Description
For cluster predictions, the excess surface density ΔΣ is a weak-lensing quantity that depends on cosmology because it is measured using distances, while the tangential shear γₜ is cosmology-independent as it is measured in angles.
The relevant equations are in arXiv:2107.10857.
Problem: we need to implement tangential shear (γₜ) support in TXPipe and coordinate with SACC.
This issue focuses on the TXPipe data implementation and SACC coordination.
Subproblems
To implement ΔΣ, we need individual redshifts for each source galaxy (to compute distances using cosmology).
For γₜ, since it is an angular measurement, we are not restricted to this:
- We can use per-galaxy redshift PDF and select the mode or mean
- We can use true or median values
- We can also use the distribution of source galaxies per redshift, N(z), as done in 3×2pt analyses
The current TXPipe options (in master) are:
pdf / mean / true / median.
We need to implement all these options plus N(z) for γₜ and test them.
Why N(z) matters
Using N(z) aligns cluster lensing with the methodology used in 3×2pt analyses (see arXiv:2503.13632).
If we want to combine probes, cluster lensing must use the same source galaxy selection as the other probes.
This makes N(z) a good addition.
Current Progress
Work already started in PR #398.
sources_select_compute.py was updated- Needs verification and finishing touches
make_ensemble_profile.py must also be updated to accept γₜ and the new source-selection options
For testing, see:
tangential_shear_selection.ipynb
What Needs to Be Done
Description
For cluster predictions, the excess surface density ΔΣ is a weak-lensing quantity that depends on cosmology because it is measured using distances, while the tangential shear γₜ is cosmology-independent as it is measured in angles.
The relevant equations are in arXiv:2107.10857.
Problem: we need to implement tangential shear (γₜ) support in TXPipe and coordinate with SACC.
This issue focuses on the TXPipe data implementation and SACC coordination.
Subproblems
To implement ΔΣ, we need individual redshifts for each source galaxy (to compute distances using cosmology).
For γₜ, since it is an angular measurement, we are not restricted to this:
The current TXPipe options (in
master) are:pdf / mean / true / median.We need to implement all these options plus N(z) for γₜ and test them.
Why N(z) matters
Using N(z) aligns cluster lensing with the methodology used in 3×2pt analyses (see arXiv:2503.13632).
If we want to combine probes, cluster lensing must use the same source galaxy selection as the other probes.
This makes N(z) a good addition.
Current Progress
Work already started in PR #398.
sources_select_compute.pywas updatedmake_ensemble_profile.pymust also be updated to accept γₜ and the new source-selection optionsFor testing, see:
tangential_shear_selection.ipynbWhat Needs to Be Done
sources_select_compute.pymake_ensemble_profile.pyto accept γₜ and new selection options