Evidence for a Stellar-Dominated UV Background and Against a Decline of Cosmic Star Formation Beyond z~3

From Faucher-Giguere et al (http://arxiv.org/abs/0806.0372). The authors use the Lyman-alpha forest opacity to estimate the photoionizing background at 2 < z < 4.2. After subtracting the contribution from AGNs, they suggest that stellar sources are dominant (and thus may be responsible for reionization). Perhaps more remarkably, they determine a cosmic star formation rate that is flat, at odds with the well accepted Hopkins and Beacom (2006) curve.