Confusion with conversion for the Hubble Constant

[Radiohannah]

Hello!

I want to get my data in terms of h₇₀ ^-1

Sometimes the estimates are in terms of h₅₀ or h₇₀, and I know how to convert those just fine.

However, sometimes they give H₀ = 100 h Mpc^-1 kms^-1 instead...

My question is, what is this in terms of h?

I know that the relation is

h = H₀ / 100 kms^-1 Mpc^-1

So, would I be right in thinking that it is as straight forward as h=H₀ for this specific case or am I being silly

Thankyou! :)

 

[cepheid]

So, would I be right in thinking that it is as straight forward as h=H₀ for this specific case

Absolutely not, because as you yourself have noted, h is actually equal to:

h = H₀ / 100 kms^-1 Mpc^-1

 

[Radiohannah]

Hah. I totally figured it out.

I was confused originally because I did use that equation, but got h=h

I thought h=70, rather than H₀ = 70

:(

So is 'h' basically just a fraction then? I understand now.

Gah. Thanks

 

[cepheid]

Hah. I totally figured it out.

I was confused originally because I did use that equation, but got h=h

Which is true! But not that informative I guess.

I thought h=70, rather than H₀ = 70

Right, so that's where your misconception was. That value of H₀ corresponds to h = 0.7

So is 'h' basically just a fraction then? I understand now.

Exactly, you got it now! The parameter h is a dimensionless version of the Hubble constant. It is H₀ normalized to a reference value of 100 km s^-1 Mpc^-1. So h is a fraction...it tells you the ratio of H₀ to that reference value.