1414

GalaxiesGalaxies

Island Universes

1414Copyright – FORS1 VLTI, European Southern Observatory

1414

Ellipticals

1414

Ellipticals

• Huge• No gas.• No dust.• No young

stars.• Nothing but

old stars.– Random

orbits.

1414

M 87 Copyright – Anglo-Australian Telescope Board

Copyright - HST

1414

Spirals

1414

Spirals

• Like Milky Way.• Disks and

bulge.• Young stars

and old.• Gas and dust.• Stars forming.• Stars dying. M81 and M82 – Copyright R. Gendler

1414M63 Copyright – S. Miyazaki, Suburu

1414NGC1365 Copyright – VLT

1414M31 The Andromeda Galaxy Copyright – Jason Ware

Copyright – S. Miyazaki, Suburu

1414M33 – Copyright NOAO

1414M51 - Copyright HST

John P. Gleason

1414NGC 4314

1414NGC 891 – Copyright J.C. Barentine, NOAO

NGC 891 – Copyright WIYN

1414Sombrero Galaxy – Copyright P. Barthel VLT

M10 – copyright Credner and Kohle

1414

NGC 4526

1414

Irregulars

1414

Nearby Galaxies

• Cepheids.• Period.• Luminosity

abs. mag.• Know app. Mag• Get Distance.

10pc

distancelog5 10Mm

1414

Groups

1414

The Local Group

1414

Clusters

1414

The Virgo Cluster

1414

1414

Distant Galaxies

• Can’t see individual stars.• Can use nearby galaxies to get

distances to further galaxies.• Distance ladder:

– Parallax nearby stars– Nearby stars H-R diagram– H-R diagram distant stars (variables)– Variable stars nearby galaxies– Nearby galaxies ?

1414

21cm Radiation

• Neutral hydrogen (HI) gives off radiation at 21cm.

Milky Way HI emission – Copyright J. Dickey

1414

Extragalactic HI

• Observe HI in other galaxies.• Measure wavelength of 21 cm radiation.• Get velocity away from us.

1414

Hubble’s Law

• Measure the velocity of every galaxy.

• Nearly all are redshifted.

• Use Cepheids to measure distances to nearby galaxies.

• Result: The faster it’s moving, the farther away it is.DH v

distance velocity

o

1414

Map the Universe• V = HoD

• If you know Ho:

• Measure v• Get D• Find:

VoidsWalls

Clusters

1414

1414

Homework #12Homework #12

• Read: Bennett Ch 22.1 – 22.4• Do Ch22:

– Problems: 1, 6, 9, 12– Math folks substitute problem 18 for 9 and

12.