Emission lines from the hydrogen Hβ line (rest wavelength of486.1 nm) are observed in the spectrum of a spiral galaxy atredshift z = 0.9. The galaxy's disk is observed to be inclined atan angle of 45 degrees to the line of sight. The central wavelengthof the line is observed to be shifted by 0.5 nm to the red on oneside of the galaxy, and by 0.5 nm to the blue on the other side ofthe galaxy. What is the rotation speed of the galaxy? Hint: youmust also account that the redshift expands wavelength differences(Δλmeasured = (1+z)Δλemitted)
