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Paper: Galaxy Evolution in the Last ∼ 11 Gyrs and the Role of Mergers
Volume: 477, Galaxy Mergers in an Evolving Universe
Page: 155
Authors: Sobral, D.; Best, P.; Smail, I.; Geach, J.; Stott, J.; Matsuda, Y.
Abstract: We present results from deep and wide multi-epoch narrow-band surveys to search for Hα emitters at z = 0.4, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyrs) using UKIRT, Subaru and the VLT. A total of over 500 Hα emitters per redshift are robustly selected (Σ>3, EW0(Hα)>25 Å) over a total of 2 deg2 in the COSMOS and UDS fields, 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 = –1.6±0.1 over z = 0–2.23, showing no significant evolution, while the characteristic luminosity of SF galaxies, L*, evolves significantly as log L*(z) = 0.45z + log L*z=0. Our uniform analysis allows to derive a fully self-consistent Hα star formation history of the Universe, showing a clear rise up to z ∼ 1, followed by a further milder increase at least up to z ∼ 2.2, which can be simply described by log ρSFR = –0.14T – 0.23 for T > 2.9 Gyrs. Furthermore, we find important morphology-Hα relations at all epochs at least up to z ∼ 1.5, showing no evolution in respect to L* at each z, but evolving if a fixed luminosity limit is applied for all redshifts. We show that it is the evolution of disk galaxies from z ∼ 1–2 to z ∼ 0 that is responsible for the decline in the cosmic star formation activity – not the decline in (major-)merger activity. Potential merger-driver star-formation activity only represents ≈ 20% of the total star formation rate density at any epoch, at least since z ∼ 1.5, and therefore the bulk of the stellar mass density assembly in the Universe is not a result of major-mergers.
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