Schechter Function of Galaxy Luminosity-Density relationship

In summary, the conversation is about a person reading "Galaxies in the Universe: An Introduction" and getting confused by Equation 1.18 which introduces a quantity called n-star without defining it. They question if it is the number of stars per Megaparsec and the text gives its value as .019h^3 per Megaparsec. They mention they will have more questions and express a desire for more time to take courses on the topic. Another person provides a link to the precise definition of n-star and explains it as the number density of L* galaxies, which are Milky Way-sized galaxies.
  • #1
sderamus
19
0
Hello. I'm plowing through Linda Sparke's "Galaxies in the Universe: An Introduction". I'm enjoying it quite well and learning a lot. But then I get to Equation 1.18 in the book and am a little confused because it uses variables not previously introduced.

Not sure if I can do it here but the equation introduces a quantity n-star, but doesn't define how it gets in there or what it is. The text gives n-star's value as .019h^3 per Megaparsec. h is the expansion rate of the universe. Is this the number of stars per Megaparsec? And of course correcting for the expansion of the Universe.

I'm sure I'll have quite a few more questons as I go along with this book. Wish I had the time to take some real courses in this. Oh well.

All feedback appreciated.

TIA

Sterling
 
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  • #2
The precise definition can be found here:

http://scienceworld.wolfram.com/astronomy/SchechtersLuminosityFunction.html"

You can think of it roughly as being the number density of L* galaxies, which are Milky Way-sized galaxies.
 
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What is the Schechter Function of Galaxy Luminosity-Density relationship?

The Schechter Function is a mathematical model that describes the distribution of galaxy luminosities in a given region of space. It takes into account both the number of galaxies and their luminosities, and is commonly used in observational studies of galaxy populations.

How is the Schechter Function used in astronomy?

Astronomers use the Schechter Function to study the properties of galaxy populations and their evolution over time. By fitting the function to observed data, they can determine the average luminosity and number of galaxies in a given region, as well as the distribution of luminosities.

What are the parameters of the Schechter Function?

The Schechter Function has three parameters: alpha, phi*, and L*. Alpha represents the slope of the function at the faint end, phi* is the characteristic number density of galaxies, and L* is the characteristic luminosity. These parameters can vary depending on the type of galaxies being studied.

How does the Schechter Function relate to the galaxy luminosity function?

The galaxy luminosity function is a specific case of the Schechter Function, where alpha is fixed at -1. This means that the function has a power-law shape at the faint end, and is often used to describe the overall distribution of galaxy luminosities in a given region.

What insights can be gained from studying the Schechter Function of Galaxy Luminosity-Density relationship?

Studying the Schechter Function can provide insights into the formation and evolution of galaxies. By comparing the parameters of the function in different regions of the universe, astronomers can learn about the effects of environment and other factors on galaxy populations. Additionally, the Schechter Function can be used to predict the number and distribution of galaxies in unobserved regions of space.

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