The TNG-Cluster catalog includes fields peakoffset_xray_x and the like. The description in the HDF5 file says that it is the offset from the X-ray peak in log pkpc; however, this is somewhat ambiguous as (presumably), the offset may be either positive or negative in either direction while also being either larger or smaller than a pkpc. It also isn't clear what the offset is relative to; the group COM, the potential minimum, etc.
The X-ray peak (or SZ signal/y-parameter peak) is found using a 'shrinking circle' (of light) algorithm, while the galaxy position is SubhaloPos
The X-ray values use the 0.5-2.0 keV X-ray emission, within a map spanning +/- r500, with a projection depth of 3r200c..
The values are only positive, i.e. this should more properly be called "magnitude of the offset".
The "pkpc" simply refers to the units, values can be >1 pkpc or <1 pkpc (when the logged values are negative), as you say.
Eliza Diggins
18 Aug
Hey Dylan,
Thanks for getting back in touch. That all makes sense - the only point I'd like clarification on: If an offset is reported as (say) -0.5 log pkpc, should that be interpreted as - 10^0.5 pkpc or as 10^-0.5 pkpc? I am assuming the latter (to allow for negative offsets); however, in that case, it seems we cannot represent offsets less than 1 pkpc?
Dylan Nelson
20 Aug
I have edited the above answer - thanks for clarifying this.
The TNG-Cluster catalog includes fields
peakoffset_xray_xand the like. The description in the HDF5 file says that it is the offset from the X-ray peak in log pkpc; however, this is somewhat ambiguous as (presumably), the offset may be either positive or negative in either direction while also being either larger or smaller than a pkpc. It also isn't clear what the offset is relative to; the group COM, the potential minimum, etc.Can someone clarify the convention?
The X-ray peak (or SZ signal/y-parameter peak) is found using a 'shrinking circle' (of light) algorithm, while the galaxy position is
SubhaloPosThe X-ray values use the 0.5-2.0 keV X-ray emission, within a map spanning +/- r500, with a projection depth of 3r200c..
The values are only positive, i.e. this should more properly be called "magnitude of the offset".
The "pkpc" simply refers to the units, values can be >1 pkpc or <1 pkpc (when the logged values are negative), as you say.
Hey Dylan,
Thanks for getting back in touch. That all makes sense - the only point I'd like clarification on: If an offset is reported as (say) -0.5 log pkpc, should that be interpreted as - 10^0.5 pkpc or as 10^-0.5 pkpc? I am assuming the latter (to allow for negative offsets); however, in that case, it seems we cannot represent offsets less than 1 pkpc?
I have edited the above answer - thanks for clarifying this.