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Introduction to active galaxies
Introduction to active galaxies

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2.3 Broadband spectra

The broadband spectrum is the spectrum over all the observed wavelength ranges. To plot the broadband spectrum of any object it is necessary to choose logarithmic axes.

  • Why is it necessary to use logarithmic axes?

  • Because both the spectral flux density, Fλ, and the wavelength vary by many powers of 10.

Figure 7 shows the broadband spectrum of the Sun: it has a strong peak at optical wavelengths with very small contributions at X-ray and radio wavelengths.

Figure 7
(Adapted from Nicolson, 1982)
Figure 7: The broadband spectrum of the Sun. The dashed lines indicate the maximum and minimum in regions where the flux density varies