What obscures low-X-ray-scattering active galactic nuclei

S. F. Hönig, P. Gandhi, D. Asmus, R. F. Mushotzky, R. Antonucci, Y. Ueda, K. Ichikawa

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

X-ray surveys have revealed a new class of active galactic nuclei (AGN) with a very low observed fraction of scattered soft X-rays, fscat <0.5 per cent. Based on X-ray modelling, these 'X-ray new-type', or low observed X-ray-scattering (hereafter, 'low-scattering') sources have been interpreted as deeply buried AGN with a high covering factor of gas. In this paper, we address the questions whether the host galaxies of low-scattering AGN may contribute to the observed X-ray properties, and whether we can find any direct evidence for high covering factors from the infrared (IR) emission. We find that X-ray low-scattering AGN are preferentially hosted by highly inclined galaxies or merger systems as compared to other Seyfert galaxies, increasing the likelihood that the line of sight towards the AGN intersects with high columns of host-galactic gas and dust. Moreover, while a detailed analysis of the IR emission of low-scattering AGN ESO 103-G35 remains inconclusive, we do not find any indication of systematically higher dust covering factors in a sample of low-scattering AGN based on their IR emission. For ESO 103-G35, we constrained the temperature, mass and location of the IR emitting dust which is consistent with expectations for the dusty torus. However, a deep silicate absorption feature probably from much cooler dust suggests an additional screen absorber on larger scales within the host galaxy. Taking these findings together, we propose that the low fscat observed in low-scattering AGN is not necessarily the result of circumnuclear dust but could originate from interference of host-galactic gas with a column density of the order of 1022 cm-2 with the line of sight. We discuss implications of this hypothesis for X-ray models, high-ionization emission lines and observed star formation activity in these objects.

Original languageEnglish
Article numberstt2234
Pages (from-to)647-656
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume438
Issue number1
DOIs
Publication statusPublished - 2014 Feb 1
Externally publishedYes

Keywords

  • G35
  • Galaxies: Seyfert
  • Galaxies: active
  • Galaxies: individual: ESO103
  • Galaxies: nuclei
  • Infrared: galaxies
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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