1Mass-Luminosity relationships−−=133.34/110)(eRReIRIFrom Binney & Merrifield, Galactic AstronomyCO give different coefficients???re∝σ01.24Ie-0.82L ∝σ02.65re0.65• Faber-Jackson relation: Le~ σ04•Dn- σ0correlation.•Dn= diameter within which <I> = 20.75 µB• Fundamental plane in log Re, <I>e, log σ0space•Re= scale factor in R1/4law•<I>e= mean surface brightness within Re Different from Ie!• Intro. to Principle Component Analysis: astro-ph/9905079True shapes requires statistical analysis• Oblate = pancakes• Prolate = footballs2True shapes requires statistical analysis• Lower luminosity Î rotationally supported •(Vrot/ σ ) ~ ε/(1-ε)•Higher L Î pressure supported•(Vrot/ σ ) << 1From Binney & Tremaine, Galactic Dynamics= low L ellipticalsx = spiral bulges high L ellipticalsdEgECurve expected for galaxies that are flattened by rotation (i.e. have isotropic random velocity dispersions)CO pgs. 988-989(V/σ)*= 0.7Rotationally SupportedStatistics of ε = (1-b/a)• Oblate, prolate spheroids can’t fit the observed distribution.• Summing over wide range of true values of ε would fill in the dip at εobs= 0.• Triaxial spheroids can fit.• Nearly oblate triaxial spheroids seem best.32100 0.2 0.4 0.6 0.8 1.00 0.2 0.4 0.6 0.8 1.043210P(εobs)P(εobs)Oblate, true ε= 0.7Prolate, true ε= 0.5ε observedTriaxial, Axis ratios 1:0.8:0.3From Binney & Merrifield, Galactic Astronomy3Other evidence for triaxial systems• Isophotal twists• Kinematics (star motions)From Binney & Merrifield, Galactic AstronomyOrbits in E galaxies• Some families of non-closed orbits in a mildly triaxialpotential.From Binney & Tremaine, Galactic Dynamics4E galaxies are transparent, but 40% still have some dust lanes• Even if complete star formation at t=0, stars must subsequently have lost gas. • Detected by:• X-rays (Brehmsstrahlung): 108-1010M• H I emission lines: 107-109M• H II emission lines: 104-105M• But gas can be lost by• Supernova-driven winds• Ram pressure strippingDistribution of galaxy types• Dense regions (cluster centers) predominantly ellipticals.• Field galaxies predominantly spirals.• On average, roughly even split between E and S.ESS0Log (Projected surface density of galaxies) ÎFraction of population ÎTotal number of galaxiesDressler 19805Schecter Luminosity Functionφ (L)dL = Lαe-L/L* dLφ(M)dM = 10 –0.4(α+1)M e –10 dM• The Milky Way is an L*galaxy.0.4(M*-M)[CO 25.36][BM
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