large scale velocities (under development)

email: [email protected]

Building tools for reconstructing and using large-scale velocity modes

Reconstructed modes are very valuable for cosmological inference as their reconstruction noise scales like and provide better signal-to-noise on largest scales. This makes velocity modes very useful for sample-variance cancellation.

This rep includes various tools and pipelines for reconstruction large-scale velocities from maps of cosmic microwave background (CMB) and galaxy-surveys.

tools include: (work on progress)

1. 3D velocity template reconstruction from halo catalogs

• uses galaxy catalog to compute 3D overdensity field.
• uses the 3D overdensity field to compute 3D velocity 3-vector.
• makes redshift-binned healpix maps out of 3D velocities

Requires: healpy nbodykit

2. stacking algoritm for moving lens effect

• uses halo distributions and CMB maps (with moving lens effect).
• orients CMB patches to be aligned with the velocity field template.
• fits a grid with fixed size in where is the scale radius. (See related stacker description.)
• stacks the grids to extract the signal.

Moving lens signal is a dipolar modulation in the CMB, alighed with the peculiar velocities of gravitational potentials, e.g. arxiv:1812.03167

where

similar to the lensing deflection angle. (See more notes at the stacker folder.)

Requires: healpy

3. moving lens effect map maker: https://github.com/jbmertens/websky_post

• uses halo catalog to paint maps of the moving-lens effect.

Requires: healpy

see also related work by Siavash Yasini https://github.com/syasini/AstroPaint

4. spherical harmonic reconstruction of the transverse velocities: https://github.com/jbmertens/websky_post (work on progress)

Requires: healpy