The case against large intensity fluctuations in the z ∼ 2.5 He II Lyα forest
Abstract
Previous studies of the 2.2 < z < 2.7 He II Lyα forest measured much larger ionizing background fluctuations than are anticipated theoretically. We re-analyse recent Hubble Space Telescope data from the two He II sightlines that have been used to make these measurements, HE 2347-4342 and HS 1700+6416, and find that the vast majority of the absorption is actually consistent with a single, spatially uniform He II photoionization rate. We show that the data constrain the root mean square fractional fluctuation level smoothed over 1 Mpc to be <2 and discuss why other studies had found 10 times larger fluctuations. Our measurement is consistent with models in which quasars dominate the z = 2.5 metagalactic He II-ionizing background (but it can accommodate less compelling models), and it suggests that quasars (rather than stars) are the dominant contributor to the H I-ionizing background. We detect a He II transverse proximity effect that is slightly offset in redshift from a known quasar. Its profile and offset may indicate that the quasar turned on 10 Myr ago.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2014
- DOI:
- 10.1093/mnras/stu242
- arXiv:
- arXiv:1306.4985
- Bibcode:
- 2014MNRAS.440.2406M
- Keywords:
-
- intergalactic medium;
- quasars: absorption lines;
- diffuse radiation;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 11 pages, 6 figures, plus appendixes