aa r X i v : . [ a s t r o - ph ] S e p To appear in “The Nuclear Region, Host Galaxy and Environment of Active Galaxies (2007)”
RevMexAA(SC)
THE BROAD LINE REGION OF QUASARS
Paola Marziani , Jack W. Sulentic , and Deborah Dultzin RESUMENA lo largo de la decada pasada se avanz´o mucho en nuestra comprensi´on de las propiedades espectroscopicas delos NAGs (Nucleos Activos de Galaxias). Esta contribuci´on revisa algunos resultados observacionales impor-tantes obtenidos tanto en el ´optico como en el UV, asi como las restricciones que imponen sobre la estructuray la din´amica de las regi´ones que emiten las l´ıneas anchasABSTRACTThe last decade saw long-awaited improvements in our understanding of active galactic nuclei (AGN) spectralproperties. This contribution reviews some important observational results obtained from optical and UV dataas well as constraints on physical parameters that control the structure and dynamics of the Broad Line Region.
Key Words:
GALAXIES: ACTIVE — QUASARS: GENERAL — QUASARS: EMISSION LINES —BLACK HOLE PHYSICS
1. INTRODUCTION“A thousand spectra are worth more than oneaverage spectrum” is perhaps an appropriate mod-ern extension of the aphorism “a spectrum is wortha thousand pictures” – at least for active galacticnuclei (Cox 2000; Dultzin-Hacyan et al. 2000). The“one thousand” spectra of a source are needed to ob-tain an estimate of the spatial extent of the broadline emitting region (BLR). The time delay betweenline and continuum flux variations (i.e. reverbera-tion) is ∼ < z ≈ . ∼ > ÷
50 eV): C IV λ IV ]+Si IV λ II λ II λ ∼ <
20 eV: Balmer lines, Fe II , C II ,Mg II λ INAF, Osservatorio Astronomico di Padova, Vicolodell’Osservatorio 5, I-35122 Padova, Italy; ([email protected]). Department of Physics and Astronomy, University ofAlabama, Tuscaloosa, AL 35487, USA; ([email protected]). Instituto de Astronom´ıa, Universidad NacionalAut´onoma de M´exico, Apartado Postal 70-264, M´exicoD.F. 04510, M´exico ([email protected]). radial velocity intervals across line profiles (i.e. 2Dreverberation mapping) have slowed since then (butsee Kollatschny 2003), not least because of techni-cal difficulties demanding dedicated instrumentation(Horne et al. 2004).Emission line properties of quasars do not scatterrandomly with reasonable dispersion around an aver-age, so that “one thousand” spectra are also neededto exploit spectral diversity as well as spectral vari-ability. The range of observed H β BC FWHM spansmore than one order of magnitude, from ≈
800 kms − , to ≈ − in some extreme sources.The Fe II prominence parameter R FeII (defined asthe intensity of the Fe II blend centered at 4570 ˚Anormalized by the intensity of H β BC ) varies fromalmost 0 to ≈ β BC ) ≤ − , Population A] and B(roader) sources. There isevidence in favor of two different BLR populationsand of a meaningful limit at FWHM(H β BC ) ≈ − (see Sulentic et al. 2007). The distinction be-tween Population A and B may be more fundamen-tal than either the RQ-RL or the NLSy1 vs. rest ofquasars (BLSy1) dichotomies. Several tests find nosignificant distributional difference between NLSy1s1 MARZIANI, SULENTIC & DULTZIN, Fig. 1. HST/FOS (left panels) and optical, ground based spectra (right panels) of two representative sources: Mark478 (Pop. A, top), and Fairall 9 (Pop. B, bottom). The strongest lines whose profiles are shown in the next figures areidentified. and sources with FWHM(H β BC ) in the range 2000 –4000 km s − , suggesting that the 2000 km s − cutoffis artificial. Intriguing differences emerge if the Pop.A/B distinction is applied. • Pop. A sources show Lorentzian H β BC profiles,most often symmetric or with slight bluewardasymmetry, while Pop. B sources show doubleGaussian H β BC profiles, often redward asym-metric (Sulentic et al. 2002, see also Fig. 1). • The C IV λ IV λ β BC profiles appear to be more similar in Pop.B. (Sulentic et al. 2007, and references therein).Figure 1 shows optical and UV spectra for typ-ical pop. A and B sources. A visual impressionis that the ionization degree is higher for Pop. B(Marziani et al. 2001), with lower R FeII and moreprominent HILs. Kinematics and physical conditionsmay not be fully unrelated, for example if both Pop.A and B sources share a low-ionization region re-sponsible for most or all of the Fe II emission, whilea high-ionization, broader component is dominant inPop. B only. 3. UV/OPTICAL SPECTROPHOTOMETRICCOMPARISON OF 2 PROTOTYPICALSOURCESWe consider two sources in more detail, Mark478 and Fairall 9, which are representative of Pop.A and Pop. B respectively (Fig. 1). HST/opticaldata allow us to analyze all the strongest emissionlines from Ly α to H β . Mark 478 (Fig. 2) –
The H β BC profile is wellfit by a Lorentzian function. If we assume thatemission with the same profile is also present inC IV λ IV λ α profile. No blueshifted compo-nent is detected in H β . Mg II λ Fairall 9 (Fig. 3) – H β BC and MgII λ α and C IV λ β and MgII λ α and C IV λ Fig. 2. Profile analysis results for Mark 478, the prototypical Pop. A source considered in this study. Ordinate isrest-frame specific flux in units of 10 − ergs s − cm − ˚A − , corrected because of Galactic extinction. Dashed linesindicate sum of line model emission, dotted lines indicate Fe II emission. Due to the heavy Fe II contamination we onlyfit the doublet core of MgII. See text for further details. , Fig. 3. Profile analysis results of Fairall 9 (Pop. B prototype). Units and meaning of symbols are the same of theprevious Figure. Due to the non-simultaneity of the observations, and to the rather variable behavior of F 9 at the timethe HST spectra were collected, it is not advisable to compare fluxes in the optical (H β ) and UV lines. as shown in Fig. 3: a redshifted component analo-gous to the one identified in H β , and an additionalblueshifted component.A tentative nebular analysis can be carried outfor the main components identified in the profile de-composition using CLOUDY photoionization compu-tations (Ferland et al. 1998).
