Spatially Resolved Circumgalactic Medium around a Star-Forming Galaxy Driving a Galactic Outflow at $z\approx 0.8$

TL;DR

This study reveals small-scale spatial variations in the CGM of a star-forming galaxy at z≈0.8, showing high coherence and evidence of a baryon cycle involving galactic outflows and extended emission halos.

Contribution

It provides the first spatially resolved measurements of Mg II absorption in the CGM of a star-forming galaxy at this redshift, demonstrating coherence and outflow characteristics.

Findings

Mg II absorption varies by over a factor of two within 54-66 kpc.

Coherence length of 2.7 kpc for Mg II absorption features.

Galactic outflow velocity approximately -179 km/s with a mass outflow rate ≥ 64 M_sun/yr.

Abstract

We report the small-scale spatial variation in cool ($T\sim 10^4 K$) Mg II absorption detected in the circumgalactic medium (CGM) of a star-forming galaxy at $z\approx 0.8$. The CGM of this galaxy is probed by a spatially extended bright background gravitationally lensed arc at $z = 2.76$. The background arc continuously samples the CGM of the foreground galaxy at a range of impact parameters between 54-66 kpc. The Mg II absorption strengths vary by more than a factor of two within these ranges. A power-law fit to the fractional variation of absorption strengths yields a coherence length of 2.7 kpc within these absorption lines. This suggests a high degree of spatial coherence in the CGM of this galaxy. The host galaxy is driving a strong galactic outflow with a mean outflow velocity $\approx$ -179 km/s and mass outflow rate $\dot{M}_{out}\geq 64_{-27}^{+31} M_{\odot}yr^{-1}$ traced by blueshifted Mg II and Fe II absorption lines. The galaxy itself has a spatially extended emission halo with a maximum spatial extent of $\approx$ 33 kpc traced by [O II], [O III] and $H\beta$ emission lines. The extended emission halo shows kinematic signatures of co-rotating halo-gas with solar metallicity. Taken together, these observations suggest evidence of a baryon cycle that is recycling the outflowing gas to form the next generation of stars.