Importance (Reionisation)
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Importance
Ionisation also leads to heating, since the ionizing photons need to have a energy excess to photoionise, albeit the excess can be zero. The excess energy from the photon goes into the kinetic energy of the released electron. So the epoch of reionisation can be considered the epoch of heating. Indeed, the heating would be much greater if some of the energy were not absorbed by the act of liberating the electron.
A non-gravitational heating source of the IntraCM may be needed to produce the observed x-ray luminosity-temperature relation of clusters (Kaiser 1991, White 1991, David Forman & Jones 1991, Metzler & Evrard 1994, Navarro Frenk & White 1995, Pen 1999, Ponman Cannon & Navarro 1999, Balogh Babul & Patton 1999, Loewenstein 2000, Wu Fabian & Nulsen 2000, Lloyd-Davies Ponman & Cannon 2000, Brighenti & Mathews 2001, Neumann & Arnaud 2001, Borgani et al 2001, Voit & Bryan 2001, Tozzi & Norman 2001, Dave et al 2001, Babul et al 2002, Bialek Evrard & Mohr 2001, McCarthy Babul Balogh 2002, Afshordi & Cen 2002, Voit et al 2002)
Can the Lyα forest tell us anything useful about basic cosmology? At scales of 1 to 40 h − 1 Mpc the only probe is the Lyα forest. Viel uses the QSO absoption spectra to confine 
and the DM spectral index to 
and finds no evidence of a running spectral index. A lower limit for the warm dark matter particle mass is found to be mwdm > 550 eV and an upper limit on the light gravitino to be mgrav < 16 eV. The sum of the neutrino masses is 
.
Reionisation can suppresses star formation, particularly in low mass galaxies. The heating due to ionisation would raise the Jeans mass. MJH05 suggest the suppression in SF may be observable in the future. Since supernovae trace SF, a drop in the SFR would lead to a drop in the supernovae rate.
Since reionisation suppresses star formation, deconvolving the star formation rate (SFR) for a population of stars that formed, at least partially, during reionisation should reveal the dip at around zreion. Since galactic halos contain an older population, they may contain the fossil record of reionisation. BC05 decide not to attempt to deconvolve the SFR but instead look at the effect on the distribution of stars within the halo. They find that a higher zreion leads to a steeper density profile. This relation is explained as a consequence of relaxation processes, which tend to steepen profiles the longer they are left to do their business.
Reionisation may also generate primordial magnetic fields (LAP05). The kinetic energy pumped into electrons by high-energy photons will create local magnetic fields. If the radiation field is inhomogeneous, currents are produced.
Broad Lyα absorbers contain a substantial fraction of the baryons in the present universe (RSST05).
Observations of 21 cm emission from reionsiation can constrain cosmological paraments (McQuinn05), particularly when coupled with the expectations of Planck.
Etittley 16:44, 22 June 2007 (BST) Back to Reionisation
