You Can't Get There From Here: Hubble Relaxation in the Local Volume

A beginning end-point for galaxy motions within the 10-Mpc Local Volume isconstructed by requiring a smooth distribution of (luminous) mass at the timeof recombination, which is shown to be equivalent to a smooth Hubble flow atearly times. It is found, by this purely kinematical method, that presentpeculiar motions are too small by a factor of at least several (and largely inthe wrong direction) to have produced the observed structures within the age ofthe universe. Known dynamical effects are inadequate to remove the discrepancy.This result is different in origin from previously known ``cold flow''problems. The simple dynamical picture often used within the Local Volume (forinstance, in deriving masses through calculation of a zero-velocity surface) isthus called into question. The most straightforward explanation (though not theonly possible) is that there exists a large quantity of baryonic matter in thisregion so far undetected, and unassociated with galaxies or groups.Comment: 23 pages, accepted by the Astronomical Journa