Broadband Intensity Tomography: Spectral Tagging the Cosmic UV Background

Yi-Kuan Chiang
Tuesday, November 6, 2018
4:00 pm
NS2 1201
Most of the photons ever recorded by astronomers are in the form of images—or broadband intensity mapping, but information on their emission redshift and frequency is largely lost. I will introduce a data-driven technique to recover these otherwise collapsed dimensions 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 Far-UV and Near-UV 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 with >95% confidence at z=1, with the luminosity density consistent with being powered by cosmic star-formation with an effective Lya escape fraction of 10%. Our approach probes all sources of radiation 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 existing broadband data at all wavelengths.
Jingzhe Ma