Transcript Document

Galaxy Formation
Formation of galaxies in cold dark matter universe
QuickTime™ and a
decompressor
are needed to see this picture.
Hubble Galaxy Sequence
Ellipticals (round through oval)
Spirals (centrally condensed with arms)
Barred Spirals (distinct bar shape with bulge)
Shapes of Galaxies
Spirals



disk shaped with spiral arms
often have bright bulges in center
contain interstellar gas, nebulae, star forming
regions, open clusters and globular clusters
Barred Spirals


spiral arms emerge from end of bar
gas from outer part of galaxy funneled to center
through the bar, forming new stars in bulge
Shapes of Galaxies
Ellipticals




range from spherical to foot-ball shapes
lots of old stars and globular clusters
star formation is over or just restarting
maybe the result of collision and merger of smaller
galaxies
Irregulars


lots of gas and new stars forming
rather small compared to spirals and ellipticals
Edge-on Spiral Galaxy
NGC 891 - we think our Galaxy looks like this
This is an
infrared
composite
image from
KPNO
Spiral sequence
Sandage
Hubble Space Telescope
NGC 7537/Sbc
Spiral Galaxies
Bulges formed over a short period very early in the young
universe, perhaps through the collapse of a single cloud of
hydrogen or merger of primeval star clusters.
NGC 1232/VLT
NGC 1288
Spiral sequence
Sandage
Hubble Space Telescope
NGC 5838/S0
Spiral sequence
Sandage
Hubble Space Telescope
NGC 5689/Sa
Barred Spiral M61
Bar across central
region is made of stars,
gas, and dust
Small bulge is
dominated by a disk of
material
Spiral arms begin at
both ends of the bar
The bar is funneling material into the hub, which
triggers star formation and feeds the bulge
Barred Spiral NGC1365
IR/HST NICMOS
Optical/Sandage
Optical/HST WFPC2
M87 Optical
Giant elliptical galaxy
At center of Virgo
cluster
Many globular clusters
surround it
Little dust and gas in the
galaxy
50 million light years
away
M87 Optical Jet
HST IR and UV
composite
Globular clusters
also seen
Note shock waves
and knot patterns
in jet
Bright point at
central black hole
Irregular Galaxies
Sextans A
5000 light years across
5 million light years away
NGC 4753/I0
Galaxy Evolution
A computer
simulation of a flat
disk-type galaxy
colliding with a dwarf
galaxy. The dwarf
galaxy cannot be
seen, but its
gravitational
influences trigger the
production of spiral
arms in the gas-rich
disk.
QuickTime™ and a
decompressor
are needed to see this picture.
Collisions and Mergers
Note: galaxies do not make noise when they
collide!
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Galaxy Collision
QuickTime™ and a
Intel Indeo® Video R3.2 decompressor
are needed to see this picture.
Galaxy Collisions, Part 2
QuickTime™ and a
Intel Indeo® Video R3.2 decompressor
are needed to see this picture.
M31/Andromeda
Our nearest
spiral
neighbor
2 million light
years away
Center of M31 has two
optical nuclei
M31/Chandra X-ray
Image of
central part of
our neighbor
M31
Bright X-ray
sources are
binaries with
black holes or
neutron stars
Central BH is
very cool, 30
million Mo
Center of
M31
Cartwheel Galaxy
Wheel shape was
formed from collision of
two galaxies
Bright stars are forming
at the edges of the
wheel (105 light years in
diameter)
Intruder galaxy is no
longer visible
This is from
HST
Active Galaxies
Quasars




Quasi-stellar radio source. (A radio source that is
so far away that it looks like a star.)
Bright nucleus
Highly variable
Most produce strong X-rays
Seyfert galaxies


Spiral galaxies with bright nucleus
Seyfert 2 galaxies are viewed through gas disk
Active Galaxies
Radio galaxies





quasars with radio emission (original quasars)
some have two lobes, connected by jets
some are wildly variable and have X-rays
not especially bright in visible light
often giant elliptical galaxies
Blazars

wildly variable, have lots of X-rays and gammarays
Unified Model of AGN
All AGN are the
same: central BH
plus disk and jets
Differences in lines,
jets, & spectra are
due to different
viewing angles
Also possible that
BHs are being fed at
different rates
Centaurus A/Optical
Giant elliptical
galaxy
10 million light
years away
Dark dust lane
obscures the
central region
Centaurus A/Radio
Double Lobe
Radio Galaxy
Image shows
radio lobes
superposed on
optical image
Central black hole
must be producing
radio jets and
lobes
Centaurus A/X-ray
X-ray image from
Chandra
Bright nucleus can
be seen in center
at location of
black hole
Small jet to lower
right ends in
shocked region
Centaurus A/IR
IR map shows a
second galaxy
(barred spiral) hiding
inside Cen A’s dust
lanes
Elliptical’s gravity
helps barred spiral
maintain its shape
Material funneled
along the spiral's bar
fuels the central
black hole which
powers the elliptical's
radio lobes
Symbiotic relationship