Unveiling the nature of infrared bright, optically dark galaxies with early JWST data

Over the last few years, both Atacama Large Millimeter/submillimeter Array (ALMA) and Spitzer observations have revealed a population of likely massive galaxies at z > 3 that was too faint to be detected in Hubble Space Telescope ( HST) rest-frame ultraviolet imaging. However, due to the very limited photometry for individual galaxies, the true nature of these so-called HST-dark galaxies has remained elusive. Here, we present the first sample of such galaxies observed with very deep, high-resolution NIRCam imaging from the Early Release Science programme CEERS. 30 HST-dark sources are selected based on their red colours across 1.6-4.4 mu m. Their physical properties are derived from 12-band multiwavelength photometry, including ancillary HST imaging. We find that these galaxies are generally heavily dust-obscured (A(V) similar to 2 mag), massive (log (M/M-circle dot similar to) similar to 10), star-forming sources at z similar to 2-8 with an observed surface density of similar to 0.8 arcmin(-2). This suggests that an important fraction of massive galaxies may have been missing from our cosmic census at z > 3 all the way into the Epoch of Reionization. The HST-dark sources lie on the main sequence of galaxies and add an obscured star formation rate density of 3.2(-1.3)(+1.8) x10(-3) M similar to yr(-1) Mpc-3at z similar to 7, showing likely presence of dust in the Epoch of Reionization. Our analysis shows the unique power of JWST to reveal this previously missing galaxy population and to provide a more complete census of galaxies at z = 2-8 based on rest-frame optical imaging.