Characterizing the evolving K-band luminosity function using the UltraVISTA, CANDELS and HUDF surveys

Abstract

We present the results of a new study of the K-band galaxy luminosity function (KLF) at redshifts z ≤ 3.75, based on a nested combination of the UltraVISTA, Cosmic Assembly Near-infrared Deep Legacy Extragalactic Survey and HUDF surveys. The large dynamic range in luminosity spanned by this new data set (3–4 dex over the full redshift range) is sufficient to clearly demonstrate for the first time that the faint-end slope of the KLF at z ≥ 0.25 is relatively steep (−1.3 ≤ α ≤ −1.5 for a single Schechter function), in good agreement with recent theoretical and phenomenological models. Moreover, based on our new data set, we find that a double Schechter function provides a significantly improved description of the KLF at z ≤ 2. At redshifts z ≥ 0.25, the evolution of the KLF is remarkably smooth, with little or no evolution evident at faint (MK ≥ −20.5) or bright magnitudes (MK ≤ −24.5). Instead, the KLF is seen to evolve rapidly at intermediate magnitudes, with the number density of galaxies at MK ≃−23 dropping by a factor of ≃5 over the redshift interval 0.25 ≤ z ≤ 3.75. Motivated by this, we explore a simple description of the evolving KLF based on a double Schechter function with fixed faint-end slopes (α1 = −0.5, α2 = −1.5) and a shared characteristic magnitude (M⋆K MK⋆). According to this parametrization, the normalization of the component which dominates the faint end of the KLF remains approximately constant, with ϕ⋆2 ϕ2⋆ decreasing by only a factor of ≃2 between z ≃0 and 3.25. In contrast, the component which dominates the bright end of the KLF at low redshifts evolves dramatically, becoming essentially negligible by z ≃3. Finally, we note that within this parametrization, the observed evolution of M⋆K MK⋆between z ≃0 and 3.25 is entirely consistent with M⋆K MK⋆ corresponding to a constant stellar mass of M⋆ ≃5 × 1010  M⊙ at all redshifts.

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