Durham E-Theses Optical polarimetry studies of Seyfert galaxies Felton, Michelle Ann How to cite: Felton, Michelle Ann (1999) Optical polarimetry studies of Seyfert galaxies, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/4573/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk Optical polarimetry studies of Seyfert galaxies Michelle Ann Felton B.Sc. (Theoretical Physics) M.Sc. (Radio Astronomy) The copyright of this thesis rests witli die author. No quotation from it should be published without the written consent of the author and information derived from it should be acknowledged. A thesis submitted to the University of Durham for the degree of Doctor of Philosophy 1 4 NOV 2000 Department of Physics University of Durham Durham September 1999 Abstract Optical imaging polarimetry has been performed on seven nearby Seyfert galaxies, three with face-on and four with edge-on host galaxies of various morphological classifications. Observations in V, /?, B and Ha wavebands are presented as maps of total intensity and of polarized intensity, overlaid with polarization vectors. Independent determinations of the interstellar polarization (ISP) contribution from our own galaxy are made where possible, and are used to produce ISP corrected maps. The polarization patterns seen in the maps show evidence of either dichroic extinction, which indicates the presence of non-spherical dust grains in large-scale galactic magnetic fields, or scattering, which is due to the illumination of regions of dust grains or elec• trons. The polarization features, which are observed at the different wavebands, are then compared to recent models of polarization in external galaxies. Estimates of the intrinsic Seyfert nuclear polarization are made where possible by correcting for ISP and for an approximation of the dilution due to the host galaxy flux by using values from previous studies. Both the measured and the corrected nuclear polarizations are compared with previously published values, and are discussed in the context of the standard models of Seyfert galaxies. Most of the observed galaxies show evidence of polarization, both from the host galaxy and from the intrinsic Seyfert nucleus. In particular, distinct polarization features: bands of polarization consistent with extended dusty disks aligned with the dusty tori proposed in Seyferts, and regions of polarization corresponding to scattering of the nuclear continuum along the biconical extended Seyfert emission-line regions, have been identified in several of the observed galaxies. 2 Contents Abstract 2 Declaration and copyright 16 1 An introduction to Seyfert galaxies 17 1.1 Classification of galaxies 17 1.1.1 Active galactic nuclei 19 1.2 Seyfert nuclei 21 1.2.1 Seyfert types 22 1.2.2 Mechanism of line emission of Seyfert nuclei 24 1.2.3 Broad-line region 24 1.2.4 Narrow-line region 26 1.2.5 Extended emission line regions 28 1.3 Unified schemes 29 1.3.1 Unification of Seyfert types 1 and 2 29 1.3.2 Unification of radio loud AGN 30 1.3.3 Unification of Seyfert Is and radio quiet quasars 31 1.3.4 Where are the high luminosity Seyfert 2 type nuclei? 31 1.4 Multi-wavelength continuum of Seyfert nuclei 32 1.4.1 Broad-band spectral energy distributions of Seyferts 33 1.4.2 X-ray continuum properties of Seyferts 34 1.4.3 Optical and UV continuum properties of Seyferts 36 1.4.4 Infra-red continuum properties of Seyferts 37 1.4.5 Radio continuum properties of Seyferts 39 1.4.6 Mechanism of continuum emission 41 3 1.5 Limitations of the orientational unified schemes: Host galaxy environments 43 1.5.1 Host galaxy morphology 43 1.5.2 Evidence for close companions 45 1.5.3 Galactic outflows 47 1.6 Summary 49 2 Optical polarization 50 2.1 Introduction 50 2.2 The theory of polarization of light 50 2.3 Polarization by dust 52 2.3.1 Rayleigh scattering 53 2.3.2 Mie scattering 53 2.3.3 Extinction and reddening 54 2.3.4 Dichroic (preferential) extinction 54 2.3.5 Galactic interstellar