Title: HST-dark galaxies: Unveiling the Nature of Infrared Bright, Optically Dark Galaxies with Early JWST Imaging and Spectroscopy
Speaker: Laia Barrufet (University of Edinburgh)
Over the past decade, low-resolution infrared observations have revealed a population of bright IR galaxies undetected with HST, termed “HST-dark galaxies. Nevertheless, their photometric redshifts and physical properties were uncertain due to the limited photometry even including ALMA data. This can result in an incomplete galaxy census at earlier times, due to UV-faint galaxy populations such as quiescent or dust-obscured sources. The key question is: how common are such sources at z>3—4 and what is their contribution to the cosmic star formation rate density? With JWST, we can study for the first time the physical properties of this enigmatic population. In this talk, I will summarise the progress in our understanding of HST-dark galaxies facilitated by JWST data, employing both photometry and spectroscopy.
In the first part of the talk, I will expose the progress made with HST-dark galaxies thanks to JWST/NIRcam photometry. I will focus on the results of 30 HST-dark sources selected based on their red colours across 1.6 to 4.4 microns with NIRCam imaging from the Early Release Science Program CEERS. These galaxies are generally highly dust-attenuated, massive, star-forming sources at z∼2—8. Our analysis underscores the unique capability of JWST in uncovering this previously elusive galaxy population and in conducting a more complete census of galaxies at z>3 based on rest-frame optical imaging. Interestingly, HST-dark galaxies present a considerable contribution to the obscured star formation rate density at z∼7, already in the Epoch of Reionization.
In the second part of the talk, I will present the initial NIRSpec spectra of HST-dark galaxies from my GO Cycle-1 program ‘Quiescent or dusty? Unveiling the nature of extremely red galaxies at z>3’. I will showcase spectra for highly attenuated dusty galaxies and quiescent galaxies and their physical characteristics. Despite the prevalence of dust in most galaxies, they exhibit distinct spectral features. Furthermore, HST-dark galaxies harbour hidden gems: quiescent galaxies at redshifts > 3, for which I will present spectra and demonstrate NIRSpec’s capacity to analyze these sources.
Finally, I will explore potential avenues for future research involving HST-dark galaxies, leveraging the synergy between JWST and ALMA.
hongo-astrotalks (at-sign) astron.s.u-tokyo.ac.jp