M31* and its circumnuclear environment
  We present a multiwavelength investigation of the circumnuclear environment
of M31. Based on Chandra/ACIS data, we tightly constrain the X-ray luminosity
of M31*, the central supermassive black hole of the galaxy, to be L (0.3-7
keV)<= 1.2x10^{36}erg/s, approximately 10^{-10} of the Eddington luminosity.
  From the diffuse X-ray emission, we characterize the circumnuclear hot gas
with a temperature of ~0.3 keV and a density of ~0.1 cm^{-3}. In the absence of
an active SMBH and recent star formation, the most likely heating source for
the hot gas is Type Ia SNe. The presence of cooler, dusty gas residing in a
nuclear spiral has long been known in terms of optical line emission and
extinction. We further reveal the infrared emission of the nuclear spiral and
evaluate the relative importance of various possible ionizing sources. We show
evidence for interaction between the nuclear spiral and the hot gas, probably
via thermal evaporation. This mechanism lends natural understandings to 1) the
inactivity of M31*, in spite of a probably continuous supply of gas from outer
disk regions, and 2) the launch of a bulge outflow of hot gas, primarily
mass-loaded from the circumnuclear regions. One particular prediction of such a
scenario is the presence of gas with intermediate temperatures arising from the
conductive interfaces. The FUSE observations do show strong OVI$\lambda$1032
and 1038 absorption lines against the bulge starlight, but the effective OVI
column density (~4x10^{14} cm^{-2}), may be attributed to foreground gas
located in the bulge and/or the highly inclined disk of M31. Our study strongly
argues that stellar feedback, particularly in the form of energy release from
SNe Ia, may play an important role in regulating the evolution of SMBHs and the
interstellar medium in galactic bulges.
