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. 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?
z=0 Häring & Rix (2004)
MBH/Msun
M* /Msun
Step 1
Step 2
Step 3
Major mergers
Minor mergers
Large scale bars
Nuclear bars
ISM turbulence …
-When I say quasar, I mean high luminosity end, actively accreting AGN
-What triggers a qso, or what can bring gas to pc scales
???

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”
How is the “merging galaxy” status achieved?
After *…depth* stop, say we need an apple to apple comparison blah
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)
-AGN best detected by xray emission
-add redshift, I band

5. Our approach 2) Comparison Sample
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 3) Visual Classification
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
Replace with classes
Strongly distorted

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

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

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

10. “AGN do not prefer to live in merging 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:
If (1), then what about observed mergers?
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. To recap… Some advertising
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: )