The Evolution of Quasars andMassive Black Holes

“Quasar Hosts and the Black Hole-Spheroid Connection”: Dunlop 2004

“The Evolution of Quasars”: Osmer 2004

David R. LawMay 23, 2005 Image: A. Siemiginowska, M. Weiss (APOD 031128)

Quasars: Introduction and Low Redshifts

• Quasars are high-luminosity AGN (MB < -23), LX >1044 erg/s• AGN distinguished by broad SED and strong emission lines.

Permitted lines (Ly,H,C IV, Mg II, etc) 5000 km/s wide, prominent forbidden lines ([O I], [O II], [O III], [S II]). Broad Fe II emission.

• Above a certain luminosity, AGN only hosted by massive elliptical galaxies, disk components occur only at low luminosities

• HST imaging indicates hosts of low redshift quasars almost entirely massive ellipticals with Mv < -24, L > L*

• Host galaxies appear to be similar for both active and quiescent quasars

We can observe local structure well, consistent with de Vaucoleurs r1/4 profile.

(Dunlop 2004)

The Black Hole - Spheroid Connection

• Detected systems probably not result of mergers: although disk galaxy mergers can produce r1/4 profiles the light is inconsistent with a nuclear starburst, and Scoville et al. (2003) detected no molecular gas in most luminous quasars (though some gas in disky hosts)

• All spheroids appear to contain black holes with masses given by a fairly precise mass ratio (Magorrian et al. 1998, et al)

• Mass relation in nearby quasars is the same as that in quiescent galaxies: MBH = 0.0012 MSph

Observed correlation between nuclear luminosityand bulge/total light fraction

(Dunlop 2004)

(Dunlop 2004)

Finding Quasars at High Redshift

• In local universe, exploit spectral differences between quasars and stars.

• Search methods: UV excess, slitless spectra, color selection criteria, spectroscopic surveys (e.g. Steidel survey of z = 3 Lyman Break Galaxies).

• Large digital surveys like 2dF and SDSS revolutionized quasar searches, using population synthesis showed weak AGN emission in almost all early and mid-type galaxies.

• Seems that quasars are still too few to account for ionization of IGM at high redshift- more out there?

Estimating Black Hole Mass

• Standard method involves virial theorem applied to broad line emission regions: Mbh = R v2/G

• Empirical correlation between radius of the broad line region and the 5100 continuum flux.

• In local universe, H the line of choice• Beyond z = 1 this gets shifted into NIR, so use Mg II (2799)

, another low ionization line.• C IV also used, but correlation with H less well understood.• Reverberation mapping. What is this?

(Dunlop 2004)

Estimating Host Mass

• Tricky- search methods at high redshift preferentially select bright quasars, which outshine hosts

• Some use of [O III] to trace velocity dispersion in central regions of host galaxy

• Predict most luminous high z quasars require elliptical hosts (or their progenitors) of L ~ 10 L*

Dunlop (2004) disparages the usefulness of this relation?

Population Evolution

• Most luminous quasars are emitting at near Eddington limit• Space densities increase dramatically with redshift-

population density increased by more than 2 dex from z=0 to 2. (This is seen in even smallest original samples of 20 objects- Schmidt 1968).

• Either space density increasing by factor of over 100, or characteristic luminosity increasing by factor of 30. These models give very different results for quasar lifetime- 107 vs. 109 years.

• Schmidt- power law and exponential forms could both fit data trend with redshift.

(Dunlop 2004)

(Osmer 2004)

(Dunlop 2004)

Assuming passive evolution, hosts of luminous quasars almost unchanged in mass between redshift z = 2 and today

Population Evolution: Conclusions

• At least 10% of present massive ellipticals were active quasars at z = 2.

• Almost every spheroidal system had an AGN phase• No evident chemical evolution in quasars from z = 3 to today• Quasars appear to have built up their mass early: over 109

solar masses at redshifts z > 3.6 (Fan et al. 2001)• Therefore low redshift Seyfert galaxies and AGN have

achieved a large fraction of their final black hole growth.• What shuts off the accretion?

Future Work

• Want to match observations of AGN over a range of redshifts to the local mass function of black holes in galaxies.

• High angular resolution studies are necessary so the morphology of host galaxies can be analyzed

• Adaptive optics with integral field spectroscopy could allow such high resolution studies and suppress the central source flux to probe faint host galaxy.