On a plane spanned by a stellar population property and some proxy of mass, galaxies are distributed following a bimodal distribution, defining a red sequence (RS) and a blue cloud (BC). In between these regions resides the transition area termed Green Valley (GV), where we believe most of the quenching processes operate. The traditional method defines the bimodal distribution, thus GV, using colour-magnitude/colour-mass diagrams. However colour is heavily affected by dust, introducing a degeneracy. Any dust correction will be model-dependent and will carry a systematic uncertainty. Thus to avoid the need for dust correction, we use instead a spectral parameter known as the 4000 Å break strength, which is less sensitive to dust. In this instance, without dust correction, we obtain a better separation between BC, GV and RS with less systematic uncertainty. Our study of GV galaxies yields a high fraction of AGN, as well as a transition timescale between 1.0-3.5 Gyr correlated with stellar mass. Moreover we find similar properties of the stellar populations between lower GV (lGV) and middle GV (mGV) galaxies than mGV and upper GV (uGV) galaxies, hinting that the transition from BC to GV might be more rapid than that from GV to RS.
Contributions to the XIV.0 Scientific Meeting (virtual) of the Spanish Astronomical Society
- Pub Date:
- July 2020