The angular diameter

The angular diameter - The angular diameter - redshift test...

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Unformatted text preview: The angular diameter - redshift test looks for a breakdown of the inversion relation between distance and angular diameter of some set of standard measuring rods (say galaxy isophotes or radio-galaxy lobe separations). Surface brightnesses must be corrected for dimming by (1+z) 4 due to expansion of space plus photon energy and arrival-time decreases. The form of this has been used as a test (the Tolman test) that redshifts really correspond to an expansion, and not to once-popular "tired-light" phenomena (Sandage and Perelmuter 1990 ApJ 350, 481; 361, 1; 1991 ApJ 370, 455, Wirth 1997 PASP 109, 344). Here again, one might have to deal with evolutionary effects in such objects as radio sources - have they always been the same size? At least with galaxy structures one has some control over how much dynamical evolution might have gone on. It is interesting that, for any given positive value of q , there exists a minimum in the ( z ) relation for any linear size; things at higher redshift look bigger again because they were quite nearby...
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The angular diameter - The angular diameter - redshift test...

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