POX 52: A dwarf Seyfert 1 galaxy with an intermediate-mass black hole

We describe new optical images and spectra of POX 52, a dwarf galaxy with an active nucleus that was originally detected in the POX objective-prism survey. 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 broad components to the permitted line profiles, and we classify POX 52 as a Seyfert 1 galaxy. The host galaxy appears to be a dwarf elliptical, and its brightness profile is best fit by a Sersic model with an index of 3.6 +/- 0.2 and a total magnitude of M-V = 17.6. Applying mass - luminosity - line width scaling relations to estimate the black hole mass from the broad Hbeta line width and nonstellar continuum luminosity, we find M-BH approximate to 1.6 x 10(5) M-.. The stellar velocity dispersion in the host galaxy, measured from the Ca II lambda8498, 8542 lines, is 36 +/- 5 km s(-1), also suggestive of a black hole mass of order 10(5) M-.. Further searches for active nuclei in dwarf galaxies can provide unique constraints on the demographics of black holes in the mass range below 10(6) M-..