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Dark Matter Substructure Probed by Strong Gravitational Lenses

Dark Matter Substructure Probed by Strong Gravitational Lenses. Aliza Malz California Institute of Technology CMU Astronomy Club. Physical Cosmology. How did the physical universe originate? What is the large-scale nature of the universe? Big Bang Theory

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Dark Matter Substructure Probed by Strong Gravitational Lenses

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  1. Dark Matter Substructure Probed by Strong Gravitational Lenses Aliza Malz California Institute of Technology CMU Astronomy Club

  2. Physical Cosmology • How did the physical universe originate? • What is the large-scale nature of the universe? • Big Bang Theory • Cosmic Microwave Background Radiation • Inflation Theory • Astronomical Consequences of General Relativity • Gravitational Lensing & Gravitational Waves • Black Holes & Compact Objects

  3. General Relativity • Einstein’s Metric Theory of Gravitation • Gravitational Time Dilation & Redshift • Light Deflection & Time Delay • Orbital Effects & Directional Relativity • Aptide Precession & Orbital Decay • Geodetic Precession & Frame-Dragging • Gravitational Waves

  4. General Relativity • Einstein’s Metric Theory of Gravitation • Gravitational Time Dilation & Redshift • Light Deflection & Time Delay • Orbital Effects & Directional Relativity • Aptide Precession & Orbital Decay • Geodetic Precession & Frame-Dragging • Gravitational Waves Unnecessary for this discussion! Spacetime grips mass, telling it how to move, and mass grips spacetime, telling it how to curve. -- John Archibald Wheeler

  5. Gravitational Lensing • Mass bends spacetime • Light curves near mass • Observe image distorted by gravity • Gravitational effects caused only by mass • Learn about dark matter

  6. Strong Gravitational Lensing • Easily visible distortions • Einstein Rings • Einstein Crosses • Image Duplication • Arcs • Seen in distant quasars

  7. Weak Gravitational Lensing • Small distortions in background objects • Analyze many objects in system • Shear map • Statistical stretching • Observed in supermassive galaxy clusters

  8. Gravitational Microlensing • Magnification distortion • Variable amount of light observed • Noticeable changes over time • Caused by stars, planets, etc.

  9. Strong vs. Microlensing • Strong lensing multiplies images • Microlensing distorts image magnification

  10. Strong & Microlensing 3 Image Numbers 1 2 • Observe both at once in PG1115 system to learn about dark matter substructure 0

  11. Caustic Maps * 2 * 4 Cusp Fold Weak • Map in source plane • Projected from lens plane • Determines type of gravitational lensing

  12. Simulate source motion over caustic map Plot path of source across caustic map Convolution processes magnification data Simulation Methods

  13. Caustic Crossings • Motion of source over caustic map • Magnification over time or space reveals substructure of dark matter • Identified by second derivative threshold on lightcurve • Learn nature of dark matter from caustic crossing

  14. The Lens Equation •  =  -  •  = -  x DS/DLS •  =  -  x DLS/DS • DS = DS - DL

  15. Identification of Crossings

  16. Identification of Crossings

  17. Identfication of Crossings

  18. Identification of Crossings

  19. Source Size • α= (4GM)/(c2b) • α(θ)= (4GM)/(c2θdl) • θds= θsds + αdls • α(θ)= ds/dls (θ – θs) • θ-θs= (4GM)/(θc2) dls/dsdl • θE =(4GM/c2 dls/dlds)1/2

  20. Source Size in Simulation • Ideally small = 0.001 θE • Observations = 0.1 – 1.0 θE • Simulations = 0.01 – 0.1 θE

  21. Source Size Variation

  22. Source Size Variation

  23. Source Size Variation

  24. Source Size Variation

  25. Practical Considerations • How far does a source move across the caustic map over time? • Einstein radius of quasar =6.6*1016 cm • Quasar moves at 300 km/s • In 2 years, quasar traverses 0.029 θE • In 10 years, quasar traverses 0.14 θE

  26. Practical identification • Better restriction method for shorter lightcurves: second derivative test • Magnification > ~50 • ~ -1 < 1st Derivative < ~1 • 2nd Derivative < ~ -100 • Slightly different thresholds for each image based on caustic density

  27. Crossings Identified in 1000 lightcurves

  28. Crossing Time • A path that has a crossing in the first 2 years of observation is 9 - 40 % more likely to have at least one more in the next 8 years. • Crossings take an average of 30 days to occur. • Feasible timescale for new telescope mission?

  29. Future Research • Eliminate convolution method • Average microlensing events to equate with strong lensing observation • Remove microlensing effect from strong lensed image

  30. Acknowledgments • Leonidas Moustakas, Jason Rhodes • SFP, SURF, and Carol Casey • IDL • NASA’s IDLAstro Library • Leonidas Moustakas’ lamlib and eidol Libraries • Fanning Consulting’s coyote Library • Aaron Barth’s ATV Library • John Moustakas’ RED Library • Craig Markwardt’s CM Library • Chuck Keeton’s dma.100 software • Wikipedia

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