The Milky Way

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Warp due to neighbors?
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• CO concentrations
• coincide with arms
• Also mapped with
• OB stars
• H II
• Supernova remnants
• Open clusters
• Cepheids
• Is this correct?

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Solar Motion

• Suns motion towards Hercules
• Oscillates relative to plane of galaxy (??)
• Motion through spiral arms extinction?
• LSR local standard of rest
• Reference frame
• Based on motion of Sun, neighbors around MW
• Assumes circular motion
• All stars not in circular motion move relative to
  LSR (Sun 14 km/s off LSR)

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Oort Formulae

• Keplerian motion of stars in MW
• Differential rotation
• Velocity variation with distance provides
  information about galaxy, our location
• This is the basis of the Oort formulae
• (same guy that did the Oort clouds for comets)

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• R? our distance from center
• Vo vel. of LSR
• R distance of object from center
• ddistance of object
• Vvel of object
• Made up of radial, tangential velocity
• l gal. longitude
• a another angle

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• Use assumption of Keplerian motion and a bunch of
  other icky math to get.
• Oort constants (A,B)
• vr radial vel.
• vt tangential vel.
• A, B observed

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• What does this tell us?
• Agt0, V/R decreases with increasing R so that
• stars at RltRo, go faster than LSR
• stars at RgtRo, go slower than LSR
• Values of A, B give relation of Vo to Ro
• Can derive rotation curve of galaxy

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And they keep on measuring it
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Spiral Arm Motion

• Moves independently of material in the disk
• Why?

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• Spiral Pattern motion fairly uniform
• Moves through material
• or
• Material moves through it

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Galactic Bulge

• Basic characteristics
• 3 kpc in radius
• Metal poor stars, Fe/H -1.25 to .5
• K giants, RR Lyrae
• 1010 M?
• Declining H I amounts
• Non-circular gas motion
• Bar?

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Sober or drunk?

• Does the Milky Way have a bar?
• Look at motions lt 3 kpc
• CRAP in the way!
• A few windows available Baades
• Measure magnitudes of stars on either side of
  l0º

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• Motions/Stars indicate
• Presence of a bar
• COBE/IR surveys
• Ring around bar also
• (remember molecular ring?)

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Sgr B2 35 pc 3 million M? Dense molecular
cloud Ring? Nothing on other side Sgr A
Nucleus Complex Structure
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Sgr A East nonthermal radiation, SNR Sgr A West
H II region? Within Sgr A West is Sgr A
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Sgr A

• Center of the Milky Way
• Structures
• Molecular ring
• 7 pc radius, tilted relative to the plane
• spiral structure ionized gas
• Gas in ring, highly ionized OB stars
• Star formation? Maybe, maybe not

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Star formation?
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Black hole?

• Mass within 0.016 pc, 2.5 million M?
• 3 million M? out to 2 pc
• Non-thermal source
• 2.4 AU size
• Uncertain luminosity
• Options?
• BH radius 5x R?

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Halo

• Radius 50 kpc
• Globular clusters
• Orbit around center
• Most randomly
• Some move with disk circular
• Gas disk, 10 kpc thick
• High eccentricity stars
• Dark matter 2 x 1011 M?