The Extragalactic Distance Scale

The Extragalactic Distance Scale - The Extragalactic...

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Unformatted text preview: The Extragalactic Distance Scale Distances to galaxies and AGNs are important, but direct means of measuring distances may be difficult and very time-consuming. Hence the mere possibility of something like the Hubble flow cz = H D would be a real boon, since we could then estimate distance (to within errors caused by peculiar motion) from a single straightforward measurement. The idea is then that for "large enough" D , the Hubble velocity will overwhelm any peculiar motions and we will see a smooth, purely radial flow. Finding the value of H has been an important part of galaxy research from its inception, with the recent additional possibility of mapping systematic departures from a smooth Hubble flow. The procedure usually follows a distance ladder , in which objects of well-known properties are used to calibrate larger/brighter kinds of objects which can in turn be used to calibrate other indicators that may be seen to greater distances, until finally we have indicators that are useful into the...
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