Public Data Access Overview / Discussion Forum

Dear Dylan,

I am trying to calculate the radial density profile of H1 and H2 of subhaloes of the galaxy cluster using the TNG50-1. I have selected the subhalos based on the given minimum mass (> 10^8.5 solar mass) and each has a minimum of 100 gas particles. I am using the available Molecular and atomic hydrogen (HI+H2) galaxy contents catalogue for TNG50-1. On the website this is a description of the catalogue :

Following the last row of the above table, this is how I am calculating the HI radial density profile.
I am using the 2d projection and assuming the S14 model.

HI_radial_density = (profile_gas_rho_2d) x (profile_f_neutral_H_2d) x (1-profile_f_mol_S14_2d)

I guess this should give me the HI radial density profile (in units of Msun/Kpc3). Is this the correct way ?, If not how could I obtain the HI density profile?
Here I have plotted the HI radial density as a function of profile bins for one of the halo(in kpcs third row in the above screenshot).

Here the red curve is for the central halo and the black curve denotes the subhaloes. I don't understand why the central halo shows an offset in the radial bin.
Thank you for your response in advance.

Regards
Avinash

Dear all,

Any suggestions/help regarding the above query?
Thanks in advance for the response.

Regards
Avinash

Hi Avinash,

your calculation looks correct, but the result will be in Msun/kpc^2 (rather than kpc^3) because you're using 2d profiles. I admit that that could be clearer in the documentation. You can test your results by multiplying the profiles with profile_bins_area, which should give you the total mass in Msun in each bin; when you add those up, you should get very close to the total HI mass in the galaxy. You can do the same for 3D profiles and profile_bins_volume to double-check.

The S14 model is probably the least reliable of the models (it was rather experimental); my recommendation is to compute your results for all models and to see how much they vary.

All the best

Benedikt

Dear Benedikt,

Many thanks for your detailed response. I also thought that the profile in 2d should have units Msun/kpc2 and not kpc^3. Thanks for clarifying this. Sorry for bothering you once again. I would appreciate it if you could further help me a bit.

As you suggested, I followed your suggestions and tried to calculate the total HI mass for different models from the radial profile for the 2d profile. i.e.

assuming a 2d profile and suppose GD14 model (or any other model) :

profile_HI         =  np.array(pro_gas_den*pro_f_neuH*(1-pro_f_molH)     [calling it equ (1)]
Total_mass_HI = np.sum(profile_HI*pro_bin_area)                                   [calling it equ(2)]

And here, Total_mass_HI (equ. 2) for a given subhalo should equal the total HI mass obtained from the HI catalogue (above table) for different models.

However, I am not getting very close values for the two measurements. You said that the two values should be very close. How close? I expected that values would be one to one, but I found that total HI values from the model [almost from all of GD14, GK11, K13] on average is 1.5 times the value obtained from equ. (2). Do you think I could see such an offset? Or maybe I have miscalculated something. Let me know what you think. I checked my scripts and could not find any mistakes, so I thought to ask you. :)

Here I show some plots for HI mass and radial profiles subhalos of primary halos.
In the top left plot, I have plotted the ratio between HI mass from the models to calculated HI mass from the radial profiles for the respective models. The top right plot just shows the ratio of HI mass from different models. I just wanted to check which models are more consistent with each other. I found that K13/GD14 gives almost the same values.
The bottom two plots show the HI radial plots of subhalos and halo for different models.

Sorry for this long message. Please let me know if something is not clear. I am looking forward to your suggestions/ideas or something I am missing.

Regards
Avinash

It's a little hard to read equation 1 cause the forum converted underscores I guess... but it looks right. One check: are you using the individual profile_bin_area for each galaxy? They differ because the radial bins differ.

Your HI mass from the profiles can be slightly lower than the total in case there is HI outside the radius of the largest profile bin. But the differences shouldn't be as large as what you see. Perhaps you can start by reproducing the total neutral mass, which is given in the files?

Dear Benedikt,

Sorry for the late follow-up. I used the following equations :

profile_HI         =  np.array(pro_gas_den*pro_f_neuH*(1-pro_f_molH)     [calling it equ (1)]
Total_mass_HI = np.sum(profile_HI*pro_bin_area)                                   [calling it equ(2)]

In the HI and H2 catalogue, for each subhalo, there is a given profile bins area, and I am using individual ones. Should I use the same bin area?
As you suggested, I calculated the neutral mass (I guess you meant neutral H mass) and for it, I get a very similar mass, calculated from the radial profile and from the catalogue. I calculated neutral H mass as follows:

prof_neutral_Hydrogen = (pro_gas_den_2d)*(pro_f_neuH_2d)
Neutral_H_mass          =  sum(prof_neutral_Hydrogen*bins_area_2d).  [calling it Neu.H Mass[calc] ]

I have plotted the ratio of Neu.H Mass[calc]/neutral H mass from the catalogue, and you can see a 1 to 1 ratio.
See the top right subplot in the following plot :

I see the same results for other selected halos. I don't understand why I am getting such a huge difference for HI mass. Thanks in advance for your suggestions.

Regards
Avinash

Indeed, it is correct to use the bin area for each individual halo; they vary because the radial bins vary.

I'm not sure I understand what's plotted with the dots in the panels above: are those from a single subhalo or from many subhaloes? Also, what do you mean by "all subhalos" and "central Halo" in this context?