The merger-AGN connection since z~1: causal or circumstantial?

1. The merger-AGN connection since z~1:causal or circumstantial? Mauricio Cisternas MPIA, Heidelberg COSMOS Meeting IfA, 09/06/2010 + K. Jahnke, K. Inskip, A. Robaina (MPIA) T. Lisker, J. Kartaltepe, A. Koekemoer, M. Scodeggio, J. Trump, K. Sheth

2. MBH/Msun Step 1 Step 3 M* /Msun z=0 Häring & Rix (2004) Co-evolution • Scaling relations: “proof” for the tied growth of galaxies and their supermassive black holes • BH mass: built up during a quasar phase • But, what triggers a quasar? Step 2 Major mergers Minor mergers Large scale bars Nuclear bars ISM turbulence … ???

3. Appealing scenario: major mergers • BUT: • Are those representative samples of QSOs? • High frequency of mergers compared to what? • Signatures heavily dependant on bandpass, image depth Since the 80’s, observations have found: • quasars with close companions • post merger features on their host galaxies • “High frequency of mergers” COSMOS AGN

4. Our approach We study the distortions of a sample of AGN host galaxies. But, what makes us special? • The Data • ~2000 X-ray sources detected with XMM and Chandra • Classification as type-1/2 from spectroscopic surveys and SED fitting • Optical counterparts: HST/ACS • Solid sample of 140 type-1/2 (IAB<24, 0.3< z <1)

5. Our approach Active Galaxy 2) Comparison Sample • The key measurement: not just the merger fraction of the AGN hosts, but the enhancement of merging over the “background level” • ~10 inactive galaxies per active galaxy • Compiled from the same dataset • Matched in redshift and brightness (including special treatment for the type-1 AGN) Control Sample

6. Our approach Smooth 3) Visual Classification • No definitive way to identify mergers automatically... …then let’s do it by eye (& brain)! • Basically: • Hubble type • Distortion level • Consistency: • We use 10 independent classifiers (people) • We classify blindly: mixing the AGN hosts with the inactive galaxies Mildly distorted Strongly distorted

7. 4 5 2 3 1 6 7 9 10 8 14 11 13 12

8. The Result • This means: No enhancement in the merger fraction of AGN host galaxies over the background level Mean difference between the distortion fractions: 2.4% ± 3.6%

9. The Result The K-S test can’t distinct between the 2 sets of measurements

10. “AGN do not prefer to live inmerging systems” This result allows for 2 possible interpretations: • There is a significant time-lag between merging and AGN triggering… • … or major merging is not the main fueling mechanism AGN lifetime: Merger timescale: time

11. Clues from the Hubble sequence • Hubble-type classification: ~60% of AGN hosted by galaxies with a significant disk • Since z~1: • Methods that do not involve destruction of the disk dominate • Minor mergers, accretion of surrounding gas, bar instabilities, nuclear bars, SN explosions, … • Tied growth of BHs and their host galaxies? not so much (Preprint coming soon)

13. Quasar-host galaxy decomposition with GALFIT (originals) z=0.67 z=0.74 z=0.91 (models) (host galaxies)

14. Comparison sample: creating mock AGN Procedure: i) For each type-1 AGN, we select 10 inactive galaxies that match in redshift and magnitude ii) Using the Host/Nucleus flux relation for a given AGN, we search for a star that fits that ratio against the inactive galaxy iii) By adding the star on top of the galaxy, we create a mock AGN iv) We treat our mock AGN exactly the same way as the original ones, which yields to a set of galaxies with the same conditions than our hosts + (inactive galaxy) (star) = (mock AGN) (galaxy + residuals)

15. www.mpia.de/coevolution To recap… • AGN host galaxies show virtually the same frequency of distortions than inactive galaxies • Large fraction of disks on our AGN sample implies alternative fueling methods not caused by recent major mergers • Since z~1, merging and quasar activity disconnect • Preprint coming soon… Some advertising Just today at astro-ph: “The non-causal origin of the black hole-galaxy scaling relations” K. Jahnke & A. Maccio (arXiv:1006.0482)