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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 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