Decrease of Velocity Differences between Baryonic Objects and Cold Dark Matter

T. Hara, S. Miyoshi
1990 Progress of theoretical physics  
It is investigated whether observed large-scale streaming of galaxies represents velocities of dark matter under explosion scenarios. It seeems that, although individual galaxies will not represent motions of dark matter, cluster of galaxies follows the velocity field of dark matter. The origin and upper limits of such field are considered. . Recent observations have reported that galaxies in large regions (~102Mpc), including some clusters of galaxies, may be streaming coherently with
more » ... ently with velocities up to 600 km/sec or more with respect to the rest frame determined by the microwave background radiation. 1) On the other hand, it is suggested that the dominant mass component of the universe is dark matter. 2 ),3) Because we can only speculate the motion of dark matter from the galaxy motions, much attention should be paid to the correlation of velocities between the observed galaxies and cold dark matter. So, in this paper, we investigate whether such coherent large-scale streaming velocities are due to dark matter or only to baryonic objects which may be formed by piling up of gases due to some explosive events. In fact, the observations of the large-scale structure of the universe 4 ),5) have changed the view of the formation of galaxies from the conservative one which mainly treates the increase of initial fluctuations in the expanding universe to some extreme ones as explosion scenarios or cosmic strings, etc. 6 ),7) In these cases, galaxies or other astronomical objects, named sometimes as population III, are formed by accumulation of baryonic gases due to some explosions. 6 ), 8) In such situations, the relative velocities between the objects and dark matter are expected. g) So it is necessary to study the correlation of velocities between the observed baryonic objects and dark matter. In the following, we calculate the decrease of velocity difference between dark matter and the baryonic object in a simplified model, considering only the gravitational interaction between a condensed object and dust-like cold dark matter within the expanding universe. We treat only the recent stage (1 +z:S::10 2 ) with the cosmological density parameter Q=l, dominantly composed of cold dark matter, and do not consider the accumulation of the baryonic and dark matter onto the object. The equation for the particle of cold dark matter is written where the first term represents the decay due to the expansion of the universe'and the second term is due to the gravitational field. 10 ) The equation of motion for the object with mass M is written as
doi:10.1143/ptp.83.660 fatcat:fdas6amtbjdbpnwtwunsxerp4y