First Statistical Detection of MgII-traced Cool Gas Outflows with JWST Towards Cosmic Dawn

TL;DR

This study uses JWST spectra to statistically detect and analyze MgII-traced cool gas outflows across a wide range of redshifts, revealing persistent feedback mechanisms in early galaxy evolution.

Contribution

First statistical detection of MgII-traced cool gas outflows from $z oughly 1$ to beyond 6 using JWST, extending understanding to low-mass, high-redshift galaxies.

Findings

Blueshifted MgII absorption detected in nearly all stellar mass and redshift bins.

Outflow equivalent width correlates positively with stellar mass at all epochs.

Outflow velocities are generally below host halo escape velocities, supporting a galactic fountain scenario.

Abstract

Galactic-scale outflows are a crucial component of galaxy evolution, yet their properties in the early universe remain poorly constrained. We present the first statistical investigation of \ion{Mg}{2}-traced cool gas outflows in galaxies spanning a wide cosmic timeline from $z \approx 1$ to $z > 6$ (with sample coverage extending to $z \sim 10$). Using thousands of public JWST/NIRSpec spectra, we employ a signal-to-noise weighted spectral stacking technique on the \ion{Mg}{2} $\lambda\lambda2796, 2803$ absorption doublet. We robustly detect blueshifted \ion{Mg}{2} absorption in nearly all stellar mass and redshift bins, with the exception of the lowest-mass systems at $z \sim 1-2$. The outflow equivalent width exhibits a positive correlation with stellar mass ($M_*$) at all epochs, with the fitted slope of $1.21 \pm 0.35$. Our work provides the first statistical constraints on \ion{Mg}{2}-traced cool outflows in the low-mass ($M_* \lesssim 10^{9.5} \, \mathrm{M}_\odot$), high-redshift ($z > 3$) regime. We also find that the outflow velocities generally remain below the host halo escape velocities, consistent with a galactic fountain scenario. The consistency of the stellar mass-outflow equivalent width relation across $z \sim 2-6$ suggests a persistent, unevolving feedback mechanism governing the baryon cycle towards cosmic dawn.