Galaxy and Mass Assembly (GAMA): Variation in Galaxy Structure Across the Green Valley

Lee S. Kelvin, Malcolm N. Bremer, Steven Phillipps, Philip A. James, Luke J. M. Davies, Roberto De Propris, Amanda J. Moffett, Susan M. Percival, Ivan K. Baldry, Chris A. Collins, Mehmet Alpaslan, Joss Bland-Hawthorn, Sarah Brough, Michelle Cluver, Simon P. Driver, Abdolhosein Hashemizadeh, Benne W. Holwerda, Jarkko Laine, Maritza A. Lara-Lopez, Jochen Liske, Witold Maciejewski, Nicola R. Napolitano, Samantha J. Penny, Cristina C. Popescu, Anne E. Sansom, Will Sutherland, Edward N. Taylor, Eelco van Kampen, Lingyu Wang

Published 2018-04-12Version 1

Using a sample of 472 local Universe (z<0.06) galaxies in the stellar mass range 10.25 < log M*/M_sun < 10.75, we explore the variation in galaxy structure as a function of morphology and galaxy colour. Our sample of galaxies is sub-divided into red, green and blue colour groups and into elliptical and non-elliptical (disk-type) morphologies. Using KiDS and VIKING derived postage stamp images, a group of eight volunteers visually classified bars, rings, morphological lenses, tidal streams, shells and signs of merger activity for all systems. We find a significant surplus of rings ($2.3\sigma$) and lenses ($2.9\sigma$) in disk-type galaxies as they transition across the green valley. Combined, this implies a joint ring/lens green valley surplus significance of $3.3\sigma$ relative to equivalent disk-types within either the blue cloud or the red sequence. We recover a bar fraction of ~44% which remains flat with colour, however, we find that the presence of a bar acts to modulate the incidence of rings and (to a lesser extent) lenses, with rings in barred disk-type galaxies more common by ~20-30 percentage points relative to their unbarred counterparts, regardless of colour. Additionally, green valley disk-type galaxies with a bar exhibit a significant $3.0\sigma$ surplus of lenses relative to their blue/red analogues. The existence of such structures rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.