Implications For Reionization Research Articles

The clustering of Lyman α emitters atz≈ 7: implications for reionization and host halo masses

The clustering of Lyman α emitters at<i>z</i>≈ 7: implications for reionization and host halo masses

Two epochs of globular cluster formation from deep field luminosity functions: implications for reionization and the Milky Way satellites

The ages of globular clusters in our own Milky Way are known with precision of about \pm 1 Gyr, hence their formation at redshifts z>~3 and their role in hierarchical cosmology and the reionization of the intergalactic medium remain relatively undetermined. Here we analyze the effect of globular cluster formation on the observed rest-frame UV luminosity functions (LFs) and UV continuum slopes of high redshift galaxies in the Hubble Ultra Deep Fields. We find that the majority of present day globular clusters have formed during two distinct epochs: at redshifts z ~ 2-3 and at redshifts z>~6. The birth of proto-GC systems produce the steep, faint-end slopes of the galaxy LFs, and because the brightness of proto-GCs fades 5 Myrs after their formation, their blue colors are in excellent agreement with observations. Our results suggest that: i) the bulk of the old globular cluster population with estimated ages >~12 Gyr (about 50% of the total population), formed in the relatively massive dwarf galaxies at redshifts z>~6; ii) proto-GC formation was an important mode of star formation in those dwarf galaxies, and likely dominated the reionization process. Another consequence of this scenario is that some of the most massive Milky Way satellites may be faint and yet undiscovered because tidal stripping of a dominant GC population precedes significant stripping of the dark matter halos of these satellites. This scenario may alleviate some remaining tensions between CDM simulations and observations.

IMPACT OF H2-BASED STAR FORMATION MODEL ON THEz⩾ 6 LUMINOSITY FUNCTION AND THE IONIZING PHOTON BUDGET FOR REIONIZATION

We present the results of a numerical study examining the effect of H_2-based star formation (SF) model on the rest-frame UV luminosity function and star formation rate function (SFRF) of z>=6 galaxies, and the implications for reionization. Using cosmological hydrodynamical simulations outfitted with an H_2-SF model, we find good agreement with our previous results (non-H_2 SF model) and observations at Muv<=-18. However at Muv>-18, we find that the LF deviates from both our previous work and current observational extrapolations, producing significantly fewer low-luminosity galaxies and exhibiting additional turnover at the faint end. We constrain the redshift evolution of this turnover point using a modified Schechter function that includes additional terms to quantify the turnover magnitude (Muv^t) and subsequent slope (Beta). We find that Muv^t evolves from Muv^t=-17.33 (at z=8) to -15.38 (z=6), while Beta becomes shallower by \Delta Beta=0.22 during the same epoch. This occurs in an Muv range which will be observable by JWST. By integrating the SFRF, we determine that even though H_2-SF model significantly reduces the number density of low luminosity galaxies at Muv>-18, it does not suppress the total SFR density enough to affect the capability of SF to maintain reionization.

Steep faint-end slopes of galaxy mass and luminosity functions at z≥ 6 and the implications for reionization

We present the results of a numerical study comparing photometric and physical properties of simulated z=6-9 galaxies to the observations taken by the WFC3 instrument aboard the Hubble Space Telescope. Using cosmological hydrodynamical simulations we find good agreement with observations in color-color space at all studied redshifts. We also find good agreement between observations and our Schechter luminosity function fit in the observable range, Muv<= -18, provided that a moderate dust extinction effect exists for massive galaxies. However beyond what currently can be observed, simulations predict a very large number of low-mass galaxies and evolving steep faint-end slopes from alpha_L = -2.15 at z=6 to alpha_L = -2.64 at z=9, with a dependence of |alpha_L| \propto (1+z)^0.59. During the same epoch, the normalization phi* increases and the characteristic magnitude Muv* becomes moderately brighter with decreasing redshift. We find similar trends for galaxy stellar mass function with evolving low-mass end slope from alpha_M = - 2.26 at z=6 to alpha_M = -2.87 at z=9, with a dependence of |alpha_M| \propto (1+z)^0.65. Together with our recent result on the high escape fraction of ionizing photons for low-mass galaxies, our results suggest that the low-mass galaxies are important contributor of ionizing photons for the reionisation of the Universe at z>=6.

Galaxies in the first billion years: implications for re-ionization and the star formation history at z&gt;6

AbstractWe discuss the selection of star-forming galaxies at z≃6 through the Lyman-break technique. Spitzer imaging implies many of these contain older stellar populations (&gt;200Myr) which produce detectable Balmer breaks. The ages and stellar masses (∼1010M⊙) imply that the star formation rate density at earlier epochs may have been significantly higher than at z≃6, and might have played a key role in re-ionizing the universe.

First Results from the Canada‐France High‐zQuasar Survey: Constraints on thez= 6 Quasar Luminosity Function and the Quasar Contribution to Reionization

We present preliminary results of a new quasar survey being undertaken with multicolor optical imaging from the Canada-France-Hawaii Telescope. The current data consist of 3.83 deg2 of imaging in the i' and z' filters to a 10 σ limit of z' -3.2 at 95% confidence. We find that the comoving space density of quasars brighter than M1450 = -23.5 declines by a factor of >25 from z = 2 to 6, mirroring the decline observed for high-luminosity quasars. We consider the contribution of the quasar population to the ionizing photon density at z = 6 and the implications for reionization. We show that the current constraints on the quasar population give an ionizing photon density 30% that of the star-forming galaxy population. We conclude that active galactic nuclei make a negligible contribution to the reionization of hydrogen at z ~ 6.