Exploring Cosmic Dawn with PANORAMIC. I. The Bright End of the UV Luminosity Function at <i>z</i> ∼ 9–17

Abstract In its first 2 yr of operation, the James Webb Space Telescope has enabled the discovery of a surprising number of UV-bright galaxies at z ∼ 10–14. Their number density is still relatively uncertain, due to cosmic variance effects, and the limited survey area with deep imaging. Here, we combine pure-parallel imaging from the PANORAMIC survey with data from legacy fields to constrain the bright end ( M UV < −18.5) of the UV luminosity function (UVLF) over 0.28 deg 2 of NIRCam imaging in six or more filters, and along 35 independent lines of sight. Using conservative color selections, we compile robust dropout samples at z ∼ 10, z ∼ 13, and z ∼ 17, and identify 16 new candidates from PANORAMIC. Our inferred UVLFs at z ∼ 10 are consistent with literature results and we confirm the high abundance of galaxies at the bright end ( M UV ≲ −21) with better number statistics. We find somewhat lower number densities at z ∼ 13 compared to previous studies, and no robust candidates at z ∼ 17, indicating a rapid evolution of the galaxy population from z ∼ 10–17. The improved upper limits at z ∼ 17 imply that the cosmic UV luminosity density drops by at least a factor ∼50 from z ∼ 10 to z ∼ 17. Comparing our results to models proposed to explain the abundance of UV-bright galaxies at z ≳ 10, we conclude that a modest increase in the star formation efficiency, or in the burstiness of star formation, a more top-heavy initial mass function, a lack of dust attenuation, or a combination of these effects at z ≳ 10, is sufficient to match our observational constraints.