Exploring spatially resolved metallicities, dynamics, and outflows in low-mass galaxies at z ∼ 7.6

Abstract

A majority of JWST/NIRSpec integral field unit (IFU) studies at high redshifts to date have focused on UV-bright or massive objects, while our understanding of low-mass galaxies at early cosmic times remains limited. In this work, we present NIRSpec/IFU high-resolution observations of two low-mass (M∗ < 109 M⊙), low-metallicity ([12 + log(O/H)]< 8$) galaxies at z ∼ 7.66, one of which we identify as hosting a Type-II active galactic nucleus (AGN). We measure flat strong-line metallicity gradients, suggestive of interstellar medium redistribution by outflows or past merging, but also identify tension with the direct-Te metallicity gradient in one galaxy. We find the ionized gas phase in both galaxies to be dispersion-dominated, consistent with previous observations of lower rotational support at early cosmic times. We identify broad kinematical components decoupled from galactic rotation with velocities of ∼ 250 − 500 km s−1 and argue these components trace outflows, for which we infer mass outflow rates of ∼ 8 − 14 M⊙ yr−1. We compare our findings to results from the new large-volume aesopica simulations, which fully incorporate different models of black hole growth and AGN feedback. We find that our observationally measured ratios of outflow to escape velocity are consistent with those of the simulated dwarf AGN population, hinting that AGN-driven feedback may contribute to quenching in early low-mass galaxies such as our targets. This novel study illustrates the necessity of deep IFU observations to decompose the complex kinematics and morphology of high-z galaxies, trace outflows, and constrain the effects of feedback in the early Universe.