An Intermediate-Mass Black Hole in the Dwarf Seyfert 1 Galaxy POX 52

Abstract

We describe new observations of POX 52, a previously known but nearly forgotten example of a dwarf galaxy with an active nucleus. While POX 52 was originally thought to be a Seyfert 2 galaxy, the new data reveal an emission-line spectrum very similar to that of the dwarf Seyfert 1 galaxy NGC 4395, with clear broad components to the permitted line profiles. The host galaxy appears to be a dwarf elliptical; this is the only known case of a Seyfert nucleus in a galaxy of this type. Applying scaling relations to estimate the black hole mass from the broad H-beta linewidth and continuum luminosity, we find M_BH ~ 1.6x10^5 solar masses. The stellar velocity dispersion in the host galaxy is 36+/-5 km/s, also suggestive of a black hole mass of order 10^5 solar masses. Further searches for AGNs in dwarf galaxies can provide crucial constraints on the demographics of black holes in the mass range below 10^6 solar masses.