MOSDEF-3D: Keck/OSIRIS Maps of the Ionized ISM in $z \sim 2$ Galaxies

TL;DR

This study uses spatially-resolved emission line maps from Keck/OSIRIS to analyze the ISM conditions in four $z \\sim 2$ galaxies, revealing high star formation activity, metallicity gradients, and no clear AGN evidence, highlighting the importance of outflows and radial mixing.

Contribution

First spatially-resolved emission line maps of $z \\sim 2$ galaxies from Keck/OSIRIS, showing consistent metallicity gradients and no AGN activity, advancing understanding of galaxy evolution at Cosmic Noon.

Findings

Emission line ratios offset from local star-forming locus but consistent with high-redshift galaxies.

Flat radial metallicity gradients suggest efficient radial mixing.

No compelling evidence for central AGN activity in the studied galaxies.

Abstract

We present spatially-resolved rest-frame optical emission line maps of four galaxies at $z \sim 2$ observed with Keck/OSIRIS to study the physical conditions of the ISM at Cosmic Noon. Our analysis of strong emission line ratios in these galaxies reveals an offset from the local star-forming locus on the BPT diagram, but agrees with other star-forming galaxies at similar redshifts. Despite the offset towards higher [O III]$\lambda5008$/H$\beta$ and [N II]$\lambda6585$/H$\alpha$, these strong-line ratios remain consistent with or below the maximum starburst threshold even in the inner $\sim 1$ kpc region of the galaxies, providing no compelling evidence for central AGN activity. The galaxies also exhibit flat radial gas-phase metallicity gradients, consistent with previous studies of $z \sim 2$ galaxies and suggesting efficient radial mixing possibly driven by strong outflows from intense star formation. Overall, our results reveal the highly star-forming nature of these galaxies, with the potential to launch outflows that flatten metallicity gradients through significant radial gas mixing. Future observations with JWST/NIRSpec are crucial to detect fainter emission lines at higher spatial resolution to further constrain the physical processes and ionization mechanisms that shape the ISM during Cosmic Noon.