The bright end of the galaxy luminosity function at z≃7 from the VISTA VIDEO survey

We have conducted a search for z≃7 Lyman break galaxies over 8.2 square degrees of near-infrared imaging from the VISTA Deep Extragalactic Observations (VIDEO) survey in the XMM-Newton – Large Scale Structure (XMM-LSS) and the Extended Chandra Deep Field South (ECDF-S) fields. Candidate galaxies were selected from a full photometric redshift analysis down to a Y+J depth of 25.3 (5σ), utilizing deep auxiliary optical and Spitzer/IRAC data to remove brown dwarf and red interloper galaxy contaminants. Our final sample consists of 28 candidate galaxies at 6.5≤z≤7.5 with −23.5≤MUV≤−21.6. We derive stellar masses of 9.1≤log10(M/M⊙)≤10.9 for the sample, suggesting that these candidates represent some of the most massive galaxies known at this epoch. We measure the rest-frame UV luminosity function (LF) at z≃7, confirming previous findings of a gradual decline in number density at the bright-end (MUV<−22) that is well described by a double-power law (DPL). We show that quasar contamination in this magnitude range is expected to be minimal, in contrast to conclusions from recent pure-parallel Hubble studies. Our results are up to a factor of ten lower than previous determinations from optical-only ground-based studies at MUV≲−23. We find that the inclusion of YJHKs photometry is vital for removing brown-dwarf contaminants, and z≃7 samples based on red-optical data alone could be highly contaminated (≳50 per cent). In comparison with other robust z>5 samples, our results further support little evolution in the very bright-end of the rest-frame UV LF from z=5−10, potentially signalling a lack of mass quenching and/or dust obscuration in the most massive galaxies in the first Gyr.

Reference: The bright end of the galaxy luminosity function at z≃7 from the VISTA VIDEO survey, R. G. VaradarajR. A. A. BowlerM. J. JarvisN. J. AdamsB. Häußler, Submitted to MNRAS, arXiv:2304.02494