Investigating the relationship between AGN activity and stellar mass in zCOSMOS galaxies at 0 < z < 1 using emission-line diagnostic diagrams

M. Vitale, M. Mignoli, A. Cimatti, S. J. Lilly, C. M. Carollo, T. Contini, J. P. Kneib, O. Le Fevre, V. Mainieri, A. Renzini, M. Scodeggio, G. Zamorani, S. Bardelli, L. Barnes, M. Bolzonella, A. Bongiorno, R. Bordoloi, T. J. Bschorr, A. Cappi, K. CaputiG. Coppa, O. Cucciati, S. De La Torre, L. De Ravel, P. Franzetti, B. Garilli, A. Iovino, P. Kampczyk, C. Knobel, A. M. Koekemoer, K. Kovač, F. Lamareille, J. F. Le Borgne, V. Le Brun, C. López-Sanjuan, C. Maier, H. J. McCracken, M. Moresco, P. Nair, P. A. Oesch, R. Pello, Y. Peng, E. Pérez Montero, L. Pozzetti, V. Presotto, J. Silverman, M. Tanaka, L. Tasca, L. Tresse, D. Vergani, N. Welikala, E. Zucca

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14 Citations (Scopus)


Context. Active galactic nuclei (AGN) are thought to play an important role in galaxy evolution. It has been suggested that AGN feedback could be partly responsible for quenching star-formation in the hosts, leading to transition from the blue cloud to the red sequence. The transition seems to occur faster for the most massive galaxies, where traces of AGN activity have been found as early as at z < 0.1. The correlation betweenAGN activity, aging of the stellar populations, and stellar mass still needs to be fully understood, especially at high redshifts. Aims. Our aim is to investigate the link between AGN activity, star-formation, and stellar mass of the host galaxy at 0 < z < 1, looking for spectroscopic traces of AGN and aging of the host. This work provides an extension of the existing studies at z < 0.1 and contributes to shed light on galaxy evolution at intermediate redshifts. Methods. We used the zCOSMOS 20k data to create a sample of galaxies at z < 1. We divided the sample into several mass-redshift bins to obtain stacked galaxy spectra with an improved signal-to-noise ratio (S/N). We exploited emission-line diagnostic diagrams to separate AGN from star-forming galaxies. Results. We found an indication of a role for the total galaxy stellar mass in leading galaxy classification. Stacked spectra show AGN signatures above the log M -/M > 10.2 threshold. Moreover, the stellar populations of AGN hosts are found to be older than star-forming and composite galaxies. This could be due to the the tendency of AGN to reside in massive hosts. Conclusions. The dependence of the AGN classification on the stellar mass agrees with what has been found in previous research. Together with the evidence of older stellar populations inhabiting the AGN-like galaxies, it is consistent with the downsizing scenario. In particular, our evidence points to an evolutionary scenario where the AGN-feedback is capable of quenching the star formation in the most massive galaxies. Therefore, the AGN-feedback is the best candidate for initiating the passive evolutionary phase of galaxies.

Original languageEnglish
Article numberA11
JournalAstronomy and Astrophysics
Publication statusPublished - 2013


  • Galaxies: active
  • Galaxies: evolution
  • Galaxies: starburst
  • Galaxies: stellar content


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