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What is Malmquist bias in astronomy, and how does it relate to galaxy distances?

I'm working with a flux-limited galaxy survey to compute luminosity functions. My advisor warned that Malmquist bias will skew my results, but I'm struggling to visualize how a simple selection effect propagates into a systematic distance error. I need a clear explanation of the mechanism and the standard correction techniques used in papers.

 

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By Prajwal Sharma Answered 3 years ago

Think of it this way: in a flux-limited survey, at large distances, you only see the most luminous galaxies. If you then assume an average luminosity to estimate those distances, you'll systematically underestimate them because you're using a luminosity brighter than the true average for the population. I've corrected for this using two main strategies. The first is to create a volume-limited sample, only using galaxies within a distance where you'd see even the faintest ones of interest. The second, more powerful method, is to use a maximum likelihood estimator that explicitly incorporates your survey's flux limit and the intrinsic scatter in the luminosity-distance relation into the fitting process itself.

 

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