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