Milky Way morphology: early research. The Milky Way at far-ir wavelengths. Milky Way morphology: early research

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3 The Milky Way at far-ir wavelengths Milky Way morphology: early research >1610: Galileo Galilei discovered the Milky Way to be a vast collection of stars Mid 1700s: Milky Way is a stellar disk in which the solar system is embedded Star counts led William Herschel ( ) to put the Sun near the center of the stellar disk. His assumptions: All stars have same absolute magnitude Number density constant Nothing to obscure them No stars too faint to see Glowing dust, heated by stars Milky Way morphology: early research Distribution of globular clusters led Harlow Shapley in 1919 to put the sun at 1/3 of the radius of the Milky Way stellar disk, which is correct. However, the calibration of his distance scale was off by a factor ~2 he overestimated the size of the Milky Way by a factor 2

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5 Solar Orbital Period Around the GC CO molecular gas in the Milky Way GIVEN: RSun ~8 kpc VSun ~220 km/s The orbital period is: P = 2 Rsun / Vsun 2 x 108 yr Mass enclosed within the solar orbit is: G M(Rsun ) / R2sun = V2sun / Rsun (for spherical distribution) M(Rsun ) 1011 Msun (almost true for disk) North America Nebula Great Orion nebula Galactic center Coal Sack Using the HI 21cm line to study our galaxy Rotation curve of molecular gas in the Milky Way Red shifted (receding) Blue shifted

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