Speakers: Giorgia Girardi (Università degli Studi di Padova)
Over the last few years, both ALMA and Spitzer/IRAC observations have revealed a population of likely massive galaxies at z>3 that was too faint to be detected in 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 Program CEERS. 30 HST-dark sources are selected based on their red colours across 1.6 μm to 4.4 μm. Their physical properties are derived from 12-band multi-wavelength photometry, including ancillary HST imaging. We find that these galaxies are generally heavily dust-obscured (AV∼2 mag), massive (log(M/M⊙)∼10), star-forming sources at z∼2−8 with an observed surface density of ∼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 Reionization epoch. The HST-dark sources lie on the main sequence of galaxies and add an obscured star formation rate density (SFRD) of 3.2+1.8−1.3×10−3M⊙/yr/Mpc3 at z∼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.