NGDEEP Epoch 1: The Faint End of the Luminosity Function at z 9-12 from Ultradeep JWST Imaging

We present a robust sample of very high redshift galaxy candidates from the first epoch of JWST/NIRCam imaging from the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey. The NGDEEP NIRCam imaging, spanning 9.7 arcmin2 in the Hubble Ultra Deep Field Parallel Field 2, reaches m = 30.4 (5s, point-source, 2" diameter apertures corrected to total) in F277W, making it the deepest public JWST GO imaging data set to date. We describe our detailed data reduction process of the six-filter broadband JWST/NIRCam imaging, incorporating custom corrections for systematic effects to produce high-quality calibrated images. Using robust photometric redshift selection criteria, we identify a sample of 38 z greater than or similar to 9 galaxy candidates. These objects span a redshift range of z = 8.5-15.8 and apparent magnitudes of m(F277W) = 27-30.5 AB mag, reaching similar to 1.5 mag deeper than previous public JWST imaging surveys. We calculate the rest-frame ultraviolet luminosity function at z similar to 9 and 11 and present a new measurement of the luminosity function faint-end slope at z similar to 11. We find a faintend slope of a = -2.5 +/- 0.4 and -2.2 +/- 0.2 at z similar to 9 and 11, respectively. This is consistent with no significant evolution in the faint-end slope and number density from z = 9 to 11. Comparing our results with theoretical predictions, we find that some models produce better agreement at the faint end than the bright end. These results will help to constrain how stellar feedback impacts star formation at these early epochs.