Loading in 5 sec....

Dark Matter in Galaxies using Einstein RingsPowerPoint Presentation

Dark Matter in Galaxies using Einstein Rings

- 65 Views
- Uploaded on
- Presentation posted in: General

Dark Matter in Galaxies using Einstein Rings

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Dark Matter in Galaxies using Einstein Rings

Brendon J. Brewer

School of Physics, The University of Sydney

Supervisor: A/Prof Geraint F. Lewis

- Use gravitational lens as a “natural telescope” and simultaneously measure total projected density profile

ER 0047-2808 (source at redshift 3.6)J1131

- I use a pseudo-isothermal elliptical potential. Realistic enough for single galaxy lenses
- Five Parameters:
b, q, (xc, yc), q

- Can have external shear: g, qg

Note: A nonparametric model is one with a lot of parameters.

- Usually leads to negative pixels
- A non-unique solution is possible, especially if we try to use a lot of pixels
- Get spiky solutions due to PSF
- Constrained (nonnegative) least squares also has problems. Bayesian interpretation it is a bad prior. The sky is dark!

Multiscale Monkey Prior

≈ John Skilling’s “Massive Inference” prior

- Achieved higher resolution
- This was only possible because the prior was actually chosen as a model of prior knowledge
- Also get tight constraints on lens parameters (no degeneracies) for the PIEP model

Claeskens et al, 2006

- Explore space of possible lens parameter values that lens the QSO images back to within ~1 milliarcsecond
- Take into account astrometric uncertainties
- Only weak information from flux ratios (microlensing, dust)

- Pixellated mass model allows more freedom
- Image positions provide linear constraints on mass pixels
- Very underdetermined linear system, solve by exploring space of possibilities
- May overestimate masses when we extend to uncertain astrometry

- Build up mass models from sets of smooth basis functions. PIEPs, SPEMDs, NFWs, …
- Has been done by Phil Marshall for weak lensing
- Good but computationally challenging. The next step?

- Projected total mass profiles are almost all close to spherical (q of potential > 0.9) but rotated wrt light profile
- Total masses within an Einstein Ring are well constrained. Core not constrained without detection of faint central images
- Attempts to measure local properties such as inner slope have all used parametric models. This needs to change.