Hubble diagram or magnitude

Hubble diagram or magnitude - Hubble diagram or...

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Hubble diagram or magnitude-redshift test. Assume we have a set of galaxies with unchanging and known intrinsic brightness. It has been popular to take radio galaxies or third- brightest cluster members for this; radio galaxies in the K-band are especially well-behaved. At small redshifts, the Hubble expansion makes the magnitude-log z relation linear, with some scatter due to galaxy properties and our ignorance of just how to select a perfectly uniform set of galaxies. At high z , the relation may curve for various q 0 . To see how, consider various measures of distance to an object of redshift z . The proper distance is that traversed by a photon in its own frame from there and then to here and now, which is to say D P = 1/ c × light travel time. The luminosity distance is that which makes the inverse-square law work as it does in a flat universe: luminosity/flux = 4 π D L ². Finally, the angular diameter distance is that for which the linear size- angular size relation has its familiar small-angle form θ = length/
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Hubble diagram or magnitude - Hubble diagram or...

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