April 8
Inner Structure and ISM of Early Galaxies from Cosmic Dawn to the EoR: Insights from FirstLight Simulations and JWST/ALMA
Speaker: Dr. Yurina Nakazato, CCA, Flatiron Institute
Abstract: The unprecedented sensitivity and resolution of JWST and ALMA have transformed our view of the early Universe. At z > 6, we observe diverse galaxy morphologies including clumpy and disk-like systems and spatially inhomogeneous ISM. In this talk, I present theoretical insights into these observations using the FirstLight cosmological zoom-in simulations.
For [OIII] emitters at z = 6–9, we have developed a physical model of HII regions for each stellar particle and calculated [OIII] line emission by combining the radiative transfer code CLOUDY. We show that high-redshift galaxies have roughly 5-10 times stronger [OIII] emission than local galaxies at the same star formation rate, driven by high ionization parameters due to low metallicity and massive stars. We also derive emission line diagrams using rest-frame optical and far-infrared line ratios accessible with JWST and ALMA, demonstrating that these diagnostics can probe the existence of multi-phase HII regions recently suggested by observations.
Beyond emission line properties, we further conducted post-processing dust radiative transfer to investigate spatially resolved attenuation curves. In massive galaxies with Ms >~ 1e9 Msun at z = 6–9, star-forming clumps show substantially flatter attenuation than system-integrated values, owing to large dust column densities and well-mixed geometries. Building on the same dust radiative transfer framework, we also present our latest results on size-mass relations derived from realistic NIRCam mock images that account for dust attenuation, noise, and PSF effects.
Host: Ankita Bera