The Major Sources of the Cosmic Reionizing Background at z ˜6

Details The Major Sources of the Cosmic Reionizing Background at z ˜6 The Major Sources of the Cosmic Reionizing Background at z ˜6

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...20314401w&link_type=abstract

American Astronomical Society Meeting 203, #144.01; Bulletin of the American Astronomical Society, Vol. 36, p.588

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We address which objects contributed most of the reionizing photons. Our argument assumes that reionization ended around z ˜6 and that this was a relatively quick process, i.e., that there was a non-negligible fraction of neutral hydrogen in the Universe at somewhat earlier epochs. Starting from our earlier estimate of the luminosity function (LF) of galaxies at z ˜6, we quantitatively show that the major sources of reionization are most likely dwarf galaxies (MAB>--17 mag).
Our approach allows us to put stronger constraints to the LF of faint galaxies at z ˜6. To have the Universe completely ionized at this redshift, the faint-end slope of the LF should be steeper than alpha=-1.6, which is the value measured at lower redshifts (z ˜3), unless either the adopted normalization (Phi*) of the LF or the clumping factor of the ionized hydrogen have been significantly underestimated. If the actual Phi* is lower than what we adopted by a factor of two, a steeper slope close to alpha=-2.0 is required. Our LF predicts a total of 50--80 z ˜6 galaxies in the upcoming HST Ultra Deep Field (UDF) to a depth of AB=28.4 mag, which can be used to constrain both Phi* and alpha.
We conclude that the least luminous galaxies that existed at this redshift should reach as low as some critical luminosity in order to accumulate the entire reionizing photon budget. On the other hand, the existence of significant amounts of neutral hydrogen at slightly earlier epochs, e.g. z ˜7, requires that the least luminous galaxies should not be fainter another critical value (i.e., the LF should converge at this point). This work was supported by NASA/JWST grant NAG5-12460.

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