Hbeta spectra of high-redshift QSOs: Eigenvector 1 at high luminosities

Abstract

We present VLT-ISAAC spectra of unprecedented S/N and resolution for the H/3 region in a sample of n = 17 quasars in the range z = 0.8-2.5. The data represent our first attempt to test source occupation and line properties for the Eigenvector I parameter space that was defined using a.sample of sources with z < 0.8. We find no strong luminosity/redshift dependent effects with the possible exception of an increase in the minimum broad line profile width from 1000 to 3000 km s(-1) between M(B) approximate to -20 and -28.

Full text

The Interplay among Black Holes, Stars and ISM
in Galactic Nuclei
ProceedingsIAU S ympo siumN o.222, 2004
T. Storchi-Bergmann, L. C. Ho &H.R.Schmitt, eds.
c
2004 International Astronomical Union
DOI: 10.1017/S1743921304003199
Hβspectra ofhigh-redshift QSOs:
Eigenvector 1at high luminosities†
G. M. Stirpe1,J.W.Sulentic
2,P.Marziani3,
R. Zamanov4,M.Calvani
3and V.Braito5
1INAF –Osservatorio Astronomico diBologna, Via Ranzani 1, 40127 Bologna, Italy
2Dept. ofPhysics and Astronomy,Univ. of Alabama, Tuscaloosa, AL35487, USA
3INAF –Osservatorio Astronomico diPadova, Vicolo dell’ Osservatorio 5, 35122 Padova, Italy
4Astrophysics ResearchInst., LiverpoolJohn Moores Univ., TwelveQuaysHouse, Egerton
Wharf, Birkenhead CH41 1LD, UK
5INAF –Osservatorio Astronomico diBrera, Via Brera 28, 20121 Milano, Italy
Abstract. WepresentVLT–ISAACspectra of unprecedented S/N and resolution for the Hβ
region in asample ofn=17 quasars inthe range z=0.8–2.5. The data representour first
attempt totest source occupation and line properties for the Eigenvector 1parameter space
that wasdefined using asample ofsources with z<0.8. Wefind no strong luminosity/redshift
dependenteffects with the possible exception of an increase in the minimum broad line profile
width from 1000 to 3000 km s−1between MB≈−20 and −28.
Wehaveobtained high S/N spectra of the Hβregion of asample of 17 HE quasars
with intermediate redshift (0.85 z2.5) and high luminosity(−26 MB−30).
Forthe first time wehaveasample of NIR spectra with resolution and S/N compa-
rable tothose obtained for 200+ lower-redshift Type1AGN (Marziani etal. 2003
(M03)). Spectra (Fig. 1) were obtained between 2001 November and 2002 February using
ESO/VLT1+ISAACproviding aresolution of ∼300 km s−1in all bands (Z, sZ, J,H).
The observations representour first attempt totest the robustness ofthe Eigenvector 1
(E1) parameter space previously defined using lower redshift sources (Boroson &Green
1992; Sulentic et al. 2000). Our goals include testing: 1) domain space occupation in the
optical E1 plane and 2) the apparentluminosityindependence of all E1 properties.
The VLTspectra enable ustomeasure both E1 optical parameters: FWHM(Hβ)and
the broad-line equivalentwidth ratio W(FeIIopt )/W(Hβ)=R
Fe ,where W(FeIIopt )mea-
sures the λ4570 blend. Broad Hβ,andthenarrow[OIII]λλ5007,4959, were isolated by
subtracting appropriately scaled FeIIemission from the spectra using atemplate based
on IZw1. FeII emission properties shownodifferences from our lower-redshift sample
(M03) and the FeII template works equally well at these high redshifts.
Wefind no significantdifferences in source occupation for the optical plane ofE1 as
defined previously (Fig. 2a). There maybeaslight tendency for higher redshift source
to displace towards the upper rightbut this requires verification with amuchlarger
sample. The results are consistentwith our previous suggestion that E1 occupation is
driven neither bysource luminositynor BH mass but rather bythe Eddington ratio
convolved with source orientation to the line ofsight.
Figure 2b showspossible evidence for asystematic increase in minimum observed
FWHM(Hβ)with source luminosity.Ageneral increase in FWHM(Hβ)with luminosity
is not certain because radio-loud sources are over-represented inthe higher luminosity
†Based onobservations collected at the European Southern Observatory,Chile. Proposal
ref.: ESO 68.B–0364(A)
539

540 G. M. Stirpeet al.
Figure 1. Twoexamples ofthe 17 spectra ofHEQSOs obtained at the ESO/VLT
Figure 2. Left: the main E1 diagram, whichshowsthe relation between broad Hβline width
and relativeFeIIintensity.The HE QSOs are represented bythe filled circles with error bars.
There isnoevidence that their distribution isdifferentfrom that ofthe open circles (sources
from M03), despite the differentluminositydistribution. Right: the broad Hβline width vs.
luminosity.Triangles representHEQSOs, circles are AGN from M03. Symbols are filled for
radio-quiet sources, emptyfor radio-loud. The curveis the estimated lowerlimit to the FWHM
as afunction of luminosity.
part of our sample and they are known to showsystematically larger FWHM(Hβ). The
increase in minimum FWHM with Lmightbe expected if we:
•assume virialized motions inthe Broad Line Region (BLR)
•use the RBLR ∝Lαrelation found byKaspi etal. (2000), with α=0.7
•assume that low-redshift NLS1 havean Eddington ratio close to 1
By combining these relations, weobtain the lowerboundary to the broad-line widths
showninFig. 2b.
Using L(5100˚
A) (rest wavelength) and the FWHM(Hβ)asdescribed byVestergaard
(2002), wecan estimate the mass ofthe central blackhole, assuming that the BLR-
size vs. luminosityrelation found byKaspi etal. (2000) can be extrapolated tohigh
luminosities and redshifts. Weused the formula derived byMcLure &Jarvis (2002). The
mass estimates yield large values, close to or reaching 1010 M⊙,for the most luminous
sources. Estimates ofthe Eddington ratios indicate that most QSOs are radiating near
∼0.3L
Edd.
References
Boroson, T.A., &Green, R.F.1992, ApJS, 80, 109
Kaspi, S., etal. 2000, ApJ, 533, 631
Marziani, P., et al. 2003, ApJS, 145, 99 (M03)
McLure, R.J., &Jarvis, M.J.2002, MNRAS, 337, 109
Sulentic, J. W., Zwitter, T., Marziani, P., &Dultzin-Hacyan, D. 2000, ApJ, 536, L5
Vestergaard, M. 2002, ApJ, 571, 733