Spectropolarimetry Surveys of Obscured

Active Galactic Nuclei

Edward Moran

Wesleyan University

Aaron Barth (UC Irvine), Laura Kay (Barnard),

Alex Filippenko (UC Berkeley), Mike Eracleous (Penn State)

Moran et al. (2000)

M. Urry & P. Padovani

Moran et al. (2000)

Where is the obscuration?

narrow lines are unpolarized

obscuration must be beyond the BLR, but interior to most of the NLR (i.e., ~ 1 – few pc)

Where is the mirror?

can extend from the opening of the torus to > 100 pc from the nucleus (i.e., in the NLR; Kishimoto 1999; Kishimoto et al. 2002a, 2002b)

Starlight dilution

N3081

N224

N3081

Seyfert 2 spectra dominated by unpolarized bulge starlight

Fg = 50–90% is typical; dilutes polarization signal

but after starlight correction, P(H) still > P(continuum)

“FC2” also dilutes polarization; caused by hot stars (e.g., Gonzalez Delgado et al. 1998)

High intrinsic polarizations obtained after correction for FC2 (Tran 1995)

Spectropolarimetry Surveys

sample: 24 “warm” IRAS galaxies & selected Seyfert 2s

instrument: AAT 3.9-m

results: some new detections, but no HBLR in majority

Young et al. (1996)

Heisler, Lumsden, & Bailey (1997)

sample: 16 IRAS-selected Seyfert 2s, S60 > 5 Jy

instrument: AAT 3.9-m

results: 1 new detection; 44% (7 objects) are HBLRs

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

results: 1 new detection, 33% (8 objects) are HBLRs

Lumsden et al. (2001)

Tran (2001, 2003)

sample: 49 objects from the CfA and 12 m samples

instrument: Lick 3-m & Palomar 5-m

results: 5 new detections; 45% (22 objects) are HBLRs

Spectropolarimetry Surveys

sample: 38 objects from Ulvestad & Wilson (1989; UW89)

31 bona fide Seyfert 2s

7 narrow-line X-ray galaxies (4 Sy 1.9s & 3 Sy 2s)

distance-limited (cz < 4600 km s–1)

instrument: Keck 10-m

results: 9 new detections, 45% (17 objects) are HBLRs

Us (Moran et al. 2000, 2001; Kay et al. 2006)

Barth, Filippenko, & Moran (1999)

sample: 14 LLAGNs objects from the Ho et al. (1997) survey

instrument: Keck 10-m

results: 3 new HBLRs in LINERs

two LINER 1.9s (NGC 315, NGC 1052)

one LINER 2 (NGC 4261)

Differences between HBLR and Non-HBLR Seyfert 2s?

Moran et al. (1992)

Sample issues:

Flux-limited surveys

clearly defined

luminosity bias

Volume-limited surveys

no bias

completeness is a concern

UW89 sample is relatively unbiased

Impotant because luminosity is one of the main issues here

Radio luminosity

Lumsden et al. (2001): not much difference in total radio power Ptot; HBLRs slightly higher core luminosity Pcore

Tran (2003): HBLRs slightly stronger in Ptot

Gu & Huang (2002): HBLRs significantly stronger in Ptot

UW89 result: HBLRs havesomwhat higher Pcore

CfA/12m sample (Tran 2003)UW89 sample

Far-infrared colors

All previous studies find that HBLRs are significantly “warmer”

than non-HBLRs (Heisler, Tran, Lumsden, Gu)

UW89 result: differences not nearly as extreme

Other indicators

L([O III])

prior studies: HBLRs tend to be more luminous

significant overlap between HBLRs and non-HBLRs

Hard X-ray

* NH distributions of HBLRs and non-HBLRs are similar

(Alexander 2001; Tran 2001; Gu et al. 2001)

* many UW89 sources too weak to model their spectra, and

many are Compton-thick (Risaliti et al. 1999)

Moran et al. (2001)

composite X-ray spectra

Luminosity differences

HBLRs tend to be more luminous

higher nuclear luminosity explains S25/S60 results (Alexander 2001; Lumsden et al. 2001; Gu & Huang 2002)

nucleus/host galaxy contrast effect? (Kay 1994; Lumsden & Alexander 2001)

do luminosity differences establish that non-HBLR objects are “true” Seyfert 2s (Tran 2003)?

before you decide, remember: spectropolarimetry is hard!

NGC 5929

but bigger is better!near misses!

UW89 sample

[O III] equivalent width as a contrast indicator

Lumsden et al. (2001)

Alternatives to simple orientation

low-luminosity = no BLR? (Tran 2003)

accretion-rate issues? (Nicastro et al. 2003)

BLR absent in low m objects

possible candidates exist (e.g., Tran 2005)

HBLRs in some LINERs? (Barth et al. 1999)

dust lanes? (e.g., Malkan, Matt, Guainazzi, Lamastra et al.)

many UW89 non-HBLRs have high NH

4/7 UW89 objects with log NH < 23 have HBLRs... torus

dust lanes could obscure fraction of UW89 non-HBLRs

non-HBLRs as edge-on NLS1s? (Zhang & Wang 2006)

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Summary

~ 50% of Seyfert 2s have polarized broad lines

some luminosity differences exist between HBLRs and non-HBLRs

but much overlap between the two types

much overlap in EW([O III]) as well

luminosity or contrast alone can’t explain polarization results

take care when interpreting spectropolatimetry non-detections

many reasons why techniques might not work

possibility that more HBLRs will turn up in deeper observaton is very real

NGC 2110

Elliptical disk fit

Early results from Lick Observatory

NGC 1068: Miller & Antonucci (1983); Antonucci & Miller

(1985); Miller, Goodrich, & Mathews (1991)

4 more hidden broad-line regions (HBLRs) among high-

polarization Seyfert 2s: Miller & Goodrich (1990)

Continuum polarizations of Seyfert 2s low, and starlight

fractions high: Kay (1990; 1994)

4 more HBLRs: Tran, Miller, & Kay (1992)

Detailed study of 10 HBLR Seyfert 2s – complex continua

and dominance of electron scattering: Tran (1995)

in the plane of the sky...

in the plane of the scattering...

Why a torus?

Polarization suggests

radiation field anisotropic prior to scattering

obscuration cylindrically symmetric, roughly

Hard X-ray evidence

NGC 788hard = 1.70log NH = 23.7