Question

Assume the validity of Freeman’s law and consider a spiral galaxy with central surface brightness µo = 21.5 mag/arcsec2 at a distance of 16 Mpc from Earth. a) If the absolute magnitude of the Sun in the B-band is M_B = 5.54, calculate the central surface brightness of the galaxy in terms of Solar luminosities per square parsec. b) The disk of the galaxy is observed to have an exponential surface brightness with angular scale length θR = 50 arcseconds. What is the total luminosity of the disk (extrapolated to infinity) in terms of solar luminosities (in the B-band)?

Answer 1