Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aj....113..755m&link_type=abstract
Astronomical Journal v.113, p.755
Astronomy and Astrophysics
Astronomy
6
Galaxies: Ism, Ism: Kinematics And Dynamics
Scientific paper
Under quite general conditions, the temperature of the hot interstellar gas at large radii in elliptical galaxies can be lower than the mean galactic virial temperature. If so, a nonlinear cooling wave can form in the hot interstellar gas and propagate slowly toward the galactic core at velocity ˜10 kpc-1. If the cooling wave survives hydrodynamic instabilities, it can intermittently deposit cold gas within about ˜15 effective radii. For a bright elliptical the total mass deposited in this manner is large, ˜0.3 x 1010 Msun. In contrast with ad hoc assumptions about "mass dropout" in galactic cooling flows, the galactic drip mechanism is a physically self consistent mechanism in which cold gas can derive from the hot interstellar gas far from the central regions of elliptical galaxies. The existence of young stars and extended gas at ˜l04 K observed in some bright ellipticals may result from this galactic drip rather than galactic mergers. Galactic drips are expected in relatively isolated (field) ellipticals provided (i) the galactic stellar velocity dispersion decreases at large galactic radii and (ii) the current Type Ia supernova rate is sufficiently small to be consistent with interstellar iron abundances found in recent x-ray studies. Ellipticals located within clusters of galaxies are immersed in generally hotter cluster gas. If the pressure in the ambient cluster gas exceeds that in the outer parts of the galactic interstellar medium, some cluster gas can flow into the galaxy, increasing the gas temperature there and suppressing the appearance of galactic drips. Furthermore, the iron abundance in the galactic ISM can be reduced when an elliptical is surrounded by hot cluster gas.
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