Stellar populations of a sample of far-IR AGN and non-AGN green valley galaxies

TL;DR

This study analyzes the stellar populations and ages of far-infrared AGN and non-AGN green valley galaxies at 0.6<z<1.0, revealing similar quenching timescales and dominant intermediate stellar populations, with no signs of negative AGN feedback.

Contribution

It provides a comparative analysis of stellar populations in FIR-selected AGN and non-AGN green valley galaxies using spectroscopy and synthesis modeling.

Findings

Both galaxy types are dominated by intermediate stellar populations.

Median stellar ages are approximately 10^8.4 to 10^8.5 years.

FIR AGN and non-AGN have similar quenching timescales of about 70 Myr.

Abstract

We present a study on the stellar populations and stellar ages of sub-sample of far-infrared AGN and non-AGN green valley analysed in Mahoro et al. (2017,2019) at 0.6 < z < 1.0 using the data from the COSMOS field. We used long-slit spectroscopy and derived stellar populations and stellar ages using the stellar population synthesis code "STARLIGHT" and analysed the available Lick/IDS indices, such as Dn4000 and $\rm{H\delta_{A}}$. We find that both FIR AGN and non-AGN green valley galaxies are dominated by intermediate stellar populations 67 % and 53 %, respectively. The median stellar ages for AGN and non-AGN are log t = 8.5 [yr] and log t = 8.4 [yr], respectively. We found that majority of our sources (62 % of AGN and 66 % non-AGN) could have experienced bursts and continuous star formation. In addition, most of our FIR AGN (38 %) compared to FIR non-AGN (27 %) might have experienced a burst of SF more than 0.1 Gyr ago. We also found that our FIR AGN and non-AGN green valley galaxies have similar quenching time-scales of ~ 70 Myr. Therefore, the results obtained here are in line with our previous results where we do not find that our sample of FIR AGN in the green valley shows signs of negative AGN feedback, as has been suggested previously in optical studies.