the merger-agn connection since z~1: causal or circumstantial?
Post on 15-Jan-2016
35 Views
Preview:
DESCRIPTION
TRANSCRIPT
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
top related