How to identify subhalos containing well-formed galaxies?

Andrés Cardona
  • 26 Oct '19

Hi.

I'm trying to study the morphology of the galaxies in Illustris-1 at z=0.

I want to make sure that the subhaloes that I'm taking, have a well-formed galaxi inside them. How can I know this?

Tnaks,

Dylan Nelson
  • 26 Oct '19

Hi Andres,

It depends perhaps what you mean by "well-formed". Do you want galaxies to satisfy some physical requirements, or numerical requirements?

Andrés Cardona
  • 29 Oct '19

Hi Dylan,

From documentation, there's ~4'400.000 subhalos in SUBFIND, but of them, only ~40.000 are refered to "galaxies"

My question is how to identificate those "galaxies.

Thanks for answer :)

Dylan Nelson
  • 29 Oct '19

Hi Andres,

In this case we mean the difference between a "galaxy" (which contains stars) and a "subhalo" (which is a dark matter object). All galaxies are subhalos, but not all subhalos are galaxies.

The minimal definition is SubhaloMassType[4] > 0, meaning that the stellar mass is nonzero.

A more stringent definition, which also excludes very small galaxies which are not going to be numerically well resolved, would be e.g. SubhaloLenType[4] > 100, meaning that the subhalo must have at least one hundred star particles.

Andrés Cardona
  • 29 Oct '19

Thank you Dylan.

This is really useful.

  • Page 1 of 1