Models of Steady State Cooling Flows in Elliptical Galaxies
Abstract
We present a comprehensive set of steady state models for spherically symmetric cooling flows in early-type galaxies. The effects and importance of several key parameters have been investigated in these models. They include the rate of supernovae, the external pressure around a galaxy, the presence of a dark matter halo, the influence of mass sinks which remove material from the general accretion flow, a reduction in the stellar mass-loss rate, and various combinations of these variables. For each model, X-ray luminosities, surface brightnesses, and mean X-ray temperatures are computed. Comparison to the general X-ray properties of the sample of galaxies detected with the Einstein Observatory establishes constraints on the parameter values. As found previously, our results show that the supernova rate in ellipticals must be lower than Tammann's value by about a factor of 4 to avoid producing too much X-ray luminosity. The value of L_X_ for an elliptical galaxy depends almost exclusively upon the properties of the galaxy and its gas content and is not affected by environmental influences, such as the high pressure of a surrounding intracluster medium. A high external pressure will result in a high mean X-ray temperature, which could be mistaken as indicating the presence of a heavy halo. The existence of a dark halo within a galaxy cannot be discerned using just the mean temperature, luminosity, or surface brightness of the gas. Measuring the radial temperature profile is the only definitive way of detecting the presence of a halo. Allowing mass to drop out of the flow at all radii, modeled using mass sinks, reduces L_X_ slightly, flattens the surface brightness distribution, and gives values of the central surface brightness that are close to those observed for the brighter ellipticals. Sinks are also needed to prevent the accumulation of too much material in the core of the galaxy over a Hubble time. Thus, any realistic cooling flow model must include mass sinks. Reduced stellar mass loss, or equivalently, a reduced rate of injection of material into the flow, has a small effect on the observed properties of the galaxy. These results suggest that the large scatter in X-ray luminosity of the Einstein sample galaxies for a given optical luminosity is not a result of internal differences, but is principally due to differences in their total gas content caused by external effects, such as variations in the efficiency of ram pressure stripping by a surrounding intracluster medium.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1988
- DOI:
- 10.1086/166689
- Bibcode:
- 1988ApJ...332..725V
- Keywords:
-
- Astronomical Models;
- Cooling;
- Elliptical Galaxies;
- Interstellar Matter;
- Supernovae;
- Dark Matter;
- Halos;
- Heao 2;
- Stellar Mass Ejection;
- X Ray Spectra;
- Astrophysics;
- GALAXIES: INTERSTELLAR MATTER;
- GALAXIES: X-RAYS;
- STARS: SUPERNOVAE