The cosmic reionization history as revealed by the cmb doppler-21-cm correlation
Dec, 2005
13 pages
Published in:
- Astrophys.J. 647 (2006) 840-852
e-Print:
- astro-ph/0512010 [astro-ph]
DOI:
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Abstract: (arXiv)
We show that the epoch(s) of reionization when the ionization fraction of the universe is about half can be determined by correlating Cosmic Microwave Background (CMB) temperature maps with 21-cm line maps at degree scales (). During reionization peculiar motion of free electrons induces the Doppler anisotropy of the CMB, while density fluctuations of neutral hydrogen induce the 21-cm line anisotropy. In our simplified model of inhomogeneous reionization, a positive correlation arises as the universe reionizes whereas a negative correlation arises as it recombines/ thus, the sign of the correlation provides information on the reionization history which cannot be obtained by presently. The signal comes mainly from large scales (k~0.01 Mpc^-1) where linear perturbation theory is valid and complexity due to patchy reionization is averaged out. Since the Doppler signal comes from ionized regions and the 21-cm comes from neutral ones, the correlation has a well-defined peak(s) in redshift when the ionization fraction of the universe is about half. Furthermore, the cross-correlation is much less sensitive to systematic errors, especially foreground emission, than the auto-correlation of 21-cm lines: this is analogous to the temperature-polarization correlation of the CMB being more immune to systematic errors than the polarization-polarization. Therefore, we argue that the Doppler-21cm correlation provides a robust measurement of the 21-cm anisotropy, which can also be used as a diagnostic tool for detected signals in the 21-cm data -- detection of the cross-correlation provides the strongest confirmation that the signal is of cosmological origin. We show that the Square Kilometer Array can easily measure the predicted correlation signal for 1~year of survey observation.- cosmic microwave background
- cosmology: theory
- diffuse radiation
- galaxies: formation
- intergalactic medium
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