Active galactic nucleus pairs from the Sloan Digital Sky Survey. II. Evidence for tidally enhanced star formation and black hole accretion

Xin Liu, Yue Shen, Michael A. Strauss

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65 Scopus citations


Active galactic nuclei (AGNs) are occasionally seen in pairs, suggesting that tidal encounters are responsible for the accretion of material by both central supermassive black holes (BHs). In PaperI of this series, we selected a sample of AGN pairs with projected separations rp < 100 h -1 70kpc and velocity offsets <600kms-1 from the Seventh Data Release of the Sloan Digital Sky Survey and quantified their frequency. In this paper, we address the BHaccretion and recent star formation properties in their host galaxies. AGN pairs experience stronger BHaccretion, as measured by their [O III] λ5007 luminosities (corrected for contribution from star formation) and Eddington ratios, than do control samples of single AGNs matched in redshift and host-galaxy stellar mass. Their host galaxies have stronger post-starburst activity and younger mean stellar ages, as indicated by stronger Hδ absorption and smaller 4000 Å break in their spectra. The BHaccretion and recent star formation in the host galaxies both increase with decreasing projected separation in AGN pairs, for rp ≲ 10-30 h -1 70kpc. The intensity of BHaccretion, the post-starburst strength, and the mean stellar ages are correlated between the two AGNs in a pair. The luminosities and Eddington ratios of AGN pairs are correlated with recent star formation in their host galaxies, with a scaling relation consistent with that observed in single AGNs. Our results suggest that galaxy tidal interactions enhance both BHaccretion and host-galaxy star formation in close AGN pairs, even though the majority of low-redshift AGNs are not coincident with on-going interactions.

Original languageEnglish (US)
Article number94
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 20 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • black hole physics
  • galaxies: active
  • galaxies: interactions
  • galaxies: nuclei
  • galaxies: stellar content


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