Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-12-31
Astronomy and Astrophysics
Astrophysics
To appear in the proceedings of the "Galaxies in the Young Universe II" workshop, held at Ringberg Castle 2-6 August 1999, pub
Scientific paper
We describe an ongoing experiment to search for the meta-galactic Lyman-continuum background at z~2-3. We are obtaining one of the deepest optical spectra ever, using LRIS/Keck-II to search for the fluorescent Ly-alpha emission from optically thick HI clouds. The null results of our pilot study (Bunker, Marleau & Graham 1998) placed a 3-sigma upper bound on the mean intensity of the ionizing background of J_{nu 0} < 2E-21 erg/s/cm^2/Hz/sr at z~3. This constraint was more than two orders of magnitude more stringent than any previously published direct limit. Our results excluded the possibility that decaying relic neutrinos are responsible for the meta-galactic radiation field. We have recently greatly extended our search, obtaining a 16-hour spectrum which is sensitive to UV background fluxes ~1E-21 erg/s/cm^2/Hz/sr (z~2.3 at 3-sigma, assuming the HI clouds are ~10arcsec in extent). We describe how the results of this study can be used to constrain the quasar luminosity function and the contribution of high-redshift star-forming galaxies to the ambient ionizing background.
Bunker Andrew J.
Graham James R.
Marleau Francine R.
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