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Exploring Galaxy Physics: Scales, Dynamics, and Recent Developments

Discover the fundamental aspects of galaxies, from scales and components to interactions and star formation, along with insights into new physics advancements. Gain knowledge on galaxy basics, constituent dynamics, and recent findings in nuclear black holes and activities.

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Exploring Galaxy Physics: Scales, Dynamics, and Recent Developments

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  1. Galaxy Physics Mark Whittle University of Virginia

  2. 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 developments

  3. 1. Galaxy Basics • Scales & constituents • Components & their morphology • Internal dynamics

  4. 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

  5. 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 important

  6. Nucleus Bulge Disk Halo Galaxy Components

  7. 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)

  8. 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 R

  9. 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

  10. 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 orbits

  11. <V> less than Vc GC more stars fewer stars • 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 dispersion

  12. 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 hydrodynamics

  13. 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 history

  14. Spiral mergers can make Ellipticals

  15. During interactions : • Gas loses angular momentum • Falls to the centre • Deepens the potential • Forms stars in starburst

  16. stars Gas/SFR

  17. Enhanced star formation

  18. Blowout : environmental pollution via superwinds

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