Properties of green valley galaxies in relation to their selection criteria

The distribution of galaxies has been studied to show the difference between the blue cloud and red sequence and to define the green valley region. However, there are still many open questions regarding the importance of the green valley for understanding the morphological transformation and evolution of galaxies, how galaxies change from late-type to early-type and the role of AGN in galaxy formation and evolution scenario. The work focused on studying in more details the properties of green valley galaxies by testing the six most used selection criteria, differences between them, and how they may affect the main results and conclusions. The main findings are that, by selecting the green valley galaxies using different criteria, we are selecting different types of galaxies in terms of their stellar masses, sSFR, SFR, spectroscopic classification and morphological properties, where the difference was more significant for colour criteria than for sSFR and SFR vs. stellar-mass criteria.Comment: Proceedings paper of the IAU symposium "Nuclear Activity in Galaxies Across Cosmic Time" (Ethiopia) accepted to be published under the Cambridge University Press, eds. M. Povic, P. Marziani, J. Masegosa, H. Netzer, S. H. Negu, and S. B. Tessem

Properties of X-ray detected far-IR AGN in the green valley

In this study, we analysed active galactic nuclei in the "green valley" by comparing active and non-active galaxies using data from the COSMOS field. We found that most of our X-ray detected active galactic nuclei with far-infrared emission have star formation rates higher than the ones of normal galaxies of the same stellar mass range.Comment: Proceedings paper of the IAU symposium "Nuclear Activity in Galaxies Across Cosmic Time" (Ethiopia) accepted to be published under the Cambridge University Press, eds. M. Povic, P. Marziani, J. Masegosa, H. Netzer, S. H. Negu, and S. B. Tessem

The [OIII] profiles of far-infrared active and non-active optically-selected green valley galaxies

We present a study of the $\rm{[OIII]\lambda\,5007}$ line profile in a sub-sample of 8 active galactic nuclei (AGN) and 6 non-AGN in the optically-selected green valley at $\rm{z\,<\,0.5}$ using long-slit spectroscopic observations with the 11 m Southern African Large Telescope. Gaussian decomposition of the line profile was performed to study its different components. We observe that the AGN profile is more complex than the non-AGN one. In particular, in most AGN (5/8) we detect a blue wing of the line. We derive the FWHM velocities of the wing and systemic component, and find that AGN show higher FWHM velocity than non-AGN in their core component. We also find that the AGN show blue wings with a median velocity width of approximately 600 $\rm{km\,s^{-1}}$, and a velocity offset from the core component in the range -90 to -350 $\rm{km\,s^{-1}}$, in contrast to the non-AGN galaxies, where we do not detect blue wings in any of their $\rm{[OIII]\lambda\,5007}$ line profiles. Using spatial information in our spectra, we show that at least three of the outflow candidate galaxies have centrally driven gas outflows extending across the whole galaxy. Moreover, these are also the galaxies which are located on the main sequence of star formation, raising the possibility that the AGN in our sample are influencing SF of their host galaxies (such as positive feedback). This is in agreement with our previous work where we studied SF, morphology, and stellar population properties of a sample of green valley AGN and non-AGN galaxies.Comment: 15 pages, 6 figures, accepted for publication in Ap

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

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.Comment: 13 pages,7 figures, 'Accepted for publication in MNRAS