A Steep Decline in the Galaxy Space Density beyond Redshift 9 in the CANUCS UV Luminosity Function
Willott, Chris J.; Martis, Nicholas S.; Rihtaršič, Gregor; Bradač, Maruša; Asada, Yoshihisa; Brammer, Gabe; Desprez, Guillaume; Estrada-Carpenter, Vince; Matharu, Jasleen; Muzzin, Adam; Mowla, Lamiya; Noirot, Gaël; Sarrouh, Ghassan T. E.; Sawicki, Marcin; Strait, Victoria; Abraham, Roberto; Iyer, Kartheik G.; Withers, Sunna
Canada, Japan, Slovenia, United States, Denmark
Abstract
We present a new sample of 158 galaxies at redshift z > 7.5 selected from deep James Webb Space Telescope (JWST) NIRCam imaging of five widely separated sight lines in the CANUCS survey. Two-thirds of the pointings and 80% of the galaxies are covered by 12–14 NIRCam filters, including seven to nine medium bands, providing accurate photometric redshifts and robustness against low-redshift interlopers. A sample of 28 galaxies at z > 7.5 with spectroscopic redshifts shows a low systematic offset and scatter in the difference between photometric and spectroscopic redshifts. We derive the galaxy UV luminosity function at redshifts 8–12, finding a slightly higher normalization than previously seen with the Hubble Space Telescope at redshifts 8–10. We observe a steeper decline in the galaxy space density from z = 8 to 12 than found by most JWST Cycle 1 studies. In particular, we find only eight galaxies at z > 10 and none at z > 12.5, with no z > 10 galaxies brighter than F277W AB = 28 or M UV = ‑20 in our unmasked, delensed survey area of 53.4 arcmin2. We attribute the lack of bright z > 10 galaxies in CANUCS compared to GLASS and CEERS to intrinsic variance in the galaxy density along different sight lines. The evolution in the CANUCS luminosity function between z = 8 and 12 is comparable to that predicted by simulations that assume a standard star formation efficiency without invoking any special adjustments.