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An Investigation of Radio-Quiet Quasars Using Gravitational Lensing

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An Investigation of Radio-Quiet Quasars Using Gravitational Lensing AN INVESTIGATION OF RADIO-QUIET QUASARS USING GRAVITATIONAL LENSING A thesis submitted to the University of Manchester for the degree of Master of Science in the Faculty of Engineering and Physical Sciences 2015 By Hannah Ruth Stacey Jodrell Bank Centre for Astrophysics School of Physics and Astronomy Contents 1 Introduction 1 1.1 Gravitational lensing . 3 1.1.1 History of gravitational lensing . 3 1.1.2 Gravitational lens theory . 7 1.1.3 Galactic substructure . 11 1.1.4 Microlensing . 14 1.2 Radiative Processes . 16 1.2.1 Thermal emission . 16 1.2.2 Synchrotron emission . 16 1.2.3 Free-free emission . 18 1.3 Radio-quiet quasars . 20 1.3.1 Quasar morphology . 20 1.3.2 Radio properties . 21 1.3.3 Source of radio emission from radio-quiet quasars . 26 2 Fundamentals of radio interferometry 29 2.1 Aperture synthesis . 29 2.2 The two-element interferometer . 31 2.3 u-v coverage . 33 2.4 Limitations . 36 2.5 Sensitivity . 37 2.6 Calibration . 37 CONTENTS 2.7 Imaging and Deconvolution . 39 3 Observations 41 3.1 Sample selection . 41 3.2 e-MERLIN observations . 42 3.3 Data reduction . 44 3.3.1 Loading the data . 44 3.3.2 Calibration . 48 3.3.3 Imaging the target . 57 4 Results 60 4.1 HS 0810+2554 . 60 4.2 RX J0911+0551 . 69 4.3 SDSS J1251+2935 . 77 4.4 SDSS J1330+1810 . 80 5 Summary and Conclusions 81 Appendix A i Appendix B iii Appendix C vii List of Tables 3.1 Details of e-MERLIN observations at L-band. 42 3.2 Details of JVLA observations. 44 3.3 List of L-band antenna weights (Argo, 2015). 58 4.1 Details of HS 0810+2554 from CASTLES (Kochanek et al., 2013). The position of each image, relative to image A, is given in arcsec- onds. The optical flux at I-band is given in apparent magnitude. 62 4.2 e-MERLIN L-band image fluxes of HS 0810+2554, from JMFIT. The error given is the RMS noise in the data. 66 4.3 JVLA X band image fluxes of HS 0810+2554. Results from Jack- son et al. (2015). 67 4.4 Model fitting results for HS 0810+2554 and RX J0911+0551 from JVLA observations. The source position is given relative to the galaxy position. For RX J0911+0551, the galaxy critical radius corresponds to the Einstein radius measured along the major axis. Results from Jackson et al. (2015). 69 4.5 Details of RX J0911+0551 from CASTLES (Kochanek et al., 2013). The position of each image, relative to image A, is given in arcsec- onds. The optical flux at I-band is given in apparent magnitude. 70 4.6 JVLA C-band image fluxes of RX J0911+0551. 74 List of Figures 1.1 The first lens discovered, quasar Q0957+561, at 4885 MHz with the JVLA from Reid et al. (1995). The two images of the quasar are shown (centre top and bottom) with large separation of 6". The core of the quasar falls within the caustic of the lens galaxy, producing a lensed image of the core (bottom). The jets of the quasar fall outside the tangential caustic and are not lensed. 4 1.2 Hubble image of so-called `Cosmic Horseshoe', SDSS J1148+1930, an elliptical galaxy lensing a background galaxy. The extended source produces large arcs, close to an Einstein ring. Image credit: ESA/Hubble. 5 1.3 Hubble image of Q2237+030, a quasar lens with image angular separation of 1.6". The compact source is close to the line of sight through the centre of the galaxy, creating four images known as an `Einstein cross'. Image credit: ESA/Hubble. 6 1.4 A simplified gravitational lens diagram. A light ray is emitted from source at diameter η and angular size β. It is deflected by the gravitational field of an object on the image plane at impact parameter ξ and angular size θ. The angle of deflection isα ^. 8 1.5 The resulting images produced when the source is on a cusp of the astroid caustic. The caustics mapped onto the source plane are in red; the lens critical curve and time-delay contours are in green. 12 LIST OF FIGURES 1.6 The resulting images produced when the source is on a fold of the astroid caustic. 12 1.7 SED for NGC 253 from Peel et al. (2011). The blue dotted line traces the thermal emission, which peaks in the infrared and drops out at microwave frequencies. Free-free emission is traced by the red dotted line, which dominates below ∼100 GHz. The syn- chrotron emission is traced by the pink dotted line, which begins to dominate at frequencies of a few GHz. 17 1.8 Synchrotron spectra of three astronomical sources at radio frequen- cies between 10 MHz and 30 GHz. The synchrotron emission from Cygnus A becomes self-absorbed at ∼20 MHz. Figure from Baars et al. (1977). 