Schedule Feb 17, 2012
A New Model of Local Group dwarfs. II. Episodic Star Formation
J. Bland-Hawthorn (Univ. of Sydney), Matthew Nichols (Univ. of Sydney), Doug Lin (UCSC, TASC)

Dwarf galaxies around the Galaxy and M31 appear stripped within 270 kpc of the host galaxy. Colour-magnitude diagrams of these dwarfs, however, show clear evidence of episodic star formation over cosmic time. We present a simple model for this behaviour. Gas not consumed in star formation is heated to large scale heights before being removed by a tenuous hot halo as small clouds. Much of this gas is lost, falling as a warm rain onto the host galaxy. Some gas that is protected from drag on the hot halo by the dwarfs shock may survive an orbit. Such gas experiences strong variations in cooling arising from azimuthal compression and a weaker radiation field at apogalacticon. The ability to survive this gas is strongly determined by the orbit of the dwarf galaxy, with dwarfs of moderate eccentricity (e>0.2) that do not come too close to the centre (R>Rdisk). Up to 40% of early infalling dwarfs may be expected to have at least one period of star formation post-infall. Such a model may also be used to restrict the orbit of observed dwarfs based upon the timing and strength of star formation bursts. The infalling gas would only be visible near apogalacticon as warm clouds contributing towards the observed deficiency of gas in dwarf galaxies.

References: Nichols, M., Lin, D., & Bland-Hawthorn J. 2012, submitted; arXiv: 1109.4146


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