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The role of galaxy mergers in triggering AGN Sara Ellison (University of Victoria)

The role of galaxy mergers in triggering AGN Sara Ellison (University of Victoria). Shobita Satyapal (GMU), Ryan Hickox (Dartmouth), Dave Patton (Trent), Trevor Mendel (MPE), Jillian Scudder (Sussex), David Rosario (Durham), Hossen Teimoorinia ( Uvic ). Galaxy pairs in the SDSS.

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The role of galaxy mergers in triggering AGN Sara Ellison (University of Victoria)

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  1. The role of galaxy mergers in triggering AGN Sara Ellison (University of Victoria) ShobitaSatyapal (GMU), Ryan Hickox (Dartmouth), Dave Patton (Trent), Trevor Mendel (MPE), Jillian Scudder (Sussex), David Rosario (Durham), HossenTeimoorinia (Uvic).

  2. Galaxy pairs in the SDSS DR7 pairs sample: Projected separation <80 kpc V <300 km/s Mass ratio 0.1 - 10 Yields: ~14,000 galaxies in pairs. Construct control samples that are matched in mass, redshift and environment: typically 100s control galaxies per pair.

  3. Post-merger sample 97 visually selected post-mergers from Galaxy Zoo. Control matching and analysis done exactly same as for pairs.

  4. AGN frequency: from optical emission lines Ellison et al. (2013) Merger AGN fraction/control AGN fraction Although AGN may be triggered by first pass, fraction increases most strongly after coalescence See also Ellison et al. (2011), Khabiboulline et al. (2014)

  5. AGN frequency: from mid-IR colours W1-W2>0.8 W1-W2>0.5 Optical BPT Significant fraction of merger triggered AGN are dust obscured and not seen as AGN in optical. Satyapal et al. (2014)

  6. Two AGN fuelling modes 1) High excitation = radiatively efficient = quasar mode (identified in optical, IR etc; may have radio jets) High accretion rates (1-10% Eddington) 2) Low excitation = radiatively inefficient = radio mode (characterized through radio emission) Low accretion rates (<<1% Eddington)

  7. LERG sample from Best & Heckman 2012. No enhancement in LERG fraction in pairs: LERGs triggered by secular (non-merger) processes. Ellison, Patton, Hickox (2015)

  8. SFRs of AGN hosts obtained from far-IR luminosities (catalog of SFRs from far-IR luminosities for SDSS galaxies: Ellison et al. 2016a). ΔSFR Radio-selected AGN (LERGs) are strongly UNDER star forming Optically-selected AGN are slightly UNDER star forming mid-IR-selected AGN are OVER star forming Ellison et al. (2016b)

  9. Summary • Mergers can trigger AGN, and enhance their accretion rate. Ellison et al. (2011, 2013). • IR selected AGN more prevalent in mergers than optically selected AGN – mergers more frequently to lead to obscured AGN. Satyapal et al. (2014) • Low excitation radio galaxy (LERG) AGN are not fuelled by mergers Ellison, Patton & Hickox 2015. • SFRs of AGN depend on how AGN is selected. Ellison et al. (2016b). Not all AGN are equal! Selection matters.

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