CLOUDY 7.0 incorpo-rates a 287-levels model of the Fe II ion followingVerner et al. (1999). This is especially useful sincewe are able to measure the Fe II emission for the 2000– 3000 ˚A range (Fe UV ), at least normalized to Ly α .We attempt to reproduce the observed line ratios forthe main components identified in the two sourcesalways assuming N H = 10 cm − , standard AGNcontinuum, and solar abundances. Mark 478: low ionization Lorentzian BC –
A very low ionization component accounts for mostemission in the H β spectral region. Emission lineratios are best fit if ionization parameter is log Γ ∼ < − n e ∼ >
12, where n e isexpressed in cm − . High density and low ionizationare especially needed to account for R FeII ≈ II UV /Ly α ≈
1. The very high n e is supported bythe ratio C III λ α ∼ . Mark 478: blueshifted component –
Theblueshifted component in Mark 478 appears to beless well constrained, partly because it is very weakin the H β range and strong in the UV lines. Ion-ization is presumably high for the gas emitting thiscomponent (log Γ ∼ − . ÷ − .
0) and density maybe log n e ∼ > ÷
11 although N H may be substantiallylower than assumed in our explorative calculations. F 9: low ionization Gaussian BC –
The lowerionization component, with narrower profile, is re-sponsible for all of the Fe II emission, which is notnegligible in F 9: Fe UV /Ly α ≈ R FeII ≈ R FeII includes allH β flux [minus the narrow component] and is ≈ ∼ − n e ∼ −
12. These physical conditions arenot much dissimilar from the ones deduced for theLorentzian component of Mark 478 and, as expected,the C
III λ F 9: high ionization, redshifted very broadGaussian component (VBC) –
The absence of“very broad” Fe II emission, and the rather promi-nent “very broad” He II λ ∼ − . ÷ − .
0, andmoderate electron density log n e ∼ . ÷
10. Theseparameters have been considered for a long time thecanonical ones for the BLR.
F 9: blueshifted component –
The high-ionization blueshifted component used to fit the Ly α and C IV λ II emission is self-similar in almostall sources within common S/N ( ∼ λ/ ∆ λ ( ∼ ) limits (Marziani et al. 2003a). The resultsobtained so far suggest that the similarity of the op-tical Fe II spectrum across Pop. A and B is dueto emission through photoionization of a very densemedium. The connection between kinematics andionization degree seems to be related to the relativeprominence of the high and low ionization compo-nents in the HILs and LILs, since it is the low ion-ization component that produces all Fe II emission.How can we tentatively account for the different lineprofiles and different average ionization conditions inPop. A and B sources?4. PHYSICAL PARAMETERS BEHIND THEOBSERVED BROAD LINE DIVERSITY4.1 . Radio Loudness First, we consider whether a powerful, radio jetsomehow affects the observational properties of theBLR. To this aim, we compared median H β BC pro-files of 56 RQ and 36 RL sources in the black holemass ( M BH ) interval 8 . < log M BH < . L / M BH ratio(Marziani et al. 2003b). Most of these will be Pop.B sources. The H β BC profiles (after Fe II and nar-row line subtraction) of RQ and RL sources are al-most identical. The BLR (but not the Narrow LineRegion!) does not seem to see whether a source isradio-loud or radio-quiet.4.2 . Luminosity VLT/ISAAC data provide IR spectra with reso-lution and S/N similar to optical data. We observed50 sources to cover redshifted H β (Sulentic et al.2004, 2006). Luminous quasars in the range 1.0 ∼ < z ∼ < . R FeII do not appear to de-pend significantly on L , even on a ∆ m ∼
10 range.FWHM(H β BC ) is expected to increase ∝ − . M B if broadening of H β BC is due to virialized gas mo-tions with r BLR ∝ L . (see Sulentic et al. 2004, fordetails). 4.3 . Gravitational Redshift The centroid at 0 intensity c (0/4) of H β BC looselycorrelates with M BH ; the correlation is significant( P ∼ − ) because such a large sample of ∼ c (0/4) and FWZI.The amplitude of redward asymmetry depends on M BH but gravitational redshift seems to be statisti-cally inadequate to produce the c (0/4) redshifts. Thedifficulty is even more serious if the high-ionizationVBC is considered alone.4.4 . Aspect Angle The angle θ between the line of sight and theradio jet axis can be estimated equalling the ob-served X-ray flux at 1 KeV to the flux expectedfrom the synchrotron self-Compton process actingon radio photons to obtain the Doppler factor. TheLorentz factor can be then retrieved from the ap-parent velocity if the source is superluminal (follow-ing Sulentic et al. 2003, and references therein). Ori-entation matters, affecting the FWHM(H β BC ) by afactor ≈