18 1.9 The unified model of active galactic nuclei: along the jet axis, the AGN is seen as a blazar; perpendicular to the jet axis, the AGN is seen as a Type 2 Seyfert galaxy; at intermediate angles, the source is observed as a Type 1 Seyfert or quasar. The different AGN mor- phological properties are labelled in the figure: the nucleus/black hole (BH) (and surrounding source of x-ray emission), broad line region (BLR), accretion disk (AD) and narrow line regions (NLR). Figure from Jovanovic and Popovic (2009). 21 1.10 Radio-loud quasar 3C175 at 4.9 GHz observed with the JVLA. The quasar can be seen in the centre, with characteristic double lobes from relativistic jets spanning 212 kpc. Figure from Bridle et al. (1994). 22 1.11 Optical against radio flux for samples of quasars at redshift 0:3 < z < 1:5 (Goldschmidt et al., 1999). 24 1.12 Optical against radio flux for samples of quasars at redshift 1:5 < z < 2:5 (Goldschmidt et al., 1999). 24 LIST OF FIGURES 1.13 The median radio flux is correlated with the optical flux. Each bin represents the median of thousands of radio-quiet quasars in the SDSS DR3 catalogue. 25 2.1 Illustration of the antenna power pattern for a single antenna and projection onto the celestial sphere. Figure from Kraus (1966). 30 2.2 Simplified diagram of a two-element interferometer. There is a time delay, τg, in the wavefront between the antennae, which must be corrected for before the signals are correlated. The incoming signal is shifted to a lower frequency by a local oscillator for analysis. The resulting signals are multiplied and integrated by the correlator. 32 2.3 Vectors describing the relations between an interferometer base- line and the target source. B is the baseline vector between two telescopes; b is the projected baseline;s ^ describes the unit vector in the direction of the source; σ is the vector from a point on the source to the source centre. 34 2.4 Plot of u-v tracks for the e-MERLIN observation of RX J0911+0551 over a period of 10 hours. The e-MERLIN array has 7 antennae (21 baselines) with a maximum baseline of 220 km. The colours represent the frequencies across the band. The source has a low declination, so there is less extension in the v-direction (y-axis) and as a result the u-v tracks are more elliptical. 35 3.1 The locations of the seven e-MERLIN telescopes around the UK (O'Brien, 2009). 43 3.2 Phase and amplitude data for point source calibrator OQ 208, without any flagging and before any calibration had been applied. Note the reduced sensitivity at the edge of each IF. The data is displayed in POSSM by baseline for stokes LL polarisation only. 46 LIST OF FIGURES 3.3 Phase and amplitude data for point source calibrator OQ 208, after flagging, before calibration. The channels at the edges of each IF have been flagged, as well as significant outliers. The data is displayed by baseline for stokes LL polarisation only. 47 3.4 Delay solution table for point source calibrator OQ 208, shown baseline by baseline for LL polarisation only. The delays are within a few nanoseconds. The plots were generated using the AIPS task SNPLT. 49 3.5 POSSM plot of OQ 208 amplitude and phases after the delay cal- ibration is applied. Note that the phase slopes have been removed and they are now flat across each IF. 50 3.6 POSSM plot of OQ 208 amplitude and phases after phase cali- bration applied, showing the LL polarisation only. The resultant phases are around zero. The amplitudes are unchanged. 52 3.7 1407+284 amplitude and phases after flux and bandpass calibra- tion. The amplitudes are smooth across the band, except for the Lovell-Cambridge baseline which is not as well calibrated. 54 3.8 u-v-distance-amplitude plot for phase calibrator, J0901+0448, af- ter calibration but before final flagging. Every 153rd visibility is plotted. The colours show the frequencies across the band. 56 4.1 CASTLES I-band image of HS 0810+2554 (Kochanek et al., 2013). North is up, and East is left. The lens system has a fold-configuration, with a merging south-western pair. The merging pair show a 0.7- magnitude difference in brightness, contrary to expectations. 61 4.2 e-MERLIN L-band observation of HS 0810+2554 with robust weight- ing.
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