1. Galaxies and Cosmology Dr Nicola Loaring SALT/SAAO nsl@saao.ac.za

2. 2 Introduction Less than 100 years ago the Sun was considered to be the centre of the Universe! Shapley, 1918, studying variable stars in globular clusters deduced size and scale of the Milky Way as well as our position within it. Hubble resolved the Andromeda nebula into individual stars a few years later, and studied variable stars in it, proving Andromeda to be a galaxy outside our own. [2.5 million light years away] Sun takes 225 MY to orbit the Galaxy, we’re out in the suburbs! Twice as much mass lies outside the luminous parts of our galaxy that inside! (6x10 11 M Sun ) 2 30 kpc ~ 96,000 LY across

4. Galaxy classification

5. NGC 1316 The radio lobes span over one million light years 3C219 Radio lobes span several hundred thousand light years Jets and Lobes M87. This jet extends at least 5000 light years from the nucleus of M87

6. The Hubble Ultra-Deep Field This is the most distant optical image taken to date using the HST The galaxies you see are nearly 13 billion light yrs away We see them as they looked just after the Universe was formed ~13.7 billion yrs ago These galaxies taken from 10 days of observing and are 4 billion times fainter than can be seen with the naked eye

7. The Hubble Ultra Deep Field Distant galaxies as they were nearly 13 million years ago Still busy forming and interacting

8. Definition of an active galaxy Over ten billion (10,000,000,000) galaxies are visible with modern telescopes. Stars produce most of the light in these galaxies. Galaxies with luminosities 1000x greater than normal galaxies are called active galaxies. Extra light is confined to the central 1pc (~3.3 LY) (smaller distance than to our nearest star).

9. Properties of Quasars Most luminous objects in the Universe! Luminosities up to 10 13 L sun Typical power of 10 40 W (~10 solar masses consumed per year). More than 300,000 known from all sky surveys. Despite being discovered at radio wavelengths, only 10% are radio loud, infact X-rays are the most efficient way to search for them!

10. Standard model of Active Galactic Nuclei NLR 10pc – 1kpc BLR ~1pc

11. Close in – the dusty torus

12. Black Holes Central engines of AGN and Quasars. Fed by infalling stellar material surrounding the black hole. Material forms an accretion disk before being sucked into the black hole

13. The Universe is really old The oldest globular clusters are between around 11-13 billion years old.

14. The Big Bang According to scientists the Universe began ~14 billion years ago in a Hot Big Bang. At creation the Universe was infinitely hot and infinitely small. Time started when the Universe began- there is no before the Big Bang!

16. Timeline of the Universe Cool enough for the first atoms

17. Observational evidence for the Big Bang Four pillars of the Big Bang Model: - Cosmic microwave background (CMB) - Expansion of the Universe - Abundance of the light elements - Formation of galaxies and large scale structure

18. The Cosmic Microwave Background: Theory Blackbody background radiation is a natural consequence of the whole universe having been in thermal equilibrium at one particular past time Continuous creation of radiation does not lead to a blackbody background − see photons from different distances, created at different times, with different redshifts − superposition of several blackbody spectra with different temperatures is not a blackbody Predicted (before it was discovered) in 1949!

19. ~380,000 yrs after the HBB the Universe cooled sufficiently for electrons and protons to form atoms. The matter and radiation then stopped interacting and radiation was free to travel to us. Initially T~3000K, now cooled to 2.7K due to the expansion of space. Light from the “surface of last scattering” has been travelling for >12 B yrs and covered a distance of ~ 1 M B B miles! The cosmic microwave background

20. The cosmic microwave background radiation Discovered in 1964 by Penzias and Wilson. The Earth is bathed in CMB at a temperature of 2.73K (-270C). Very smooth in all directions, temperature variations of only 1 part in 10 5 The temperature fluctuations are due to density fluctuations in the “soup” of particles. WMAP probe currently measuring the CMB 1992 2004 http://map.gsfc.nasa.gov/

21. CMB Observations COBE (~1990) T = 2.73 K smooth black body –Evidence for tiny, small-scale fluctuations expected from gathering of matter to form superclusters

22. Big Bang – Evidence II Abundance of light elements –H, D, He and trace amounts of Li produced in first 3 mins of the Universe –Predicted amount of D, He and Li depends on density of ordinary matter, can compare with the amount observed in stars and galaxies. –He is relatively insensitive to the density, expect ~24% of ordinary matter to be He produced in the BB in agreement with observations –The other light elements are more sensitive and the overall density of ordinary matter must be ~4% of the critical density –Heavier elements not formed in the BB because temp dropped too rapidly before they could be formed –Complicated by the fact that these elements could also be produced later during stellar nucleosynthesis

23. Big Bang Nucleosynthesis Predictions from BB nucleosynthesis models closely match the observed relative abundances of the light elements

24. Moving sources: Doppler shifts Police use this property in the radar boxes they use to track speed!

25. Doppler shifts using light waves Colour coded image of the doppler shift of the FeXIV 5308 Å line from the Sun’s corona. Supercluster of distant galaxies (right), as compared to the Sun (left).

