Which volume should i use?

Lorenzo Cavallo
  • 18 May '23

I am sorry for the probably naive question.

Currently, I am using the data from TNG100-2 and I am trying to compute SFRD and SMF.

For the SFRD (in order to retrieve something similar to the MD+14) I dived the SFR by the comoving volume (i.e. 75 [h^-1Mpc]**3)

On the other side... when I compute the SMF I use the physical volume (i.e. 110 [Mpc] ** 3 )...

is it correct? And why?

Thanks in advance for your kind answers...


Dylan Nelson
  • 22 May '23

There is no right answer, you can use either the volume in physical or comoving units. In simulation papers you will often see "pMpc" or "cMpc" as the units, to make clear the distinction. Unfortunately in many papers it is never actually stated. If you are trying to compare to an observational result, you need to adopt the same definition, whatever that was.

There are some typical "conventions", but you should always double-check. For both the SMF and SFRD the normalization is usually "cMpc^3".

  • Page 1 of 1