GALAXIES!

M82, nearby active galaxy, at 3.2 Mpc ~ 10 million lyrs

Optical Infrared X-ray

NGC 4594 Optical

NGC 4594 8 mm

NGC 628 (M74)

The merging Antennae Galaxy (NGC4038/4039)

Cartoon of a galaxy Halo Bulge Disk Spiral arms and Bars are found in the disks Haloes contain Globular Clusters

What a Globular Cluster looks like… From HST. A cluster of stars all born at the same time. An excellent `clock’, as most globular clusters are roughly as old as the Universe.

Our Own Galaxy (Milky Way)

Galaxies have at least four basic shapes (morphologies) Spirals Progression from Sa to Sb, Sc, Sd, Sm depends on how tight the spiral arms are wound and how big is the bulge

Spiral arms can also show a variety of shapes flocculent Grand design Spiral arms are easy to `see’ because they contain young, luminous stars (OB stars)

Barred spirals Same progression as regular spirals: SBa, SBb, etc.

Ellipticals: E0, E3, E6 Ellipticals range in mass from about 20 times to as small as 1/100,000 our own Milky Way

Irregulars

This is the Hubble Turning Fork

A few more differences Ellipticals do not rotate; they have `roundish’ shapes Spirals do rotate; hence they appear as flattened pancakes

Disk rotation different from that of rigid bodies

Hence the idea of Dark Matter

Appearance of a galaxy is also linked to the history of its stellar populations Elliptical galaxy: very old stars (red), formed very early in the life of the Universe Irregular galaxy: stars have been forming more or less at a constant pace for most of the life of the Universe; many young stars, often blue in appearance Spiral galaxy: stars have been forming at a decreasing pace over the entire life of the Universe, many young stars, esp. in spiral arms

Finally: most galaxies host SuperMassive Black Holes These SMBHs are many million times heavier than normal BHs.

The Milky Way hosts a MBH! The region towards the center of the MW, as seen by the Chandra X-ray telescope; Our own MBH is about 4 million solar masses

The mass of the central BH is proportional to the mass of the galaxy’s bulge Bulge Mass SMBH Mass A recent discovery

Quasars Stands for `Quasi Stellar Radio Source’ They only exist in the distant Universe, and are linked to the young galaxies; Perhaps when galaxies were forming, a lot of material was available to fall into the central BH, accrete it, and produce fantastic levels of energy and radiation.

Some of the unanswered questions How have galaxies evolved to the large diversity we observe today? How are the different morphologies formed, and when did they form? How are stellar populations linked to the different morphological components (bulge, disk, halo)? What are these components telling us about the link between the dark matter and the baryonic (ordinary) matter? How does the bulge knows about the central black hole?