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# an astrophysics question need help watch

1. Galaxy NGC2300 has an flat disk dominating the visible light image. Surface brightness is given by
the exponential law
I(R) = I0 exp(−R/Rd)
where I0 is the central surface brightness, R distance from the center, and Rd = 4 kpc the exponential
radial scale of the disk (e-folding distance). The total luminosity of the galaxy equals L = (2.5·10^10)L(sun).
Considering that the total luminosity is surface brightness I(R) integrated over the area of the
whole disk from R = 0 to R = ∞ (not over the radial distance, a mistake some people make!), compute
I0 (in units of L(sun)/pc^2
).

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