The effect of pressure in the Local Supercluster and the anisotropy of the Hubble flow

The authors consider the Local Supercluster (LS) as imbedded in an expanding universe characterized by an homogeneous and isotropic geometry and a dust content (Friedmann-Robertson-Walker, hereafter FRW universe). Observers placed far away from the centre of the LS can represent their surroundings (Z ⪉ 10^-2), exterior to the Local Group circle, by a spherically-symmetric perturbation of the FRW background in the Newtonian approximation. These observers possess an infall velocity toward the Virgo cluster, with a behaviour v ≡ r^1-N, and the matter is distributed with spherical symmetry around this cluster (δ ≡ r^-N for the density contrast). The authors apply this model to the Local Group (LG) and other galactic samples in the small density contrast zone. In the general case, they obtain a dominant quadrupole pattern for the LG redshifts. For other samples (outside the LG circle), the redshift has a quasi-dipole form.