In the documentation, it says that the SubhaloMassType field in the subhalo catalog represents the "Total mass of all member particle/cells which are bound to this Subhalo, separated by type". So for example, this field would give me the mass of all gas cells bound to a given subhalo. But is there a physical radius within which this is calculated? If I found that a given subhalo has, say a gas mass of 1e9, is there a defined radius from the center of the subhalo within which this is true?

Similarly, GroupMassType lists the "Sum of the individual masses of every particle/cell, split into the six different types, in this group". Is the gas mass then calculated within, say the virial radius, or some other radius from the center of a group?

Thanks,
Farhan

Dylan Nelson

11 Oct '22

Halos and subhalos will both have a maximum radius, within which all their members are found. This value is not stored anywhere, but you could calculate it.

However, such a radius is not used in their identification. Instead, halos are based on the friends-of-friends algorithm, while subhalos are based on the physical gravitational unbinding algorithm in Subfind. Neither uses a radius.

Farhanul Hasan

12 Oct '22

Thank you. So if I wanted to calculate this maximum radius, would I have to look at particle data also?

Dylan Nelson

13 Oct '22

Yes that's correct, but it is a fairly quick calculation, since you only need to consider the particles belonging to each (sub)halo, to calculate this radius.

Hi,

In the documentation, it says that the

SubhaloMassTypefield in the subhalo catalog represents the "Total mass of all member particle/cells which are bound to this Subhalo, separated by type". So for example, this field would give me the mass of all gas cells bound to a given subhalo. But is there a physical radius within which this is calculated? If I found that a given subhalo has, say a gas mass of 1e9, is there a defined radius from the center of the subhalo within which this is true?Similarly,

GroupMassTypelists the "Sum of the individual masses of every particle/cell, split into the six different types, in this group". Is the gas mass then calculated within, say the virial radius, or some other radius from the center of a group?Thanks,

Farhan

Halos and subhalos will both have a maximum radius, within which all their members are found. This value is not stored anywhere, but you could calculate it.

However, such a radius is not used in their identification. Instead, halos are based on the friends-of-friends algorithm, while subhalos are based on the physical gravitational unbinding algorithm in Subfind. Neither uses a radius.

Thank you. So if I wanted to calculate this maximum radius, would I have to look at particle data also?

Yes that's correct, but it is a fairly quick calculation, since you only need to consider the particles belonging to each (sub)halo, to calculate this radius.