photon—quasar correlations

Schiminovich and I figured out that one possible method for working out the sources of the metagalactic ionizing radiation impinging on the Milky Way (local extragalactic intensity field at 912 Å) is to cross-correlate the far-ultraviolet (and also near-ultraviolet) photons recorded with GALEX with quasars at various redshifts. I have waxed poetic about cross-correlations before, because they can be measured at very high signal-to-noise in common situations, and often contain all the information you can possibly have (see yesterday's post, for example, and posts on statistical gravitational lensing previously).

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