Conveners
Helium in the IGM
- Jamie Bolton (University of Nottingham)
Helium in the IGM
- There are no conveners in this block
Helium in the IGM
- There are no conveners in this block
Helium in the IGM
- There are no conveners in this block
Dr
David Syphers
(University of Colorado, Boulder)
25/06/2013, 09:30
Invited Talk
The reionization of He II at z~3 was the last major change in the ionization state of the IGM. In addition, the reionization of He II may also aid theoretical understanding of the later stages of hydrogen reionization. In recent years we have dramatically increased the number of He II Gunn-Peterson trough observations. Previously there were only two Gunn-Peterson observations at medium...
Dr
Wei Zheng
(Johns Hopkins University)
25/06/2013, 10:10
Contributed Talk
From the HST/COS spectra of selected quasars at z~>3.5, we find significant flux blueward of the HeII Lyα wavelength. The absorption profile suggests large "bubbles" of ionized helium embedded in the intergalactic medium. We find that the intensity of He+ ionizing field weakens considerably at z~3, and the reionization of the intergalactic helium started around z=3.5.
Dr
Gabor Worseck
(Max-Planck-Institut für Astronomie)
25/06/2013, 10:40
Invited Talk
The advent of GALEX and HST/COS have revolutionized studies of HeII reionization. In HST Cycle 17 we pioneered an effective strategy to statistically probe the HeII reionization epoch with HST/COS spectroscopy of the UV-brightest quasars. The clear picture emerging from the 13 sightlines probing z<3 is that HeII reionization likely ended at z~2.7. At z>2.7 the large scatter in the mean HeII...
Dr
Matthew McQuinn
(UC Berkeley)
25/06/2013, 11:50
Invited Talk
I will discuss the impact of intensity fluctuations on HI and HeII Lyα forest data. This will include a summary of recent work to measure and model eta fluctuations in the z~2.5 HeII Lyα forest and its implications for the sources of the UV background. In addition, I will summarize what numerical simulations plus radiative transfer predict for the abundance of z>3 HI Lyman-limit systems, and a...
Mr
Frederick Davies
(UCLA)
25/06/2013, 12:30
Contributed Talk
The standard cosmological radiative transfer method used to estimate the He II ionizing background assumes a uniform radiation field despite the discrete nature of the (rare) bright quasars that dominate the background. We estimate, for the first time, the effects of fluctuations on the evolving continuum opacity in two ways: by incorporating the complete distribution of ionizing background...
Dr
Luca Graziani
(Max Planck Institute for Astrophysics - MPA Garching)
25/06/2013, 14:30
Contributed Talk
The helium reionisation and the cosmic UV background (UVB) at z=3 have been investigated in recent years both theoretically and observationally. Spatial fluctuations of the eta parameter in the Lyα forest show that the He II opacity is “patchy” and a theoretical modelling of the UVB spectral shape is necessary to constrain these fluctuations. Metal ions in the IGM help constraining the UVB...
Dr
Keri Dixon
(University of Sussex)
27/06/2013, 16:25
Contributed Talk
Recent HeII Lyα forest observations from 2.0 < z < 3.4 show large fluctuations in the optical depth at z > 2.7. These results point to a fluctuating HeII-ionizing background, possibly due to the end of helium reionization. We present a fast, semi-numeric procedure to approximate detailed cosmological simulations. Spanning a large parameter space, we find order-of-magnitude fluctuations in the...
Mr
Michele Compostella
(Argelander Institute for Astronomy, Bonn)
27/06/2013, 16:55
Contributed Talk
I will present results on the topology of HeII reionization obtained from AMR hydrodynamic simulations of the intergalactic medium post-processed with the radiative transfer code RADAMESH. Ionizing radiation is propagated from a realistic population of active galactic nuclei considering different scenarios for the time evolution of the ionizing sources. During the early phases of the...
