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Premium member Presentation Transcript Galaxy Physics: Galaxy Physics Mark Whittle University of VirginiaOutline : Outline Galaxy basics : scales, components, dynamics Galaxy interactions & star formation Nuclear black holes & activity (Formation of galaxies, clusters, & LSS) Aim to highlight relevant physics and recent developments1. Galaxy Basics : 1. Galaxy Basics Scales & constituents Components & their morphology Internal dynamicsGalaxies are huge : Galaxies are huge Solar sys = salt crystal Galaxy = Sydney Very empty Sun size = virus (micron) @ sun : spacing = 1m @ nucleus : spacing = 1cm Collisionless Average 2-body scattering ~ 1 arcsecond Significant after 10^4 orbits = 100 x age of universe Stars see a smooth potential Constituents : Constituents Dark matter Dominates on largest scales Non-baryonic & collisionless Stars About 10% of total mass Dominates luminous part Gas About 10% of star mass Collisional lose energy by radiation Can settle to bottom of potential and make stars Disk plane : gas creates disk stars (“cold” with small scale height) Nucleus/bulge : generates deep & steep potentials Historically ALL stars formed from gas, so behaviour importantGalaxy Components : Galaxy Components Nucleus Bulge Disk Halo Bulges & disks : Bulges & disks Radically different components Ratio spread ( E – S0 – Sa – Sb – Sc – Sd ) Concentrations differ (compact vs extended) Dynamics differ (dispersion vs rotation) Different histories (earlier vs later)Disks : Spiral Structure: Disks : Spiral Structure Disk stars are on nearly circular orbits Circular orbit, radius R, angular frequency omega Small radial kick oscillation, frequency kappa View as retrograde epicycle superposed on circle Usually, kappa = 1 – 2 omega orbits not closed (Keplerian exception : kappa = omega ellipse with GC @ focus) Near the sun : omega/kappa = 27/37 km/s/kpc Consider frame rotating at omega – kappa/2 orbit closes and is ellipse with GC at centre Consider many such orbits, with PA varying with RSlide22: Depending on the phase one gets bars or spirals These are kinematic density waves They are patterns resulting from orbit crowding They are generated by : Tides from passing neighbour Bars and/or oval distortions They can even self-generate (QSSS density wave) Amplify when pass through centre (swing amplification) Gas response is severe shocks star formation Disk & Bulge Dynamics: Disk & Bulge Dynamics Both are self gravitating systems Disks are rotationally supported (dynamically cold) Bulges are dispersion supported (dynamically hot) Two extremes along a continuum Rotation asymmetric drift dispersion What does all this mean ? Consider circular orbit, radius R speed Vc Small radial kick radial oscillation (epicycle) Orbit speeds : V<Vc outside R, V>Vc inside R Now consider an ensemble of such orbitsSlide24: GC more stars fewer stars <V> less than Vc Consider stars in rectangle Mean velocity mean rotation rate (<V>) Variation about mean dispersion (sig) In general <V> less than Vc For larger radial perturbations, <V> drops and sig increases Vc^2 ~ <V>^2 + sig^2 This is called asymmetric drift (clearly seen in MW stars) Extreme cases : Cold disks <V> = Vc and sig = 0 pure rotation Hot bulges <V> = 0 and sig ~ Vc pure dispersionSlide25: More complete analysis considers : Distribution function = f(v,r)d^3v d^3r This satisfies a continuity equation (stars conserved) The collisionless Boltzmann equation Difficult to solve, so consider average quantities <Vr>, <sig>, n (density), etc This gives the Jean’s Equation (in spherical coordinates) Which mirrors the equation of hydrostatic support : dp/dr + anisotropic correction + centrifugal correction = Fgrav Hence, we speak of stellar hydrodynamics2. Interactions & Mergers: 2. Interactions & Mergers Generate bulges (spiral + spiral = elliptical) Gas goes to the centre (loses AM) Intense star formation (starbursts) Supernova driven superwinds Chemical pollution of environment Cosmic star formation historySlide35: Spiral mergers can make EllipticalsSlide39: During interactions : Gas loses angular momentum Falls to the centre Deepens the potential Forms stars in starburst Slide40: stars Gas/SFREnhanced star formation: Enhanced star formationBlowout : environmental pollution via superwinds: Blowout : environmental pollution via superwindsCosmic star formation history: Cosmic star formation historySlide57: HDF3. Nuclear Black Holes & Activity: 3. Nuclear Black Holes & Activity Difficulties & methods Example #1 : the milky way Other examples : gas, stars, masers Black hole demographics – links to the bulge Black hole accretion : nuclear activity Cosmic evolution – ties to mergers and SFSlide66: Example #1 : the milky waySlide73: Other galaxies : methods Need tracer of near-nuclear velocity field Defines potential M(r) If more than M(stars) dark mass present Obvious tracers : stars and/or gas Doppler velocities (proper motions) Note : both rotation &/or dispersion present Use Jeans Equation M(r)Slide74: Pure rotation – gas or cold star disk isotropic dispersion anisotropic dispersion * Gas &/or star disks are best * Bulge stars are poor, unless isotropy known Activity : accretion onto the BH: Activity : accretion onto the BH Gravitational energy near Rs ~ 50% rest mass Accretion requires AM loss : MHD torques Energy liberated as photons & bulk flow Luminous across the EM spectrum Powerful outflows, some at relativistic speeds Accretion associated with galaxy interactions ? Black hole formation associated with mergers ? Quasar history linked to merger/SFR historyQuasar and Galaxy Evolution: Quasar and Galaxy Evolution Quasar/Starburst/Galaxy evolution related ? Major mergers Extreme star formation rates Elliptical/bulge formation BH formation and feeding = QSO Evidence Comparable luminosity in QSO and starburst Most luminous nearby mergers are also QSOs QSO evolution loosely follows SFR history Currently speculative – active area of research4. Galaxy Formation Theory: 4. Galaxy Formation Theory Mature subject – semi-analytic & numerical Two important observational constraints Galaxy luminosity function (many small, few large) Galaxy large scale structure (clusters, walls, voids) Start with uniform DM (+ baryon) distribution Add perturbations matched to CMB Embed in comoving expansion & add gravity Follow growth of perturbations : linear – non-linear Semi-analytic useful but limited Numerical follows full non-linear development + mergers Baryon physics recently included (pressure, cooling, SF,…) You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.