weak gravitational lensing slides

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Weak Gravitational Lensing Image Source: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University) By Patrick Kantorski & Cory Gerrity

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Presentation slides for the Weak Lensing presentation Patrick Kantorski and Cory Gerrity gave for UC Berkeley's Astro C161 Course, Spring 2015.

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  • Weak Gravitational Lensing

    Image Source: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

    By Patrick Kantorski & Cory Gerrity

  • Introduction What is Weak Gravitational Lensing?

    Image Source: Astrophysicist Dr. Katherine J Mack

    Why is Weak Gravitational Lensing important? What are some of the fundamental limitations and assumptions?

  • Methodology

    Previous Presentation: Thin-Lens Approximation

    Transformation: Lensed Un-lensed via Jacobian Matrix Formalism

    Symmetry of Partial Derivatives -> Decomposition [Diagonal Convergence Term + Trace-Free Shear Term]

  • What is Convergence?

    What is Shear?

    Convergence by Jackson Pollock

    The second term in action.

    Methodology

    Image Source: Schneider, P. 2005

    Shear and Convergence Transformations

  • Scale of Weak Lensing Survey

    Small Scale Limits - Intrinsic ellipticities

    - Add Shot Noise - Limited by Depth of Survey

    Large Scale Limits: - Large Sky Coverage

    - Limited by Variance Image Source: Wikipedia.org

  • Observational Considerations Applying the Shear Method

    Source to Image Ellipticity Minimum Lens Strength Magnication Eects

    Observational Instruments Size of Telescope Size of CCD Camera

    Working with Instruments Exposure Time Seeing Conditions

    Apparent Size of Galaxies vs. Faintness

    Image Source: Schneider, P. 2005

  • Observational Considerations Mean Number Density of Galaxy Images vs. Seeing

    Source: Schneider, P. 2005

  • Observational Challenges Data Reduction

    Individual Frames

    Coaddition

    Image Analysis The Point-Spread Function

    Shape Measurements Numerical Algorithms

    Shear Observations from Space Image Source: Wikipedia.org

    Point-Spread Function (PSF)

  • Mass Reconstruction

    Kaiser ~ Squires Inversion Surface Mass Density from Shear

    Convolution Product: Fourier Transform Solve for Mass Density -> Transform Back

    Discrete Process Requires Smoothing > Kernel Prevents Summation

    [Kaiser & Squires (1993)]

  • Dark Matter Mass Reconstruction (k contours) for COSMOS Advanced Camera for Surveys (ACS) 2 square degree eld. The Mass Density along LOS is Proportional to k.

    Dark Matter Map from Hubble Space Telescope Survey and the Cosmic Evolution Survey

  • Dark Matter Map from Hubble Space Telescope Survey and the Cosmic Evolution Survey

  • Dark Matter Map from Hubble Space Telescope Survey and the Cosmic Evolution Survey

  • Creation of cosmic structure in the complex galaxy cluster merger Abell 2744

    Image Source: Merten, J. 2011

  • On the Horizon Euclid (2020), ESA

    15,000 Square Degree Weak Lensing Survey in 3 NIR Filters 24.5 Magnitude Resolution, 550-900 nm

    Square Kilometer Array (2022), Australia/South Africa Large RA Instrument will allow 50x higher sensitivity than any other

    Large Synoptic Survey Telescope (2022), El Pen, Chile Large Field/High Z Capability Mass Map of Universe to Half Current Age

  • On the Horizon

    The LSST is a new kind of telescope. With a light-gathering power among

    the largest in the world, it can detect

    faint objects with short exposures. Its

    uniquely wide eld of view allows it

    to observe large areas of the sky at

    once; compact and nimble, it can

    move quickly between images.

    Taking more than 800 panoramic

    images each night, it can cover the

    sky twice each week. - LSST.org

    Large Synoptic Survey Telescope

    Image Source: news.slac.stanford.edu

  • Conclusion Why pursue research applying Gravitational Lensing?

    Gravitational Lensing is used to produce large-eld survey maps of the Universe!

    By mapping where regions of Dark Matter, we can understand more about its properties and properties of galaxy clusters!

    Weak-lensing is a fairly new method due to recent technological advancements! There will also be many improvements to its

    application the coming years! (Euclid, LSST, etc)

    Gravitational Lensing Video