H0H0H0H0 Joshua Zhou UC Davis COSMOS Cluster 4: Astrophysics 30 July 2015

B1608 Gravitationally lensed quasar Located in the circle … somewhere ( 他妈的，怎么看不见！ ) 2

Hubble Constant 3

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Gravitational Lenses Fermat’s Principle: light takes fastest path Massive object curves spacetime Light bends Multiple images of same object Act as lenses – Magnification 5

Gravitational Lens 6

Gravitational Lenses 7

Einstein Ring Lensing of a galaxy directly behind the lens causes a near-perfect ring Image: ESA/Hubble & NASA d. Bulwersator (Wikipedia) 8

Data Reduction Divide curves by the mean to have an average of 1 – Eliminate magnitude differences – Some sources are brighter Shift curves horizontally to align – Find time delay 9

Data Reduction Original (varied range) 10

Time Delay Cross Correlation X, Y: sequences, d: delay – Measures correlation of delayed sequences – Delay at which correlation is at a peak is the delay that fits curves the most 11

Correlation & Delay Indices B (red): +0 ; auto A (blue): -8 C (cyan): -9 D (magenta): -21 Days B (red): 0 ; auto A (blue): C (cyan): D (magenta):

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Mass Model 14

Hubble Constant 15

Hubble Constant 16

Citations Fassnacht, C. D., E. Xanthopoulos, L. V. E. Koopmans, and D. Rusin. "A Determination of H 0 with the CLASS Gravitational Lens B III. A Significant Improvement in the Precision of the Time Delay Measurements." ApJ The Astrophysical Journal (2002): Print. Fassnacht, C. D., T. J. Pearson, A. C. S. Readhead, I. W. A. Browne, L. V. E. Koopmans, S. T. Myers, and P. N. Wilkinson. "A Determination of H 0 with the CLASS Gravitational Lens B I. Time Delay Measurements with the VLA." ApJ The Astrophysical Journal (1999): Print. Joye, William. SAOImage DS9. Vers Computer software. Future Directions for Astronomical Image Display Windows 7, 10.5 MB, download. C. D. Fassnacht 17