A lower limit to the binding mass of early-type galaxies

• Published in: Monthly notices of the Royal Astronomical Society Vol. 221; no. 4; pp. 1049 - 1056
• Main Authors: Fabian, A. C., Thomas, P. A., Fall, S. M., White, R. E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford University Press 01-08-1986; Blackwell Science
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Interstellar medium (ism) and nebulae in external galaxies; Stellar systems. Galactic and extragalactic objects and systems. The universe; Mass; Data table; Binding mass; Mass to light ratio; Dark matter; First type galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/221.4.1049

We derive a lower limit to the gravitational binding mass of a galaxy in which gas at some high temperature T0 and pressure P0 is observed at radius r0 $M_\text T\geqslant \frac {5 kT_0r_0[1-(P_\infty/P_0)^{0.4}]} {2G \mu m_\text H(1-r_0/r_\infty)}$. It is assumed that the gas is confined by a hydrostatic outer atmosphere that is convectively stable and extends to r∞ where the pressure is P∞. When applied to the early-type galaxies studied in X-rays by Forman, Jones & Tucker and by Trinchieri, Fabbiano & Canizares, we deduce total masses of between 2 and $12\times10^{12}\enspace M_\odot$. The average mass-to-light ratio of the galaxies exceeds 74 and so dark matter must be present. If this dark matter is distributed as an isothermal halo then it is ‘hotter’ than the visible stars in the inner regions of the galaxies.