Today Kate Alexander (Harvard) gave the Astro Seminar. She talked about the observational properties of jets across wavelength but especially in the radio. And unresolved jets, understood through their spectral energy distributions. One point which came up is that there does still seem to be a beaming puzzle: The models of the observations imply high beaming factors, but off-axis examples are very hard to find. So is the model ruled out? MacFadyen (NYU) implied yes, even though he is one of the principal authors of the theories! I think this is a super-important area for multi-messenger and time-domain astrophysics.
Before lunch, Kate Storey-Fisher (NYU) and I had an absolutely great discussion with Roman Scoccimarro (NYU) about our correlation function estimator. He started off very skeptical and ended up a huge fan, which was fun to see, because I am pretty stoked about it! But then he said something off-topic but super-interesting: He has a standard experience on huge projects of the following form: While the correlation-function team is waiting for the data center to compute the correlation-function estimator (which involves an enormous pair-count operation in data and (much more importantly) random catalogs), he computes the power spectrum for the same data sample on his laptop! And yet the correlation function and the power spectrum are (in principle) the same information! What gives?
The answer—which I have to say I haven't fully figured out yet—is in part that the standard power-spectrum estimation doesn't consider explicitly the off-diagonal (k not equal to k-prime) mode cross-correlations, and in part that the standard power-spectrum estimation assumes that the window function is simple enough that a random catalog is not necessary. Those are huge approximations! However, if they are good enough for the power spectrum on baryon-acoustic scales, then they must be good enough for the correlation function on those same scales and maybe we can build a far, far faster estimator?
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