Abstract

We use spatially resolved spectroscopy of a distant giant gravitational arc to test orientation effects on Mg ii absorption equivalent width (EW) and covering fraction () in the circumgalactic medium of a foreground star-forming galaxy (G1) at z similar to 0.77. Forty-two spatially-binned arc positions uniformly sample impact parameters (D) to G1 between 10 and 30 kpc and azimuthal angles alpha between 30 degrees and 90 degrees (minor axis). We find an EW-D anticorrelation, akin to that observed statistically in quasar absorber studies, and an apparent correlation of both EW and with alpha, revealing a non-isotropic gas distribution. In line with our previous results on Mg ii kinematics suggesting the presence of outflows in G1, at minimum a simple 3D static double-cone model (to represent the trace of bipolar outflows) is required to recreate the EW spatial distribution. The D and alpha values probed by the arc cannot confirm the presence of a disc, but the data highly disfavour a disc alone. Our results support the interpretation that the EW-alpha correlation observed statistically using other extant probes is partly shaped by bipolar metal-rich winds.