Adi Nusser

We present a Bayesian reconstruction of the local density and velocity fields traced by the 2MASS Redshift Survey (2MRS) and test the inferred gravitational flow against independent Cosmicflows-4 (CF4) galaxy-group peculiar velocities. The fiducial reconstruction is the maximum-a-posteriori (MAP) solution of a Zel'dovich-approximation forward model, constrained by the 2MRS redshift-space distribution through an unbinned Poisson point-process likelihood. The model assumes Gaussian initial conditions and includes the 2MRS selection function, the Zone of Avoidance, redshift-space distortions, and a distance-dependent galaxy-bias prescription. Hamiltonian Monte Carlo provides posterior samples and constrained realizations within the same framework. The reconstructed velocity field agrees well with CF4 in object-by-object, density--velocity-correlation, and shell-by-shell reflex-dipole tests. These comparisons are made at the CF4 redshift-space positions and do not require smoothing the observed CF4 velocities to the MAP resolution. We also evolve constrained initial conditions with Gadget-4. The real-space density retains the large-scale Zel'dovich structure while developing additional nonlinear small-scale structure, and the redshift-space distribution develops nonlinear Fingers of God. The results show that the 2MRS field-level reconstruction captures the large-scale gravitational flow of the nearby Universe and provides initial conditions suitable for constrained simulations.