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The Population and Luminosity Function of AGNs from SDSS

Lei HaoLei HaoCollaborators: Michael Strauss

SDSS collaboration

Princeton University

CFA Lunch Talk: November, 14, 2002

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Introduction: AGN emission lines

Broad-line AGNs

Star-forming galaxies

Narrow-line AGNs

Veilleux & Osterbrock (1987)

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Introduction:Sloan Digital Sky Survey

• AGNs are interesting but rare• SDSS is very promising in having a large AGN

sample:– one-quarter of the sky

– collect spectra of ~ 106 galaxies, 105 quasars, …

• Galaxies: r<17.77• Quasars: i<19.0; color selection• Spectra resolution: ~ 2000• Over 400,000 spectra have been taken.

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Data Sample

• 114,772 galaxy and quasar spectra in 1151 sq degrees

• 58,038 low redshift (z<0.33) emission line galaxies.

• AGNs are identified by their emission line characteristics.

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Stellar Subtraction

• Emission lines are very easy to be contaminated by the underlying absorption lines.

• Apply Principle Component Analysis (PCA) to pure absorption line galaxies.

• Use Eigenspectra as stellar templates.

• Plus an A star spectrum; Power-law continuum

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Stellar Subtraction

• The emission lines of AGN are often contaminated by the host galaxy absorption lines.

• To correct the contamination,the underlying stellar absorption spectrum is removed from the original spectrum.

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AGN Selections

– FWHM(Hα)>1,200 km/s – 3069 are identified

• Broad Line AGNs

• Narrow Line AGNs

Distinguishing AGNs from star-forming galaxies

Theoretical separation lines predicted by Kewley et.al 2001

Theoretical separation lines predicted by Kewley et.al 2001

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AGN Selections

– FWHM(Hα)>1,200 km/s – 3069 are identified

• Broad Line AGNs

– 3456 are identified

• Narrow Line AGNs

• Seyferts: Galaxy targeted for spectra in SDSS

• Quasars: Quasar targeted for spectra in SDSS

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The Redshift and Magnitude Distribution

• Seyfert sample– r-band Petrosian <17.77

– 1281 broad line AGNs

– 2696 narrow line AGNs

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The Luminosity Function (LF) of Seyferts • We measure the luminosity function as a function

of Hα luminosity.

• Assumption– The luminosity of the nuclei is independent of the

luminosity of its host galaxy.

• We measure the detection probability function for each AGN.

Nucleus SpectrumHost galaxy

Weakened nucleus

Noise

New Spectrum AGN?

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Luminosity Function: Seyfert 2s

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Luminosity Function: Seyfert 2s vs. Seyfert 1s

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Luminosity Function Result and Check

• Divide the AGN sample into subgroups by their redshifts.

• For each group, evaluate the expected AGN luminosity distribution using the LF calculated.

• If LF is correct, the expected distribution should match the observed distribution.

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Luminosity Function Result and Check

• Divide the AGN sample into subgroups by their host galaxy magnitudes.

• No systematic discrepancy

the nuclei luminosity is not strongly correlated with its host galaxy luminosity.

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Host galaxy luminosity vs. Nuclear luminosity

• Galaxy Magnitude vs. Hα Luminosity plot

0.01<z<0.03

0.03<z<0.06

0.06<z<0.09

0.09<z<0.12

0.12<z<0.14

0.14<z<0.20.12<z<0.14

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Host galaxy luminosity vs. Nuclear luminosity

• Correlation test (Kendall’s -statistic) study to check the independency.

• L(host) ~ L(nuclei)

• The principal quantity that determines the AGN luminosity is the Eddington ratio, not the black hole mass.

• Galaxy Magnitude vs. Hα Luminosity plot

• L(host) ~ L(nuclei) (0.0062±0.0005)

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Summary and Future Work

• From SDSS, we compiled an AGN sample including over 3000 broad-line AGNs and over 3000 narrow-line AGNs

• The LF of the AGNs are calculated and carefully checked.

• Nuclear luminosity is independent to the host galaxy luminosity.

• Future work:– Seyfert LF normalization and low redshift quasar LF– AGN LF evolution– The connection btw. AGNs and host galaxies– The accretion rate of AGNs

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Galaxies in Diagnostic Diagram

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Sersic Index

• Animation