Thumbnail Image

Feedback from galactic stellar bulges and hot gaseous haloes of galaxies

We demonstrate that the feedback from stellar bulges can, in principle, play an essential role in shaping the halo gas of galaxies with substantial bulge components by conducting 1D hydrodynamical simulations. The feedback model we consider consists of two distinct phases: (i) an early starburst during the bulge formation and (ii) a subsequent long-lasting mass and energy injection from stellar winds of low-mass stars and Type Ia supernovae. An energetic outward blastwave is initiated by the starburst and maintained and enhanced by the long-lasting stellar feedback. For a Milky Way like galactic bulge, this blastwave heats up the circum-galactic medium to a scale much beyond the virial radius, thus the gas accretion into the halo can be completely stopped. In addition to that, the long-lasting feedback in the later phase powers a galactic bulge wind that is reverse-shocked at a large radius in the presence of circum-galactic medium and hence maintains a hot gaseous halo. As the mass and energy injection decreases with time, the feedback evolves to a subsonic and quasi-stable outflow, which is enough to prevent halo gas from cooling. The two phases of the feedback thus re-enforce each other's impact on the gas dynamics. The simulation results demonstrate that the stellar bulge feedback may provide a plausible solution to the long-standing problems in understanding the Milky Way type galaxies, such as the ‘missing stellar feedback’ problem and the ‘overcooling’ problem. The central point of the present model is that the conspiracy of the two-phase feedback keeps a low density and a high temperature for the circum-galactic medium so that its X-ray emission is significantly lowered and the radiative cooling is largely suppressed. The simulations also show that the properties of the hot gas in the subsonic outflow state depend sensitively on the environment and the formation history of the bulge. This dependence and variance may explain the large dispersion in the X-ray to B-band luminosity ratio of the low LX/LB elliptical galaxies.