Exploring Spatially-Resolved Metallicities, Dynamics and Outflows in Low-Mass Galaxies at $z\sim 7.6$

Abstract

A majority of JWST/NIRSpec/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/IFS high-resolution observations of two low-mass ($M_{\ast }<10^9{M}_{\odot }$), low-metallicity ($[12+\log (\text{O/H})]<8$) galaxies at $z\sim 7.66$, one of which we identify as hosting a Type-II AGN. We measure flat strong-line metallicity gradients, suggestive of ISM redistribution by outflows or past merging, but also identify tension with the direct-$T_{\text{e}}$ metallicity gradient in one galaxy. We measure $v_{\text{rot}}/\ddot{I}ƒ<1$ in both galaxies, consistent with observations of lower rotational support at early cosmic times. We identify broad kinematical components decoupled from galactic rotation with velocities of $\sim 250-500\text{km}{\text{s}}^{-1}$ and argue these components trace outflows, for which we infer outflow rates of $\sim 8-14M_{\odot }{\text{yr}}^{-1}$ with $v_{\text{out}}/v_{\text{esc}}\sim 1$. 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 observational results of $v_{\text{out}}/v_{\text{esc}}$ are consistent with the simulated dwarf AGN population, hinting AGN-driven feedback may contribute to quenching both in our systems and in a wider population of low-mass galaxies in the early Universe. 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 effect of feedback in the early Universe.

Submitted to MNRAS. 28 pages, 18 figures, 5 tables