The Central Regions of M81

Abstract

High angular resolution optical and near-infrared images are used to investigate the central regions of the nearby Sb galaxy M81 (NGC3031). The spectral-energy distribution of the circumnuclear region, which extends out to 1.5 arcsec (~ 24 pc if μ_0 = 27.5) from the nucleus, can be modelled as a combination of an old metal-rich population and emission from hot dust. Thermal emission has been detected near other AGN, and simple models indicate that hot dust can account for ~20% of the light in K within 0.5 arcsec of the M81 nucleus. An elongated structure with M_V ~ -7, which may be an area of active star formation, is detected 0.45 arcsec from the nucleus. At distances in excess of 1.5 arcsec from the nucleus the J-K color of the M81 bulge is not significantly different from what is seen in M31. The HST data are also used to search for bright globular clusters within 2kpc of the center of M81. The area within 0.26 kpc of the M81 nucleus is largely devoid of bright globular clusters, in agreement with what is seen in the central regions of the Galaxy and M31. However, our survey indicates that there may be ~45 +/- 12 globular cluster candidates with M_V \leq -7 within 2 kpc of the galaxy center, which is consistent with what would be infered from the Milky-Way cluster system.