Distinct seed formation mechanisms are imprinted upon the fraction of dwarf galaxies currently containing a central supermassive black hole. Seeding by Population III remnants is expected to produce a higher occupation fraction than is generated with direct gas collapse precursors. Chandra observations of nearby early-type galaxies can directly detect even low-level supermassive black hole activity, and the active fraction immediately provides a firm lower limit to the occupation fraction. Here, we use the volume-limited AMUSE surveys of 200 optically selected early-type galaxies to characterize simultaneously, for the first time, the occupation fraction and the scaling of L X with Mstar, accounting for intrinsic scatter, measurement uncertainties, and X-ray limits. For early-type galaxies with M star < 1010 MO, we obtain a lower limit to the occupation fraction of >20% (at 95% confidence), but full occupation cannot be excluded. The preferred dependence of log L X upon log M star has a slope of 0.7-0.8, consistent with the "downsizing" trend previously identified from the AMUSE data set, and a uniform Eddington efficiency is disfavored at 2σ. We provide guidelines for the future precision with which these parameters may be refined with larger or more sensitive samples.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- black hole physics