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Physics and Astronomy


Galaxies broadly fall into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated “green valley". Some of these galaxies are suspected to be in the process of ceasing their star-formation through a gradual exhaustion of gas supply or already dead and are experiencing a rejuvenation of star-formation through fuel injection. We use the Galaxy And Mass Assembly database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley against those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found disc features such as rings and lenses are more prominently represented in the green valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new KiDS images. Our aim is to compare qualitatively the results from expert classification to that of citizen science. We observe that ring structures are indeed found more commonly in green valley galaxies compared to their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral arm structure.


© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.

Original Publication Information

Dominic Smith, Lutz Haberzettl, L E Porter, Ren Porter-Temple, Christopher P A Henry, Benne Holwerda, Á R López-Sánchez, Steven Phillipps, Alister W Graham, Sarah Brough, Kevin A Pimbblet, Jochen Liske, Lee S Kelvin, Clayton D Robertson, Wade Roemer, Michael Walmsley, David O’Ryan, Tobias Géron, Galaxy And Mass Assembly: galaxy morphology in the green valley, prominent rings, and looser spiral arms, Monthly Notices of the Royal Astronomical Society, Volume 517, Issue 3, December 2022, Pages 4575–4589,