PDA

View Full Version : Redshift luminosity relation



john hunter
2006-Jul-31, 11:53 AM
This question is about the redshift-luminosity relation, which has been used to decide about the value of q(z), the deceleration parameter. Its being discussed in ATM 'How good are the best alternatives to Big Bang theory'.


In textbooks l = [LH(0)^2/4*pi*c^2*z^2]*(1+(q-1)z+........)

l = apparent luminosity
L= intrinsic luminosity

Does anyone know the next term in the ........??

Thanks,

John Hunter.

Peter Wilson
2006-Aug-01, 10:11 PM
Yes

john hunter
2006-Aug-02, 10:18 AM
Dear Peter,

Do you know it? If so what is it please?

John Hunter.

Tim Thompson
2006-Aug-05, 05:32 AM
I don't have my handy-dandy formula monsters around home But, see
Corrections in the Luminosity-Redshift Relations of the Homogeneous Fried-Mann Models (http://adsabs.harvard.edu/abs/1969ApJ...155...89K), R. Kantowski, Astrophysical Journal 155: 89, January 1969. You can download & examine the papre in PDF. I doubt the formula has changed much, if at all. It involves an infinite series which I will not try to reproduce entirely, but here is the part of equation 55, page 100, which is linear in q0.

Lbol = (LH02/4*pi*z2c2) * {1 + (q0-1)z + [ (1/4)*(q0-3)(q0-1) - q0*(rhoi/rhof) ]*z2 + ... }

Where rhof is a Freidman mass density = -(d2R/dT2)/R and rhoi is an integrated mass density defined as Integralinf0 n(m)mdm, and Lbol is a bolometric luminosity, which is the total luminosity, as integrated over all wavelengths, from 0 to infinity.

I hope this looks like fun.

john hunter
2006-Aug-05, 11:06 AM
Dear Tim,

Its good to get a helpful response.

The analysis assumes lambda = 0, but even with positive lambda, the result is probably similar. The question was posted see whether the people who have decided the q(z) function, have come to false conclusions, by using an incorrect redshift-luminosity relation.

Thanks very much.

John Hunter.

Tim Thompson
2006-Aug-05, 04:08 PM
The question was posted see whether the people who have decided the q(z) function, have come to false conclusions, by using an incorrect redshift-luminosity relation.
Whether or not the relation is correct is entirely model dependent. The only way to determine the true luminosity is to know the true distance, and that is entirely dependent on the cosmological model. So correctness, in this case, depends on context, the context being the specific cosmological model used for distance determination.