%0 Generic %1 Worseck2011 %A Worseck, Gábor %A Prochaska, J. Xavier %A McQuinn, Matthew %A Dall'Aglio, Aldo %A Fechner, Cora %A Hennawi, Joseph F. %A Reimers, Dieter %A Richter, Philipp %A Wisotzki, Lutz %D 2011 %K cosmology reionization %T The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption Spectra %U http://arxiv.org/abs/1103.5752 %X We report on the detection of strongly varying intergalactic HeII absorption in HST/COS spectra of two z~3 quasars. From our homogeneous analysis of the HeII absorption in these and three archival sightlines, we find a marked increase in the mean HeII effective optical depth from tau~1 at z~2.3 to tau>5 at z~3.2, but with a large scatter of 2< tau <5 at 2.7< z <3 on scales of ~10 proper Mpc. This scatter is primarily due to fluctuations in the HeII fraction and the HeII-ionizing background, rather than density variations that are probed by the co-eval HI forest. Semianalytic models of HeII absorption require a strong decrease in the HeII-ionizing background to explain the strong increase of the absorption at z>2.7, probably indicating HeII reionization was incomplete at z>2.7. Likewise, recent 3D numerical simulations of HeII reionization qualitatively agree with the observed trend only if HeII reionization completes at z=2.7 or even below, as suggested by a large tau>3 in two of our five sightlines at z<2.8. By doubling the sample size at 2.7< z <3, our newly discovered HeII sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized.

@misc{Worseck2011, abstract = { We report on the detection of strongly varying intergalactic HeII absorption in HST/COS spectra of two z~3 quasars. From our homogeneous analysis of the HeII absorption in these and three archival sightlines, we find a marked increase in the mean HeII effective optical depth from tau~1 at z~2.3 to tau>5 at z~3.2, but with a large scatter of 2< tau <5 at 2.7< z <3 on scales of ~10 proper Mpc. This scatter is primarily due to fluctuations in the HeII fraction and the HeII-ionizing background, rather than density variations that are probed by the co-eval HI forest. Semianalytic models of HeII absorption require a strong decrease in the HeII-ionizing background to explain the strong increase of the absorption at z>2.7, probably indicating HeII reionization was incomplete at z>2.7. Likewise, recent 3D numerical simulations of HeII reionization qualitatively agree with the observed trend only if HeII reionization completes at z=2.7 or even below, as suggested by a large tau>3 in two of our five sightlines at z<2.8. By doubling the sample size at 2.7< z <3, our newly discovered HeII sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized. }, added-at = {2011-03-31T18:06:16.000+0200}, author = {Worseck, Gábor and Prochaska, J. Xavier and McQuinn, Matthew and Dall'Aglio, Aldo and Fechner, Cora and Hennawi, Joseph F. and Reimers, Dieter and Richter, Philipp and Wisotzki, Lutz}, biburl = {https://www.bibsonomy.org/bibtex/250b3fc58b4f84d85fc37021ac7a5ac61/miki}, description = {[1103.5752] The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption Spectra}, interhash = {6a4c7de1bf2858164f8213dd20a463d2}, intrahash = {50b3fc58b4f84d85fc37021ac7a5ac61}, keywords = {cosmology reionization}, note = {cite arxiv:1103.5752 Comment: 6 pages, 4 color figures. submitted to ApJL}, timestamp = {2011-03-31T18:06:16.000+0200}, title = {The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption Spectra}, url = {http://arxiv.org/abs/1103.5752}, year = 2011 }