Fueling QSOs: The Relevance of Fueling QSOs: The Relevance of MergersMergers

Nicola BennertNicola Bennert

University of California RiversideUniversity of California Riverside

in collaboration within collaboration with

Gabriela Canalizo (UCR), Bruno Jungwiert (UCR/Prague), Alan Stockton (IfA), Gabriela Canalizo (UCR), Bruno Jungwiert (UCR/Prague), Alan Stockton (IfA), Francois Schweizer (Carnegie), Mark Lacy (SSC), Chien Peng (HIA)Francois Schweizer (Carnegie), Mark Lacy (SSC), Chien Peng (HIA)

The Central Kiloparsec: AGNs and Their Hosts June 6The Central Kiloparsec: AGNs and Their Hosts June 6thth, 2008, Ierapetra, , 2008, Ierapetra, CreteCrete

What mechanism triggers AGN activity? - ubiquity of SMBHsWhat mechanism triggers AGN activity? - ubiquity of SMBHs

ULIRGs: close connection between mergers and QSO activityULIRGs: close connection between mergers and QSO activity

(e.g. Canalizo & Stockton 2001; Surace et al. 1998, 2000)(e.g. Canalizo & Stockton 2001; Surace et al. 1998, 2000)

Mergers?Mergers?

Steep evolution of activity with z: - accretion onto BH more common Steep evolution of activity with z: - accretion onto BH more common

- triggering mechanism more common- triggering mechanism more common

What is the relevance of mergers for fueling AGNs? What is the relevance of mergers for fueling AGNs?

– – helpful helpful (e.g. Toomre & Toomre 1972, Stockton 1982)(e.g. Toomre & Toomre 1972, Stockton 1982)

- not sufficient - not sufficient (e.g. any catalogue of interacting galaxies)(e.g. any catalogue of interacting galaxies)

- necessary for QSOs only? - necessary for QSOs only?

(e.g. Malkan et al. 1998, Combes et al. 2006, Woo et al. 2004)(e.g. Malkan et al. 1998, Combes et al. 2006, Woo et al. 2004)

also: Moshe‘s „final speculations“also: Moshe‘s „final speculations“

The Relevance of Mergers for Fueling AGNsThe Relevance of Mergers for Fueling AGNs

Dunlop et al. (2003): 33 AGNs (RQQs, RLQs, RGs, 0.1<z<0.25; WFPC2, Dunlop et al. (2003): 33 AGNs (RQQs, RLQs, RGs, 0.1<z<0.25; WFPC2, 30min)30min)

hosts are massive ellipticals that are hosts are massive ellipticals that are

„ „indistinguishable from quiescent, evolved, indistinguishable from quiescent, evolved,

low-redshift ellipticals at comparable mass“ low-redshift ellipticals at comparable mass“

Most QSOs: - begin life as mergers Most QSOs: - begin life as mergers (e.g. Sanders et al. 1988)(e.g. Sanders et al. 1988) ??

- reside in old ellipticals - reside in old ellipticals (e.g. Dunlop et al. 2003)(e.g. Dunlop et al. 2003) ??

Evolutionary merger sequence: ULIRGs – QSOs – Ellipticals? Evolutionary merger sequence: ULIRGs – QSOs – Ellipticals? (e.g. Sanders et al. 1988, Surace et al. 1998, 2000)(e.g. Sanders et al. 1988, Surace et al. 1998, 2000)

The Nature of QSO Host GalaxiesThe Nature of QSO Host Galaxies

QSO activity triggered by merger, activity can outlast the signs of QSO activity triggered by merger, activity can outlast the signs of interactions? interactions?

Deep HST/ACS Images of QSO Pilot Sample Deep HST/ACS Images of QSO Pilot Sample (z~0.2)(z~0.2)

Signs of recent merger events (shells, tidal tails…) in 4 of the 5 QSOsSigns of recent merger events (shells, tidal tails…) in 4 of the 5 QSOs

(Bennert et al. 2008, ApJ, 677, 846; Canalizo, Bennert, et al. 2007, ApJ, 669, 801)(Bennert et al. 2008, ApJ, 677, 846; Canalizo, Bennert, et al. 2007, ApJ, 669, 801)

Comparison with Numerical SimulationsComparison with Numerical Simulations

Minor merger remnant? Minor merger remnant?

here: dwarf + spiral here: dwarf + spiral

(1:8 in total mass)(1:8 in total mass)

thanks to TJ Coxthanks to TJ Cox

gasgas starsstars

(time in Gyr)(time in Gyr)