26. Evidence for the Big Bang III Hubbles observations –Using Cepheid Variable stars in galaxies, assuming these are standard candles. – –Found redshifts (interpreted as a velocity of recession) were proportional to their distances (obtained from distance modulus equation). –Slope is the Hubble Constant, been very difficult to pin down due to galaxy peculiar velocities which can swamp cosmological redshift value (eg Andromeda which has a blue shift!)

27. The Unverse is expanding! Hubble’s Law In 1929 Hubble found that the recession velocity of galaxies is proportional to their distance: v = HD, where H is the Hubble constant. Modern measurements place H 0 at 74.2 +/- 3.6 km/s/Mpc. (1 Mpc = 3 MLY) DEMO

28. Redshift and time z z Age(z) Lookback Time (yr) (yr) 0.0 1.3e+10 0.0e+00 0.5 7.9e+09 4.8e+09 1.0 5.4e+09 7.3e+09 2.0 3.0e+09 9.7e+09 5.0 1.1e+09 1.2e+10 9.0 5.0e+08 1.2e+10 10 4.3e+08 1.2e+10

29. Gravity – The most influential force In 1687, Sir Isaac Newton put forward the inverse-square law of universal gravitation.

30. Build up of structure via gravity - Galaxies 1 Light Year = 63,255 AU = 9500 billion km! Have 100s of billions of stars. Size ~30,000 LY. Mass ~10 Billion x Sun M33 spiral galaxy M83 – Spiral galaxy M32 - Elliptical galaxy

31. Clusters: Sizes 3.3-33 M LY. Mass ~ 10 14 -10 15 SM. Several 1000 galaxies. Galaxy groups & clusters Groups: < 50 galaxies. Sizes 3 to 6 MLY. Mass ~ 10 13 SM.

32. Structure we see today, could not have formed already unless substantial “dark matter” is present. The dark matter collapses before ordinary matter because it is not subject to radiation pressure, which resists gravitational collapse. 32 Large Scale Structure – thanks to gravity http://cosmicweb.uchicago.edu/filaments.html

33. Evidence for Dark Matter Bullet cluster collision: Hot gas (normal matter) detected by the Chandra X-ray Observatory in X-rays (pink). Bullet-shaped clump on the right is hot gas from one cluster, which passed through the hot gas from the other larger cluster. In the collision between the giant galaxy clusters, hot gas clouds in the clusters encounter friction as they pass through one another. The dark matter isn't affected by this friction either so passed through easily and is shown in blue. Distribution of dark matter Calculated via lensing observations.

34. Evidence for Dark Matter The cluster includes the galaxies and a hot gas (tens of millions of degrees) detected in X-rays. By studying the distribution and temperature of the hot gas we can measure how much it is being squeezed by gravity from all the material in the cluster. There is 5x more material in clusters of galaxies than we would expect from the galaxies and hot gas we can see. Most of the matter in clusters of galaxies is invisible.

35. Gravitational Lensing

36. Curved Spacetime DEMO

37. Universal acceleration Because all white dwarfs achieve the same mass before exploding, they all achieve the same luminosity and can be used by astronomers as "standard candles”. Observing their apparent brightness -> distance Knowing the distance to a SN, we know how long ago it occurred. Measuring the redshift of the supernova, astronomers can determine how much the Universe has expanded since the explosion. By studying many supernovae at different distances, astronomers can piece together a history of the expansion of the Universe. In the 1990's astronomers found the supernovae to be fainter than expected. Hence, the expansion of the universe was accelerating! This expansion requires energy

38. SNe as probes of expansion The Universal expansion is currently accelerating!

39. Composition of the Universe

40. The Fate of the Universe Dark energy introduced by Einstein, anti-gravity energy to stop collapse Appears to dominate the total mass-energy content of the Universe

41. Cosmology still has a lot to answer! We only understand 5% of the constituents of our universe! We do not know what the dark matter is We do not know what the dark energy is We do not know the fate of our Universe