Public Data Access Overview / Discussion Forum

Hi there,

I am writing to ask some questions on looking for the mock image for a given halo. I am using sunpy to extract fits files from illustris database, so as is shown in the instruction, I need to input the subhaloID to specify the image. Say here is a Halo (haloID = 2), how could I find the FOF image of this halo? I assume that the subhaloID of the this image should be the subhaloID of the first subhalo of this halo, so I use the code below to read out the subhaloID :

GroupFirstSub = il.groupcat.loadHalos(basePath,135,fields=['GroupFirstSub'])

When HaloID=2, GroupFirstSub=1030. But sunpy can not find the image of subhalo-1030. I think I must misunderstand something. Could you please instruct me to figure it out?

PS: One more native question, "the SubfindDensity in dm class shows the the local total comoving mass density", the "total" means all the components ( dm+stars/wind+gas+.....), right? If I want to calculate the total density map of a halo, I can just load in the SubfindDensity then perform linear interpolation, do I understand right?

If you could help me out about these questions, I really appreciate it. Thank you so much!

All the best, Nan Li

Hi Nan Li,

• The mock images only exist for Illustris-1 (the highest resolution), and not for Illustris-2 or Illustris-3. It seems you were looking at Illustris-3, where HaloID=2 has GroupFirstSub=1030. In Illustris-1, Halo=2 has GroupFirstSub=30430, which you can view here in the galaxy observatory.
• Yes 'total' does mean all components. If you are wanting to make a 2D image of total density, I suppose this might work, although I've never tried this. You will still only have these density values at the positions of the individual particles, so you will need to distribute/smooth them onto a 2D image grid.

Let me know if I can clarify anything further

Hi Dylan,

Thank you so much for your reply, it is pretty clear to me now, and extremely helpful. really appreciate it.

All the best, Nan Li