Spectropolarimetry Surveys of Obscured

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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)
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Moran et al. (2000)
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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)

Moran et al. (2000)
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Starlight dilution

• Seyfert 2 spectra dominated
• by unpolarized bulge starlight
• Fg 5090 is typical dilutes
• polarization signal
• but after starlight correction,
• P(Ha) still gt P(continuum)
• FC2 also dilutes polarization
• caused by hot stars (e.g.,
• Gonzalez Delgado et al. 1998)
• High intrinsic polarizations
• obtained after correction for

N3081
N224
N3081
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Spectropolarimetry Surveys
Young et al. (1996)

• sample 24 warm IRAS galaxies selected
  Seyfert 2s
• instrument AAT 3.9-m
• results some new detections, but no HBLR in
  majority

Heisler, Lumsden, Bailey (1997)

• sample 16 IRAS-selected Seyfert 2s, S60 gt 5 Jy
• instrument AAT 3.9-m
• results 1 new detection 44 (7 objects) are
  HBLRs

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Spectropolarimetry Surveys
Lumsden et al. (2001)

• sample 24 IRAS-selected Seyfert 2s, S60 gt 3 Jy,
• LFIR gt 1010 L, S60/S25 lt 8.85
• instrument AAT 3.9-m, WHT 4.2-m
• results 1 new detection, 33 (8 objects) are
  HBLRs

Tran (2001, 2003)

• sample 49 objects from the CfA and 12 mm
  samples
• instrument Lick 3-m Palomar 5-m
• results 5 new detections 45 (22 objects) are
  HBLRs

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

• 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 lt 4600
  km s1)
• instrument Keck 10-m
• results 9 new detections, 45 (17 objects) are
  HBLRs

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)

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Differences between HBLR and Non-HBLR Seyfert 2s?
Moran et al. (1992)
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Sample issues

• Flux-limited surveys
• clearly defined
• luminosity bias
• Volume-limited surveys
• no bias
• completeness is
• a concern
• UW89 sample is relatively
• unbiased

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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

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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

UW89 sample
CfA/12mm sample (Tran 2003)
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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)

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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)?

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NGC 5929
but bigger is better!
near misses!
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O III equivalent width as a contrast indicator

• Lumsden et al. (2001)

UW89 sample
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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 lt 23 have
  HBLRs... torus
• dust lanes could obscure fraction of UW89
  non-HBLRs

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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 cant
  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

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NGC 2110
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Elliptical disk fit
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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

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Why a torus?

• Polarization suggests
• radiation field anisotropic
• prior to scattering
• obscuration cylindrically
• symmetric, roughly

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Hard X-ray evidence
NGC 788 Ghard 1.70 log NH 23.7