Comparison with Numerical SimulationsComparison with Numerical Simulations

Plummer sphere (r_eff = 7.6 kpc; M=10^11 M_sun)Plummer sphere (r_eff = 7.6 kpc; M=10^11 M_sun)

(Canalizo et al. 2007, Bennert et al. 2008, Jungwiert et al. 2008)(Canalizo et al. 2007, Bennert et al. 2008, Jungwiert et al. 2008)

Host galaxy subtractionHost galaxy subtraction(Galfit, Peng et al. 2002)(Galfit, Peng et al. 2002)

Spectacular Shells in MC2-1635+119Spectacular Shells in MC2-1635+119

Minor merger: - regular inner shell structure (merger age ~few hundred Myr)Minor merger: - regular inner shell structure (merger age ~few hundred Myr)

Major merger: - total light contribution from inner shells (~6%)Major merger: - total light contribution from inner shells (~6%)

- outer arcs/tidal tails (merger age up to 1.7 Gyr) - outer arcs/tidal tails (merger age up to 1.7 Gyr)

- inner shell structure formed by material raining back in?- inner shell structure formed by material raining back in?

Canalizo, Bennert et al. (2007)Canalizo, Bennert et al. (2007)

Stellar PopulationsStellar Populations

Deep Keck spectroscopy of 14 QSO host galaxies (z~0.2):Deep Keck spectroscopy of 14 QSO host galaxies (z~0.2):

- starburst component - starburst component

in all but one of the hostsin all but one of the hosts

- best fit typically 10 Gyr pop. + - best fit typically 10 Gyr pop. +

intermediate age starburstintermediate age starburst

- major starburst episodes (10-90% of mass)- major starburst episodes (10-90% of mass)

with ages 0.6-2.2 Gyr with ages 0.6-2.2 Gyr

(Canalizo et al. 2006, 2007, 2008)(Canalizo et al. 2006, 2007, 2008)

Hosts of most luminous AGNs: Hosts of most luminous AGNs:

- bulge-dominated but significantly bluer - bulge-dominated but significantly bluer

than inactive ellipticals than inactive ellipticals

- evidence for starburst in relatively recent - evidence for starburst in relatively recent

past (1-2 Gyr)past (1-2 Gyr)

(e.g. Kauffmann et al. 2003, Sanchez et al. 2004, (e.g. Kauffmann et al. 2003, Sanchez et al. 2004,

Jahnke et al. 2007)Jahnke et al. 2007)Canalizo et al. (2008)Canalizo et al. (2008)

Comparison with numerical simulations: ~Gyr or less agoComparison with numerical simulations: ~Gyr or less ago

(Bennert et al. 2008, Canalizo et al. 2007)(Bennert et al. 2008, Canalizo et al. 2007)

Comparable to starburst ages from Keck spectroscopy Comparable to starburst ages from Keck spectroscopy (Canalizo & Stockton (Canalizo & Stockton 2008)2008)

but longer than AGN duty cycle but longer than AGN duty cycle (e.g. Yu & Tremaine 2002)(e.g. Yu & Tremaine 2002)

Time delay between interaction and fueling of BH? Time delay between interaction and fueling of BH? (e.g. Barnes 1998, Springel et al. 2005, Hopkins et al. 2006)(e.g. Barnes 1998, Springel et al. 2005, Hopkins et al. 2006)

Or episodic QSO activity? Or episodic QSO activity?

(e.g. Norman & Scoville 1988, Hopkins et al. 2006)(e.g. Norman & Scoville 1988, Hopkins et al. 2006)

How can we „prove“ that merger triggered QSO activityHow can we „prove“ that merger triggered QSO activity??

Recent Merger Events in at least some QSO HostsRecent Merger Events in at least some QSO Hosts

Signs of recent merger events (shells, tidal tails…) in 4 of the 5 QSOs of recent merger events (shells, tidal tails…) in 4 of the 5 QSOs

(Bennert et al. 2008, Canalizo et al. 2007)(Bennert et al. 2008, Canalizo et al. 2007)

A Control Sample of Inactive EllipticalsA Control Sample of Inactive Ellipticalsz=0.279 z=0.160 z=0.182

z=0.287 z=0.245

z=0.220

z=0.190

z=0.190 z=0.220

Preliminary results: No comparable fine structurePreliminary results: No comparable fine structure

Outlook: 13 more QSOs with HST/WFPC2Outlook: 13 more QSOs with HST/WFPC2

Fine structure in at least some hostsFine structure in at least some hosts