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Luminosity Functions



 
 
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Old September 1st 07, 08:47 AM posted to sci.astro.research
Steve Willner
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Default Luminosity Functions

In article ,
"PoorRichard" writes:
I compiled from the literature a list of all known
objects, of the type, in a region of the sky that was covered by a
particular survey. n ~ 100.


With that few objects, you aren't going to be able to do anything
fancy.

As for the completeness of the sample, that is a good question. For
one thing, I restricted z 0.03. How might I further test such a
sample for completeness?


If it's strictly one survey, you have to know details of how it was
done, though there are some tests you can apply. For example, in a
magnitude-limited, the average V/V_max should be 0.5. In an ideal
world, the authors of the survey would have stated their
completeness, but we know that isn't always done.

If it's multiple surveys, you have to understand each one and correct
separately for incompleteness. In effect, you weight each object by
the number of similar but undetected objects it represents. In a
magnitude-limited survey, this is 1/V_max. Or if the surveys cover
only a limited area of sky, just divide by the fraction of the sky
that was covered.

As Philip mentioned, for nearby, bright objects, the surveys may well
be complete, in which case the data directly give the LF.

--
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Cambridge, MA 02138 USA
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