Where Do Cooling Flows Cool?

Although only about 5 percent of the total baryonic mass in luminouselliptical galaxies is in the form of cooled interstellar gas, it isconcentrated within the optical effective radius r_e where it influences thelocal dynamical mass. The mass of cooled gas must be spatially distributedsince it greatly exceeds the masses of central black holes. We explore here theproposition that a population of low mass, optically dark stars is created fromthe cooled gas. We consider a wide variety of radial distributions for theinterstellar cooling, but only a few are consistent with observed X-ray surfacebrightness profiles. In a region of concentrated interstellar cooling, theX-ray emission can exceed that observed, suggesting the presence of additionalsupport by magnetic stresses or non-thermal pressure. In general we find thatthe mass of cooled gas contributes significantly to stellar dynamical mass tolight ratios which vary with galactic radius. If the stars formed from cooledinterstellar gas are optically luminous, their influence on the the mass tolight ratio would be reduced. The mass of cooled gas inside r_e is sensitive tothe rate that old stars lose mass, which is nearly independent of the initialmass function of the old stellar population.Comment: 18 pages with 6 figures; accepted by Astrophysical Journa