Research output: Contribution to journalArticle


We present the X-ray spectral analysis of the 1855 extragalactic sources in the Chandra COSMOS-Legacy survey catalog having more than 30 net counts in the 0.5-7 keV band. A total of 38% of the sources are optically classified type 1 active galactic nuclei (AGNs), 60% are type 2 AGNs, and 2% are passive, low-redshift galaxies. We study the distribution of AGN photon index Γ and of the intrinsic absorption based on the sources' optical classification: type 1 AGNs have a slightly steeper mean photon index Γ than type 2 AGNs, which, on the other hand, have average times higher than type 1 AGNs. We find that ∼15% of type 1 AGNs have cm-2, i.e., are obscured according to the X-ray spectral fitting; the vast majority of these sources have 1044 erg s-1. The existence of these objects suggests that optical and X-ray obscuration can be caused by different phenomena, the X-ray obscuration being, for example, caused by dust-free material surrounding the inner part of the nuclei. Approximately 18% of type 2 AGNs have cm-2, and most of these sources have low X-ray luminosities (L2-10keV < 1043 erg s-1). We expect a part of these sources to be low-accretion, unobscured AGNs lacking broad emission lines. Finally, we also find a direct proportional trend between and host-galaxy mass and star formation rate, although part of this trend is due to a redshift selection effect.


  • S. Marchesi
  • G. Lanzuisi
  • F. Civano
  • K. Iwasawa
  • H. Suh
  • A. Comastri
  • G. Zamorani
  • V. Allevato
  • R. Griffiths
  • T. Miyaji
  • P. Ranalli
  • M. Salvato
  • K. Schawinski
  • J. Silverman
  • E. Treister
  • C. M. Urry
  • C. Vignali
External organisations
  • University of Barcelona
  • University of Hawaii
  • University of Helsinki
  • Max Planck Institute for Extraterrestrial Physics
  • ETH Zürich
  • University of Tokyo
  • Clemson University
  • University of Bologna
  • Harvard–Smithsonian Center for Astrophysics
  • National Autonomous University of Mexico
  • Yale University
  • University of Concepción
  • INAF Osservatorio Astronomico di Bologna
  • Pontifical Catholic University of Chile
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology


  • galaxies: active, galaxies: nuclei, X-rays: galaxies
Original languageEnglish
Article number100
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2016 Oct 20
Publication categoryResearch