12/28/2023 0 Comments Redshift equation zOn this plot the red curve is the recessional velocity when the light was emmited, and the brown curve when the light reaches the observer (as you can see at z=10 there is already a difference of a factor ≈2, and like the previous speakers already mentioned c is at z≈1.5Īt z≈1.9 the curves cross and it was the same recessional velocity then as it is now again, so objects with z1. Cosmic age t(z): the age of the universe at that redshift Let's calculate this for one model: Omega M 1, Lambda0. Slightly less reliable are Lyman-break redshifts, the highest of which is the lensed galaxy A1689-zD1 at a redshift z 7.5 and the next highest being z 7.0. Lookback time t L (z): How far back in time we are looking. Thismeansthateithertheuniverseisin¯nitelyold, oritstartedatsome¯nitescalefactorandtherefore cannot getarbitrarilylarge. The previous record was held by UDFy-38135539 at a redshift of z 8.6, corresponding to 600 million years after the Big Bang. But holdon Thissaysthatif yougotoanarbitrarilylargeredshiftz, yougettoanarbitrarilylargelookbacktimetL. The factor 1 + z is often called the stretch factor. where emit is the emitted wavelength, 0 is the received wavelength (once again using the subscript '0' to represent 'today'), and z is the redshift. The higher the redshift, the larger the difference (for example, the last scattering surface with z=1089 had a recessional velocity of 63c when it emmited its light, and now has around 3c, since the Hubble parameter was higher in the past). 0(1+z0)12¤ Since¤1, thissays that tLln(1+z)H0. Redshift z is the fraction by which the wavelength increases. One is calculated by the present distance times the Hubble constant, and the other by multiplying the former distance with the Hubble parameter at that time. Calculate the average redshift value, then find the velocity of the quasar in km/s using the formula z v/c, where v is the velocity, c is the speed of light, and z is the redshift. If you have a redshift associated with a comoving object you get two answers one for the recessional velocity it had when it emmited its light, and one for the recessional velocity it has now when its light reaches you.
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