I am working on a project related to tSZ effect. As part of my work, I need to obtain radial pressure profiles of galaxies with stellar mass in the range 10^9.5 to 10^11.5, upto a few Mpc. I was wondering how one would go about calculating this, in particular pressure profile relevant to the tSZ effect.
Also, in one of your data release papers, you mention that "the predictions for the Sunyaev-Zel’dovich
signals from Illustris clusters are not reliable". Does it apply to my case where I am interested calculating pressure profiles for galaxies with stellar masses in a particular range.
If you need radial profiles to several Mpc, then this requires particles outside of the halos. To do this, you will need to download the full snapshot at the redshift(s) you are interested in. Although, you can download just the few fields of the gas that you'll need (i.e. following task #11).
Roughly, I would just calculate the pressure for every gas cell, then loop over galaxies of interest, and for each, calculate the (periodic) radial distance to every gas cell, then bin the pressure in radial bins (mass-weighted would be good) e.g. with binned_statistic.
Because of the actions of the BH radio-mode feedback, we had issues in Illustris related to the gas contents of halos (Mstar > 11.0 or so). This you will also see in the tSZ effect. It depends on what you want to do: if you want to use Illustris as some sort of calibrator or assessment of observational biases or accuracy, I would suggest against this. However, if you want to make a comparison of the data against the simulation to assess the level of (dis)agreement in the model, this would be ok. I suspect (although no one ever looked specifically at this) that the tSZ effects you see will be below the observational constraints, at least within halos (<r500 or <200).
utkarsh giri
17 Nov '17
Hi Dylan,
Thank you so much for your response.
There was something more I wanted to ask you. If I understand it correctly, the pressure profile needed in tSZ is not the ususal gas pressure profile but rather its that of hot electrons which is a function of electron number density and electron temperature. How would I go about calculating this electron pressure from the usual gas pressure? And are the gas and electron temperatures the same or are they different ?
Thank you again!
Regards,
Utkarsh
Dylan Nelson
18 Nov '17
Hi Utkarsh,
As far as I know, what you say is all correct. I would look at some papers which have computed the y-parameter from hydro simulations in the past, e.g. this one. We have n_e and you want to use this. But we don't have a different T_e, I guess the typical assumption is that this is equal to T_gas.
Hi,
I am working on a project related to tSZ effect. As part of my work, I need to obtain radial pressure profiles of galaxies with stellar mass in the range 10^9.5 to 10^11.5, upto a few Mpc. I was wondering how one would go about calculating this, in particular pressure profile relevant to the tSZ effect.
Also, in one of your data release papers, you mention that "the predictions for the Sunyaev-Zel’dovich signals from Illustris clusters are not reliable". Does it apply to my case where I am interested calculating pressure profiles for galaxies with stellar masses in a particular range.
Thank you!
Hi Utkarsh,
If you need radial profiles to several Mpc, then this requires particles outside of the halos. To do this, you will need to download the full snapshot at the redshift(s) you are interested in. Although, you can download just the few fields of the gas that you'll need (i.e. following task #11).
Roughly, I would just calculate the pressure for every gas cell, then loop over galaxies of interest, and for each, calculate the (periodic) radial distance to every gas cell, then bin the pressure in radial bins (mass-weighted would be good) e.g. with binned_statistic.
Because of the actions of the BH radio-mode feedback, we had issues in Illustris related to the gas contents of halos (Mstar > 11.0 or so). This you will also see in the tSZ effect. It depends on what you want to do: if you want to use Illustris as some sort of calibrator or assessment of observational biases or accuracy, I would suggest against this. However, if you want to make a comparison of the data against the simulation to assess the level of (dis)agreement in the model, this would be ok. I suspect (although no one ever looked specifically at this) that the tSZ effects you see will be below the observational constraints, at least within halos (<r500 or <200).
Hi Dylan,
Thank you so much for your response.
There was something more I wanted to ask you. If I understand it correctly, the pressure profile needed in tSZ is not the ususal gas pressure profile but rather its that of hot electrons which is a function of electron number density and electron temperature. How would I go about calculating this electron pressure from the usual gas pressure? And are the gas and electron temperatures the same or are they different ?
Thank you again!
Regards, Utkarsh
Hi Utkarsh,
As far as I know, what you say is all correct. I would look at some papers which have computed the y-parameter from hydro simulations in the past, e.g. this one. We have
n_eand you want to use this. But we don't have a differentT_e, I guess the typical assumption is that this is equal toT_gas.