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The Unification Model of Active Galaxies: Implications from Spectropolarimetric Surveys Hien D. Tran W. M. Keck Observatory.

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Presentation on theme: "The Unification Model of Active Galaxies: Implications from Spectropolarimetric Surveys Hien D. Tran W. M. Keck Observatory."— Presentation transcript:

1 The Unification Model of Active Galaxies: Implications from Spectropolarimetric Surveys Hien D. Tran W. M. Keck Observatory

2 2 Optical Spectra of Various Types of AGNs Bill Keel

3 3 Seyfert 1 & 2 Optical Spectra Bill Keel Narrow lines only Narrow forbidden lines: eg. [O III], [N II] Broad permitted lines: H, H

4 4 Hidden Sey1 Nucleus Inside a Sey2 Galaxy Bill Keel Miller, Goodrich & Mathews (1991) NGC 1068 Miller & Antonucci (1983) Antonucci & Miller (1985)

5 NGC 1068 Hidden Broad-Line Region (HBLR)

6 6 Mrk 348: Another HBLR Sey2 Typical Seyfert 2 (S2) spectrum Appears like a Seyfert 1 (S1)! HBLR = Hidden Broad-Line Region

7 7 AGN Unification Paradigm: Obscuring Torus Narrow-line region (NLR): [O III], [N II] Obscuring torus Nuclear Engine + Broad-line region (BLR): broad H H Scattering e -, dust Urry & Padovani Sey 1 view Sey 2 view

8 NGC 5252 Ionization Cones Morse et al. 1998

9 9 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 & 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 ).

10 10 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?

11 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, S 60 > 5 Jy instrument: AAT 3.9-m sample: 24 IRAS-selected Seyfert 2s, S 60 > 3 Jy, L FIR > 10 10 L, S 60 /S 25 < 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 Surveys

12 Summary 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

13 13 Viewing Angle Hypothesis C. Heisler (1997) Miller & Goodrich (1990)

14 14 Diagnostic 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 25 m luminosity (L 25 ); IR color f 25 /f 60 Radio: 20cm radio power (S 20 ); S 20 /f 60 X-ray: Hard X-ray (2-10 keV, HX) luminosity; HX/f 60 Obscuration: H /H ; N H ; HX/[O III]; Fe K equivalent width [EW(Fe)] Star formation: Far-IR luminosity L FIR = L 60 + L 100

15 15 [O III] Luminosity vs f 25 /f 60 [O III] Luminosity vs f 25 /f 60 HBLR Sey 2 Non-HBLR Sey 2 Sey 1 HII, LINERs, Starburst hotter cooler weaker stronger f 25 /f 60 is the IR color dust temp. around AGN [O III] Lum. AGN strength HBLRs are more luminous and warmer than non- HBLRs

16 16 [O III] Luminosity HBLR S2 Non-HBLR S2 S1

17 17 IR Color: f 25 /f 60 HBLR S2 Non-HBLR S2 S1

18 18 Radio Strength: S 20cm /f 60 vs f 25 /f 60 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.

19 19 CfA + 12 m samples: HX/f 60 vs f 25 /f 60 Blue: N H < 10 23 cm -2 Green: 10 23 < N H < 10 24 cm -2 Red: N H > 10 24 cm -2 Yellow: Unknown N H Solid curves are iso-N H models of Risaliti et al. (2000). For a same range of N H, stronger AGN lie to the upper right. Decreased obscuration shifts points vertically up. HBLR S2s tend to be stronger, but not necessarily less obscured than non-HBLRs. decreasing obscurationweakest strongest

20 20 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 12 m samples. Note: L in solar luminosity, EW(Fe) in eV, N H in cm -2 K-S P null 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 S2 Comparison between S1, HBLR S2 & non-HBLR S2

21 21 Comparison between S1s, HBLR S2s & non-HBLR S2s Comparison between S1s, HBLR S2s & non-HBLR S2s S1 = Sey 1 S3 = HBLR Sey 2 S2 = non-HBLR Sey 2

22 22 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 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%

23 23 Mid-IR ISO Spectra of Seyfert Gals HBLR S2 Non-HBLR S2 S1 From Clavel et al. 2000 PAH features

24 24 HBLR Detection Rates Percentage of detection for different classes of AGNs More powerful type of AGN has more HBLR detections Evolutionary connection between HBLR and non-HBLR S2s ? SB/LINER non-HBLR S2 HBLR S2/S1

25 25 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.

