High-ionization clouds in the circumnuclear region of M31

We present two-dimensional spectroscopy of the 125 x 125 pc(2) circumnuclea r region of M31, obtained using two optical fiber systems, INTEGRAL and 2D- FIS, installed at the 4.2 m William Herschel Telescope at the Rogue de los Muchachos Observatory on the island of La Palma, Spain. We present continuu m and emission-line maps, emission-line quotients, and stellar and ionized gas velocity fields obtained under subarcsecond seeing conditions. We have discovered H beta, [O III] lambda lambda 4959, 5007, H alpha, and [N II] la mbda lambda 6548, 6584 emission in the inner 40 x 40 pc(2) circumnuclear re gion. The intensity maps obtained from the emission lines show several isol ated systems of ionized gas (clouds) a few parsecs in size. The kinematics of the clouds is decoupled from the stellar rotation, and strong radial mot ions are likely to be present. We have also discussed the ionization mechan isms present in the clouds. Although the emission-line quotients are compat ible with ionization produced by post-asymptotic giant branch stars, the es timated ionization fluxes exceed what is expected according to the distribu tion of planetary nebulae in the bulge of M31. Comparison of the line quotients and spectra found in M31 with those found in the extended narrow-line region of the Seyfert galaxy NGC 4151 indicates that we could be in presence of ultralow-intensity nuclear activity. These results would be compatible with the existence of a "dead quasar" in the n ucleus of M31 and underline the hybrid character of the LINER phenomenon.