%0 Generic %1 davies2017method %A Davies, Frederick B. %A Hennawi, Joseph F. %A Eilers, Anna-Christina %A Lukić, Zarija %D 2017 %K IGM reionization transmission %T A New Method to Measure the Post-Reionization Ionizing Background from the Joint Distribution of Lyman-$\alpha$ and Lyman-$\beta$ Forest Transmission %U http://arxiv.org/abs/1703.10174 %X The amplitude of the ionizing background that pervades the intergalactic medium (IGM) at the end of the epoch of reionization provides a valuable constraint on the emissivity of the sources which reionized the Universe. While measurements of the ionizing background at lower redshifts rely on a simulation-calibrated mapping between the photoionization rate and the mean transmission of the Ly$\alpha$ forest, at $z\gtrsim6$ the IGM becomes increasingly opaque, and transmission arises solely in narrow spikes separated by saturated Gunn-Peterson troughs. In this regime, the traditional approach of measuring the average transmission over large $50$ Mpc$/h$ regions is less sensitive and sub-optimal. Additionally, the five times smaller oscillator strength of the Ly$\beta$ transition implies the Ly$\beta$ forest is considerably more transparent at $z\gtrsim6$, even in the presence of contamination by foreground $z5$ Ly$\alpha$ forest absorption. In this work we present a novel statistical approach to analyze the joint distribution of transmission spikes in the co-spatial $z6$ Ly$\alpha$ and Ly$\beta$ forests. Our method relies on Approximate Bayesian Computation (ABC), which circumvents the necessity of computing the intractable likelihood function describing the highly correlated Ly$\alpha$ and Ly$\beta$ transmission. We apply ABC to mock data generated from a large-volume hydrodynamical simulation combined with a state-of-the-art model of ionizing background fluctuations in the post-reionization IGM, and show that it is sensitive to higher IGM neutral hydrogen fractions than previous techniques. As a proof of concept, we apply this methodology to a real spectrum of a $z=6.54$ quasar and measure the ionizing background from $5.4z 6.4$ along this sightline with $\sim0.2$ dex statistical uncertainties.

@misc{davies2017method, abstract = {The amplitude of the ionizing background that pervades the intergalactic medium (IGM) at the end of the epoch of reionization provides a valuable constraint on the emissivity of the sources which reionized the Universe. While measurements of the ionizing background at lower redshifts rely on a simulation-calibrated mapping between the photoionization rate and the mean transmission of the Ly$\alpha$ forest, at $z\gtrsim6$ the IGM becomes increasingly opaque, and transmission arises solely in narrow spikes separated by saturated Gunn-Peterson troughs. In this regime, the traditional approach of measuring the average transmission over large $\sim 50$ Mpc$/h$ regions is less sensitive and sub-optimal. Additionally, the five times smaller oscillator strength of the Ly$\beta$ transition implies the Ly$\beta$ forest is considerably more transparent at $z\gtrsim6$, even in the presence of contamination by foreground $z\sim 5$ Ly$\alpha$ forest absorption. In this work we present a novel statistical approach to analyze the joint distribution of transmission spikes in the co-spatial $z\sim 6$ Ly$\alpha$ and Ly$\beta$ forests. Our method relies on Approximate Bayesian Computation (ABC), which circumvents the necessity of computing the intractable likelihood function describing the highly correlated Ly$\alpha$ and Ly$\beta$ transmission. We apply ABC to mock data generated from a large-volume hydrodynamical simulation combined with a state-of-the-art model of ionizing background fluctuations in the post-reionization IGM, and show that it is sensitive to higher IGM neutral hydrogen fractions than previous techniques. As a proof of concept, we apply this methodology to a real spectrum of a $z=6.54$ quasar and measure the ionizing background from $5.4\leq z \leq 6.4$ along this sightline with $\sim0.2$ dex statistical uncertainties.}, added-at = {2017-03-31T10:04:32.000+0200}, author = {Davies, Frederick B. and Hennawi, Joseph F. and Eilers, Anna-Christina and Lukić, Zarija}, biburl = {https://www.bibsonomy.org/bibtex/2152ebf3f65b0121e4149214d150feae9/miki}, description = {[1703.10174] A New Method to Measure the Post-Reionization Ionizing Background from the Joint Distribution of Lyman-$\alpha$ and Lyman-$\beta$ Forest Transmission}, interhash = {554e120d4967d3b335f0d2369b511cfc}, intrahash = {152ebf3f65b0121e4149214d150feae9}, keywords = {IGM reionization transmission}, note = {cite arxiv:1703.10174Comment: 15 pages, 18 figures, ApJ submitted}, timestamp = {2017-03-31T10:04:32.000+0200}, title = {A New Method to Measure the Post-Reionization Ionizing Background from the Joint Distribution of Lyman-$\alpha$ and Lyman-$\beta$ Forest Transmission}, url = {http://arxiv.org/abs/1703.10174}, year = 2017 }