# Gravitational Maps

The code on this page calculates the Newtonian potential \Phi, gravitational acceleration a and (approximate) Kretschmann scalar K at any point in space within 200 Mpc, as documented in Desmond et al 2018 (D18). The primary application is determining environmental screening. For more information please contact Harry Desmond (harry.desmond@physics.ox.ac.uk).

GravityMaps__Calc_CorrFacs.py (click for code)

This program uses an N-body box to calculate the correction factors that must be applied to the \Phi, a and K values calculated from a magnitude limited galaxy survey in order to derive the total values due to all halos with Mvir > 7.63e10 h^-1 Msun. In D18, the Rockstar halo catalogue of the DarkSky-400 simulation was used, the K-band magnitude limit of the survey was taken to be 12.5 (2M++), and the observable predictors of the correction factors were distance to the test point, d, number of visible objects within 10 Mpc, N_10, and potential due to these objects, \Phi_vis.

INPUTS

-- Halo_Catalogue.npy: A list of halos in the N-body box with measured properties including Mvir, Rvir, concentration and x, y and z positions. The halos are also assumed to have absolute magnitudes in the band in which the magnitude limit of the survey is specified; in D18 K-band magnitudes are calculated using abundance matching.

-- Extinction.dat: A list of dust absorption coefficients for the halos, required to convert between absolute and apparent magnitude. In D18 these are taken from the maps of Schlegel, Finkbeiner & Davis 1998, assuming the Solar System to be at the centre of the box and z=0 to be the celestial equator.

OUTPUTS

-- Correction.dat: The correction factors c_\Phi, c_a, c_\theta and c_K at the positions of the well-resolved halos in the box, along with the observable predictors {d, N_10, \Phi_vis}. These will be used in Calc_Proxies.py to estimate the total \Phi, a and K values from those generated solely by objects visible to the survey.

GravityMaps__Calc_Proxies.py (click for code)

Calculates the total \Phi, a and K at given test points by summing the halo contribution (from a galaxy catalogue corrected for mass above the magnitude limit) to that from a smoothed density field. Requires the output of Calc_CorrFacs.py.

INPUTS

-- TestPoints.dat: A list of {Ra (deg), Dec (deg), Dist (Mpc)} values for all the points at which to calculate the gravitational variables.

-- Sources.dat: A list of galaxy-halo objects that provide the primary contribution to the proxies. In D18 the 2M++ catalogue was used with halo properties determined by inverse abundance matching. The data required for each object are {Ra (deg), Dec (deg), Dist (Mpc), M (Msun), Rvir (kpc), concentration}.

-- Smooth_Field.dat: A list of masses representing the smoothed density field not captured by the halo model. D18 used the field of Lavaux & Jasche (2016). The data takes the form {x (Mpc), y (Mpc), z (Mpc), M (Msun)}, where z=0 is the celestial equator.

-- Correction.dat: The output of Calc_CorrFacs.py, above.

OUTPUTS

-- Output.dat: The values of \Phi/c^2, a (km s^{-2}) and K (cm^{-2}) at each test point specified in TestPoints.dat, along with the position of that point.