Abstract

We report the small-scale spatial variation in cool (T ? 104 K) Mg ii absorption detected in the circumgalactic medium (CGM) of a star-forming galaxy at z ? 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 and 66 kpc. The Mg ii absorption strengths vary by more than a factor of 2 within these ranges. A power-law fit to the fractional variation of absorption strengths yields a coherence length of 5.8 kpc within this range of impact parameters. 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 ? ?179 km s?1 and mass outflow rate M ? out ? 6 4 ? 27 + 31 M? 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 ?33 kpc traced by [O ii], [O iii], and H? emission lines. The extended emission halo shows kinematic signatures of corotating 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. © 2025. The Author(s). Published by the American Astronomical Society.