Transonic solutions of isothermal galactic winds in a cold dark matter
  halo
  We study fundamental properties of steady, spherically symmetric, isothermal
galactic outflow in appropriate gravitational potential models. We aim at
constructing a universal scale free theory not only for galactic winds, but
also for winds from clusters/groups of galaxies. In particular, we consider
effects of mass-density distribution on the formation of transonic galactic
outflows under several models of the density distribution profile predicted by
cosmological simulations of structure formation based on the cold dark matter
(CDM) scenario. In this study, we have clarified that there exists two types of
transonic solutions: outflows from the central region and from distant region
with a finite radius, depending upon the density distribution of the system.
The system with sufficiently steep density gradient at the center is allowed to
have the transonic outflows from the center. The resultant criterion
intriguingly indicates that the density gradient at the center must be steeper
than that of the prediction of conventional CDM model including Navarro, Frenk
& White (1997) and Moore et al. (1999). This result suggests that an additional
steeper density distribution originated by baryonic systems such as the stellar
component and/or the central massive black hole is required to realize
transonic outflow from the central region. On the other hand, we predict the
outflow, which is started at the outskirts of the galactic center and is
slowly-accelerated without any drastic energy injection like starburst events.
These transonic outflows may contribute secularly to the metal enrichment of
the intergalactic medium.
