Metallicity Evolution of Active Galactic Nuclei

Tohru Nagao (National Astronomical Observatory of Japan)

Roberto Maiolino (INAF — Roma)

Alessandro Marconi (INAF — Arcetri)

Why Metallicity?

~ heavy elements SNe of massive stars, mass-loss from less-massive stars~ “imprint” of past star-formation history in each (host) galaxy~ metallicity evolution star-formation / metal-production history of the universe~ investigating metallicity as a function of the age of the universe (= redshift)

by focusing on …

Galaxies or AGNs ??

◎ high number density × low × rest-optical important lines ◎ rest-UV

× 0<z<3 (or less) target redshift ◎ 0<z<6 (or more) × faint intrinsic luminosity ◎ bright

Study on BLR metallicity

SDSS-DR2 5344 spectra of quasars @ 2.0<z<4.5

making Composite Spectra

for each (z, LAGN) bins

very high S/N spectra

example:Composites at 2.0 < z < 2.5

-24.5>MB>-25.5 (643 QSOs)

-25.5>MB>-26.5 (1497 QSOs)

-26.5>MB>-27.5 (917 QSOs)

-27.5>MB>-28.5 (105 QSOs)

-28.5>MB>-29.5 (5 QSOs)

TN, AM, RM (2006a)

Rest Wavelength (A)

Dependences of emission-line flux ratios on (z, L)

Redshift absolute B magTN, AM, RM (2006a)

Dependences of BLR metallicity on (z, L)

TN, AM, RM (2006a)

BLR metallicity is strongly correlated

with AGN luminosity, but…

NO redshift evolution up to

z=4.5 !!

ZB

LR /

Zsu

nZ

BLR

/ Z

sun

Study on NLR metallicityN

V1

240

/ HeI

I16

40

NV1240 / CIV1549

DeBreuck et al. (2000)

2 < z < 5Narrow-Line Radio Galaxies

BLR model

NLR model

NV emission from NLRis generally VERY weak

Only upper limits on F(NV) have been obtained formost of radio galaxies…

Metallicity diagnosticswithout NV emissionshould be applied !!

NLR metallicity diagnostic

CLOUDY calculationsone-zone, dust-free cloudsCIV/HeII : sensitive to ZNLR

CIII]/CIV : correction for U

TN, RM, AM (2006b)

49 radio galaxies at 1.2 < z < 3.8correlation: consistent to modelhow depends on z and LAGN ??

Dependences of NLR metallicity on (z, L) TN, RM, AM (2006b)

Not only BLR, the NLR metallicity also depends on LAGN

but does not show any redshift evolution at 1.2<z<3.8

Why no metallicity evolution?M

eta

llici

ty

Galaxy Mass

z=0

z=2

Erb et al. (2006)

redshiftevolution

galaxies

INCONSISTENT !?

AGNs

NV/H

eII N

V/C

IV

absolute B mag

TN, AM, RM (2006a)

a possible interpretation:

SDSS QSOs are too bright host galaxies are too massive Z evolution has been completed

Metallicity studies onhigh-z low-luminous AGNsare crucially important !!

Summary

BLR metallicityComposite spectra of 5344 SDSS quasarsCorrelations with LAGN: non-correlations with z NV/CIV, NV/HeII, (SiIV+OIV])/CIV, AlIII/CIV, etc.LAGN-ZBLR relation does not show z-evolution up to z = 4.5

NLR metallicityCompiled data of 49 narrow-line radio galaxies at 1.2 < z < 3.8Correlations with LAGN: non-correlations with z new metal diagnostic CIV/HeII with U-corrector CIII]/CIV

LAGN-ZNLR relation does not show z-evolution up to z = 3.8

Possible interpretationMain star-formation activities in host galaxies ofbright AGNs might be already completed even at z ~ 4 studies on lower-LAGN / higher-z AGNs are important

Appendix

Photoionization ModelCalculations