Demographics of black holes in nearby galaxies.
Smita Mathur (The Ohio State University) , Himel Ghosh (Ohio State)
The cumulative mass function needed to explain the energetics of high redshift quasars implies that all galaxies in the local universe should host supermassive black holes (SBHs). Low-mass SBHs, however, are impossible to detect dynamically because their sphere of influence cannot be resolved with current telescopes. On the other hand, the "downsizing" of AGN activity with cosmic epoch suggests that the lowest-mass SBHs should be active now, and therefore should be X-ray sources. Given the M_BH - M_Bulge relationship, we expect the low-mass SBHs to be in late-type spirals. We present results from a Chandra archival study - preliminary to an ongoing bigger Chandra survey - of six nearby "quiescent" spirals that shows that all six indeed harbor nuclear X-ray sources. We use available multiwavelength data to weigh the arguments for and against each object being in fact an accreting SBH. We show how X-ray observations are effective in uncovering hidden SBHs.