milky-way - The Milky Way (Kulner, Ch. 16; also Bennett el...

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Unformatted text preview: The Milky Way (Kulner, Ch. 16; also Bennett el al. Ch. 19, Shu Ch. 12) AST 203 (Spring 2011) Milky Way (Mnkipedia:User:Moondigger, CCA license) AST 203 (Spring 2011) radio continuum (408 MHz) manually V ' " -‘ ya. , mm" V m- mums,‘ w- The Infrared Milky Way: GLIMPSE/MIPSGAL Spitzer Space Telescope - IRAC - MIPS NASA / JFL—Caltech / E. Churchwell (Univ. of Wisconsin]. GLIMPSE Team 8 8. Carey [SSC-Calmch], MIPSGAL Team sscEflDB-1 1a NASA’s Fermi telescope reveals best-ever View of the gamma-ray sky PMS r50). HIE G PER Jinn»;st G) LEI H51 JuJ Unlunlmlim Credit: NASNDOElFermi LAT Collaboration http://antwrp.gsfc.nasa.gov/apod/ap090321 .html AST 203 (Spring 2011) Milky Way Shapley mapped distribution of globulars using variable stars. Sun is ~ 10 kpc from the center of the MW Population | stars (high metalicity) are found in ‘ galactic clusters, near interstellar gas/dust :, : In galactic disk a: Population II stars are In globular clusters and octane 1‘ form spherical distribution (h) In galactic halo. 40 3—y—y—y—,—viy—r~‘~r +~ Have a wider velocity distribution 4O Li_i_l_i_i_ A AST 203 (Spring 2011) (Kumer) y (Mommas * A M ’ >>yxisk~xx o 20 077 i old stars % (c) an ) Milky Way halo: Spherically symmetric distribution of older stars. Density falls off with distance from galactiy center disk: Distribution of stars orbiting the galactic center in the thin plane ‘‘‘‘‘‘‘‘ """"""""""""""""""""""""""" bulge: 1.000 liglil-years 3/ Spherical distribution surrounding the galactic center. 100,000 llg gamma» w.”an WW "Shawn-1M AST 203 (Spring 2011) Differential Rotation Rigid rotation: disk material has the same period, independent of how far it is from the center. This is solid-body rotation—think of an old record This is not observed. Material at the center orbits faster (shorter period) The galaxy is differentially rotating. Measure the rate at which stars orbit the galactic center —> determine the mass of the galaxy Just like Kepler's laws AST 203 (Spring 2011) Differential Rotation Spherically symmetric mass distribution: gravitational force same as if all mass concentrated at center. Orbital velocity depends only on enclosed mass and orbital radius The enclosed mass a some radius is: Newtonian mechanics tells us that mv2(R) _ GM(R)m R _ T 02(R)R G :> M(R): Also true for a thin disk under certain conditions (see, for ex. Shu, roblem 12.5) A T 203 (Spring 2011) Differential Rotation Angular velocity: 9(R) : v(R)/R This follows from 27f 92 R R3 M (R) — —( ) Q R If all the mass were at the center, M (R) is constant orbits are Keplerian. Measure the rotation curve ( (MR) vs. R) via Doppler shifts of interstellar clouds Doppler shift depends only on the relative velocity of a cloud and the Sun along the line of sight. AST 203 (Spring 2011) Differential Rotation / / \ * (Shu) ZleemJine intensity 4 + local gas U "H radial velocity V iigure 12.14 A schematic diilgl’i’lm of the Zl-em line profile along i diiemon oi Galactic longitude I as m Figure 12.1.2. Except for the effects ofslighi iioncireular motions. the maximum iadial velocit) recorded, m should occur for the cloud 2 at the "hingcnl point." imcmi 'me posllIVC Velocities dllSC from the sum of the Contributions of eloudr like I and 3. whieh lie intetior m the solur circle on eitliei side of the tangent point. Zero-Velocity gas corresponds [0 nuienai on the solar eirele. either in the immediate VlC‘il‘llly ofthe Sun or zit the intersection point 4 in Figure 1213. Negative ieiocny gas iii. the first quadrant: o <1< 90‘, corresponds to gas heymd the solar circle. Figure 12,13, The pattern of ltirge- 1e differential rotation LlL‘COi'dmg l0 an obsetver who mime» with the speed oniie incui standiitd arrest. Notice that clouds 1 and 3 have the same line- ofesight l"radiiil“l velocity relative to the Sun. and cltiutl 2 has the maximum positive velocuy (re 11) Notice also that cloud 5. which lies outside the solar circle. has A negative radial velocit). and cloud 4. which lies on the soil“ circle. is ill rest relative to the Sun. Points 1 and 3 are at the same distance from galactic center —> have the same relative orbital velocity. Point 2 is the closest to galactic center —> highest radial velocity. Point 5 is outside the Sun's orbit —> appears to move toward us. AST 203 (Spring 2011) ...
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This note was uploaded on 05/04/2011 for the course AST 203 taught by Professor Simon,m during the Spring '08 term at SUNY Stony Brook.

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