Astr 5460 Wed., Mar. 5, 2003
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Today: Reminders/Assignments |
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Longair, Chapter 4, Clusters |
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Chapter 5 for Friday: |
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- Getting into Theory/GR |
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Unless noted, all figs and eqs from Longair. |
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Reminders/Preliminaries
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Astro-ph preprints on Friday: |
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http://xxx.lanl.gov/ |
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Galaxy Spectra/Modeling Assignment |
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Reading Bennett et al. 2003 (MAP) paper |
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WIRO cautions, still to be scheduled… |
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Register an account on MAST |
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Galaxy Spectra assignment
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The textbook is rather weak when it
comes to observational properties like spectra – as budding young observers
you need to know more! |
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Find and download the galaxy spectra
templates of Kinney et al. (1996) – and read the paper! |
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Find and download the spectral
synthesis population models of Bruzual and Charlot. |
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“Fit” the elliptical template and one
spiral galaxy. |
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Show some plots indicating how
broad-band colors change with redshift assuming not evolution (up to z=2). |
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Write up your results like you would
for publication with clarity, citations, etc. |
Gravitational Lensing by
Clusters
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Mass bends space and hence light paths
(Einstein 1915; General relativity). |
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Angular deflection by point mass is: |
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Where p is the “collision parameter.” |
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What happens when p goes to zero? |
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Gravitational Lensing by
Clusters
Gravitational Lensing by
Clusters
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Previous derivation assumes Euclidean
geometry (which WMAP says is OK!).
Still OK if the distances are angular diameter distances (chapter 5). |
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Expressing the result in physical
terms: |
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So, what is the typical size for
clusters? |
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Gravitational Lensing by
Clusters
Gravitational Lensing by
Clusters
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OK, but clusters are not point sources. |
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See discussion on P. 96-97. |
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For our isothermal gas sphere can
derive the result that: |
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Gravitational Lensing by
Clusters
Gravitational Lensing by
Galaxies
Gravitational Lensing by
Galaxies
Forms of Dark Matter???
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We’re certain it is present. |
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Some is baryonic. |
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More is non-baryonic. |
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Baryonic Dark Matter
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Protons, Neutrons, electrons (include
black holes here too). |
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Text example of bricks (yes bricks!). |
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Brown dwarfs and the like. |
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BB nucleosynthesis constrains baryons
to less than 0.036 h-2 of closure density. |
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Baryonic Dark Matter
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Black holes constrained by lensing
effects (or lack thereof). |
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MACHOs (Alcock et al. 1993): |
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Baryonic Dark Matter
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MACHOs: |
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http://www.owlnet.rice.edu/~spac250/coco/spac.html |
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MACHOs are rather massive, around half
a solar mass, and can contribute up to half of the dark halo mass. |
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White dwarfs??? |
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Non-Baryonic Dark Matter
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I’m no expert on this stuff (and in
some sense NO ONE is). Particle
physicists play in this area more than astronomers. |
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Leading candidates include |
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Axions.
Cold, low mass, avoid strong CP violation. |
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Neutrinos. Hot, low mass (getting better constrained),
lots of them. SN helps. |
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WIMPs.
Gravitino, photino, etc. |
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Mirror Matter. May use in my next novel. |
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