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how to get the bulge(star) mass or ratio between bulge(star) mass and total(star) mass?

wang lei
  • 2
  • 16 Jan

hi professor:
I want to use the illustris-3 data to calculate the ratio between bulge(stars) mass and total(stars) mass of galaxy for filtering massive spiral galaxys ,but i can not get directly the bulge mass from the data.if i want to use the algorithm as the page shows:epsilon=Jz/J(E); how could i get the J(E) from the data? otherwise,can i get the epsilon directly from the Supplementary Data? And i did not find the function to read the a member of the Supplementary Data Catalogs in the illustris_python file,could you give me a example ? Expecting your answer.
Thank you

Dylan Nelson
  • 17 Jan

HI Wang Lei,

You're right there is no "bulge stellar mass" measurement available already in the group catalogs. (There is a "total stellar mass").

So you would want to calculate this, from the star particles themselves, according to whatever definition you like.

As you point out, something using the epsilon circularities could be used, but this is fairly complicated. I would suggest you start with a simple radial aperture definition, e.g. define the bulge as "all particles within 3 pkpc of the galaxy center".

wang lei
  • 1
  • 19 Jan

if i want the use the file 'stellar_circle.hdf5' to read out the SubfindID and CircAboveFrac as two arrays respectively .There is two questions for me:Whether SubfindID[ i ] correspond to CircAboveFrac[ i ] ? if it is true; How shound us use a value of SubfindID[ 1 ] to uniquely match the subhalo which has the value of CircAboveFrac[ 1 ]?

Dylan Nelson
  • 19 Jan

Hi Wang Lei,

The value CircAboveFrac[i] corresponds to SubhaloID[i] yes. Then you need to use SubhaloID[i] to determine which subhalo in the group catalogs of the simulation this value corresponds to. E.g., to get its total mass, it would then be SubhaloMass[ SubhaloID[i] ].

wang lei
  • 1
  • 19 Jan

but professor,the file 'stellar_circle.hdf5' contain SubfindID rather than SubhaloID

Dylan Nelson
  • 19 Jan

We use these names interchangeably, they are the same.

wang lei
  • 2
  • 20 Jan

ok,thankyou

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