Presentation on theme: "Cosmology from the Cosmic Microwave Background"— Presentation transcript:
1 Cosmology from the Cosmic Microwave Background Katy LancasterAstrophysics Group
2 Who am I?Postdoc in the Physics department working with Professor Mark BirkinshawPreviously:PhD at the Cavendish Laboratory, Cambridge, working on similar topicsMSci at Bristol !
3 Astrophysics: ‘That branch of astronomy which treats of the physical or chemical properties of the celestial bodies. Hence astrophysicist, a student of astronomical physics.’
4 OBSERVATIONALObserve celestial bodies (stars, galaxies etc) at various wavelengthsFit theoretical models to data to choose the most appropriateTHEORETICALSimulate celestial bodies (stellar evolution, galaxy formation etc)Create models of possible physical processes
5 OBSERVATIONALObserve celestial bodies (stars, galaxies etc) at various wavelengthsFit theoretical models to data to choose the most appropriateTHEORETICALSimulate celestial bodies (stellar evolution, galaxy formation etc)Create models of possible physical processes
7 ie towards the red end of the visible spectrum. StarsCMBAGNPlanetsGalaxiesClustersREDSHIFTAside…..Redshift: The Doppler shift observed due to the expansion of the UniverseThe light from an object moving away from us is shifted to longer wavelengthsie towards the red end of the visible spectrum.StarsPlanetsREDSHIFTAGNGalaxiesGalaxiesClustersClustersClustersCMB
9 Multi-wavelength information is essential in all branches of Astronomy In my work: mainly radio frequencies, but still spanning the range GHz (requires different technology)Can also combine with X-ray data and lensing data (optical)More about this later!Now onto the specifics
10 Topics in Astrophysics….. Solar System: planets, the sunStars: stellar composition, stellar evolution, star formation, supernovae, extra-solar planetsGalaxies: structure, properties, stellar velocities (dark matter), formation, evolution, clustering…Active galaxies: mechanisms, power sources (black holes)High-energy phenomena: Gamma ray burstsGalaxy clusters: galaxy properties, gas properties, lensing (dark matter), super clustering….Large scale structure, structure formation theoriesCosmology: properties of the Universe as a whole, formation (the Big Bang), fate??
11 Cosmology: ‘The science or theory of the universe as an ordered whole, and of the general laws which govern it. Also, a particular account or system of the universe and its laws.’
12 Big questions in cosmology Critical density: Universe expands foreverLess dense: Expansion rate increasesMore dense: Universe will collapseAccelerating: Dark energy???Big questions in cosmologyIs the Universe open or closed?Depends on the mean densityWe can constrain this using the CMBWhat is the Universe made from?‘Normal’ stuff plus Dark MatterWhat is Dark Matter? Particle physicists working on it!Why does it appear to be accelerating?It is being ‘pushed’ by Dark Energy
13 My Work: Very hot topics in Astrophysics at the moment! COSMOLOGY from:The ‘Cosmic Microwave Background Radiation (CMB)’The interaction of the CMB with ‘Galaxy Clusters’ via the ‘Sunyaev Zel’dovich Effect’OBSERVATIONAL - ie obtaining data, data processing, extracting scienceTenerife, Poland, Hawaii, Taiwan…..Very hot topics inAstrophysicsat the moment!
14 Talk Structure:The Big Bang and production of the Cosmic Microwave BackgroundGalaxy Clusters and the Sunyaev Zel’dovich EffectThe Science we can hope to learn via observations of the aboveCurrent Research
17 The Big Bang Not really an ‘explosion’ Universe expanded rapidly as a wholeUniverse is still expanding today as a result of the Big BangMatter was created in the form of tiny particles (protons, neutrons, electrons)Too hot for normal ‘stuff’ to form (eg atoms, molecules)
19 Much cooled, atoms form, photons escape 300,000 years laterMuch cooled, atoms form, photons escape
20 Formation of the CMB The Universe is initially hot, dense and ionised Photons continually scatter from charged particles until….….temperature decreases and atoms form (neutral particles)Photons ‘escape’ and stream freely through the Universe.Observe the same photons today, much cooled, as the Cosmic Microwave Background
21 The CMB todayCan observe the CMB photons today, 13.7Gyr after the Big BangRadiation has been highly redshifted by the Hubble ExpansionMuch cooled: 2.73 K (compare this with 3000K at recombination)Conclusive evidence for the Big Bang theory - proves Universe was once in thermal equilibriumSo what does it look like?
