Satellites of Isolated Early-type Galaxies and the Missing Satellite Galaxy Problem

The standard hierarchical galaxy formation scenario in the popular LCDM cosmogony has been very successful in explaining the large-scale distribution of galaxies. However, one of the failures of the theory is that it predicts too many satellite galaxies associated with massive galaxies compared to observations, which is called the missing satellite galaxy problem. Isolated groups of galaxies hosted by passively evolving massive early-type galaxies are ideal laboratories for finding the missing physics in the current theory. We discover through a deep spectroscopic survey of galactic satellite systems that bright isolated early-type galaxies have almost no satellite galaxies fainter than the r-band absolute magnitude of about Mr=-14. The cutoff is at somewhat brighter magnitude of about Mr=-15 when only early-type satellites are used. Such a cutoff is not observed in the luminosity function of galaxies in the field. Physical properties of the observed satellites depend sensitively on the host-centric distance. All these are strong evidence that galactic satellites can become invisible due to astrophysics of satellite-host galaxy interaction. A recent state-of-the-art hydrodynamic simulation of galaxy formation does not reproduce such a cutoff in the satellite galaxy luminosity function. But the past history of the simulated satellites shows that many satellite galaxies near or somewhat fainter than the cutoff magnitude have recently become extinct through fatal encounters with the host or other satellite galaxies. Our observation indicates that the missing satellite galaxy problem could be mitigated if the astrophysics of galaxy interaction is more elaborated in the theory.