26 Mid-Infrared line ratios Wu et al. (2011)

27 Obscuration Wu et al. (2011) Obscuration plays a role for high-luminosity AGNs L [O III] > 10 41 ergs/s L [O III] < 10 41 ergs/s Luminous S2s: More likely to find HBLRs in less obscured objects more obscured less obscured

28 Eddington Ratios Eddington Ratios 28 Marinucci et al. (2012) Clear separation between HBLRs and non-HBLRs, especially in Compton-thin sources. Only objects with good quality data and M BH 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 L bol /L edd threshold.

29 Two Key Questions Non-detections real or due to limited depth of surveys? Lower AGN luminosity of non-HBLRs leads to intrinsic differences? 29

30 30 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.

31 Deep 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

32 Results 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

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

34 A non-HBLR: NGC 5347

35 [O III] Luminosity – IR Color Diagram f 25 /f 60 is the IR color dust temp. around AGN [O III] Lum. AGN strength warmer cooler weaker stronger

36 Receding Torus: Evolution of AGN Obscuration Receding 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)

37 Evolution? Yu & Hwang (2011) HBLR Non-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

38 Evolution? (2) 38 HBLR S2s Non-HBLR S2s Starbursts Wu et al. (2011) S1s

39 39 HBLR S2s Non-HBLR S2s Starbursts Wu et al. (2011)

40 Naked 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 (~ 10 20 - 10 21 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

41 Spectropolarimetric 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.

42 Near-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. Conclusions If typical broad lines were present, their non- detections would indicate an extinction of A V ~ 11- 26, inconsistent with the ``naked'' nature of these galaxies. While the obscuration may be due to different material for X-ray and optical light, it appears that the BLRs in these objects are anemically small or absent, due to the weakness of their active central engines. Conclusions If typical broad lines were present, their non- detections would indicate an extinction of A V ~ 11- 26, inconsistent with the ``naked'' nature of these galaxies. While the obscuration may be due to different material for X-ray and optical light, it appears that the BLRs in these objects are anemically small or absent, due to the weakness of their active central engines. Conclusions If typical broad lines were present, their non- detections would indicate an extinction of A V ~ 11- 26, inconsistent with the ``naked'' nature of these galaxies. While the obscuration may be due to different material for X-ray and optical light, it appears that the BLRs in these objects are anemically small or absent, due to the weakness of their active central engines. If typical broad lines were present, their non-detections would indicate an extinction of A V ~ 11-26

43 Why dont 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 A V < 1.6 mag - Heavy obscuration in BLR itself? High A V /N H ratio?

44 Most 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/L Edd 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)

45 Correlation with Broad H α Luminosity 45 Stern & Laor (2012) For NGC 3147, Bianchi et al (2012) found upper limit of broad H ~ two orders of magnitude smaller!

46 Seyfert 2 Spectropolarimetry Some Surprises

47 NGC 2110: A Hidden Double-Peaked Emitter Moran et al, Dec. 2005February 2007November 2007 FWHM ~ 15,000 km/s FWZI ~ 28,000 km/s

48 Double-Peaked Emission-Line AGN

49 NGC 2110NGC 5252 Hidden (Polarized) Hα Profile Variability Timescales 1 yr (similar to dynamical timescales of accretion disks)

50 HDPE: 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

51 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

52 Constraining the Properties of the Scatterers No smearing of line profile T e 10 6 K Polarization PA to cone axis polar distribution Scattering spherical blob model: f = L sc /L in σ T n e 2r ΔΩ assume = σ T n e 2r ~ 1 (optically thin) ΔΩ ¼ (2r/d) 2 = r 2 /d 2 2r ~ 1 ly f ~ 1% n e ~ 10 7 cm -3 ; d 10 pc r d ΔΩΔΩ Scatterers lie just outside the obscuring torus between BLR and NLR Much more compact and close-in than previously thought τeτe

53 Compact 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

54 Type 2 characteristics (narrow lines) Type 1 characteristics (broad lines) Type 2 View (obscured/absorbed) Type 1 View (unobscured/unabsorbed) Unified Model of AGN

55 Type 2 characteristics (narrow lines) Type 1 characteristics (broad lines) Type 2 View (obscured/absorbed) - Very red quasars Type 1 View (unobscured/unabsorbed) - Naked (true) S2s - Host-obscured type 2 QSOs - XBONGs? Unified Model of AGN

