Extended Lyman- α haloes around high- z star-forming galaxies. Nearly all the sky is covered by Lyman- α emission around high-redshift galaxies. Extended Lyman α haloes around individual high-redshift galaxies revealed by MUSE. The Keck Cosmic Web Imager integral field spectrograph. The MUSE second-generation VLT instrument. Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations with explicit stellar feedback. Detection of large-scale X-ray bubbles in the Milky Way halo. We demonstrate that this CGM-scale outflow is prevalent among galaxies with stellar mass M * ≳ 10 9.5 M ⊙. We interpret these findings as supporting the idea that outflows typically have a bipolar cone geometry perpendicular to the galactic disk. We find a strong dependence of the detected signal on the inclination of the central galaxy, with edge-on galaxies clearly showing enhanced Mg II emission along the minor axis, whereas face-on galaxies show much weaker and more isotropic emission. Here we present an ultra-deep Multi-Unit Spectroscopic Explorer (MUSE) image of the mean Mg II emission surrounding a sample of galaxies at z ≈ 1 that strongly suggests the presence of outflowing gas on physical scales of more than 10 kpc. Galactic outflows are usually of low gas density and low surface brightness and therefore difficult to observe in emission towards high redshifts. At higher redshifts, cosmological simulations of galaxy formation predict an increase in the frequency and efficiency of galactic outflows owing to the increasing star-formation activity 4. They have been directly observed in the local Universe in several individual galaxies, for example, around the Milky Way and M82 (refs. Theoretical models assume bipolar shapes for the outflows that extend well into the circumgalactic medium (CGM), up to tens of kiloparsecs (kpc) perpendicular to the galaxies. Galactic outflows are believed to play a critical role in the evolution of galaxies by regulating their mass build-up and star formation 1.
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