Galaxy And Mass Assembly: Galaxy Morphology in the Green Valley, Prominent rings and looser Spiral Arms
Authors: Dominic Smith (University of Louisville), Lutz Haberzettl (University of Louisville), L. E. Porter (University of Louisville), Ren Porter-Temple (University of Louisville), Christopher P. A. Henry (University of Louisville), Benne Holwerda (University of Louisville), A. R. Lopez-Sanchez (Macquarie University), Steven Phillipps (University of Bristol), Alister W. Graham (Swinburne), Sarah Brough (New South Wales), Kevin A. Pimbblet (University of Hull), Jochen Liske (Hamburger Sternwarte), Lee S. Kelvin (Princeton), Clayton D. Robertson (UofL), Wade Roemer (UofL), Michael Walmsley (Jodrell Bank), David O'Ryan (Lancaster University), Tobias Geron (Oxford University)
Abstract: 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.
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