King, Lindsay J.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3127
Lindsay King is a faculty member in the Physics Department. Her interests are:
- Physical cosmology and extragalactic astrophysics
- Dark matter and dark energy
- Galaxy formation and evolution
- Galaxy clusters, including bullet clusters
- The cosmic web (large scale structure)
- Weak and strong gravitational lensing (theory and observations)
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Item The Distribution of Dark and Luminous Matter in the Unique Galaxy Cluster Merger Abell 2146(Oxford University Press) King, Lindsay J.; Clowe, D. I.; Coleman, Joseph E.; Russell, H. R.; Santana, R.; White, Jacob A.; Canning, R. E. A.; Deering, Nicole J.; Fabian, A. C.; Lee, Brandyn E.; Li, B.; McNamara, B. R.; 0000 0001 2437 3571 (King, LJ); 0000-0001-8445-0444 (White, JA); King, Lindsay J.; Clowe, D. I.; Coleman, Joseph E.; Russell, H. R.; Santana, R.; White, Jacob A.; Canning, R. E. A.; Deering, Nicole J.; Fabian, A. C.; Lee, Brandyn E.; Li, B.; McNamara, B. R.Abell 2146 (z = 0.232) consists of two galaxy clusters undergoing a major merger. The system was discovered in previous work, where two large shock fronts were detected using the Chandra X-ray Observatory, consistent with a merger close to the plane of the sky, caught soon after first core passage. A weak gravitational lensing analysis of the total gravitating mass in the system, using the distorted shapes of distant galaxies seen with Advanced Camera for Surveys - Wide Field Channel on Hubble Space Telescope, is presented. The highest peak in the reconstruction of the projected mass is centred on the brightest cluster galaxy (BCG) in Abell 2146-A. The mass associated with Abell 2146-B is more extended. Bootstrapped noise mass reconstructions show the mass peak in Abell 2146-A to be consistently centred on the BCG. Previous work showed that BCG-A appears to lag behind an X-ray cool core; although the peak of the mass reconstruction is centred on the BCG, it is also consistent with the X-ray peak given the resolution of the weak lensing mass map. The best-fitting mass model with two components centred on the BCGs yields M200 = 1.1_{-0.4}^{+0.3} × 10¹⁵ and 3_{-2}^{+1} × 10¹⁴ M_⊙ for Abell 2146-A and Abell 2146-B, respectively, assuming a mass concentration parameter of c = 3.5 for each cluster. From the weak lensing analysis, Abell 2146-A is the primary halo component, and the origin of the apparent discrepancy with the X-ray analysis where Abell 2146-B is the primary halo is being assessed using simulations of the merger.Item Dynamical Analysis of Galaxy Cluster Merger Abell 2146(Oxford Univ Press, 2015-09-03) White, Jacob A.; Canning, R. E. A.; King, Lindsay J.; Lee, Brandyn E.; Russell, H. R.; Baum, S. A.; Clowe, D. I.; Coleman, Joseph E.; Donahue, M.; Edge, A. C.; Fabian, A. C.; Johnstone, R. M.; McNamara, B. R.; O'Dea, C. P.; Sanders, J. S.; White, Jacob A.; King, Lindsay J.; Lee, Brandyn E.; Coleman, Joseph E.We present a dynamical analysis of the merging galaxy cluster system Abell 2146 using spectroscopy obtained with the Gemini Multi-Object Spectrograph on the Gemini North telescope. As revealed by the Chandra X-ray Observatory, the system is undergoing a major merger and has a gas structure indicative of a recent first core passage. The system presents two large shock fronts, making it unique amongst these rare systems. The hot gas structure indicates that the merger axis must be close to the plane of the sky and that the two merging clusters are relatively close in mass, from the observation of two shock fronts. Using 63 spectroscopically determined cluster members, we apply various statistical tests to establish the presence of two distinct massive structures. With the caveat that the system has recently undergone a major merger, the virial mass estimate is M_{vir} = 8.5_{-4.7}^{+4.3} x 10¹⁴ M_⊙ for the whole system, consistent with the mass determination in a previous study using the Sunyaev-Zel'dovich signal. The newly calculated redshift for the system is z = 0.2323. A two-body dynamical model gives an angle of 13⁰-19⁰ between the merger axis and the plane of the sky, and a time-scale after first core passage of 0.24-0.28 Gyr.Item Galaxy Cluster Lensing Masses in Modified Lensing Potentials(2015-10-28) Barreira, Alexandre; Li, Baojiu; Jennings, Elise; Merten, Julian; King, Lindsay J.; Baugh, Carlton M.; Pascoli, Silvia; King, Lindsay J.We determine the concentration-mass relation of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble survey in theories of gravity that directly modify the lensing potential. We model the clusters as Navarro-Frenk-White haloes and fit their lensing signal, in the Cubic Galileon and Nonlocal gravity models, to the lensing convergence profiles of the clusters. We discuss a number of important issues that need to be taken into account, associated with the use of non-parametric and parametric lensing methods, as well as assumptions about the background cosmology. Our results show that the concentration and mass estimates in the modified gravity models are, within the error bars, the same as in Λ cold dark matter. This result demonstrates that, for the Nonlocal model, the modifications to gravity are too weak at the cluster redshifts, and for the Galileon model, the screening mechanism is very efficient inside the cluster radius. However, at distances ~ (2-20) Mpc h⁻¹ from the cluster centre, we find that the surrounding force profiles are enhanced