2. This technique can be applied only toquasars with detected superluminal motion. Thereis yet no known way to retrieve individual θ s for therest of AGN (Collin et al. 2006).4.5 . Eddington Ratio and Black Hole Mass The H β BC profiles change strongly as a func-tion of Eddington ratio with profiles being gener-ally Lorentzian if log L / M BH ∼ > . M BH , esti-mated according to the virial assumption, yields sec-ond order effects, mainly in the line wings. TheEddington ratio also strongly affects high ionizationlines like C IV λ v r ∼ < −
500 km s − ) are confined to Pop. A sourcesonly (Sulentic et al. 2007). These results suggestthat the Pop. A/B separation is physically moti-vated and driven by Eddington ratio.4.6 . Where is the Accretion Disk? Few ( ≈
2% in the SDSS), very broad sources,with FWHM ∼ ∼ < β BC , we expect that at the line base thecentroid shift is due to gravitational and transverseredshift, but this is not always the case, not even inPop. B sources.5. CONCLUDING REMARKSSeveral BLR physical and kinematical propertiesseem to be governed primarily by the Eddington ra-tio. It was not so clear ten years ago. LILs propertiesare remarkably similar over a very wide range of lu-minosity, even at very high z , and broad line profileshapes (both LILs and HILs) show only second-ordereffects that can be directly ascribed to M BH . Wehave also learned with more assurance that the BLRappears to be transparent to radio loudness. Thisdoes not mean that RL and RQ samples show simi-lar spectra: only Pop. B RQ quasars and lobe dom-inated RL quasar show very similar spectra, withlow Fe II emission and broad H β BC (Marziani et al.1996; Dultzin-Hacyan et al. 2000). This may pointtoward a parallel evolution for RL and part of theRQ quasars: what makes them radio-different is anas yet unknown parameter that has little, if any, ef-fect on their BLR.We are still left with many conundrums concern-ing the actual origin of the BLR gas, its dynam-ics and spatial disposition. High-ionization gas (anaccretion disk wind?), showing non-radial, outwardmotion and producing the blueshifted component ob-served in Mark 478 and, to a lesser extent, in F 9,may decrease in importance crossing the boundaryfrom Pop. A, where it is strong in the HILs, to Pop.B where it may become almost hidden by the red-shifted, very broad component. The central enginemay sustain a most prominent outflow only if theEddington ratio is relatively high, as in the case ofPop. A sources.Placing these considerations on a firmer observa-tional basis requires renewed efforts involving nebu-lar diagnostics and line profile analysis, as well as theability to understand how the viewing angle affectsobserved BLR parameters on a source-by-source ba-sis, if we cannot count on 2D reverberation mapping.4DE1 offers promise for decoupling source orienta-tion from physics. PM wishes to thank the SOC for inviting her tospeak in Huatulco. It was a valuable opportunity toreview past and current work of Deborah Dultzin &collaborators on the emitting regions in quasars, towhich this paper – given the vastness of the subject– is limited. REFERENCES(Marziani et al.1996; Dultzin-Hacyan et al. 2000). This may pointtoward a parallel evolution for RL and part of theRQ quasars: what makes them radio-different is anas yet unknown parameter that has little, if any, ef-fect on their BLR.We are still left with many conundrums concern-ing the actual origin of the BLR gas, its dynam-ics and spatial disposition. High-ionization gas (anaccretion disk wind?), showing non-radial, outwardmotion and producing the blueshifted component ob-served in Mark 478 and, to a lesser extent, in F 9,may decrease in importance crossing the boundaryfrom Pop. A, where it is strong in the HILs, to Pop.B where it may become almost hidden by the red-shifted, very broad component. The central enginemay sustain a most prominent outflow only if theEddington ratio is relatively high, as in the case ofPop. A sources.Placing these considerations on a firmer observa-tional basis requires renewed efforts involving nebu-lar diagnostics and line profile analysis, as well as theability to understand how the viewing angle affectsobserved BLR parameters on a source-by-source ba-sis, if we cannot count on 2D reverberation mapping.4DE1 offers promise for decoupling source orienta-tion from physics. PM wishes to thank the SOC for inviting her tospeak in Huatulco. It was a valuable opportunity toreview past and current work of Deborah Dultzin &collaborators on the emitting regions in quasars, towhich this paper – given the vastness of the subject– is limited. REFERENCES