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.Comment: Submitted to MNRAS, 33 pages, 9 figures. Comments welcom

Detection of Ne VIII in the Low-Redshift Warm-Hot IGM

High resolution FUSE and STIS observations of the bright QSO HE 0226-4110 (zem = 0.495) reveal the presence of a multi-phase absorption line system at zabs(O VI) = 0.20701 containing absorption from H I (Ly alpha to Ly theta), C III, O III, O IV, O VI, N III, Ne VIII, Si III, S VI and possibly S V. Single component fits to the Ne VIII and O VI absorption doublets yield logN(Ne VIII) = 13.89+/-0.11 and logN(O VI) = 14.37+/-0.03. The Ne VIII and O VI doublets are detected at 3.9 sigma and 16 sigma significance levels, respectively. This represents the first detection of intergalactic Ne VIII, a diagnostic of gas with temperature in the range from 5x10(5) to 1x10(6) K. The O VI and Ne VIII are not likely created in a low density medium photoionized solely by the extragalactic background at z = 0.2 since the required path length of ~11 Mpc implies the Hubble flow absorption line broadening would be ~10 times greater than the observed line widths. A collisional ionization origin is therefore more likely. Assuming [Ne/H] and [O/H] = -0.5, the value N(Ne VIII)/N(O VI) = 0.33+/-0.10 is consistent with gas in collisional ionization equilibrium near T=5.4x10(5) K with logN(H)= 19.9 and N(H)/N(H I) = 1.7x10(6). The observations support the basic idea that a substantial fraction of the baryonic matter at low redshift exists in hot very highly ionized gaseous structures.Comment: 32 pages text and 9 pages of figures. Accepted by the Astrophysical Journa