We present the results of a search for bright (-22.7 ≤ MUV≤ -20.5) Lyman-break galaxies at z ≃ 6 within a total of 1.65deg2 of imaging in the UltraVISTA/Cosmological EvolutionSurvey (COSMOS) and United Kingdom Infrared Telescope Deep Sky Survey(UKIDSS) Ultra Deep Survey (UDS) fields. The deep near-infrared imagingavailable in the two independent fields, in addition to deep optical(including z'-band) data, enables the sample of z ≃ 6star-forming galaxies to be securely detected longward of the break (incontrast to several previous studies). We show that the expectedcontamination rate of our initial sample by cool Galactic brown dwarfsis ≲3 per cent and demonstrate that they can be effectively removedby fitting brown dwarf spectral templates to the photometry. At z ≃6, the galaxy surface density in the UltraVISTA field exceeds that inthe UDS by a factor of ≃ 1.8, indicating strong cosmic varianceeven between degree-scale fields at z > 5. We calculate the brightend of the rest-frame Ultraviolet (UV) luminosity function (LF) at z≃ 6. The galaxy number counts are a factor of ˜1.7 lower thanpredicted by the recent LF determination by Bouwens et al. In comparisonto other smaller area studies, we find an evolution in thecharacteristic magnitude between z ≃ 5 and z ≃ 7 of ΔM*˜ 0.4, and show that a double power law or a Schechter functioncan equally well describe the LF at z = 6. Furthermore, the bright endof the LF appears to steepen from z ≃ 7 to z ≃ 5, which couldindicate the onset of mass quenching or the rise of dust obscuration, aconclusion supported by comparing the observed LFs to a range of theoretical model predictions.
|Journal||Monthly Notices of the Royal Astronomical Society|
|Publication status||Published - 1 Sep 2015|
- galaxies: evolution
- galaxies: formation
- galaxies: high-redshift
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- School of Physics and Astronomy - Personal Chair in Extragalactic Astrophysics
Person: Academic: Research Active