This paper presents new deep and wide narrow-band surveys undertaken with UKIRT, Subaru and the VLT; a unique combined effort to select large, robust samples of Hα star-forming galaxies at z = 0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyrs) in a uniform manner over ∼ 2 deg 2 in the COSMOS and UDS fields. The deep multi-epoch Hα surveys reach a matched 3 σ flux limit of ≈ 3 M yr −1 out to z = 2.2 for the first time, while the wide area and the coverage over two independent fields allow to greatly overcome cosmic variance and assemble by far the largest samples of Hα emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 Hα emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the Hα luminosity function and its evolution. The faint-end slope of the Hα luminosity function is found to be α = −1.60 ± 0.08 over z = 0 − 2.23, showing no significant evolution. The characteristic luminosity of SF galaxies, L * Hα , evolves significantly as log L * Hα (z) = 0.45z + log L * z=0 . This is the first time Hα has been used to trace SF activity with a single homogeneous survey at z = 0.4−2.23. Overall, the evolution seen with Hα is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as FIR and UV, jointly pointing towards the bulk of the evolution in the last 11 Gyrs being driven by a statistically similar SF population across cosmic time, but with a strong luminosity increase from z ∼ 0 to z ∼ 2.2. Our uniform analysis allows to derive the Hα star formation history of the Universe (SFRH), showing a clear rise up to z ∼ 2.2, for which the simple parametrisation log 10 ρ SFR = −2.1(1 + z) −1 is valid over 80 per cent of the age of the Universe. The results reveal that both the shape and normalisation of the Hα SFRH are consistent with the measurements of the stellar mass density growth, confirming that our Hα SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last ∼ 11 Gyrs is responsible for producing ∼ 95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyrs between z = 1.2-2.2, and the other half in 8 Gyrs (since z < 1.2). If the star-formation rate density continues to decline with time in the same way as seen in the past ∼ 11 Gyrs, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value.

We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 deg 2 of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited, and contains 786 clusters with richness λ > 20 (roughly equivalent to M 500c 10 14 h −1 70 M ) and 0.2 < z < 0.9. The DR8 catalog consists of 26311 clusters with 0.08 < z < 0.6, with a sharply increasing richness threshold as a function of redshift for z 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the σ z /(1 + z) ∼ 0.01 level for z 0.7, rising to ∼ 0.02 at z ∼ 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and massrichness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.

We explore a large uniformly selected sample of Hα selected star-forming galaxies (SFGs) at z = 0.40, 0.84, 1.47, 2.23 to unveil the evolution of the star formation rate (SFR) function and the stellar mass function. We find strong evolution in the SFR function, with the typical SFR of SFGs declining exponentially in the last 11 Gyrs as SFR * (T [Gyr])=10 4.23/T +0.37 M yr −1 , but with no evolution in the faint-end slope, α ≈ −1.6. The stellar mass function of SFGs, however, reveals little evolution: α ≈ −1.4, M * ∼ 10 11.2±0.2 M and just a slight increase of ∼ 2.3× in Φ * from z = 2.23 to z = 0.4. The stellar mass density within SFGs has been roughly constant since z = 2.23 at ∼ 10 7.65±0.08 M Mpc −3 , comprising ≈ 100% of the stellar mass density in all galaxies at z = 2.23, and declining to ≈ 20% by z = 0.40, driven by the rise of the passive population. We find that SFGs with ∼ 10 10.0±0.2 M contribute most to the SFR density (ρ SFR ) per d log 10 M, and that there is no significant evolution in the fractional contribution from SFGs of different masses to ρ SFR or ρ SFR (d log 10 M) −1 since z = 2.23. Instead, we show that the decline of SFR * and of ρ SFR are primarily driven by an exponential decline in SFRs at all masses. Our results have important implications not only on how SFGs need to be quenched across cosmic time, but also on the driver(s) of the exponential decline in SFR * from ∼ 66 M yr −1 to 5 M yr −1 since z ∼ 2.23.

No abstract

The KMOS Redshift One Spectroscopic Survey (KROSS) is an ESO guaranteed time survey of 795 typical star-forming galaxies in the redshift range z = 0.8−1.0 with the KMOS instrument on the VLT. In this paper we present resolved kinematics and star formation rates for 584 z ∼ 1 galaxies. This constitutes the largest near-infrared Integral Field Unit survey of galaxies at z ∼ 1 to date. We demonstrate the success of our selection criteria with 90% of our targets found to be Hα emitters, of which 81% are spatially resolved. The fraction of the resolved KROSS sample with dynamics dominated by ordered rotation is found to be 83 ± 5%. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ∼ 35%, and the majority are consistent with being marginally unstable (Toomre Q ∼ 1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star-formation rates in these typical z ∼ 1 galaxies, leading to the ten-fold enhanced starformation rate density. Finally, by comparing the gas masses obtained from inverting the starformation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2 r e (9.5 kpc) of 65 ± 12%, in agreement with the results from hydrodynamic simulations of galaxy formation.