Galaxies

1
Galaxies Types and Structures

• Other galaxies like our own Milky Way? Appear as
  small globules like globular clusters in our
  galaxy.
• Harlow Shapeley NO, only other globular
  cluster of stars
• Heber Curtis YES, other galaxies like island
  universes
• Hubble settled the debate by measuring the large
  distances to other galaxies using the bright
  Cepheid stars

2
Twin galaxies Spiral and Dwarf
Whirlpool Galaxy disintegrates its small neighbor
3
Mult-wavelength Far-Infrared map of M81 Bodes
Galaxy 12 million Lys Ursa Major constellation
4
Andromeda
5
Variety of Spiral Galaxies
6
(No Transcript)
7
(No Transcript)
8
Elliptical Galaxies
9
(No Transcript)
10
Types of Galaxies

• Spirals nucleus, bulge, halo, spiral arms
• Barred Spirals barred nucleus, ....
• Ellipticals various kinds of ellipticity,
  from near-circular E0 to highly oval and flat E7
  (need to distinguish from edge-on view) no
  disks, spiral arms, or dust lanes
• Irregulars Not like spirals or ellipticals
• Hubble Classification Tuning Fork Diagram

11
Ordinary Spirals
Ellipticals
Barred Spirals
12
Hubble Classification

• Ordinary Spirals classified according to
  relative bulge strength and tightness of spiral
  arms
• - Sa prominent bulge and tight but
  indistinct arms
• - Sb less prominent bulge and looser arm
  structure
• - Sc small bulge and loose and clearly seen
  arms
• i.e. from Sa to Sc, from tight to
  unwinding arms
• Barred Spirals bar-shaped nucleus (jet??) as
  many as ordinary spirals bar rotates like solid
  spiral arms emerge from either end (SBa, SBb,
  SBc)
• Irregulars chaotic structure, no systematic
  rotation, many dwarf irregular galaxies
  (classified as dI)

13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
Barred Spirals Powered by Rotating Jets
20
New Galaxy (General) Catalog (NGC)
21
(No Transcript)
22
Clusters of galaxies
23
Local Group of Galaxies Around Milky Way
24
Collision of Galaxies

• Galaxy-galaxy collision can induce gravitational
  tidal effects and lead to starbursts rapid
  stellar formation

25
Colliding Galaxies (Simulations)
26
Constant rotation Curves of Galaxies Dark Matter
27
Properties of Galaxies
28
Stellar Birthrate Ellipticals have older stars
than spirals
No significant star formation after 1 billion
years
Ongoing star formation
29
Distance Scale Hubbles law

• Hubble also discovered that the farther a galaxy
  is, the faster it is receding from us ? the
  Universe is expanding ? Big Bang !
• Hubbles Law Velocity is proportional to
  distance
• v H d (H Hubbles
  constant)
• H 71 km/s/Mpc
• Observe the redshift (like Doppler shift) from
  the spectrum and determine the distance

30
(No Transcript)
31
Redshift of the Ca II line in the spectra of
galaxies
32
Cosmological Distance Ladder

• Several methods
• - Trigonometric parallax (d 1/p), Earth as
  baseline
• up to 100 pc (gd based) - 1 kpc
  (Hipparcos Satellite)
• - Spectroscopic parallax (spectral type of
  star gives absolute L on H-R diagram, up to 50-60
  kpc
• - Cepheids and RR Lyrae, up to 30-40 Mpc
  (using Hubble Space Telescope), out to about
  Virgo cluster
• - Tully-Fisher Relation L is proportional
  to the Doppler width of the 21 cm H-line
  (proportional to mass and L)
• - Supernovae Ia up to a few hundred Mpc
  (using HST)
• Each step calibrates the next one bootstrap
  method

33
Observed Flux and Luminosity
Distance Modulus m M 5 Log (d/10) m
measured (apparent) magnitude M absolute
magnitude at 10 pc
34
(No Transcript)
35
Period-Luminosity RelationPulsating Cepheid, RR
Lyrae Stars
36
Apparent Magnitude (m) vs. T(d)
37
The Hydrogen 21-cm radio map of the Sky and the
Galaxy
Tully-Fisher Relation Width of 21-cm line, due
to Doppler blue and redshifts, is proportional
to mass of the galaxy, and therefore to
intrinsic Luminosity L ? Distance Modulus (m-M)
gives d
38
H I 21 cm Hyperfine Transition
39
Light Curves of Supernovae
40
Ho depends fit to data
41
Methods to determine the cosmological distance
scale
42
Multiple images by gravitational lensing
43
Gravitational Lensing and Multiple Images
44
Gravitational lensing of a quasar two images
a,b