Thomson optical depth τ measurements from Planck provide new insights into the reionization of the universe. In pursuit of model-independent constraints on the properties of the ionizing sources, we determine the empirical evolution of the cosmic ionizing emissivity. We use a simple two-parameter model to map out the evolution in the emissivity at z 6 from the new Planck optical depth τ measurements, from the constraints provided by quasar absorption spectra and from the prevalence of Lyman α emission in z ∼ 7-8 galaxies. We find the redshift evolution in the emissivityṄ ion (z) required by the observations to be (d log 10Ṅion /dz) z=8 = −0.15 +0.08 −0.11 ((d log 10Ṅion /dz) z=8 = −0.19 +0.09 −0.11 for a flat prior), largely independent of the assumed clumping factor C HII and entirely independent of the nature of the ionizing sources. The trend inṄ ion (z) is well-matched by the evolution of the galaxy U V -luminosity density (dlog 10 ρ UV /dz = −0.11 ± 0.04) to a magnitude limit −13 mag, suggesting that galaxies are the sources that drive the reionization of the universe. The role of galaxies is further strengthened by the conversion from the UV luminosity density ρ UV toṄ ion (z) being possible for physically-plausible values of the escape fraction f esc , the Lyman-continuum photon production efficiency ξ ion , and faint-end cut-off M lim to the luminosity function. Quasars/AGN appear to match neither the redshift evolution nor normalization of the ionizing emissivity. Based on the inferred evolution in the ionizing emissivity, we estimate that the z ∼ 10 UV-luminosity density is 8 +15 −4 × lower than at z ∼ 6, consistent with the observations. The present approach of contrasting the inferred evolution of the ionizing emissivity with that of the galaxy UV luminosity density adds to the growing observational evidence that faint, star-forming galaxies drive the reionization of the universe.

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We investigate the properties and clustering of halos, galaxies and blackholes to z = 0 in the high resolution hydrodynamical simulation MassiveBlack-II (MBII). MBII evolves a ΛCDM cosmology in a cubical comoving volume of V box = (100Mpc/h) 3 and is able to resolve halos of mass M halo = 10 9 M /h. It is the highest resolution simulation of this size which includes a self-consistent model for star formation, black hole accretion and associated feedback. We provide a simulation browser web application which enables interactive search and tagging of halos, subhalos and their properties and publicly release our galaxy catalogs to the scientific community. Our analysis of the halo mass function in MBII reveals that baryons have strong effects, with changes in the halo abundance of 20-35% below the knee of the mass function (M halo 10 13.2 M /h at z = 0) when compared to fits based on dark matter only simulations. We provide a fitting function for the halo mass function valid for the full range of halo masses in MBII out to redshift z = 11 and discuss how the onset of nonuniversal behavior in the mass function limits the accuracy of our fit. We examine the halo occupation distribution of satellite galaxies and present results valid over 5 orders of magnitude in host halo mass. We study the clustering of galaxies, and in particular the evolution and scale dependence of stochasticity and bias. Comparison with observational data for these quantities for samples with different stellar mass thresholds yields reasonable agreement. Using population synthesis, we find that the shape of the cosmic spectral energy distribution predicted by MBII is consistent with observations, but lower in amplitude. The Galaxy Stellar Mass Function (GSMF) function is broadly consistent with observations at z ≥ 2. At z < 2, observations probe deeper into the faint end and the population of passive low mass (for M * < 10 9 M ) galaxies in the simulation makes the GSMF too steep. At the high mass end (M * > 10 11 M ) galaxies hosting bright AGN make significant contributions to the GSMF. The quasar bolometric luminosity function is also largely consistent with observations. We note however that more efficient AGN feedback (beyond simple thermal coupling used here) is likely necessary for the largest, rarest objects/clusters at low redshifts.

The Galaxy And Mass Assembly (GAMA) survey furnishes a deep redshift catalog that, when combined with the Wide-field Infrared Explorer (WISE), allows us to explore for the first time the mid-infrared properties of > 110, 000 galaxies over 120 deg 2 to z ≃ 0.5. In this paper we detail the procedure for producing the matched GAMA-WISE catalog for the G12 and G15 fields, in particular characterising and measuring resolved sources; the complete catalogs for all three GAMA equatorial fields will be made available through the GAMA public releases. The wealth of multiwavelength photometry and optical spectroscopy allows us to explore empirical relations between optically determined stellar mass (derived from synthetic stellar population models) and 3.4µm and 4.6µm WISE measurements. Similarly dust-corrected Hα-derived star formation rates can be compared to 12µm and 22µm luminosities to quantify correlations that can be applied to large samples to z < 0.5. To illustrate the applications of these relations, we use the 12µm star formation prescription to investigate the behaviour of specific star formation within the GAMA-WISE sample and underscore the ability of WISE to detect star-forming systems at z ∼ 0.5. Within galaxy groups (determined by a sophisticated friends-of-friends scheme), results suggest that galaxies with a neighbor within 100 h −1 kpc have, on average, lower specific star formation rates than typical GAMA galaxies with the same stellar mass.

We present a compilation of measurements of the stellar mass density as a function of redshift. Using this stellar mass history we obtain a star formation history and compare it to the instantaneous star formation history. For z < 0.7 there is good agreement between the two star formation histories. At higher redshifts the instantaneous indicators suggest star formation rates larger than that implied by the evolution of the stellar mass density. This discrepancy peaks at z= 3 where instantaneous indicators suggest a star formation rate around 0.6 dex higher than those of the best fit to the stellar mass history. We discuss a variety of explanations for this inconsistency, such as inaccurate dust extinction corrections, incorrect measurements of stellar masses and a possible evolution of the stellar initial mass function.