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GASP XXIX-unwinding the arms of spiral galaxies via ram-pressure stripping

Bellhouse, Callum; McGee, Sean L.; Smith, Rory; Poggianti, Bianca M.; Jaffé, Yara L.; Kraljic, Katarina; Franchetto, Andrea; Fritz, Jacopo; Vulcani, Benedetta; Tonnesen, Stephanie; Roediger, Elke; Moretti, Alessia; Gullieuszik, Marco; Shin, Jihye


Callum Bellhouse

Sean L. McGee

Rory Smith

Bianca M. Poggianti

Yara L. Jaffé

Katarina Kraljic

Andrea Franchetto

Jacopo Fritz

Benedetta Vulcani

Stephanie Tonnesen

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Dr Elke Roediger
Reader in Astrophysics, Director of the E.A. Milne Centre for Astrophysics

Alessia Moretti

Marco Gullieuszik

Jihye Shin


We present the first study of the effect of ram pressure ‘unwinding’ the spiral arms of cluster galaxies. We study 11 ram-pressure stripped galaxies from GASP (GAs Stripping Phenomena in galaxies) in which, in addition to more commonly observed ‘jellyfish’ features, dislodged material also appears to retain the original structure of the spiral arms. Gravitational influence from neighbours is ruled out and we compare the sample with a control group of undisturbed spiral galaxies and simulated stripped galaxies. We first confirm the unwinding nature, finding that the spiral arm pitch angle increases radially in 10 stripped galaxies and also simulated face-on and edge-on stripped galaxies. We find only younger stars in the unwound component, while older stars in the disc remain undisturbed. We compare the morphology and kinematics with simulated ram-pressure stripping galaxies, taking into account the estimated inclination with respect to the intracluster medium (ICM) and find that in edge-on stripping, unwinding can occur due to differential ram pressure caused by the disc rotation, causing stripped material to slow and ‘pile up’. In face-on cases, gas removed from the outer edges falls to higher orbits, appearing to ‘unwind’. The pattern is fairly short-lived (


Bellhouse, C., McGee, S. L., Smith, R., Poggianti, B. M., Jaffé, Y. L., Kraljic, K., …Shin, J. (2020). GASP XXIX-unwinding the arms of spiral galaxies via ram-pressure stripping. Monthly notices of the Royal Astronomical Society, 500(1), 1285-1312.

Journal Article Type Article
Acceptance Date Oct 16, 2020
Online Publication Date Oct 28, 2020
Publication Date Nov 18, 2020
Deposit Date Dec 18, 2020
Publicly Available Date Dec 21, 2020
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 500
Issue 1
Pages 1285-1312
Keywords Space and Planetary Science; Astronomy and Astrophysics
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Copyright Statement
© The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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