What does L star mean in the Schechter function?

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Discussion Overview

The discussion focuses on the Schechter function, specifically the meaning and implications of the L star term within the context of galaxy luminosity distributions. Participants explore its theoretical and empirical significance in astrophysics.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant seeks clarification on the definition of L star as the 'characteristic galaxy luminosity where the power-law form of the function cuts off'.
  • Another participant explains that the Schechter function is an empirical fitting function that describes how the number of galaxies in a brightness range behaves, noting a power-law increase at the faint end and an exponential drop-off at the bright end, with L* marking the transition point.
  • A different participant claims that L* corresponds to the luminosity of giant galaxies like the Milky Way or Andromeda, emphasizing their rarity compared to brighter galaxies.

Areas of Agreement / Disagreement

Participants present differing perspectives on the significance of L star, with some focusing on its empirical fitting nature and others emphasizing its association with specific types of galaxies. No consensus is reached regarding its implications.

Contextual Notes

The discussion does not clarify the underlying assumptions about the empirical data or the definitions of terms used, which may affect interpretations of L star.

I_laff
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I'm trying to understand the Schechter function, I read on Wikipedia that the L star term in the function is the 'characteristic galaxy luminosity where the power-law form of the function cuts off'. What does this mean exactly?
 
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It's just an empirical fitting function to the brightness distributions. It's found empirically that the number of galaxies in a certain brightness range increases as a power law at the faint end, but drops off more quickly (exponentially) at the bright end. The L* luminosity is where the function transitions from one behavior to the other. These slides have a nice description.
 
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Thanks for the explanation [emoji846]
 
L* is the luminosity of a giant galaxy like the Milky Way or Andromeda. Such galaxies are rare, and galaxies much brighter are even rarer.

See this article on super spiral galaxies for more.
 

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