What's the Dark Matter Density in Universe?

[RyanH42]

In wikipedia says Physical baryon density: $Ω_bh^2=0.02230±0.00014$ and
Physical dark matter density:$Ω_ch^2=0.1188±0.0010$
Matter density:$Ω_m=0.3089±0.0062$
so If we collect baryonic matter density and dark matter density we cannot get matter density

https://en.wikipedia.org/wiki/Lambda-CDM_model

 

[Orodruin]

Notice the appearance of h^2 in the values you quote for DM and baryon abundances.

 

[RyanH42]

Lets suppose I want to calculate dark matter mass/baryonic matter mass ? What should I do

 

[RyanH42]

Whats the meaning of $h^2$ in here

 

[ruarimac]

You ignore the h² which tells you the result scales with H₀. Substituting h~0.7 you get the correct results.

 

[RyanH42]

I got it thanks.

 

[Orodruin]

$h$ is the Hubble constant H today divided by 100, i.e., $h \simeq 0.6780\pm 0.0077$ (PLANCK 2013).

 

[RyanH42]

I add them and I get 0.287 not 0.3089

 

[Orodruin]

I add them and I get 0.287 not 0.3089

What did you use for $h$? Using 0.678 gives me 0.3069.

 

[RyanH42]

I used 0.49

 

[Orodruin]

You mean you used $h^2 = 0.49$? For $h = 0.678$ you will get $h^2 = 0,46$. You should however note that $h$ also comes with an error. The reason that the abundance is given in $\Omega h^2$ is that this quantity is better bounded.

 

[RyanH42]

Yeah I used h²=0.49

 

[Chalnoth]

To get the right answer, you have to use the value of $h$ that was used to measure those parameters. As $h = H_0 / 100 km/s/Mpc$, and $H_0 = 67.74 km/s/Mpc$ in that data set, $h = 0.6774$. Use that number, and it will work. There will be some small differences, due to the fact that these numbers aren't published with full accuracy. But it'll be well within the errors.

 

[RyanH42]

To get the right answer, you have to use the value of $h$ that was used to measure those parameters. As $h = H_0 / 100 km/s/Mpc$, and $H_0 = 67.74 km/s/Mpc$ in that data set, $h = 0.6774$. Use that number, and it will work. There will be some small differences, due to the fact that these numbers aren't published with full accuracy. But it'll be well within the errors.

Finally.Thank you