The Unification Model The Unification Model of Active Galaxies: of Active Galaxies: Implications from Implications from

Spectropolarimetric SurveysSpectropolarimetric Surveys

Hien D. TranW. M. Keck Observatory

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Optical Spectra of Various Types of AGNs Optical Spectra of Various Types of AGNs Optical Spectra of Various Types of AGNs Optical Spectra of Various Types of AGNs

Bill Keel

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Seyfert 1 & 2 Optical SpectraSeyfert 1 & 2 Optical SpectraSeyfert 1 & 2 Optical SpectraSeyfert 1 & 2 Optical Spectra

Bill Keel

Narrow lines only

Narrow forbidden lines: eg. [O III], [N II]

Broad permitted lines: H, H

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Hidden Sey1 Nucleus Inside a Sey2 GalaxyHidden Sey1 Nucleus Inside a Sey2 GalaxyHidden Sey1 Nucleus Inside a Sey2 GalaxyHidden Sey1 Nucleus Inside a Sey2 Galaxy

Bill Keel

Miller, Goodrich & Mathews (1991)

NGC 1068

Miller & Antonucci (1983)Antonucci & Miller (1985)

NGC 1068NGC 1068

Hidden Broad-Line Region (HBLR)

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Mrk 348: Another “HBLR Sey2” Mrk 348: Another “HBLR Sey2” Mrk 348: Another “HBLR Sey2” Mrk 348: Another “HBLR Sey2”

Typical Seyfert 2 (S2) spectrum

Appears like a Seyfert 1 (S1)!

HBLR = Hidden

Broad-Line Region

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AGN Unification Paradigm: Obscuring TorusAGN Unification Paradigm: Obscuring TorusAGN Unification Paradigm: Obscuring TorusAGN Unification Paradigm: Obscuring Torus

Narrow-line region (NLR): [O III], [N II]

Obscuring torus

Nuclear Engine + Broad-line region (BLR): broad HH

Scattering e-, dust

Urry & Padovani

Sey 1 view Sey 2 view

NGC 5252 Ionization ConesNGC 5252 Ionization ConesNGC 5252 Ionization ConesNGC 5252 Ionization Cones

Morse et al. 1998

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S2s more likely to be in found in hosts with enhanced star formation (Maiolino et al. 1995; Gu et al. 1998).

Puzzling Differences between Sey1 & Sey2Puzzling Differences between Sey1 & Sey2Puzzling Differences between Sey1 & Sey2Puzzling Differences between Sey1 & Sey2

S2s tend to be in hosts with higher frequency of companions

(de Robertis, Yee, & Hayhoe 1998; Dultzin-Hacyan et al. 1999). S2 hosts tend to show richer dust features (Malkan, Gorjian, &

Tam 1998).

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Spectropolarimetric Study of Seyfert Galaxies Spectropolarimetric Study of Seyfert Galaxies Spectropolarimetric Study of Seyfert Galaxies Spectropolarimetric Study of Seyfert Galaxies

Spectropolarimetric survey of complete samples of Seyfert 2s to look for hidden broad-line regions (HBLRs)

General applicability of the Unification Model (UM)? What determines the detectability of hidden broad lines? Is there a connection to AGN power? How are the HBLR S2s different from non-HBLR S2s? Correlation of presence of hidden broad lines with

observational properties?

• sample: 24 “warm” IRAS galaxies & selected Seyfert 2s• instrument: AAT 3.9-m

Young et al. (1996)

Heisler, Lumsden, & Bailey (1997)

• sample: 16 IRAS-selected Seyfert 2s, S60 > 5 Jy• instrument: AAT 3.9-m

• sample: 24 IRAS-selected Seyfert 2s, S60 > 3 Jy, LFIR > 1010 L, S60/S25 < 8.85• instrument: AAT 3.9-m, WHT 4.2-m

Lumsden et al. (2001)

Tran (2001, 2003)• sample: 49 objects from the CfA and 12 m samples• instrument: Lick 3-m & Palomar 5-m

• sample: 38 objects from Ulvestad & Wilson (1989); distance-limited (cz < 4600 km s–1)• instrument: Keck 10-m (“snapshot” mode, ~20min per object)

Moran et al. 2000

Brief History of Spectropolarimetric Seyfert 2 SurveysBrief History of Spectropolarimetric Seyfert 2 SurveysBrief History of Spectropolarimetric Seyfert 2 SurveysBrief History of Spectropolarimetric Seyfert 2 Surveys

