Quasars, Host Galaxies, and their Role in Galaxy Evolution

Gabriela CanalizoUniversity of California, Riverside

Irvine, March 2, 2011

UCR Team: Mariana Lazarova, Kyle Hiner, Nathaniel Stickley, Kyle Lee (undergrad). UCSD: Aleks Diamond-Stanic.

UCSB: Vardha Nicola Bennert

The study of quasar host galaxies can shed light on some outstanding questions:

• Is quasar activity really triggered by mergers?• Is there a merger-starburst-AGN connection?• Is there evidence that star formation is really

quenched after AGN activity is triggered?• What are the relevant time scales?• How do black hole - galaxy scaling relations change:

– over cosmic time?– with galaxy morphology?– with merger stage?

On the triggering of Starbursts and Quasar activity

• Galaxies merge and cause starbursts– Generally accepted, although there is still no consensus

on precise relation between starbursts and mergers– Mergers helpful but not sufficient

• Can mergers also trigger quasar activity?– Plausible, but still debated: many studies based on

circumstantial evidence– The fact that quasar host galaxies are interacting does

not necessarily imply that interactions triggered the quasars

Springel et al. (2005)

Results from Low-z StudiesQuasar host galaxies tend to fall in two main groups:

1. Galaxies with young stellar populations (1-4 x108 yr) and morphologies indicative of ongoing mergers Samples: FIR Color-selected quasars, ‘post-starburst’

quasars, dust-reddened quasars

2. Galaxies with intermediate age populations (1-2 x 109 yr) and morphologies indicative of older merger events Samples: Dunlop et al. 2003, Wold et al. 2010, Letawe et al.

2008, Canalizo et al.

• Goal: To determine whether elliptical quasar host galaxies formed at high redshifts and have been passively evolving since, or whether they are relatively recent mergers (Canalizo et al. 2006, 2007, 2011; Bennert et al. 2008).

• Observations: – Deep Keck LRIS spectroscopy of quasar hosts dominated by

spheroids (no disk) show that they are dominated by intermediate-age starbursts of ages 0.6 to 2.2 Gyr

– Deep HST/ACS and WFPC2 imaging shows merger remnants with dynamical ages consistent with those of the starbursts

The relevance of mergers in early-type quasar host galaxies

0736+2010054+144

2141+175

0923+201

Bennert et al. (2008)

• Deep ACS images of quasar host previously classified as ellipticals

In summary…• Quasar host galaxies that appear to be spheroidal in shape are

the products of relatively recent mergers (~1 Gyr) • These mergers resulted in massive star formation at that epoch

Bottom line:Quasar activity may occur > 1 Gyr after merger and onset of star

formation (although in most cases in our particular samples it occurs < 0.5 Gyr after)

Possible interpretation:• Activity is likely episodic and can be triggered again

(“rejuvenated”) over long timescales by, e.g., infalling material from tails

Control Sample of Inactive Ellipticals• Goal: Would we find similar structure in inactive ellipticals if we

looked “hard enough”? • Tools: A control sample of inactive elliptical galaxies at z~0.2: Deep

(3+ orbits) HST/ACS imaging

Kyle LeeGALFIT subtracted de Vaucouleurs profile

Vardha Nicola Bennert (UCSB)

z=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

- Deep Keck Spectra well fit by purely old pops.

Canalizo et al., in prep

Control Sample of Inactive Ellipticals

LoBALs and Feedback• Goals:

– To investigate whether low-ionization broad absorption line quasars (LoBALs) are in an early evolutionary stage by determining whether 1) they are hosted in recent mergers 2) there is recent SF activity.

– To investigate whether outflows are in the process of or have just quenched star formation.

• Sample:– Volume limited sample of all (22) SDSS DR3 LoBALs

@ 0.5 < z < 0.6• Observations:

– Spitzer IRS, MIPS– HST WFC3/UVIS F475W, WFC3/IR F125W– Keck LRIS spectroscopy

Mariana Lazarova

LoBALs: Spitzer results

• IRS spectra mostly featureless. Very similar to non-BAL type-1 quasars.

Lazarova, Canalizo & Lacy, in prep

However, SEDs show that • LoBALs are, on average, more IR luminous than PG QSOs • Dust warmed by star formation contributes more significantly to their

FIR emission

Lazarova, Canalizo & Lacy, in prep

LoBALs: HST observations• Observations in progress - will be able to study morphologies

and detect current or past mergers

LoBALs: LRIS spectra

• Post-starburst populations in some hosts• Upcoming run in April

Velocity Dispersions of Quasar Host Galaxies• Goal: To develop a method to measure σ* in quasar host

galaxies in order to study MBH-σ* at higher z and higher luminosities (masses?)

• Method: Spectra of the central regions of dust-reddened quasars show simultaneously broad Hα (to measure MBH) and stellar absorption features (to measure σ*) at shorter wavelengths.

Canalizo et al. 2008, 2011

Pilot sample of 9 objects: results possibly consistent with those of Treu et al., Woo et al.

Canalizo et al. 2008, 2011

Velocity Dispersions of Quasar Host Galaxies

• Goal: Investigate the evolution of MBH-σ* in quasars out to redshift of z ~ 1

• Samples:– 28 dust reddened quasars– 29 post-starburst quasars

• Observations:– ESI and LRIS spectroscopy (still collecting)– NIR spectra with NOT (done) and IRTF (proposing)– HST ACS imaging of poststarburst (done) and

red (proposing) quasars.– Other ground-based high-resolution imaging (done)

Kyle Hiner

MBH-σ* in quasars @ 0 < z < 1

Post-starburst quasars: flux contrast between quasar continuum and stellar population is particularly low in regions that contain useful features to measure σ*

MBH-σ* in quasars @ 0 < z < 1

MBH-σ* in quasars @ 0 < z < 1Potential biases:1. Specific subsamples of quasars studied may be in an

(early) evolutionary stage and not representative of the entire population.

We are studying two different types of quasars that potentially represent two distinct evolutionary stages

We have large samples for better statistics2. Objects may be involved in recent mergers

Need to understand how σ* evolves in a merger

3. Objects may be dusty Need to understand how the measurement

of σ* is affected by dust.

4. Stellar pops that are the result of merger- induced starbursts may not be relaxed

Need to be able to track pops separately

• Goal: To investigate the effects of dust and merger activity upon MBH and σ*

• Problem: – Current numerical simulations do not have sufficient time

resolution to follow the evolution of σ* during a merger.

– The methods commonly used to measure σ* from simulations (mass-weighted σ*) are not compatible with observational techniques (flux-weighted σ*).

• Method: Use high temporal resolution numerical

simulations to measure σ* in a way that is fully

consistent with observations.Nathaniel Stickley

The evolution of σ* during mergers

• First steps:– Low resolution simulations of small, dissipationless spheroidal stellar

systems– Toy model for dust attenuation– Measure mass-weighted and flux-weighted σ* from 150 random l.o.s.

The evolution of σ* during mergers

Stickley et al, in prep.

Next steps:• Use GADGET-2 + AGN feedback, BH growth, star formation and SN

feedback sub-resolution methods to run high-resolution galaxy merger simulations

• Analyze snapshots at < 50 Myr intervals using traditional mass and velocity methods as well as simulated observation techniques

• Use SUNRISE to create images and high resolution spectra.

Results will help us to

• quantify the scatter in MBH - σ* due to dust, anisotropy and merger evolution

• determine observational parameters that indicate whether a system is “sufficiently relaxed” to measure a meaningful σ*

• track the σ* of different stellar populations

The evolution of σ* during mergers