L14 ellipticals

Question 1

elliptical vs spirals dust content ?

Answer 1

spiral—dust (youg blue stars)

E— dust low

Question 2

ellipticals rotat slowly why?

Answer 2

1. not a disk like spirals
2. ??????
   bcoz vel dispersion was wrongly assumed isotropic

Question 3

what s faber jackson relation?

distance determination of FJR?

Answer 3

L ~ v_dis ^4

used to calc dist
not acc coz based on lum,
L diff to measure acc– comes form faint outer parts of gal

Question 4

fundamental plane relation?

Answer 4

measuring in terms of isophates

relation

Question 5

reason for galaxy flattening?

Answer 5

rotat x

right: vel anisotropy

observed: elliptical rotation slower
wrong prediction bcoz of wrong assumption: isotropy

Question 6

vel dispersion anisotropic

Answer 6

vel
complete it XXXX

Question 7

virial th?
meaning
formual
limitation?
derive?

Answer 7

relation bw KE n PE of a sys

the total kinetic and the total potential energy have a fixed ratio,
-1/2 in case of a gravitational system.

limitation: applicable only to systems in steady state.

Question 8

use of virial th?

Answer 8

mass estimate of star cluster/ gal fro non-circular orbit

assume a steady state system
M/L const— brightness I(x) measure of mass

measure the stellar radial velocities Vr relative to the cluster’s mean motion, and find the velocity dispersion σr.

use that n virial th to estimate mass

Question 9

box vs tube orbit

Answer 9

tube: orbit around 1 of the axis (aka loop: A star on a loop orbit is prevented by its angular momentum from passing through the center, but always circles it in the same sense, keeping a minimum distance.)

box: orbit around 1 of the axis, fills area, passes thorugh center

both found in triaxial sys

Question 10

evidence of DM in terms of M/L?

calc DM?

Answer 10

M/L larger away from the center

Most of whatever makes up the outer parts of a spiral emits very little light; we call it dark matter.

find M/L for center and outer region, compare w VT