22 Observe ‘blank’ sky with a radio telescope. Rather than darkness, see Uniform, high-energy glowHigh sensitivity measurements reveal......
24 Tiny temperature differences When the CMB photons ‘escaped’, structures were starting to formThese structures have now become galaxiesThe structure formation processes have affected the CMB and we see the imprint as ‘hot’ and ‘cold’ spotsVery difficult to measure!
25 What does the CMB tell us? Measure the strength of the temperature differences on different scales, eg:
26 What does the CMB tell us? Measure the strength of the temperature differences on different scales, eg:
27 What does the CMB tell us? Measure the strength of the temperature differences on different scalesTheorists: come up with a model including all of the physics of CMB/structure formationObservers: fit the model to real observations of the CMBThe model contains many parameters which describe the Universe
29 ParametersThe function on the previous slide is complex and involves many parameters including:Density of Universe in ORDINARY MATTERDensity of Universe in DARK MATTERDensity of Universe in DARK ENERGY(The sum of which is the total density, and governs the fate of the Universe as discussed earlier).We can constrain some of the big questions in cosmology by observing the CMB
30 Current ‘best model’ The Universe appears to be flat Ratio of total density to critical density =1But measurements suggest that only 30% of this density can come from matterContributions from ‘ordinary’ and ‘dark’ matterThis points towards the existence of ‘something else’ which we call Dark EnergyDark energy is believed to be pushing the Universe outwards, i.e. accelerating the expansion
32 What next for CMB research? New satellite, Planck, launch date 2008?This, and some ground based experiments are trying to measure CMB polarisation (difficult!)Another route: look for ‘secondary’ features in the CMB (ie those that have occurred since the Big Bang)
33 Other imprints on the CMB Let’s forget the tiny temperature fluctuations for now!Majority of CMB photons have travelled through the Universe unimpededSome have interacted with ionised material on the wayMain contributor: Galaxy clusters
34 Rich Clusters - congregations of hundreds or even thousands of galaxies See cluster galaxies and lensing arcs in the opticalBut only around 5% of a cluster’s mass is in galaxies (Most of the mass is in Dark Matter)But a sizeable fraction is found in hot gas......
35 X-rays - see hot gasvia Bremstrahlung emission10-30% of total massChandra Image of the Coma cluster
36 Cluster Gas Gas trapped in huge gravitational potential Hot, dense and energeticIonised - may interact with incident radiation (such as the CMB)Believed to share the same characteristics as Universal matter
37 Sunyaev and Zel’dovich Postulated that the CMB could interact with the gas in galaxy clustersThe ‘Sunyaev Zel’dovich (SZ) Effect’
38 The SZ EffectLow energy CMB photon collides with high energy cluster electronPhoton receives energy boostNet effect: shift CMB to higher frequencies in the direction of a cluster
39 No dependence on redshift!!! At low radio frequencies, observe decrement (shadow) towards a cluster.Strength is proportional to the temperature and density of the cluster gasNo dependence on redshift!!!
41 SZ Science Very briefly: SZ can be used to find how much gas there is in a cluster compared with its total mass. This tells us about the matter density of the UniverseSZ can also be used to constrain the distance scale - because we don’t understand the geometry of the Universe it is difficult to infer distances directly
42 Exciting new Science!In most branches of Astronomy, it is difficult to observe very distant objectsThe SZ effect is redshift-independent, so in theory we can observe ALL clusters in existenceCurrent hot topic: surveying the sky using radio telescopes to find new clusters via the SZ effect
43 Cluster surveys Generate catalogues of ALL clusters Cluster evolution Study how cluster properties change as a function of distance (and hence cluster age)Evolution of the UniverseStudy how the cluster number density changes with redshift: cosmology
48 Can overcome most problems but it’s not easy! The SZ effect is TINYGalaxy clusters contain galaxies, which may emit radio waves and drown the SZ signalRequire further information, or observations at multiple frequencies.Radio galaxies are less bright at higher frequencies, but higher frequency observations suffer from atmospheric contaminationRemember the fluctuations in the CMB itself? They can also contaminate!Go to higher resolutionCan overcome most problems but it’s not easy!
49 Summary The CMB is relic radiation from the Big Bang Contains the imprint of early structure formationThe CMB may interact with ionised structures along its path towards usThe dominant process is the ‘Sunyaev Zel’dovich effect’ in galaxy clustersObserving the CMB can tell us about important cosmological parameters…….but Sunyaev Zel’dovich studies are really the next step