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  F g = 50–90% is typical; dilutes polarization signal  but after starlight correction, P(H  ) still > P(continuum)  “F C2 ” also dilutes polarization; caused by hot stars (e.g., Gonzalez Delgado et al. 1998)  High intrinsic polarizations obtained after correction for F C2 (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, S 60 > 5 Jy  instrument: AAT 3.9-m  results: 1 new detection; 44% (7 objects) are HBLRs

 sample: 24 IRAS-selected Seyfert 2s, S 60 > 3 Jy, L FIR > L , S 60 /S 25 < 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 P tot ; HBLRs slightly higher core luminosity P core  Tran (2003): HBLRs slightly stronger in P tot  Gu & Huang (2002): HBLRs significantly stronger in P tot UW89 result: HBLRs have somwhat higher P core

CfA/12  m 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 * N H 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 S 25 /S 60 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 N H  4/7 UW89 objects with log N H < 23 have HBLRs... torus  dust lanes could obscure fraction of UW89 non-HBLRs  non-HBLRs as edge-on NLS1s? (Zhang & Wang 2006)

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 788  hard = 1.70 log N H = 23.7