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Broadband Intensity Tomography: Spectral Tagging the Cosmic UV Background

Most of the photons ever recorded by astronomers are in the form of imagesâ€"or broadband intensity mapping, while the photons’ redshift and frequency information has largely lost. I will introduce a data-driven technique to recover these otherwise collapsed dimensionalities by exhausting information in the spatial fluctuations. As the first application, we measure the spectrum of the ultraviolet background (UVB) at 0<z<2 in GALEX Imaging surveys. We spatially cross-correlate photons in the FUV and NUV bands with spectroscopic objects in SDSS as a function of redshift, and use the observed shapes of the K-corrections to constrain the rest-frame spectrum of the UVB. We fit simultaneously a parameterized UVB volume emissivity and a clustering bias factor both as function of frequency and cosmic time. With minimum assumptions, our measured non-ionizing continuum emissivity is broadly consistent with that in the Haardt & Madau model. Cosmic Lya emission is tentatively detected at the 2sigma level at z=1, with the luminosity density constant with being powered by cosmic star-formation with an effective Lya escape fraction of 10%. Our approach probes all contributing sources without surface brightness thresholding, which includes potential IGM emission. The technique brings some of the future line-intensity mapping science to within the reach of a rich set of existing broadband data at all wavelengths.

Speaker: Yi-Kuan Chiang (Johns Hopkins University)

Friday, 09/14/18


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Kavli Institute Astrophysics Colloquium

SLAC Fred Kavli Building (51) 3rd Fl Conference Room
2575 Sand Hill Rd
Menlo Park, CA 94305