Decoupled and Inhomogeneous Gas Flows in S0 Galaxies

A recent analysis of the "Einstein" sample of early-type galaxies hasrevealed that at any fixed optical luminosity Lb S0 galaxies have lower meanX-ray luminosity Lx per unit Lb than ellipticals. Following a previousanalytical investigation of this problem (Ciotti & Pellegrini 1996), we haveperformed 2D numerical simulations of the gas flows inside S0 galaxies in orderto ascertain the effectiveness of rotation and/or galaxy flattening in reducingthe Lx/Lb ratio. The flow in models without SNIa heating is considerablyordered, and essentially all the gas lost by the stars is cooled andaccumulated in the galaxy center. If rotation is present, the cold materialsettles in a disk on the galactic equatorial plane. Models with a timedecreasing SNIa heating host gas flows that can be much more complex. After aninitial wind phase, gas flows in energetically strongly bound galaxies tend toreverse to inflows. This occurs in the polar regions, while the disk is stillin the outflow phase. In this phase of strong decoupling, cold filaments arecreated at the interface between inflowing and outflowing gas. Models with morerealistic values of the dynamical quantities are preferentially found in thewind phase with respect to their spherical counterparts of equal Lb. Theresulting Lx of this class of models is lower than in spherical models with thesame Lb and SNIa heating. At variance with cooling flow models, rotation isshown to have only a marginal effect in this reduction, while the flattening isone of the driving parameters for such underluminosity, in accordance with theanalytical investigation.Comment: 32 pages LaTex file, plus 5 .ps figures and macro aasms4.sty -- Accepted on Ap