by similar to 20-40 per cent in the Cubic Galileon model. This has an impact on dynamical mass estimates, which means that tests of gravity based on comparisons between lensing and dynamical masses can also be applied to the Cubic Galileon model.Item Refractive Convergent Plasma Lenses Explain Extreme Scattering Events and Pulsar Scintillation(2012-02-27) Pen, Ue-Li; King, Lindsay J.; 0000 0001 2437 3571 (King, L); King, Lindsay J.We propose convergent plasma lenses, possibly from current sheets, as a generic solution to strong interstellar scattering. These lenses resolve the overpressure problem by geometric alignment as noted by Goldreich & Shridhar. Our new model further quantitatively explains properties of extreme scattering events and pulsar parabolic arcs. It makes quantitative predictions testable by VLBI on scattering events. It differs conceptually from previous models by occurring through rare, localized underdense sheets. Such sheets are thermally and kinematically stable, and could be consequences of reconnection. The apparent diffractive effects are a result of coherent interference of refractive images. We propose that these lenses can be used for precision distance determination to pulsars, enabling accurate gravity source localization.Item Shock Fronts, Electron-Ion Equilibration and Intracluster Medium Transport Processes in the Merging Cluster Abell 2146(2012-02) Russell, H. R.; Mcnamara, B. R.; Sanders, J. S.; Fabian, A. C.; Nulsen, P. E. J.; Canning, R. E. A.; Baum, S. A.; Donahue, M.; Edge, A. C.; King, Lindsay J.; O'Dea, C. P.; 0000 0001 2437 3571 (King, LJ); King, Lindsay J.We present a new 400-ks Chandra X-ray observation of the merging galaxy cluster Abell 2146. This deep observation reveals detailed structure associated with the major merger event including theMach numberM =2.3±0.2 bowshock ahead of the dense, ram pressure stripped subcluster core and the first known example of an upstream shock in the intracluster medium (ICM) (M = 1.6 ± 0.1). By measuring the electron temperature profile behind each shock front, we determine the time-scale for the electron population to thermally equilibrate with the shock-heated ions.We find that the temperature profile behind the bow shock is consistent with the time-scale for Coulomb collisional equilibration and the post-shock temperature is lower than expected for instant shock heating of the electrons. Although like the Bullet cluster the electron temperatures behind the upstream shock front are hotter than expected, favouring the instant heating model, the uncertainty on the temperature values is greater here and there is significant substructure complicating the interpretation. We also measured the width of each shock front and the contact discontinuity on the leading edge of the subcluster core to investigate the suppression of transport processes in the ICM. The upstream shock is ∼440 kpc in length but appears remarkably narrow over this distance with a best-fitting width of only 6+5 −3 kpc compared with the mean free path of 23 ± 5 kpc. The leading edge of the subcluster core is also narrow with an upper limit on the width of only 2 kpc separating the cool, multiphase gas at 0.5–2 keV from the shock-heated surrounding ICM at ∼6 keV. The strong suppression of diffusion and conduction across this edge suggests a magnetic draping layer may have formed arou0nd the subcluster core. The deep Chandra observation has also revealed a cool, dense plume of material extending ∼170 kpc perpendicular to the merger axis, which is likely to be the disrupted remnant of the primary cluster core. This asymmetry in the cluster morphology indicates the merger has a non-zero impact parameter. We suggest that this also explains why the south-western edge of the subcluster core is narrow and stable over ∼150 kpc in length, but the north-eastern edge is broad and being stripped of material.Item Testing Metallicity Indicators at Z ~ 1.4 with the Gravitationally Lensed Galaxy CASSOWARY 20*(Oxford University Press, 2014-03-27) James, Bethan L.; Pettini, Max; Christensen, Lise; Auger, Matthew W.; Becker, George D.; King, Lindsay J.; Quider, Anna M.; Shapley, Alice E.; Steidel, Charles C.; 0000 0001 2437 3571 (King, LJ); King, Lindsay J.We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ~ 6 M⊙ yr⁻¹) galaxy at z = 1.433, magnified by a factor of 11.5 by the gravitational lensing produced by a massive foreground galaxy at z = 0.741. We analysed the integrated physical properties of the H II regions of CSWA 20 using temperature- and density-sensitive emission lines. We find the abundance of oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the Sun. The unusually low C/O ratio may be an indication of a particularly rapid time-scale of chemical enrichment. The wide wavelength coverage of X-shooter gives us access to five different methods for determining the metallicity of CSWA 20, three based on emission lines from H II regions and two on absorption features formed in the atmospheres of massive stars. All five estimates are in agreement, within the factor of ~2 uncertainty of each method. The interstellar medium (ISM) of CSWA 20 only partially covers the star-forming region as viewed from our direction; in particular, absorption lines from neutrals and first ions are exceptionally weak. We find evidence for large-scale outflows of the ISM with speeds of up 750 km s⁻¹, similar to the values measured in other high-z galaxies sustaining much higher rates of star formation.