Hello, I drawed a M_tot vs M_stellar plot of subhalos at snap=99 (z=0), in TNG-100-1, and it was like below:
There were several things that I found unusual:
Red dotted line denotes the baryonic mass resolution, 9.4e5 / h. However, there are many galaxies which has stellar mass below the limit. How can this be possible?
I found that many galaxies below M_tot < 1e10, are concentrated at high-stellar mass end (the deep blue line-like thing). I wonder why this kind of distribution happens.
May you provide the brief answers for those questions?
Thank you,
Jaewon Choi
Dylan Nelson
30 Jun
First, the existence of the horizontal feature is a clear marker of the resolution limit of the simulation. Certainly, for this simulation, you would never want to consider M_tot < 10.5 or so, as you can see even the pink trend line becomes wrong (certainly the outliers and scatter become problematic even earlier).
Second, I see that it is possible to have stellar mass less than the baryonic mass resolution. Presumably all of these subhalos just have 1 star particle (you can check). Then remember that star particles lose mass over time due to stellar evolution and the resulting mass return. A general rule of thumb is that a stellar population can lose ~50% of its entire mass over a Hubble time, so this would allow the "galaxy stellar mass" (albeit very poorly resolved) to be slightly belong the baryon mass resolution.
As to the stripe feature in the upper left, I would first again say they should (always) be excluded, as they are below the halo mass limit where things are well resolved. Other than that, we would need to look at some examples to see why they form that relation.
Dear Dr. Nelson,
Hello, I drawed a M_tot vs M_stellar plot of subhalos at snap=99 (z=0), in TNG-100-1, and it was like below:
There were several things that I found unusual:
May you provide the brief answers for those questions?
Thank you,
Jaewon Choi
First, the existence of the horizontal feature is a clear marker of the resolution limit of the simulation. Certainly, for this simulation, you would never want to consider
M_tot < 10.5or so, as you can see even the pink trend line becomes wrong (certainly the outliers and scatter become problematic even earlier).Second, I see that it is possible to have stellar mass less than the baryonic mass resolution. Presumably all of these subhalos just have 1 star particle (you can check). Then remember that star particles lose mass over time due to stellar evolution and the resulting mass return. A general rule of thumb is that a stellar population can lose ~50% of its entire mass over a Hubble time, so this would allow the "galaxy stellar mass" (albeit very poorly resolved) to be slightly belong the baryon mass resolution.
As to the stripe feature in the upper left, I would first again say they should (always) be excluded, as they are below the halo mass limit where things are well resolved. Other than that, we would need to look at some examples to see why they form that relation.
Thank you!