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Evidence for ram-pressure stripping in a cluster of galaxies at z = 0.7

A. Boselli, B. Epinat, T. Contini, V. Abril-Melgarejo, L. A. Boogaard, E. Pointecouteau, E. Ventou, J. Brinchmann, D. Carton, H. Finley, L. Michel-Dansac, G. Soucail, P. M. Weilbacher

Multi-Unit Spectroscopic Explorer (MUSE) observations of the cluster of galaxies CGr32 (M200 ≃ 2 × 1014 M) at z = 0.73 reveal the presence of two massive star-forming galaxies with extended tails of diffuse gas detected in the [O II]λλ3727–3729 Å emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10−18 erg s−1 cm−2 arcsec−2, extend up to ≃100 kpc (projected distance) from the galaxy discs, and are not associated with any stellar component. All this observational evidence suggests that the gas was removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe was only half its present age. The density of the gas derived using the observed [O II]λ3729/[O II]λ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail.

galaxies: clusters: general / galaxies: clusters: individual: CGr32 / galaxies: evolution / galaxies: interactions / galaxies: ISM / galaxies: high-redshift

*The reduced datacube is also available at the CDS via anonymous ftp to ( or via
**Based on observations made with ESO telescopes at the Paranal Observatory under programmes 097.A-0254, 100.A-0607, 101.A-0282.

Astronomy and Astrophysics
Volume galax, Article Number A114, Number of pages 10
2019 November

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia