Hello,
In Nelson+ (2018a), a 3d radial restriction of at most 30 pkpc is imposed when calculating galaxy magnitude, but this restriction is not mentioned in the Data Specification page (although there is a rad30pkpc in the name of dataset). I wonder whether this restriction is imposed to the final catalog. And it seems like that this cut off is only applied to high mass galaxies in Nelson+ (2018a), is that true?
Dylan Nelson
11 Feb '22
Dear Furen,
You are correct, "Model C" of Nelson+18 includes an aperture restriction of 30pkpc, so this is also the case for the supplementary data catalog.
This makes sense for most observational comparisons. It is applied to all galaxies. For low-mass galaxies, it won't change anything, since there are no stars so distant (galaxy sizes are too small). It will impact only the high-mass end (e.g. M* > 1e10.8 Msun or so).
I will update the docs to add this clarification, thanks!
Thank you. Is the 30 pkpc with respect to the SubhaloCM in subhalo catalog, or some luminosity center? It seems like SubhaloCM deviate from the luminosity center for a substantial distance for lots of galaxies.
Dylan Nelson
11 Feb '22
We almost always use SubhaloPos (which is equal to GroupPos for centrals), as it represents the position of the gravitational potential minimum, and doesn't suffer from this issue you point out, e.g. that the center of mass can be biased due to asymmetric distant mass e.g. during a merger.
Hello,
In Nelson+ (2018a), a 3d radial restriction of at most 30 pkpc is imposed when calculating galaxy magnitude, but this restriction is not mentioned in the Data Specification page (although there is a rad30pkpc in the name of dataset). I wonder whether this restriction is imposed to the final catalog. And it seems like that this cut off is only applied to high mass galaxies in Nelson+ (2018a), is that true?
Dear Furen,
You are correct, "Model C" of Nelson+18 includes an aperture restriction of 30pkpc, so this is also the case for the supplementary data catalog.
This makes sense for most observational comparisons. It is applied to all galaxies. For low-mass galaxies, it won't change anything, since there are no stars so distant (galaxy sizes are too small). It will impact only the high-mass end (e.g. M* > 1e10.8 Msun or so).
I will update the docs to add this clarification, thanks!
Thank you. Is the 30 pkpc with respect to the SubhaloCM in subhalo catalog, or some luminosity center? It seems like SubhaloCM deviate from the luminosity center for a substantial distance for lots of galaxies.
We almost always use
SubhaloPos(which is equal toGroupPosfor centrals), as it represents the position of the gravitational potential minimum, and doesn't suffer from this issue you point out, e.g. that the center of mass can be biased due to asymmetric distant mass e.g. during a merger.