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Distances to Galaxie1

Distances to Galaxie1 - standard candle techniques...

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Distances to Galaxies Just like you found for the determination of stellar properties, finding the distance to the galaxies is essential for comparing the galaxies against each other. In order to determine the luminosities and masses of the galaxies and the distribution of the mass inside the galaxies, you must first know the distances to them. Is that galaxy in our telescope bright because it is producing a lot of energy or because it is close to us? Are the stars moving quickly in a galaxy because the combined mass is large or because the distances inside the galaxy are small? You need to find the distance to the galaxy to be sure. One method of determining the distance discussed above uses the period-luminosity relation of Cepheid variable stars to derive the distance from the apparent brightness of the Cepheids. This works for the nearby galaxies. To find the distance to galaxies farther away, other
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Unformatted text preview: standard candle techniques involving objects more luminous than Cepheids like Type Ia supernova explosions or supergiant stars are used. Supergiant luminosities are not as well known or uniform as the Type Ia supernovae, so astronomers prefer to use the Type Ia supernovae to derive the distances to the very distant galaxies. Another method uses the width of a galaxy's spectral lines. The width of the absorption lines from the stars or the radio emission lines from the gas in a galaxy depend on the amount of stellar motion in the galaxy. Most galaxies are too far away for us to resolve the fine-scale details of the internal motions in the galaxies. The spectrum of far away galaxies is from the combined motions of all of the material in them....
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