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Galactic Astronomy

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Fig. 8.31 : rotation vel. Central part : region of solid-body rotation ... Closed contours in spider diagram : decline in rot.vel. ... – PowerPoint PPT presentation

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Title: Galactic Astronomy


1
Galactic Astronomy
  • Velocity fields of disks

Dong-hyun Lee 2007/08/23
2
Velocity fields of disks
  • Focus on the central freq. of the received
    radiation
  • Central vel. dispersion line profile
  • Fig. 8.36 collection of concentric, circular
    rings
  • r center to point, n(r) unit vector normal
    to the ring of r
  • Omega(r) ang. Vel. Of ring
  • R unit vector to observer
  • Flat disk

3
Velocity fields of disks
  • Fig. 8.31 rotation vel.
  • Central part region of solid-body rotation
  • Fig. 8.32 contours of const. v_los ? spider
    diagram
  • Closed contours in spider diagram decline in
    rot.vel.
  • Kinematic minor axis locus of pt.s having same
    sys. Vel.
  • Kinematic major axis run through nucleus
    everywhere perpendicular to local const-vel
    contours
  • Fig. 8.32 kin. Minor magor axes coincide
    apparent optical axes

4
Circular-speed curves
  • V_c (r ) deduce mass interior to rad.
  • R_25 usually beyond ½ R_25
  • Fig. 8.33 left panels in kpc / right ones
    func.of R_25
  • Kinematic minor axis locus of pt.s having same
    sys. Vel.
  • At large R/R_25 is correlated with lum.

5
Circular-speed curves
  • Sc at small R/R_25 max. rot. Speeds (lum. Than
    faint) at large R/R_25 flat or falling (lum.
    Than faint)
  • Correl. b/w lum amp. In cir-sp. Curves ?
    Tully-Fisher rel
  • Observed cir-sp.curves mass-to-light ratio
    Gamma(d) Gamma(b) (disk, bulge)
  • Fig. 8.34 left disagreement of theory
    observation
  • Fig. 8.35 at least 3 times as much mass within
    12R_d as within R_25 R_d disk sacle length
  • Cir-sp.curves extend to more than 5R_d generally
    require significant masses to reside beyond R_25
    DM

6
Circular-speed curves
  • DH emits no light unknown spatial dist.
  • Assume
  • physically unmotivated
  • N-body sim. NFW law
  • M_0, a free parameters
  • Gamma increases sharply as the surf. Brightness
    of gal.s falls below a frac of a percent of the
    brightness of night sky.

7
Kinematic warps
  • Tilted-ring model Fig. 8.36 right
  • Each ring projects into an ellipse ellipse vel.
    contour (fig.8.32)
  • Within each ellipse, kin. Axes will be mutually
    perpendicular
  • K func.of r throug n(r) , kin.maj.axis
    will twist ? Fig. 8.37
  • Fig. 8.38 l.o.s pass through disk twice ? line
    profile will normally have more than one peak
  • Evidence of warps studies in p.512

8
Oval distortions
  • Observed spidergram kin. Axes arent mutually
    perpendicular Fig. 8.39 ? gas moving on
    elliptical rather than circular orbits
  • Models complex rotation mat. model-dep. Rel.
    b/w disks shape vel. Field dep.on nature of
    driving non-axisym. Grav.potential
  • Fig. 8.40 key points viewing angle
  • Kin.axes are not perpendicular, although
    photometric axes are for face-on
  • Kin. photo. Minor axes do not coincide
  • Kin.maj.axis lies close to line of nodes, esp. at
    high inclinations
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