56 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 SummarySummary

57 57 Backup Slides

58 Unified Model of AGN is undoubtedly correct Orientation, evolution, luminosity, and obscuration may all play important roles SummarySummary

59 Laor: Origin of Radio Emission

60 Eddington ratios Lack of HBLRs below some accretion threshold Compton-thin S2s HBLR Non-HBLR Bian & Gu (2007)

61 AGN Unification Model Type 2 AGN (direct light) Type 1 AGN (scattered/ polarized light) Type 1 AGN (direct light)

62 62 Mid-IR Luminosity: 25 m HBLR S2 Non-HBLR S2 S1

63 63 CfA + 12 m samples: HX/f 60 vs f 25 /f 60 Blue: N H < 10 23 cm -2 Green: 10 23 < N H < 10 24 cm -2 Red: N H > 10 24 cm -2 Yellow: Unknown N H Solid curves are iso-N H models of Risaliti et al. (2000). HX/f 60 : mainly a measure of obscuration, but also indicates AGN strength.

64 64 Central AGN: Double Absorber Model Risaliti et al. (2000) X rays from the nucleus are heavily absorbed, while the 25 m emission, originating from the warm dust of the torus, is much less obscured.

65 65 Far-IR Luminosity: (60 m+100 m) S1 HBLR S2 Non-HBLR S2 L FIR : indicator of star- forming (non-AGN) activity in host galaxy. Indistinguishable distributions for all 3 Seyfert types.

66 66 AGN and Normal Galaxy Optical Spectra Wavelength (A) IntensityIntensity Typical active gal spectrum Typical normal gal spectrum: integrated light of stars H, [O III]H, [N II] absorption lines emission lines

67 67 CfA & 12 m Seys: [O III]/H vs f 25 /f 60 Sey 1 (narrow H comp. only) HBLR Sey 2 Non-HBLR Sey 2 HII, LINERs, Starburst

68 68 Correlation of HX/[O III] with EW(Fe) & N H There is a good anticorrelation between HX/[O III] and both N H and EW(Fe), indicating that these parameters can be used as measures of the nuclear obscuration. HBLR Sey 2, Non-HBLR Sey 2, HII, LINERs, Starburst

69 69 Obscuration: Hard X-ray/[O III] & N H HBLR S2 Non-HBLR S2 Similar obscuration between HBLR and non-HBLR S2s

70 70 Hard X-ray vs. [O III] Luminosities HBLR Sey 2 Non-HBLR Sey 2 HII, LINERs, Starburst HBLRs and non-HBLRs can be well separated by their HX and [O III] luminosities.

71 71 Figure 4.- Hard X-ray vs. [O III] Luminosities The diagram can be divided into four quadrants with the dividing lines roughly at L(HX) = 10 42.4 erg/s and L([O III]) = 10 41.5 erg/s. There is a good positive correlation between these two quantities, as would be expected. In the upper right quadrant lie exclusively the HBLRs; these are the strong AGNs with genuine hidden S1 nuclei. The lower right quadrant is occupied by similarly powerful AGN with HBLRs, but these suffer from high obscuration; they are the so-called Compton-thick AGNs. All of the four labeled HBLR occupants in this quadrant (IC3639, N424, N1068, N7674) have N H > 10 24 cm -2. The vast majority of the non-HBLRs lie in the lower left quadrant; these are the intrinsically weak AGNs. The lack of objects in the the upper left quadrant is real: hard X-ray luminous AGNs are not expected to show weak [O III]. This diagram shows that HBLRs and non-HBLRs can be well separated by their HX and [O III] luminosities.

72 72 Spectropolarimetric Study of Seyfert Galaxies Spectropolarimetric survey of complete samples of Seyfert 2s (CfA and 12 m samples) to look for hidden broad-line regions (HBLRs) –Observations: Lick & Palomar Observatories 59 Seyfert 2 galaxies –Results: HBLRs detected in 1/2 of Seyfert 2 population How are the HBLR S2s different from non-HBLR S2s? Is the Unification Model (UM) applicable to all AGN types? –Generality of UM for Seyfert galaxies? –Correlation of presence of hidden broad lines with observational properties Extension to other types of AGN: –Is there a connection to AGN power?

73 Figure 9 from Parsec-scale Dust Emission from the Polar Region in the Type 2 Nucleus of NGC 424 S. F. Hönig et al. 2012 ApJ 755 149 doi:10.1088/0004-637X/755/2/149


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