Abstract:
Massive quiescent galaxies (QGs) that no longer form stars emerged at least as early as redshift z ~ 5. Understanding their evolutionary history is a critical piece of building a coherent picture of cosmic evolution. One key revelation from multiple decades of Hubble Space Telescope (HST) observations was that the majority of massive QGs at cosmic noon have extremely compact stellar distributions. But those measurements were limited to z < 2.5 where the rest-optical (stellar) morphologies can still be measured with HST. With James Webb Space Telescope (JWST), we can now extend the study of the structure of QGs beyond z>3.
In my talk, I will first present our recent study of the UV-to-NIR size evolution of massive QGs over 0.5<z<5 using deep JWST/NIRCam imaging. We find that the members of the first generation of massive QGs at z > 3 are even smaller than those at z ∼ 2, and their stellar morphologies are extremely compact with stellar mass surface densities approaching the maximum allowed value set by stellar feedback.
With JWST’s MIRI, we can further constrain the structure of those earliest QGs at rest-frame > 3um where the hot dust emission, if present, becomes increasingly important relative to starlight. I will present a case study of one of the earliest known massive QGs, GS-9209, at z~4.7. We obtained 9-band MIRI imaging covering up to ~25 um. We show that the observed MIRI fluxes cannot be reproduced by starlight alone, i.e. the need for hot dust emission. Relative to the extremely compact (size ~ 200pc) stellar morphology of GS-9209, its hot dust emission is significantly more extended. Moreover, evidence that the hot dust has preferentially been evacuated in the galaxy center is also found in our MIRI imaging. Further, we obtained deep ALMA/Band-7 (160um rest-frame) observation at a 0".2 angular resolution to constrain the cold dust emission of GS-9209. The FIR dust emission is robustly detected. Like the hot dust emission detected by MIRI, the cold dust emission is also extended, and shows a clear deficit at the center of GS-9209.
Putting together the observations from HST, JWST/NIRCam and MIRI, and ALMA, for the first time we have a truly panchromatic view of the (stellar, gas/dust) structure of the earliest massive QGs. I will finally discuss the implications of our findings for the formation of the first generation of QGs.
