Host: Xianzhong Zheng
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Abstract:
JWST observations have confirmed the existence of UV-luminous galaxies at z>14 and the emergence of first massive quiescent galaxies at z>4. The presence of these two populations suggests that the most massive galaxies at z~8 should undergo vigorous starburst with star formation rate (SFR) ~ 100 Msun/yr. However, such galaxies are missing from the current JWST observations. I show that the brightest galaxies at z~8 might have been already highly dust-obscured, and thus remain dark and undetected from the current JWST surveys. This is demonstrated by the discovery of two "NIRCam-dark" galaxies as companions of UV-luminous quasars at z=6.6 with ALMA. These galaxies are more obscured than galaxies like Arp 220, matching the mass and SFR of the progenitors of z~4 quiescent galaxies, while remain undetected in medium-deep NIRCam images. Although their number density is highly unconstrained, they could be as abundant as ~30% of both the quiescent galaxies at z~4 and UV-luminous galaxies at z>10. Simply placing these galaxies at z~8, they will remain undetected with the major JWST and ALMA wide-field surveys. To fully trace the evolution of massive galaxies and dust-obscured cosmic star formation at z≳ 8, wide-field JWST/NIRCam imaging and slitless spectroscopic surveys of early protoclusters are essential. I highlight the emerging opportunities in this regard with the ongoing JWST survey campaigns totaling more than 1000 telescope hours with myself as PI / co-PI and key co-PIs.
Biography:
Fengwu Sun is a postdoctoral researcher at Harvard University. He obtained B.S. degree at Peking University in 2018 and Ph.D. degree at the University of Arizona in 2023. He is a member of the James Webb Space Telescope (JWST) near-infrared camera (NIRCam) instrument science team. He commissioned and calibrated the wide-field slitless spectroscopic mode of NIRCam. He is the PI / co-PI / co-I of multiple JWST programs totaling more than 2000 telescope hours.
