The Galaxy UV Luminosity Function Before the Epoch of Reionization

Abstract

We present a model for the evolution of the galaxy ultraviolet (UV) luminosity function (LF) across cosmic time where star formation is linked to the assembly of dark matter halos under the assumption of a mass dependent, but redshift independent, efficiency. We introduce a new self-consistent treatment of the halo star formation history, which allows us to make predictions at z > 10 (lookback time ∼ < 500 Myr), when growth is rapid. With a calibration at a single redshift to set the stellar-to-halo mass ratio, and no further degrees of freedom, our model captures the evolution of the UV LF over all available observations (0 ∼ < z ∼ < 10). The significant drop in luminosity density of currently detectable galaxies beyond z ∼ 8 is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, we derive a reionization optical depth τ = 0.056 +0.007 −0.010 , fully consistent with the latest Planck measurement, implying that the universe is fully reionized at z = 7.84 +0.65 −0.98 . In addition, our model naturally produces smoothly rising star formation histories for galaxies with L ∼ < L * in agreement with observations and hydrodynamical simulations. Before the epoch of reionization at z > 10 we predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope (α ∼ −3.5 at z ∼ 16). Finally, we construct forecasts for surveys with JWST and WFIRST and predict that galaxies out to z ∼ 14 will be observed. Galaxies at z > 15 will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.

Measurement of the Dark Matter Velocity Dispersion with Galaxy Stellar Masses, UV Luminosities, and Reionization

“…Thereafter hydrogen is highly ionized. For Table 2: At z = 8, for each k fs (t eq ) are presented the velocity dispersion cut-off M vd /M ⊙ of the linear total (dark matter plus baryon) mass M/M ⊙ ≈ νL UV /L ⊙ from Table 1, the corresponding cut-off AB-magnitude M UV ≈ 5.9 − 2.5 log 10 (νL UV /L ⊙ ), and the corresponding reionization optical depth τ from Figure 13 of [24]. A somewhat lower value of τ is obtained from Figure 2 of [12].…”

Scientific discovery with the James Webb Space Telescope

“…The lack of observational constraints provides little leverage to test models with different assumptions on star formation efficiency and feedback. As an example, the models of [238] and [239] are shown and diverge by large amounts at higher redshifts. The first Webb extragalactic surveys will resolve the differences in these models by extending measurements of the cosmic star formation rate to higher redshifts and with robust samples of galaxies.…”

“…These data can test for the detection of first light by distinguishing between divergent theoretical luminosity functions that predict the early redshift distribution of galaxies (e.g., see Figure 16) and also through galaxy color analysis of individual objects to explore their metal content. As successfully demonstrated on Hubble, Webb will also take advantage of natural gravitational lensing by massive galaxy clusters to explore the very high-redshift galaxy census [239,276]. At redshifts >15, deep integrations with the aid of lensing can reveal an order of magnitude more galaxies than standard blank fields.…”

Simulating Structure Formation with Ultra-light Bosonic Dark Matter

“…This turnover has indeed been found by investigating the Hubble Frontier Field (HFF) data, suggesting a best fit FDM mass 0.8 < m 22 < 3.2 [Leung et al, 2018]. JWST has the potential to probe even fainter lensed galaxies [Mason et al, 2015] especially employing the same deep lenses as the HFF for which magnification maps are best understood [Lam et al, 2014;Diego et al, 2015].…”