Summary of SurveysSummary of Surveys

HBLRs detected in 1/2 of Seyfert 2 population Two possibilities:

– HBLRs are there but hard to detect– Something wrong with the UM

Some explanations:– Only HBLR S2s are true counterparts to Seyfert 1s – Non-HBLR S2s are too weak to possess or sustain any BLRs– Broad-line variability– Non-HBLRs are narrow-line Seyfert 1s– Evolution– Obscuration / torus inclination– Scattering material

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Viewing Angle HypothesisViewing Angle HypothesisViewing Angle HypothesisViewing Angle Hypothesis

C. Heisler (1997)Miller & Goodrich (1990)

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Diagnostic Diagrams and Luminosity DistributionsDiagnostic Diagrams and Luminosity DistributionsDiagnostic Diagrams and Luminosity DistributionsDiagnostic Diagrams and Luminosity Distributions

Compare various properties among the HBLR, non-HBLR S2s and S1s, illustrating their similarities and differences.

These properties include:AGN Strength: Optical: [O III] 5007 luminosity

Infrared: Mid-IR 25m luminosity (L25); IR color f25/f60 Radio: 20cm radio power (S20); S20/f60

X-ray: Hard X-ray (2-10 keV, HX) luminosity; HX/f60

Obscuration: H/H; NH; HX/[O III]; Fe K equivalent width [EW(Fe)]

Star formation: Far-IR luminosity LFIR = L60 + L100

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[O III] Luminosity vs f[O III] Luminosity vs f2525/f/f6060 [O III] Luminosity vs f[O III] Luminosity vs f2525/f/f6060

HBLR Sey 2 Non-HBLR Sey 2 Sey 1 HII, LINERs, Starburst

hottercooler

weaker

stronger

f25/f60 is the IR color

dust temp. around AGN

[O III] Lum. AGN strength

HBLRs are more luminous and warmer than non-HBLRs

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[O III] Luminosity[O III] Luminosity[O III] Luminosity[O III] Luminosity

HBLR S2

Non-HBLR S2

S1

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IR Color: fIR Color: f2525/f/f6060 IR Color: fIR Color: f2525/f/f6060

HBLR S2

Non-HBLR S2

S1

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Radio Strength: SRadio Strength: S20cm20cm/f/f6060 vs f vs f2525/f/f6060 Radio Strength: SRadio Strength: S20cm20cm/f/f6060 vs f vs f2525/f/f6060

HBLR Sey 2 Non-HBLR Sey 2 Sey 1 HII, LINERs, Starburst

HBLR S2s are stronger and hotter than non-HBLR S2s.

HBLR S2s are similar to S1s.

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N Mean N Mean N Mean S1-S3 S1-S2 S3-S2

log [O III]/H 25 0.971 0.223 22 0.972 0.145 27 0.831 0.23 24.9 3.6 6.3 AGN Strength

log f25/f60 46 -0.37 0.281 22 -0.27 0.179 27 -0.678 0.239 13.6 0.079 8E-04 AGN Strength

log S20/f60 43 -1.77 0.409 22 -1.55 0.6 27 -2.07 0.358 11.1 1.1 0.8 AGN Strength

log L(O III) 44 7.56 0.637 22 7.56 0.78 26 6.85 0.703 94.8 0.016 0.36 AGN Strength

log L25 46 10.2 0.66 22 10.6 0.506 27 9.92 0.735 8.8 26.2 0.23 AGN Strength

log Lrad 43 3.37 0.668 22 3.87 0.597 27 3.1 0.824 4.5 15.5 1.5 AGN Strength

log LFIR 46 10.2 0.614 22 10.5 0.564 27 10.3 0.765 12.7 52.5 58.2 SF Activity

log HX/[O III] 15 0.33 0.915 13 -0.196 0.971 36.5 Obscuration

log EW(Fe) 13 2.63 0.139 8 2.84 0.231 57-68 Obscuration

log NH 13 23.84 0.24 14 23.86 0.29 88-100 Obscuration

H/H 23 7.16 4.7 26 7.39 5.51 36 Obscuration

K-S Pnull (% ) IndicatorProperty Seyfert 1 (S1) HBLR Seyfert 2 (S3) non-HBLR Seyfert 2 (S2)

Mean, standard deviation () and K-S statistical test results for various properties of the S1, HBLR S2s and non-HBLR S2s in the CFA and 12m samples.

