gaitskell cmb polarization dasi recent results 021009 brown astro journal club rick gaitskell (brown...

Gaitskell

CMB PolarizationDASI Recent Results

021009 Brown Astro Journal Club

Rick Gaitskell (Brown University)

Brown APJC Oct 2002 Rick Gaitskell

Andy Warhol - Pop Artist 1960’s - “Exactly”

The pop artist Andy Warhol once approached me at a party and told me that he collected scientific journals, but he couldn't understand them.

He drifted away, then came back and said, "Do you mind if I ask you a question?…Why does science take so long?"

I said, "Mr. Warhol, when you do a picture of Marilyn Monroe, does it have to be exactly like her, as close to being her as you can make it?"

He said, "Oh no."

I said, "Well, in science it has to be exact, as EXACT as you can make it."

He looked at me with sympathy and said, "Isn't that terrible?"

Gerald M. Edelman Bright Air, Brilliant Fire (1992)


DASI


References - used for talk

• DASI Exp Results: Leitch et al. astro-ph/0209476• DASI Instrumentation Paper Kovac et al. astrop-ph/0209478• Animations of CMB l-power spectra: Angelica de Oliveira-

Costa Dependence on various cosmological parameters http://www.hep.upenn.edu/~angelica/polarization.html

• Pictures and some of slides taken from (COSMO-02 Conference: John Kovac)

http://astro.uchicago.edu/dasi/DASIPOL-science.pdf

• DASI Experimenta Site http://astro.uchicago.edu/dasi/

• “Polarization Primer”: Hu and White http://xxx.lanl.gov/abs/astro-ph/9706147

• Harvard - Journal Archive http://adswww.harvard.edu Rees’s original 1968 paper (ApJ 153 L1)

http://adsabs.harvard.edu/journals_service.html


Why is Polarization Important?

• CMB polarization is induced via Thomson scattering Occurs either at decoupling (or during a later epoch of

reionization). The level of polarization is linked to the local quadrupole

anisotropy of the incident radiation on the scattering eletrons, • Expected to be 1-10% of the amplitude of the temperature

anisotropies depending on the angular scale.

• CMB polarization is important for two reasons: Can substantially improve the accuracy with which parameters

are measured by breaking the degeneracy between certain parameter combinations

Offers an independent test of the basic assumptions that underlie the standard cosmological model.

• CMB field we make use of two scalar fields E and B that are independent of how the coordinate system is oriented,

Are related to the tensor field (Q,U) [Stokes parameters] by a non-local transformation.

• Scalar CMB fluctuations have been shown to generate only E-fluctuations, whereas gravity waves, CMB lensing and foregrounds generate both E and B.


DASI (2)

• 13-element interferometer measure temperature and polarization anisotropy of CMB l multipole range ~ 140–900 Horn separations 25 - 120 cm HEMT amplifiers running between 26-36GHz, in ten 1

GHz channels Operates from the NSF Amundsen-Scott South Pole

station

• Recent Results Data: Two 3.4 degree FWHM fields (separated by 1 hour

RA) run in 2001 and 2002, • Selected from 2000 scans

— Wish to avoid point sources— High galactic lattitude


• Astro-ph/0209478


Curvature

QuickTime™ and aGIF decompressorare needed to see this picture.


Baryon



Tensor



Questions Arising

• How is quadrapole generated by velocity flows, and how does it actually lead to E-polarization Try Rees, M J 1968 ApJ 153 L1

• How does one interpret visual examples of E-field and B-field, especially wrt to Curl = 0, and Curl ≠ 0

• Check how Sum and Difference cross-checks are performed

gaitskell cmb polarization dasi recent results 021009 brown astro journal club rick gaitskell (brown...

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