The Post-starburst Quasars

The Post-starburst Quasars

Zhaohui Shang(University of Wyoming / Tianjin Normal University)

Mike Brotherton (University of Wyoming)Aleks Diamond-Stanic (Wyoming/Steward Observatory)Rebecca Stoll (Wyoming/Wellesley)Cassandra Paul (University of Wyoming)

Lijiang 8/16/05

What are they?

Brotherton et al. (1999, 2002), Canalizo et al. (2000)

Prototype: UN J1025-0040Nuclear starburst: 400 Myr

Also known as Q+A

Why Important?

Direct link between AGN and starburst

• Transition Stage in ULIRG to Quasar Evolutionary Schemes (e.g., Sanders et al. 1998)?

• Black Hole/Bulge Correlations (M-sigma) Indicate Mutual AGN/Galaxy Evolution (e.g., Ferrarese & Merritt 2000; Gebhardt et al. 2000)

• Clocks on Triggers of AGN Activity?

• …

But post-starburst quasars are rare.

Post-starburst Quasars in the SDSS

• More than 16000 quasars in SDSS DR3• Spectroscopiclly selecting PSQs using the algorithm similar to

Zabludoff et al (1996) Balmer jump strength Balmer absorption line equivalent widths Significance of detecting absorption lines

We found• 708 candidates in DR3 => 609 post-starburst quasars• a few percent of quasar population


SDSS Images of PSQs• Environment/morphology• Looking for companions and interacting/mergering evidence

Spectral Modeling of PSQs (starburst + quasar)• Starburst age and mass.

Using Bruzual-Charlot stellar models (1996) of solar metalicity.• Quasar black hole mass and Eddington accretion rate L/Ledd.

Using quasar emission line width and continuum luminosity + empirical formula from reverberation mapping results (e.g., Kaspi et al 2000).

PSQ Spectral Modeling: starburst + quasar

PSQ Spectral Modeling: Preliminary results

• 80 objects• 0.25 < z < 0.45• significant starburst

No obvious correlation.

PSQ Spectral Modeling: Preliminary results

• 80 objects• 0.25 < z < 0.45• significant starburst

Results are not conclusive.• Need higher S/N spectra to

reduce uncertainties.• Keck spectra are coming.

PSQ Environment: SDSS Images

• Resolution 1.4 arcsec• 40 X 40 arcsec• 40% appear to be

interacting or have nearby companions

PSQ Environment: SDSS Images

• Resolution 1.4 arcsec• 40 X 40 arcsec• 40% appear to be

interacting or have nearby companions

Sequence?

Pre Merger Merging

Post Merger Merger Long Over?

PSQ Environment Different from Quasar Enviroment?

Searching for companions: within 100 kpc of the objects

Set z > 0.1• PSQ: 541• Quasar: 15098

For each PSQ:• Find all sources within 100 kpc at the redshift of the PSQ.• Get photometric redshifts of these sources.• Apply K-corrections.• Obtain the radial separations between the sources and the PSQ.• Count the real companions within 100 kpc.

For each Quasar:• Same as above

Environment: Number of Companions

No difference.Faint companions?

No difference.Faint companions?

Average Number of Companions:PSQ: 2.12Quasar: 1.82

Environment: Number of Companions

PSQs do not seem to be in a much richer environment than normal quasars in large scale.

PSQ Local Environment: Interacting

SDSS

30”x30”

HST/ACS

Conclusions

• Post-starburst quasars are now found in statistically significant numbers in SDSS.

• The large scale enviroment of PSQs is similar to that of normal quasars.• It is likely that PSQs have close companions and show

interacting/mergering evidence.• PSQs may reveal the intrisic connection between AGN and starburst and

their mutual evolution, allow us to investigate the origin of the M-sigma relationship.

Future work• Obtain higher quality spectra to improve modeling.• Combine starburst and quasar properties with morphological information.• Compare post-starburst quasars with normal quasars in physical

parameters, such as black hole masses and Eddington accretion rates.• Compare with non-AGN post-starburst systems in the galaxy survey.

The Post-starburst Quasars

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