Flows of Local Sheet dwarfs in relation to the Council of Giants

Abstract

ABSTRACT The kinematics of isolated dwarf galaxies in the Local Sheet have been studied to ascertain how the Council of Giants has affected flows. Peculiar velocities parallel to the Sheet in the frame of reference of the Council ascend steeply from negative to positive values on the near side of the Council at a heliocentric radius of $2.4 \pm 0.2 \, \rm Mpc$ . They descend to pre-ponderantly negative values at a radius of $3.9^{+0.4}_{-0.5} \, \rm Mpc$, which is near the middle of the Council realm. Such behaviour is evidence for a flow field set up by the combined gravitational effects of the Local Group and Council, the ascending node being where their gravitational forces balance. Receding dwarfs on the near side of the Council are pre-dominantly located in the direction of M94, although this may be a manifestation of the limitations of sampling. If M94 were entirely responsible for the placement of the ascending node, then the galaxy’s total mass relative to the Local Group would have to be $0.8^{+0.4}_{-0.3}$, the same as indicated by the orbits of satellite galaxies. Rather, if the placement of the ascending node were set by matter distributed evenly in azimuth at the Council’s radius, then the required total mass relative to the Local Group would have to be $4^{+3}_{-2}$, which is 30 per cent to 40 per cent lower than implied by satellite motions but still consistent within errors. The mere existence of the ascending node confirms that the Council of Giants limits the gravitational reach of the Local Group.