Interpreting AGN polarization at innermost spatial scales Makoto Kishimoto KSU - Kyoto Sangyo Univ
A map of an AGN
The key for AGN pol interpretation Continuum pol PA: parallel or perpendicular Emission line pol w.r.t. continuum pol system axis spectropol linear jet structure, ionization cone Capetti+97 Martel 98
Continuum pol Let's put aside Synch-origin pol (differentiated by variability) We first think about scat's, worry about others later Phenomenologically parallel - Type 1s, perpendicular - Type 2s NGC4151 NGC1068 Pedlar+93 Capetti+97
Unified Model is based on... perpendicular pol in Type2 Broad lines in Type 2s are polarized just as continuum no PA rotation across the lines Key: scat region scale is much larger than BLR NLR scale pol, as confirmed by HST pol images Antonucci & Miller 85 Tran 95 Capetti+95
Parallel continuum pol in Type 1s *Not* intrinsic to the BBB (Big Blue Bump) - putative AD equatorial scat, effectively opt.thin Then what about the BL pol in these objects? NGC4151 obs d PA broad-line clouds Pedlar+93
Lines in Type 1 pol Broad line pol is not the same as continuum pol PA often rotates across the line scat region scale comparable to BLR some show no pol in BL: scat region interior to the BLR f λ scaled total flux polarized flux Smith+ 02 K+ 03
"Map" of these AGN pol scale Type 2 NLR? UM Rsub BLR e-/d-scat d-abs/emis BLR info BBB Type 1 e-scat BBB info viewing angle
Size comparison as a function of Luminosity K+11 K+11 K+11,15 Bentz+09 BLR IR interferometric radii Near-IR reverb Suganuma+06 Type 1 Type 2 13 μm 11 μm 2.2 μm Pol flux reverb Gaskell+12 Afanasiev+15
Polarization interior to BLR
Nature of Big Blue Bump emission One major problem: BBB spectrum always contaminated by outer emissions Putative accretion disk atmospheric spectral feature structure at outermost radii Polarization interior to BLR cuts off BLR and torus ν +1/3 ν +2 log λ
Pol interior to BLR: Big Blue Bump spectrum copy We actually managed to see Balmer edges : seen in absorption thermal and opt-thick nature near-ir spectral shape : as blue as nu^1/3 f λ scaled total flux excluded torus emission polarized flux K+03 K+08
Prospects for BBB study Toward longer wavelengths explore the outer region of AD, real accretion region? This is where pol study and interferometry meets Both can "cut off" outer, non-bbb stuff Toward shorter wavelengths microlensing X-ray pol
Polarization around BLR
Pol at the scale of BLR Pol PA often shows sinusoidal rotation but not always: sometimes a bit more complicated The Astrophysical Journal Letters, 800:L35 (4pp), 2015 February 20 Afanasiev & Popović 4 Lira et al. Afanasiev+15 Smith+02,05 Fig. 2. Rest-frame, ISP corrected, spectropolarimetry of NGC 3783. From top to bottom: total flux (I -fullrangeanddetail),degree of polarization (p), polarized flux (p I) and polarization position angle(pa). Mrk 509. As observed by Young et al. (1999) the lower polarization at the line cores is indicative of an intrinsic lower polarization at the line centers, or of polarization at a significantly different position angle. To explain this further, consider the intensity of the polarized continuum and line flux as f cont and f line,respectively. Thenfora PA 0, p I f cont + f line ;butif PA ±90, then p I ±(f cont f line ). For 0 < PA < ±90,intermediate cases would be found 2.Hence,depolarization occurs for PA 0,andthereforeitisadirectconsequence of a different spatial distribution of the emitting 2 Note that this happens because the two signals are incoherent, and therefore their sum is not the result of the vectorial addition Lira+ in prep and/or scattering regions. Our observations clearly show that the depolarization of the lines affects not only the narrow components, but to a significant degree, the center of the broad lines too. This is particularly clear for Mrk 509. We will seek to reproduce this effect with the modeling presented in Section 4. Rotation of the position angle (PA) across the broad lines has long being recognized as common in Seyfert 1galaxies(Miller&Goodrich,1994;Youngetal.,1999; Schmid et al., 2000; Smith et al., 2002, 2004). We observe PA rotation in both, Mrk 509 and NGC 3783 and will discuss the details in Sections 3.2 and 3.3. The lower polarization below 4000Å seeninfigures 2and3isinstrikingcontrastwiththebehaviorofthe Lots of modelling efforts by e.g. Smith+,Afanasiev+,Goosmann+,Marin+,Lira+
BL Pol interpretation illumination source spatially finite: lower P resolved in velocity: PA rot scat BLR observer PA v
BL Pol interpretation illumination source spatially finite: lower P resolved in velocity: PA rot scat BLR observer PA v
BL Pol interpretation illumination source spatially finite: lower P resolved in velocity: PA rot scat BLR observer PA PA v v
BL Pol interpretation illumination source spatially finite: lower P resolved in velocity: PA rot scat BLR scat BLR observer PA PA observer v v
BL Pol interpretation illumination source spatially finite: lower P resolved in velocity: PA rot scat BLR scat BLR observer PA PA observer PA v v v
Prospects for BLR pol study Can be hard to decode, but info is definitely there A big wish: real-time movie modeling
Prospects for BLR pol study Can be hard to decode, but info is definitely there A big wish: real-time movie modeling Model BLRPOL: real-time analyzer P/F/PF/PA spectra scat The Astrophysical Journal Letters, 800:L35 (4pp), 2015 February 20 Afanasiev & Popović BLR Kinematics radial / rotational velocity ratio -10 +10 rotation keplerian Geometry BLR radius scat radius 10 3 10 4 Rg start stop quit
Aligned dust grains
Aligned grains : dichroic abs / dichroic emission Can become significant toward long λ NGC1068: nuclear IR pol believed to d-abs/d-emis NIR PF too big (Young+95), PA flips in MIR (Lumsden+99, Packham+07) can provide unique info on B (Lopez-Rodriguez+15) HST Pol 2.0 µm Simpson+02 pol flux SED from NIR to UV Pier+94 6 Relative Declination (arcsec) 4 2 0-2 -4 NE Knot SW Lobe -6-8 20% Polarization 6 4 2 0-2 -4-6 Relative Right Ascension (arcsec) 20000
Alternatively... Scattering? Note that NIR pol peak is quite off-set from UV/opt peak 6 HST Pol 2.0 µm reconstruction @ 8um jet 4 Relative Declination (arcsec) 2 0-2 -4 NE Knot SW Lobe 1pc -6 20% Polarization -8 6 4 2 0-2 -4-6 Relative Right Ascension (arcsec) Simpson+02 K 99
I can't forget to note that... Once illuminator becomes comparable in size to scat, PA starts to rotate differently in different places Detailed, clumpy modeling such as that of Marin+15 can lead to 3D geometry info HST opt pol, affected by [OIII] scat MIR pol image Packham+07 Capetti+95
Summary When interpreting AGN pol, it's always good to remind ourselves: parallel or perpendicular, line pol w.r.t. cont. Referring to these, we can interpret AGN pol, recognizing spatial scales of illuminator and scatterer. NLR illuminated by BBB and BLR: UM eq scat region illuminated by BBB: BBB physics eq scat region illuminated by BLR: more structural info D-abs/D-emission : unique info on B Alternatively, IR scat might give more geometrical info