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A.J. Barth (Caltech), L.C. Ho (OCIW), W.L.W. Sargent (Caltech)
The recently discovered tight correlation between black hole mass and stellar velocity dispersion in galaxy bulges offers a new way to estimate the black hole masses in nearby galaxies. We have obtained new optical spectra of the BL Lac object Markarian 501 at the Palomar Observatory. From the widths of the Ca II triplet lines, we derive a stellar velocity dispersion of 390 km/s in the nuclear region of the host galaxy. If this galaxy follows the locally-defined M-\sigma correlation, then its central black hole has M ~(1.5-3.5)\times109 solar masses. This is significantly larger than some previous estimates for the black hole mass in Mrk 501, but similar to central masses observed in nearby radio galaxies in giant elliptical hosts such as M87.