Exponential surface brightness profiles
Galactic discs have surface brightness profiles that very closely follow exponential functions in both the radial and vertical directions.
Radial profile 展开

Most of a disc galaxy's gas lies within the disc. Both cool atomic hydrogen (HI) and warm molecular hydrogen (HII) make up most of the disc's gaseous component. This gas serves as the fuel for the formation of new stars in the disc. Although the distribution … 展开

• Thick disk
• Thin disk 展开

Three stellar components with varying scale heights can be distinguished within the disc of the Milky Way (MW): the young thin disc, the old thin disc, and the thick disc. The young thin disc … 展开