Lecture 8. Galaxies- Normal Galaxies To Quasars

Modern Astronomy Stars & Galaxies Lecture 8 Galaxies: From normal Galaxies to quasars q Geraint F. Lewis University of Sydney 2005

Outline The Milky Way: A reminder ‹ The family of galaxies ‹ Colliding C llidi galaxies l i ‹ AGN: The eccentric cousins ‹ Cosmological Spaghetti ‹

The Milky Way: A reminder

Scientific notation & units Scientific numbers; 103=1000 and 4.1£ 4.1£ 102 = 410 Solar mass: M¯ = 1.99£ 1.99£1030 kg Solar luminosity: L¯ = 3.90£ 3.90£1026 W Parsec: pc = 3.09£ 3 09£ 3.09 09£1016 m

The family of galaxies

Spiral Elliptical

Irregular

Spiral Galaxies Mass: ‹ Luminosity: ‹ Diameter: Di t ‹ Stars: ‹ Gas & dust: ‹ Rotation: ‹

109!4£1011 M¯ 108!2£1010 L¯ 5!50 kpc k All ages Some Yes

Classifying spirals: Sa

Large bulge bulge--to to--disk ratio!

Classifying spirals: Sb

Lower bulge bulge--to to-disk ratio

ESO

Classifying spirals: Sc

Small bulge bulge--to to--disk ratio

HST

Classifying spirals: bars Sa Sb Sc

Lenticular (S0)

Elliptical Galaxies Mass: ‹ Luminosity: ‹ Diameter: Di t ‹ Stars: ‹ Gas & dust: ‹ Rotation: ‹

105!1013 M¯ 3£105!1010 L¯ 1!200 kpc k Intermediate + Old Very little Very little

Classifying Elliptical Ellipticals are classified on the basis of their shape and are assigned a number

where a is the longest length and b is the shortest length (i.e. circular is equal to zero)

E1

E5

Hubble tuning fork

http://www.uni-sw.gwdg.de/~bziegler/images/galaxies/tuningfork_Frei.gif

Classification…. Classification

… is art!!

Irregular Galaxies: The dustbin Mass: ‹ Luminosity: ‹ Diameter: Di t ‹ Stars: ‹ Gas & dust: ‹ Rotation: ‹

108!3£1010 M¯ 107!109 L¯ 1!10 kpc k Young & Intermediate Lots Yes & No

Irregular galaxies

Large Magellanic Cloud

Irregular galaxies

Image credit: Westmoquette (UCL), WIYN/NASA/HST

The big and the small Big galaxies are relatively easy to see ‹ Small galaxies are hard to see ‹ Whenever Wh we look l k hard, h d we see many small galaxies for every large galaxy! ‹ This is true in our very own backyard ‹

The Local Group

Where do galaxies live? Galaxies rarely live alone ‹ The Milky Way is part of the Local Group with Andromeda and many smaller galaxies ‹ Most M t galaxies l i iin th the Universe U i are seen to live in groups similar to our own! ‹

Galaxy groups

Stephan’s Quintet

Hickson Group Gemini images

Galaxy clusters While rarer, rarer galaxy clusters represent the largest bound objects in the Universe ‹ The can contain thousands of galaxies ‹ Galaxy G l clusters l t can b be grouped d together t th to make superclusters of galaxies! ‹

The Coma Cluster

The not not--so so--local Universe The little black dot is out Local Group of galaxies. The side length of the box is ~200Mpc (more than 200x the distance between us and Andromeda). The Local Group is pulled by the gravitational attraction of the clusters and we are falling into the Virgo Cluster!!!

Mike Hudson (U Waterloo)

Abell 1689 (HST)

Galaxy clusters Usually at the centre of galaxy clusters we mind cD galaxies, the most massive galaxies we know ((100x Milky g y Way) y) ‹ Galaxies whip around clusters at thousands of km/s ((evidence for dark matter) ‹ The immense g gravitational field squeezes gas in the cluster, making it hot and glow in XX-rays! ‹

X-ray clusters

The Centaurus Cluster

Large scale structure

www.sdss.org

Numbers The observable Universe contains ‹ Around 100 billion galaxies ‹ C t i i Containing ~10 1022 stars t ‹ Galaxies sit on a cosmological foam ‹ Mainly ellipticals in clusters ‹ Mainly spirals “in in the field” field

Galaxy collisions With so many galaxies in a small volume collisions occur. volume, occur What happens? Material is thrown over a large region. Stars: rush passed one another and Stars: do not collide p , Gas: clouds collide and collapse, Gas: resulting in a burst of star formation

Galaxy collisions

John Dubinski http://www.cita.utoronto.ca/~dubinski/nbody/

Galaxy collisions Painting by Adolf Sch haller

Sometimes gas pools into the centre of the colliding system, resulting in a massive burst of star formation (more than 1000 new stars per year!) This burst produces masses of dust in supernovae making the galaxy glow supernovae, brightly in the infrared.

Feeding the monster! Remember that the heart of the Milky Way houses a supermassive black hole ‹ Detailed observations of stars in the centres of other nearby galaxies reveal that they too have black holes ‹ What happens when gas sinks into the centre t off a galaxy l during d i a collision? lli i ? ‹

AGN: Eccentric cousins ‹

‹

‹

The light we receive from a galaxy is simply the sum of the light of each star Sometimes So et es galaxies ga a es have a e a bright b g t core, co e, but the radiation is not starlight Often this bright g core outshines the entire starlight of a galaxy

Such bright cores are the signatures of Active Galactic Nuclei (AGN)

Active galaxies

Active galaxy

Starlight

• Non-thermal emission: High speed electrons, l t strong t magnetic ti fi fields, ld extreme environments •Broad emission line: High speed gas •~10% have strong radio emission

Radio jets

Jets can cover several hundred kiloparsecs to a couple of megaparsecs (remember the Milky Way has a diameter of several 10s of kiloparsecs). Cygnus A (6cm Carilli NRAO/AUI)

Active galaxies There e e are a e many a y different d e e t kinds ds of o AGN G Quasars, Seyferts, Blazars, Liners, BL Lac, FR I, FR II etc. Classification depends upon energy output, how th they were discovered… di d The idea is is, however however, that all AGN are variants of the same theme, a power source which consists of a supermassive p black hole.

The unified model ‹ ‹ ‹ ‹ ‹ ‹

Supermassive black hole Accretion disk of hot gas Jets High velocity clouds Thick torus of gas, dust & stars Low velocity clouds

All of this is packed in a volume not much larger than the solar system, t b butt can output t t as much h energy as a 100,000 billion Suns.

The unified model

What you see depends upon which angle you are looking at the central black hole!

Cosmological spaghetti Where do galaxies come from? • Were they born fully formed? • Did they grow over time?

Such S h questions ti are nott easy to t answer, and require building a universe inside a computer. t W We will ill llook k att thi this in i more detail next week, but for now..

A numerical universe ‹ ‹ ‹

Little things g form first Little things merger to become bigger Ultimately a few large things dominate and continually feed on the smaller objects

This suggests that an object like the Milky Way has not finished feeding. As we saw last week, there are several dwarf galaxies, including the Sagittarius dwarf and Canis Major dwarf which are being consumed at the moment!

Elliptical vs spiral Ellipticals: Violent formation, all gas used up Ellipticals: quickly, rotation destroyed Spirals: Spirals Sp a s: Formed o ed more o e sedately, sedate y, slow s o recycling ecyc g of gas, rotation maintained What does this mean for Andromeda and the Milky Way who meet in 3 billion years?

See you next week!

http://www.c cita.utoronto..ca/~dubinsk ki/tflops/