# Galaxy And Mass Assembly (GAMA): Timescales for galaxies crossing the green valley

## TL;DR

This study uses GAMA survey data to estimate that low-redshift galaxies transition from blue to red over 2-4 billion years mainly by gradually decreasing star formation, without requiring abrupt quenching events.

## Contribution

It provides new constraints on galaxy evolution timescales, showing green valley galaxies decline star formation gradually over several billion years based on spectral energy distribution fitting.

## Key findings

- Green valley galaxies decrease star formation over 2-4 Gyr.
- No evidence of recent rapid quenching in green galaxies.
- Galaxies will redden further if current star formation decline continues.

## Abstract

We explore the constraints that can be placed on the evolutionary timescales for typical low redshift galaxies evolving from the blue cloud through the green valley and onto the red sequence. We utilise galaxies from the GAMA survey with 0.1 < z < 0.2 and classify them according to the intrinsic (u-r?) colours of their stellar populations, as determined by fits to their multi-wavelength spectral energy distributions. Using these fits to also determine stellar population ages and star formation timescales, we argue that our results are consistent with a green valley population dominated by galaxies that are simply decreasing their star formation (running out of gas) over a timescale of 2-4 Gyr which are seen at a specific epoch in their evolution (approximately 1.6 e-folding times after their peak in star formation). If their fitted star formation histories are extrapolated forwards, the green galaxies will further redden over time, until they attain the colours of a passive population. In this picture, no specific quenching event which cuts-off their star formation is required, though it remains possible that the decline in star formation in green galaxies may be expedited by internal or external forces. However, there is no evidence that green galaxies have recently changed their star formation timescales relative to their previous longer term star formation histories.