Questions for Illustris simulation data and galaxy main sequence

Yunwoo Nam
  • 26 Nov '19

I'm a student with a major in astronomy in college in Korea

First. I want to plot galaxy main sequence according to z

스크린샷 2019-11-26 오후 8.00.42.png

this code is alright? I want to use stellar mass. so, I think
mass_msun = subhalos['SubhaloMassInRadType'][4]
but this code is dimension error. why?

Second I want to plot starformation density rate according to z
I think each galaxy main sequence plot data is list for.m
And My plane is sum all star formation rate according to z
and plotting starformation density rate

how to sum of starformaiton rate density. this data is list form? and how can I handle it

for example

스크린샷 2019-11-26 오후 8.11.08.png

Sorry for my poor English and Thank you

Dylan Nelson
  • 26 Nov '19

Hi Yunwoo,

Your code for mass_msun seems ok, what is the error? What is subhalos (how do you load it)?

For SFRD(z), you could load SubhaloSFR (one number per galaxy) at one snapshot, and sum this numpy array. Then loop over all snapshots, e.g.

sfrd = []
snaps = np.arange(10,100)

for snap in snaps:
    sfr_galaxies = il.groupcat.loadSubhalos(fields=['SubhaloSFR'])
    sfrd.append( sfr_galaxies.sum() )

ax.plot( snaps, sfrd )
Yunwoo Nam
  • 26 Nov '19

my new mass code : mass_msun = subhalos['SubhaloMassInRadType'][:,4] * 1e10 / 0.704

I understand ['SubhaloMassInRadType'][4] is STARS & WIND PARTICLES
If ['SubhaloMassInRadType'][4] is stellar mass, multiply 1e10 / 0.704 should not be multiplied.

Your code means I needs to download all snapshots?
How can I all snapshots 135 ~ 0 at once ??

Dylan Nelson
  • 26 Nov '19


SubhaloMassInRadType[4] is a mass of only stars, it does not contain wind.

It requires a unit conversion to obtain solar masses, so you must multiply by (1e10/0.704).

Second: I assumed that you have already downloaded all group catalogs. You will have to download at least the Star Formation Rate field for every snapshot, yes.

Yunwoo Nam
  • 27 Nov '19

Thank you for your kind reply.

I downloaded only Illustris-3, FoF & Subfind group cat file( z 135 ~ 10, step 10 ). My notebook's memory is not enough to save snapshot files and
I will plane to use FoF & Subfind group cat. Is it hard to get to SFRD(z) only use FoF & Subfind group cat?

I think each 'SubhaloMassInRadType[4]' is list data so I sum 'SubhaloMassInRadType[4]' data
This value (Sum of starformation rate) is not SFRD? because we know z

Dylan Nelson
  • 29 Nov '19


There are many possible definitions of SFRD. If you sum from the FoF+Subfind catalog, then you will obtain a SFRD which includes SFR within those objects.

If you sub-select a fraction of the FoF+Subfind catalog, then you will obtain a SFRD which includes, similarly, only the SFR within that subset of objects.

The units of SubhaloSFR are solar masses per year. If you divide by the volume, you obtain a SFRD value.

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