> to anything new, but rather that there was some possibility that >> >>>>>>>> Ger had made a presentation somewhere regarding a limit. >> >>>>>>>> >> >>>>>>>> Dave >> >>>>>> >> >>>>>> >> >>>>>> -- >> >>>>>> Sent from Gmail Mobile >> >> >> > >> > >> > >> >> >> >
