Affiliation: Rutgers University

Contribution: Oral

Title: Using Galaxies at z>10 to Probe Burstiness and the IMF

Abstract: z>10 galaxies confirmed by JWST display less evolution in their luminosity functions and higher inferred stellar masses than is expected in a Lambda CDM cosmology. The likely explanation is some combination of stochastic star formation, with galaxies experiencing rapid bursts dominating the observed samples, and a non-standard Initial Mass Function (IMF), which is likely present since the Cosmic Microwave Background temperature sets a meaningful floor at these redshfits. Unfortunately, even JWST does not offer sufficient rest-frame optical photometry at z>10 to measure galaxies’ stellar masses or star formation histories robustly. I will present results obtained by applying our novel Gaussian Process method of non-parametric star formation history (SFH) reconstruction (Iyer & Gawiser 2017; Iyer et al. 2019; Iyer et al. 2022) to spectroscopically confirmed galaxies at 5<z<10 with photometry in JWST-CEERS. We have shown that galaxy SFHs can be reconstructed reliably over 1-2 Gyr back in time from the moment of observation. For galaxies at 5<z<10, that brings them all the way back to the Big Bang. At these lower redshifts, JWST offers sufficient rest-frame UV-through-optical photometry to perform SFH reconstruction. We use the GUREFT simulations (Yung et al. 2023) to determine the average stellar mass growth as a function of redshift for galaxies with properties matching the observed 5<z<10 sample.
I will present the star formation rates and stellar masses of these galaxies’ progenitors at z>10. Reconciling the progenitor properties with the photometry of the observed z>10 galaxies breaks the degeneracy between IMF evolution and star formation stochasticity to enhance our knowledge of the first galaxies.

This contribution can be found here (pdf).