SCI238 Lecture Notes - White Dwarf, Density, Before Present
9 Jul 2013
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Document Summary
Rotation curve: works well for nearby, edge-on spiral galaxies, best measured from gas (hi or hii), needs orderly, systematic orbits, not applicable to faint or elliptical galaxies. Velocity dispersion: measure the spread in velocities from the width of the spectral lines, velocity spread depends on mass. Motions of galaxies in orbit around each other or in a cluster. From measurements of the doppler shift we can measure the rate at which galaxies rotate but the rotation rate is determined by the mass of the galaxy. Milky way rotational speed around 200-250 km/s. V2/r = acceleration in circular motion mass of luminous matter (mainly stars) is not enough to match rotation curve spectral line width of a galaxy -> rotation rate -> mass. Is the mass of a galaxy divided by its luminosity: we measure both mass [msun] and luminosity [lsun] in solar units.