polarization 56 2.4 Polarization from electrons 59 2.4.1 Thomson scattering (lower-energy electron scattering) 60 2.4.2 Inverse Compton effect (high-energy electron scattering) 61 2.4.3 Synchrotron radiation 61 3 Polarization observations of spirals and Seyferts 62 3.1 Introduction 62 3.2 Polarization studies of spiral galaxies 62 3.2.1 Radio polarization 63 3.2.2 Optical polarization 63 3.2.3 Face-on spiral galaxies 64 3.2.4 Edge-on spiral galaxies 64 3.2.5 Problems in polarization interpretation 67 3.3 Polarization studies of Seyfert nuclei 68 3.3.1 Evidence of polarization from dust 68 3.3.2 Evidence of polarization from electrons 69 4 3.3.3 Infra-red polarization observations 69 3.3.4 Optical-UV polarization observations 71 3.3.5 Seyfert 1 galaxies 72 3.3.6 Seyfert 2 galaxies 74 3.3.7 Problems in polarization interpretation 75 3.4 Summary of polarization studies and their support for the unified scheme ... 76 4 Optical polarimetry techniques 78 4.1 Introduction 78 4.2 Measurement of polarization 78 4.3 The Durham Polarimeter 80 4.3.1 Resolution of CCD detector 81 4.4 Data reduction 82 4.4.1 CDPRELUDE 82 4.4.2 FLATFIELD 83 4.4.3 REDUCE 83 4.4.4 POLCALC, POLPLOT 83 4.4.5 Measurement errors and ISP corrections 84 4.5 Observations 85 5 Face-on Seyfert galaxies 89 5.1 Introduction 89 5.2 Markarian 348 89 5.2.1 Introduction 89 5.2.2 Observational details 92 5.2.3 Image details 93 5.2.4 Interstellar polarization 94 5.2.5 Results: V-band 97 5.2.6 Results: V-band - after correction for ISP 101 5.2.7 NPM1G +31.0016 106 5.3 Markarian 573 118 5.3.1 Introduction 118 5.3.2 Observational details 121 5 5.3.3 Image details 122 5.3.4 Interstellar polarization 123 5.3.5 Results: V-band 123 5.3.6 Results: R-band 126 5.3.7 Results: B-band 127 5.3.8 Results: Wavelength dependence of polarization in the host galaxy . 129 5.3.9 Results: Polarization of the Seyfert nucleus 132 5.4 NGC 1566 147 5.4.1 Introduction 147 5.4.2 Observational details 149 5.4.3 Image details 149 5.4.4 Interstellar polarization 150 5.4.5 Results: V-band 150 5.4.6 Results: R-band 152 5.4.7 Results: Ha band 153 5.4.8 Results: Discussion 155 6 Edge-on Seyfert galaxies 171 6.1 Introduction 171 6.2 Markarian 3 171 6.2.1 Introduction 171 6.2.2 Observational notes 173 6.2.3 Image details 175 6.2.4 Interstellar polarization 176 6.2.5 Results: V-band 176 6.2.6 Results: V-band after correction for ISP 179 6.3 Markarian 1376 - NGC 5506 187 6.3.1 Introduction 187 6.3.2 Observational details 188 6.3.3 Image details 189 6.3.4 Interstellar polarization 189 6.3.5 Results: V-band 190 6.3.6 Results: V-band after ISP correction 192 6 6.4 NGC 2992 198 6.4.1 Introduction 198 6.4.2 Observational details 200 6.4.3 Image details 201 6.4.4 Interstellar polarization 201 6.4.5 Results: V-band 202 6.4.6 Results: l-band 203 6.4.7 Results: NGC 2993 206 6.5 NGC 3079 216 6.5.1 Introduction 216 6.5.2 Observational notes 216 6.5.3 Image details 218 6.5.4 Interstellar polarization 218 6.5.5 Results: V-band 218 7 Summary and conclusions 224 7.1 Modelling of the Seyfert nuclear polarization 225 7.1.1 The Unified scheme Seyfert model 225 7.1.2 Numerical modelling of polarization features 225 7.2 Modelling of the host galaxy polarization 228 7.3 Previous studies of other Seyfert nuclei 229 7.4 Summary of the observations 232 7.4.1 Markarian 573 (Face-on host galaxy) 233 7.4.2 Markarian 348 (Face-on host galaxy) 233 7.4.3 Markarian 3 (Edge-on host galaxy) 235 7.4.4 Markarian 1376 (Edge-on host galaxy) 237 7.4.5 NGC 2992 (Edge-on host galaxy) 240 7.4.6 NGC 3079 (Edge-on host galaxy) 240 7.4.7 NGC 1566 (Face-on host galaxy) 242 7.5 Conclusions from observations 242 7.6 Conclusions for further work 245 7 7.6.1 Limitations: of the observations 246 7.6.2 Further work ............. 247 Acknowledgements 264 8 List of Figures 1.1 The Hubble classification of galaxies 18 1.2 A strong AGN unification scheme 32 1.3 The standard model for Seyferts 33 1.4 The galactic dust model of Malkan et al.