Note:

• L in solar luminosity, EW(Fe) in eV, NH in cm-2

• K-S Pnull is the probability for the null hypothesis that the two distributions are drawn at random from the same parent population.

Comparison between S1, HBLR S2 & non-HBLR S2Comparison between S1, HBLR S2 & non-HBLR S2 Comparison between S1, HBLR S2 & non-HBLR S2Comparison between S1, HBLR S2 & non-HBLR S2

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Comparison between S1s, HBLR S2s & non-HBLR S2sComparison between S1s, HBLR S2s & non-HBLR S2s Comparison between S1s, HBLR S2s & non-HBLR S2sComparison between S1s, HBLR S2s & non-HBLR S2s

S1 = Sey 1 S3 = HBLR Sey 2 S2 = non-HBLR Sey 2

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De Robertis et al. 1998 environment study:– Very significant difference found in mean environment between S1s and S2s.

– Sample contains few known HBLR S2s (NGC 4388). Schmitt et al. 2001 study of a far-IR selected sample (Keel et al):

– No statistically significant difference between S1s and S2s in terms of host galaxy morphology and freq. of companions.

– However, sample was selected for warm IR color, and hence HBLR S2s.

– 70% of S2s in this sample are HBLRs, compared to ~ 50% or less for others. Clavel et al. 2000 ISO study:

– Mid-IR ISO spectra of HBLR S2s are similar to S1s.• 7 m continuum, PAH luminosities and EW.

– Those of non-HBLR S2s are different (indistinguishable from SBs). • Smaller 7 m conti. L and higher PAH EW, but similar PAH lum.

Large-scale Properties of Seyfert GalaxiesLarge-scale Properties of Seyfert GalaxiesLarge-scale Properties of Seyfert GalaxiesLarge-scale Properties of Seyfert Galaxies

Malkan et al. 1998 HST snapshot survey:– S2s richer in dust than S1s.

– However, when grouped into HBLR and non-HBLR S2s, differences in dust

morphology and incidence disappear.• non-HBLR S2: 55%, HBLR S2: 27%, S1: 23%

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Mid-IR ISO Spectra of Seyfert GalsMid-IR ISO Spectra of Seyfert GalsMid-IR ISO Spectra of Seyfert GalsMid-IR ISO Spectra of Seyfert Gals

HBLR S2

Non-HBLR S2

S1

From Clavel et al. 2000

PAH features

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Two types of Seyfert 2s?Two types of Seyfert 2s?Two types of Seyfert 2s?Two types of Seyfert 2s?

Not only are HBLR S2s stronger than non-HBLR S2s, they are comparable in a lot of ways to S1s.

Non-HBLR S2 properties, on the other hand, generally do not match well with those of HBLR S2s or S1s.

Proposal: HBLRs are visible largely because their AGNs are intrinsically

more powerful

Many non-HBLR S2s maybe too weak to represent “real” hidden S1s, and HBLR S2s may be the only true counterparts to normal S1s.

Mid-Infrared line ratiosMid-Infrared line ratios

Wu et al. (2011)

ObscurationObscuration

Wu et al. (2011)

Obscuration plays a role for high-luminosity AGNs

L [O III] > 1041 ergs/s L [O III] > 1041 ergs/s

L [O III] < 1041 ergs/s L [O III] < 1041 ergs/s

Luminous S2s: More likely to find HBLRs in less obscured objectsmore obscured

less obscured

Eddington Ratios Eddington Ratios Eddington Ratios Eddington Ratios

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Marinucci et al. (2012)

Clear separation between HBLRs and non-HBLRs, especially in Compton-thin sources.

Only objects with good quality data and MBH estimated from stellar velocity dispersion.

Theoretical models: BLR unable to form when AGN luminosities or accretion rates are too low to support outflows from accretion disks (Nicastro 2000; Elitzur & Shlosman 2006; Cao 2010)

Inclusion of Compton-thick sources blurs out the separation, but no HBLR falls below Lbol/Ledd threshold.

Two Key QuestionsTwo Key QuestionsTwo Key QuestionsTwo Key Questions

Non-detections real or due to limited depth of surveys?

Lower AGN luminosity of non-HBLRs leads to intrinsic differences?

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HBLR Detection: Flux Comparison HBLR Detection: Flux Comparison HBLR Detection: Flux Comparison HBLR Detection: Flux Comparison

HBLR Sey 2 Non-HBLR Sey 2 HII, LINERs, Starburst

There is no separation in the observed fluxes for the most common AGN indicators between the two S2 types.

