A Large Population of Faint 8<z<16 Galaxies Found in the First JWST NIRCam Observations of the NGDEEP Survey

Abstract

We present an early analysis on the search for high redshift galaxies using the deepest public JWST imaging to date, the NGDEEP field. This data consists of 6-band NIRCam imaging on the Hubble Ultra Deep Field-Par2, covering a total area of 6.3 arcmin${}^2$. Based on our initial reduction of the first half of this survey, we reach 5$\ddot{I}ƒ$ depths up to mag = 29.5--29.9 between $1-5$ um. Such depths present an unprecedented opportunity to begin exploring the early Universe with JWST. As such, we find high redshift galaxies in this field by examining the spectral energy distribution of these systems and present 18 new $z>8$ systems identified using two different photometric redshift codes: LePhare and EAZY, combined with other significance criteria. The highest redshift object in our sample is at $z=15.57_{-0.38}^{+0.39}$, which has a blue beta slope of ${\hat{I}}^2=-3.25_{-0.46}^{+0.41}$ and a very low inferred stellar mass of $M_{\ast }=10^{7.39}$ M_0,. We also discover a series of faint, low-mass dwarf galaxies with $M_{\ast }<10^{8.5}$ M_0 at $z\sim 9$ that have blue colors and UV slopes. The structure of these galaxies is such that they all have very flat surface brightness profiles and small sizes $<1\mathrm{kpc}$. We also compare our results to theory, finding no significant disagreement with some CDM based models.The discovery of these objects, most of which are low luminosity and inferred stellar mass, demonstrates the power of probing continuously deeper into the Universe, pointing the way to deeper, or similar depth but wider area, surveys and demonstrate the critical need for JWST deep fields to explore this aspect of the early Universe.

ApJL submitted. Added acknowledgements and slight change in title. Mosaics of our NGDEEP reductions are available here: tinyurl.com/yckcfnxu