Millimetric Observations of the Center of M81: A Starved Nucleus with Intraday Variability

The central kiloparsec of M81 has been observed in the CO(J=1-0) line and the3 mm continuum at 100 pc resolution in an attempt to probe molecular gas, andto search for the nuclear inner Lindblad resonance (NILR), around thelow-luminosity AGN M81*. We found the following. (1) Molecular gas in thecentral kpc is mainly on a ``pseudoring'' or a spiral arm at a radius of about500 pc. (2) The region within ~300 pc from the nucleus is mostly devoid ofmolecular gas except for diffuse one; in particular, there is neither a giantmolecular cloud that is now accreting on the nucleus nor a conspicuous gasfeature that can be identified as an NILR. (3) The 3 mm continuum emissionshows significant intraday variation, suggesting an emitting region of ~100 AU.(4) The 3-sigma upper limit for CO absorption toward the continuum source istau_CO(0->1) dV < 0.1 for a linewidth of 10 km/s. The dearth of accretingmolecular gas in the vicinity of the nucleus may explain the low luminosity ofM81*.