1. Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
2. CRAL-Observatoire, 9 Avenue Charles-André, 69230 Saint-Genis-Laval, France
3. Leiden Observatory, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
4. Astrophysics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK

Correspondence to: R. J. Wilman¹ Correspondence and requests for materials should be addressed to R.J.W. (Email: r.j.wilman@durham.ac.uk).

Abstract

High-velocity galactic outflows, driven by intense bursts of star formation and black hole accretion, are processes invoked by current theories of galaxy formation¹ to terminate star formation in the most massive galaxies and to deposit heavy elements in the intergalactic medium. From existing observational evidence^{2, 3} (for high-redshift galaxies) it is unclear whether such outflows are localized to regions of intense star formation just a few kiloparsecs in extent, or whether they instead have a significant impact on the entire galaxy and its surroundings. Here we present two-dimensional spectroscopy of a star-forming galaxy⁴ at redshift z = 3.09 (seen 11.5 gigayears ago, when the Universe was 20 per cent of its current age): its spatially extended Ly line emission appears to be absorbed by H i in a foreground screen covering the entire galaxy, with a lateral extent of at least 100 kpc and remarkable velocity coherence. This screen was ejected from the galaxy during a starburst several 10⁸ years earlier and has subsequently swept up gas from the surrounding intergalactic medium and cooled. This demonstrates the galaxy-wide impact of high-redshift superwinds.

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