For 10 points, name this proportionality constant which relates recessional velocity or redshift to distance.
The physical baryon density is equal to the baryon density multiplied by the reduced form of this value, and measures of this value are subject to the Malmquist bias. This value is equal everywhere for a given co-moving time, and taking the speed of light divided by this value gives the radius outside of which objects are moving at greater than the speed of light relative to the observer. Three times the square of this value divided by 8 pi G gives the critical density, and it can be defined by taking the quotient of the time derivative of the scale factor with the scale factor. This value, which shows up to the second power on the left side of the Friedman equation, can also be used to define the deceleration parameter. The reciprocal of this value is the age of the universe, and it is approximately 71.0 kilometers per second per megaparsec according to WMAP. For 10 points, name this proportionality constant which relates recessional velocity or redshift to distance.
The physical baryon density is equal to the baryon density multiplied by the reduced form of this value, and measures of this value are subject to the Malmquist bias.
Hubble constant or parameter