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

**Authors:** 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  
**arXiv:** [1804.04470](https://arxiv.org/abs/1804.04470)  
**Date:** 2018-04-12  
**Summary page:** https://www.summarizepaper.com/en/paper/1804.04470v1/

## Key points

- Study investigates variation in galaxy structure across the "green valley"
- Sample of 472 local Universe galaxies with stellar masses ranging from 10.25 to 10.75 times that of the Sun
- Sample divided into red, green, and blue color groups, as well as elliptical and non-elliptical morphologies
- Researchers use KiDS and VIKING derived postage stamp images for analysis
- Eight volunteers visually classify features such as bars, rings, lenses, tidal streams, shells, and signs of merger activity
- Disk-type galaxies transitioning across the green valley show a significant surplus of rings and lenses compared to blue cloud or red sequence disk-types
- Approximately 44% of galaxies in sample possess bars; no significant variation based on color
- Presence of a bar influences occurrence of rings and lenses in disk-type galaxies
- Violent transformative events not necessarily responsible for rapid transition across the green valley; suggests more passive scenario favored
- Rings and lenses in disk-type galaxies during transition phase point towards a more gradual evolutionary process
- Bars can influence these structures further emphasizing complexity in galaxy evolution

## Summary

This study investigates the variation in galaxy structure across the "green valley," a region of the color-magnitude diagram where galaxies transition from the blue cloud to the red sequence. The researchers use a sample of 472 local Universe galaxies with stellar masses ranging from 10.25 to 10.75 times that of the Sun. They divide their sample into red, green, and blue color groups, as well as elliptical and non-elliptical (disk-type) morphologies. To analyze galaxy structures, the researchers employ KiDS and VIKING derived postage stamp images and enlist eight volunteers to visually classify various features such as bars, rings, morphological lenses, tidal streams, shells, and signs of merger activity for all systems. The results reveal interesting findings about galaxy structures within different color groups and morphologies. Disk-type galaxies transitioning across the green valley exhibit a significant surplus of rings ($2.3\sigma$) and lenses ($2.9\sigma). When combined, this implies a joint ring/lens green valley surplus significance of $3.3\sigma$ compared to equivalent disk-types within either the blue cloud or red sequence. The study also reveals that approximately 44% of galaxies in their sample possess bars; however there is no significant variation based on color. Nevertheless, they observe that the presence of a bar influences the occurrence of rings and lenses: barred disk-type galaxies are more likely to have rings by around 20–30 percentage points compared to their unbarred counterparts regardless of color; furthermore green valley disk-type galaxies with a bar show a significant $3.0\sigma$ surplus of lenses relative to their blue/red analogues. These findings suggest that violent transformative events are not necessarily responsible for most galaxies rapidly transitioning across the green valley; instead they indicate that a more passive scenario is favored as these structures point towards a less dramatic transformation process. In summary, this study provides insights into the variation of galaxy structure as a function of morphology and color across the green valley which suggests that rings and lenses in disk-type galaxies during this transition phase point towards a more gradual evolutionary process; moreover it highlights how bars can influence these structures further emphasizing complexity in galaxy evolution.