Non-detections of HBLRs cannot simply all be due to

the detection limit of the survey.

HBLR detection reaches to very low flux level, below those of many non-HBLR S2s.

Deep Keck Spectropolarimetric SurveyDeep Keck Spectropolarimetric Survey

Same sample as Tran (2003)– CfA and 12μm samples

Target mainly non-HBLR Seyfert 2s– ~ 25 objects

LRIS + polarimeter– Typical exposure times: 80-160 min per object

– Multiple epochs

– 4 - 15 X deeper than previous surveys Six new southern objects observed at CTIO

Results of the Deep Keck SurveyResults of the Deep Keck Survey

Six new HBLRs– Non-HBLR HBLR: Mrk 573, NGC 3892, NGC 5929, UGC 6100 (Keck)

– ESO 541-IG12, NGC 1125 (CTIO) Five new non-HBLRs

– HBLR non-HBLR: NGC 5347 (called “HBLR” by Moran et al.)

– ESO 33-G2, ESO 253-G3, NGC 3147, NGC 4968

New HBLRs: NGC 3982 & UGC 6100New HBLRs: NGC 3982 & UGC 6100

NGC 3982 UGC 6100

A non-HBLR: NGC 5347 A non-HBLR: NGC 5347

[O III] Luminosity – IR Color Diagram[O III] Luminosity – IR Color Diagram

f25/f60 is the IR color

dust temp. around AGN

[O III] Lum. AGN strength

warmer

cooler

weaker

stronger

Receding Torus: Evolution of AGN ObscurationReceding Torus: Evolution of AGN Obscuration Receding Torus: Evolution of AGN ObscurationReceding Torus: Evolution of AGN Obscuration

Obscured AGN fraction decreases with luminosity

Consistent with receding torus model: larger opening angle for higher luminosity AGN

Hasinger (2008)

Evolution?Evolution?Yu & Hwang (2011)

HBLRNon-HBLR Wu et al. (2011)

solar 5x solar

Significant difference in [N II]/Ha ratio

Can be explained by an increase in nitrogen abundance in non-HBLR S2s

Stellar evolution overabundance of N/O evolutionary connection between HBLR and non-HBLR S2s

Evolution? (2)Evolution? (2)Evolution? (2)Evolution? (2)

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HBLR S2s

Non-HBLR S2s

Starbursts

Wu et al. (2011)

S1s

““Naked” View of Type 2 SeyfertsNaked” View of Type 2 Seyferts““Naked” View of Type 2 SeyfertsNaked” View of Type 2 Seyferts

NGC 3147, NGC 4698, 1ES 1927+654 Other candidates in Shi et al (2011) and Bianchi et al (2012)

(IRAS 01428-0404, NGC 4594, Q2131-427 …) All are Compton-thin, consistent with little or no intrinsic X-ray

absorption above Galactic column density (~ 1020 - 1021 cm-2 ) Rapid, persistent, and strong X-ray variability observed over 12 year

time scale in 1ES 1927+654 X-ray variability also observed in NGC 3147 High hard X-ray to [O III] ratios (1-100) indicate little obscuration Inferred nuclear optical extinction is less than ~ 1 mag. All classified as type 2 AGNs (no broad lines observed)

contrary to expectation from the AGN unification model

Spectropolarimetric ResultsSpectropolarimetric Results

In each case, a small amount of polarization is detected but no polarized broad lines indicative of a hidden broad-line region are seen in the polarized flux spectra.

Deep, repeated observations to probe weak lines.

Near-Infrared Spectroscopy ResultsNear-Infrared Spectroscopy Results

The spectra are dominated by galactic starlight, and we do not detect any emission in Paβ or Brγ. No direct broad emission lines are present.

If typical broad lines were present, their non-detections would indicate an extinction of AV ~ 11-26

Why don’t we see any broad lines, given the naked nature of these AGNs?

Why don’t we see any broad lines, given the naked nature of these AGNs?

Misclassified Compton-thin AGNs? - High spatial resolution Chandra and XMM-Newton observations rule out

confusion from external sources - Temporal variation in X-ray flux implies X-ray is likely not scattered

Variable broad emission lines? - Multi-epoch spectropolarimetric observations designed to search for

variability failed to find any - Available spectra over timescales of years do not show any evidence of

broad-line appearance

Hidden narrow-line Seyfert 1 (NLS1) galaxies? - No emission lines of any kind, broad or narrow, are seen in polarized

flux spectra - No polarized FeII emission

X-ray unobscured, but optically highly obscured? - Narrow-line Balmer decrements are fairly normal, giving AV < 1.6 mag - Heavy obscuration in BLR itself? High AV/NH ratio?

