TY - JOUR
T1 - Re-ionizing the universe without stars
AU - Dopita, Michael A.
AU - Krauss, Lawrence
AU - Sutherland, Ralph S.
AU - Kobayashi, Chiaki
AU - Lineweaver, Charles H.
N1 - Funding Information:
Acknowledgements We thank both the referee and Sir Martin Rees for their constructive comments, which have much improved this paper. Mike Dopita acknowledges the support of the Australian Research Council (ARC) through Discovery projects DP0984657. He would also like to thank Andrew Bunker for his inspiring seminar on star formation in the early universe, which triggered the ideas presented here. Krauss acknowledges Australian National University for its support and hospitality as a Distinguished Visiting Professor, as well as travel funds from Brian Schmidt, making possible this collaboration. He also acknowledges support from the U.S. Department of Energy. Finally, we also acknowledge Ben Moore for constructive discussions and his valued input.
PY - 2011/10
Y1 - 2011/10
N2 - Recent observations show that the measured rates of star formation in the early universe are insufficient to produce re-ionization, and therefore, another source of ionizing photons is required. In this Letter, we examine the possibility that these can be supplied by the fast accretion shocks formed around the cores of the most massive haloes (10. 5ȯ<12) on spatial scales of order 1 kpc. We model the detailed physics of these fast accretion shocks, and apply these to a simple 1-D spherical hydrodynamic accretion model for baryonic infall in dark matter halos with an Einasto density distribution. The escape of UV photons from these halos is delayed by the time taken to reach the critical accretion shock velocity for escape of UV photons; 220 km s-1, and by the time it takes for these photons to ionize the surrounding baryonic matter in the accretion flow. Assuming that in the universe at large the baryonic matter tracks the dark matter, we can estimate the epoch of re-ionization in the case that accretion shocks act alone as the source of UV photons. We find that 50% of the volume (and 5-8% of the mass) of the universe can be ionized by z~7-8. The UV production rate has an uncertainty of a factor of about 5 due to uncertainties in the cosmological parameters controlling the development of large scale structure. Because our mechanism is a steeply rising function of decreasing redshift, this uncertainty translates to a re-ionization redshift uncertainty of less than ±0. 5. We also find that, even without including the UV photon production of stars, re-ionization is essentially complete by z~5. 8. Thus, fast accretion shocks can provide an important additional source of ionizing photons in the early universe.
AB - Recent observations show that the measured rates of star formation in the early universe are insufficient to produce re-ionization, and therefore, another source of ionizing photons is required. In this Letter, we examine the possibility that these can be supplied by the fast accretion shocks formed around the cores of the most massive haloes (10. 5ȯ<12) on spatial scales of order 1 kpc. We model the detailed physics of these fast accretion shocks, and apply these to a simple 1-D spherical hydrodynamic accretion model for baryonic infall in dark matter halos with an Einasto density distribution. The escape of UV photons from these halos is delayed by the time taken to reach the critical accretion shock velocity for escape of UV photons; 220 km s-1, and by the time it takes for these photons to ionize the surrounding baryonic matter in the accretion flow. Assuming that in the universe at large the baryonic matter tracks the dark matter, we can estimate the epoch of re-ionization in the case that accretion shocks act alone as the source of UV photons. We find that 50% of the volume (and 5-8% of the mass) of the universe can be ionized by z~7-8. The UV production rate has an uncertainty of a factor of about 5 due to uncertainties in the cosmological parameters controlling the development of large scale structure. Because our mechanism is a steeply rising function of decreasing redshift, this uncertainty translates to a re-ionization redshift uncertainty of less than ±0. 5. We also find that, even without including the UV photon production of stars, re-ionization is essentially complete by z~5. 8. Thus, fast accretion shocks can provide an important additional source of ionizing photons in the early universe.
KW - Cosmology: early universe
KW - Cosmology: theory
KW - Galaxies: formation
KW - Galaxies: halos
KW - Shock waves
KW - Ultraviolet: ISM
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U2 - 10.1007/s10509-011-0786-7
DO - 10.1007/s10509-011-0786-7
M3 - Letter
AN - SCOPUS:80052459871
SN - 0004-640X
VL - 335
SP - 345
EP - 352
JO - Astrophysics and Space Science
JF - Astrophysics and Space Science
IS - 2
M1 - 345
ER -