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

Mauricio CisternasMauricio CisternasMPIA, HeidelbergMPIA, Heidelberg

COSMOS MeetingCOSMOS MeetingIfA, 09/06/2010IfA, 09/06/2010

+ K. Jahnke, K. Inskip, A. Robaina (MPIA)

T. Lisker, J. Kartaltepe, A. Koekemoer, M. Scodeggio, J. Trump, K. Sheth

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 1Step 1 Step 2Step 2 Step 3Step 3

???z=0 Häring & Rix (2004)

MB

H/M

sun

M* /MsunMajor mergersMinor mergers

Large scale barsNuclear bars

ISM turbulence…

Appealing scenario: major mergers

COSMOS AGN

Since the 80’s,observations have found:

• quasars with close companions

• post merger features on their host galaxies

• “High frequency of mergers”

BUT:Are those representative samples of QSOs?

High frequency of mergers compared to what?

Signatures heavily dependant on bandpass, image depth

Our approachWe study the distortions of a sample of AGN

host galaxies. But, what makes us special?

1) 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)

Our approach2) 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 SampleControl Sample

Active GalaxyActive Galaxy

Our approach3) 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

SmoothSmooth

Mildly distortedMildly distorted

Strongly distortedStrongly distorted

1

2 34 5

67

89

10

1112 13

14

The Result

• This means: No enhancement in the merger fraction of AGN host galaxies over the background level

Mean difference between thedistortion fractions: 2.4% ± 3.6%

The Result

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

“AGN do not prefer to live inmerging systems”

This result allows for 2 possible interpretations:

1. There is a significant time-lag between merging and AGN triggering…

2. … or major merging is not the main fueling mechanism

time

Merger timescale:

AGN lifetime:

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)

Quasar-host galaxy decomposition with GALFIT

z=0.67 z=0.74 z=0.91

(originals)

(models)

(host galaxies)

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)

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)

www.mpia.de/coevolution