Galactic Kinematics

Galactic KinematicsThe Local Standard of Rest (LSR)

Solar motiondisk velocity dispersion

Galactic Rotation

LSR - local standard of rest

More generally, if the Galactic potential is not axis-symmetric(e.g., because of the Galactic bar), then the LSR orbit is oval.

Solar motion: sun moving “upwards” at7 km/s wrt other stars

The residual solar motion wrt the average of local stars is

U! = −10 km s−1

V! = 5 km s−1

Currently we are near the mid-plane

Some say V = 15 km/s!

W! = 7 km s−1

σz =√∑

W 2i

Oort limit - imagine the disk as a plane parallel slab

Are we happywith these sums?

How might we get R0?

termina

l velo

city c

urve

terminal velocity curve

bumps & wiggles in rotation curves

terminal v

elocity

curve

stars

stars

gas

gas

Renzo’s rule: When you see a feature in the light,you see a corresponding feature in the rotation curve.

Fitting the bumps & wiggles at small radiisuccessful in predicting the rotation curve

at large radii.

BHB stars from SDSS

gas

stars

dark matter