Calculating the luminosity density of the universe

In summary, the Sloan Digital Sky Survey (SDSS) has measured the Schechter parameters for the r passband as a = -1.16 +/- 0.03, M* = -20.80 +/- 0.03, and Phi* = (1.50 +/-0.13). With the sun's absolute magnitude in the SDSS r band being M = 4.62, the luminosity density in solar units can be calculated. However, there may be an error in taking L* as -20.80 +/- 0.03 instead of M*. Luminosity and absolute magnitude have a confusing relationship and further clarification is needed.
  • #1
IRNB
16
0
l = Phi*L*Gamma(a+2)

b)

The Sloan Digital Sky Survey (SDSS) has recently measured the following Schechter
parameters in the r passband: a = -1.16 +/- 0.03, M*= -20.80 +/- 0.03, Phi* = (1.50 +/-0.13). Given that the sun has absolute magnitude M = 4.62 in the SDSS r band, calculate the luminosity density in this band in solar units. Estimate the error on this quantity.
Gamma(0.84) = 1.122, Gamma(0.81) = 1.153, Gamma(0.87) = 1.094.

I done the entire question and then realized i had made a grave error. And this is what I think it is; I took L* as being -20.80 +/- 0.03 ie M*, and I am pretty sure this is wrong. Luminosity confuses me and I'm not sure how to relate the absolute magnitude M* to the Luminosity L*. I know that L* is supposed to be in the order of 10^10. Can anyone out there help? Its kind of urgent (due in tomorrow!).
 
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  • #2
sorry i posted this in the wrong section. I've posted it again in the homework section. This can be deleted if need be.
 

1. What is luminosity density and why is it important in understanding the universe?

Luminosity density refers to the total amount of light emitted from all sources within a given volume of space. It is important because it can provide valuable information about the energy output and distribution of galaxies and other celestial objects, which can in turn help us understand the evolution and structure of the universe.

2. How is luminosity density calculated?

Luminosity density is calculated by measuring the total amount of light emitted by all sources within a specific volume of space, usually in a specific wavelength range. This measurement is then divided by the volume of space to obtain the luminosity density.

3. What units are used to measure luminosity density?

Luminosity density is typically measured in units of watts per cubic meter (W/m³), as it represents the amount of energy emitted per unit of volume.

4. How does luminosity density vary across different regions of the universe?

Luminosity density can vary greatly across different regions of the universe, as it is influenced by the distribution and types of objects within a given volume of space. For example, regions with a higher concentration of galaxies will have a higher luminosity density compared to regions with fewer galaxies.

5. What can the study of luminosity density tell us about the history of the universe?

By studying the changes in luminosity density over time, scientists can gain insights into the evolution of the universe. For instance, a decrease in luminosity density could indicate a decrease in the formation of new stars, while an increase could suggest an increase in the activity of galaxies. This information can help us understand the overall history and development of the universe.

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