Most Likely ExplanationMost Likely ExplanationMost Likely ExplanationMost Likely Explanation

Low-powered AGNs with weak or absence of BLRs

- All three objects are low-luminosity AGNs

- Observed Eddington ratios are consistent with being below minimum threshold needed to support BLRs (L/LEdd ≲ 10-3)

(e.g.: Nicastro 2000)

More recent X-ray & optical analysis of NGC 3147 confirms it as a best candidate for a “true” S2 (Matt et al 2012, Bianchi et al 2012)

However, NGC 4698 is likely Compton-thick (Bianchi et al 2012)

Correlation with Broad HCorrelation with Broad Hαα Luminosity Luminosity Correlation with Broad HCorrelation with Broad Hαα Luminosity Luminosity

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Stern & Laor (2012)

For NGC 3147, Bianchi et al (2012) found upper limit of broad H ~ two orders of magnitude smaller!

Seyfert 2 SpectropolarimetrySeyfert 2 Spectropolarimetry

Some Surprises

NGC 2110: A Hidden Double-Peaked EmitterNGC 2110: A Hidden Double-Peaked EmitterNGC 2110: A Hidden Double-Peaked EmitterNGC 2110: A Hidden Double-Peaked Emitter

Moran et al, Dec. 2005 February 2007 November 2007

FWHM ~ 15,000 km/s FWZI ~ 28,000 km/s

NGC 2110 NGC 5252

Hidden (Polarized) HHidden (Polarized) Hαα Profile Variability Profile VariabilityHidden (Polarized) HHidden (Polarized) Hαα Profile Variability Profile Variability

Timescales ≲ 1 yr (similar to dynamical timescales of accretion disks)

HDPE: Observed Polarization VariabilityHDPE: Observed Polarization VariabilityHDPE: Observed Polarization VariabilityHDPE: Observed Polarization Variability

NGC 2110: Blue

NGC 5252: Green

continuum and broad-line polarization PAs are the same similar polarization mechanism and geometry

polarization PA does not change with time

polarization PA (~70º) perpendicular to ionization cone axes scattering is the source of polarization

What Causes the Rapid Variations?What Causes the Rapid Variations?What Causes the Rapid Variations?What Causes the Rapid Variations?

Variability timescales ≲ 1 yr very compact scatterers– Discrete clouds ≲ 1 ly, NOT filled cones with large filling factor

Dramatic line profile changes in polarized flux– NOT due to “light echo” or “search light” effect

Non-changing polarization PA changes in line-emitting flux, not scattering medium

Constraining the Properties of the ScatterersConstraining the Properties of the ScatterersConstraining the Properties of the ScatterersConstraining the Properties of the Scatterers

No “smearing” of line profile Te ≲ 106 K Polarization PA ⊥ to cone axis polar distribution Scattering spherical “blob” model: f = Lsc/Lin ≈ σT ne 2r ΔΩ

assume = σT ne 2r ~ 1 (optically thin) ΔΩ ≈ ¼ (2r/d)2 = r2/d2

2r ~ 1 ly f ~ 1%

ne ~ 107 cm-3; d ≲ 10 pc

r

dΔΩ

Scatterers lie just outside the obscuring torus between BLR and NLR

Much more compact and close-in than previously thought

τe

Compact Scattering Region, Close to NucleusCompact Scattering Region, Close to NucleusCompact Scattering Region, Close to NucleusCompact Scattering Region, Close to Nucleus Line-emitting “ejectiles” from the nucleus

– Ejection (bi-polar) outflow model

– Simple: same material for both scatterer and line-emitting gas

– Well-defined bi-cones Radio hot spots or material entrained in the base of jets

– Preference of DPEs in radio-loud AGNs

– Problematic for accretion disk model as scattering angle must be small (< 15°) Material from outskirts of obscuring torus itself

– Clumpy obscuring torus model (Elitzur & Schlosman 2006; Nenkova et al 2008)

– Properties similar to scattering clumps

– Viewing angle (i ~ 65°) more consistent with extended cone morphology

Unified Model of AGN is undoubtedly correct Orientation, evolution, luminosity, and obscuration

may all play important roles Scatterers can be very compact, (≲ 1 ly), and located

close (< 10 pc) to central nucleus, giving rise to variability of polarized light

SummarySummarySummarySummary

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