astro330 31oct

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Published on November 5, 2007

Author: Oceane

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Astronomy 330:  Astronomy 330 31 October 2006 Class #17 Happy Halloween!!! Outline:  Outline Review Basic properties Results of stellar kinematics Fundamental Plane Hot Gas and Dark Matter Centers of Elliptical Galaxies Dwarf Ellipticals Formation and Galactic Cannibalism Basic Properties of Elliptical Galaxies (Review):  Basic Properties of Elliptical Galaxies (Review) Have a look at Figure 6.6 in the book Round things occupy a variety of loci on a plot of central surface brightness vs total luminosity Surface photometry I(r)=Ieexp{-7.67[(r/re)1/4-1]} “r1/4” law Re = effective radius at which ½ of light is emitted Comparable to bulges of disk galaxies Classification: E0-E7 describing increase in flattening Stellar populations: old, metal rich Environment: dense, usually in clusters (morphology-density relationship) Sample Spectra:  Sample Spectra How do you do this?:  How do you do this? Main lines are Hβ, Mg II, Fe I (generally in blue part of the spectrum Case study: NGC 1399 (cD in Fornax) V ~ 20-40 km s-1 σ2 ~ 250-350 km s-1 h3~0.02, h4~0.02 Next step: pick a potential that will fit observed kinematics and surface brightness profile Results:  Results Stellar Kinematics :  Stellar Kinematics Line of sight velocity distributions (LOSVD) Four parameters Mean velocity, velocity dispersion, two measures of how the line profile (velocity distribution) deviates from being Gaussian (h3, h4) M/L ratio increases with R M/r = 5 x 1012 M0 kpc-1 M/L ~ 100-200 in some cases Kinematics dominated by a dark halo beyond 1-2 Re “flat” σ vs R curves (just like spirals) (further confirmation of dark halo comes from power law like distribution of hot x-ray emitting gas) Mass model components:  Mass model components e.g.: Φ(R,Z)=(1/2)v02ln(Rc2+R2) Maximize the things you know (stars) Use four key kinematic parameters Fit weirdness (e.g. steep rise in velocity dispersion in the center by including a black hole – see SOS program) Alternatively, use tracers at large radii (PN and GCs) to obtain overall velocity Some results:  Some results M/L ratio increases with R M/r = 5 x 1012 M0 kpc-1 M/L ~ 100-200 in some cases Kinematics dominated by a dark halo beyond 1-2 Re “flat” σ vs R curves (just like spirals) (further confirmation of dark halo comes from power law like distribution of hot x-ray emitting gas) Velocity Field/Dispersion:  Velocity Field/Dispersion True Shape of Ellipticals:  True Shape of Ellipticals We see the 2-dimensional projection of a three dimensional thing: how can we tell the true shape? Orbits Viewing angle Velocity fields Look for deviations in the 2-dimensional data  twists in the isophotes Peng, Ford, Freeman (2004) use planetary nebula to map kinematics in NGC 5128 PNs  bright, emission line sources, widely distributed 1141 PNe  velocity field for N5128 Twist in isovelocity contours suggests triaxiality Can do this with stellar velocity fields within the galaxy as well (see papers by Statler et al) Fundamental Plane:  Fundamental Plane Scaling relationship between size, velocity dispersion, and surafce brightness Faber-Jackson: L ~ σ4 E’s occupy a plane in re, σ, μe space re ~ σAμB (A~1.3, B~-0.8) virial theorem: <re> = <σ2><μe>-1<M/L>-1 Observed fit: log re = 0.36(<I>e/μB)+1.4logσ Why the discrepancy? M/L is not constant? Es are really anisotropic? Fundamental Plane:  Fundamental Plane Fundamental Plane (3-D):  Fundamental Plane (3-D) Fundamental Plane:  Fundamental Plane Scaling relationship between size, velocity dispersion, and surafce brightness Faber-Jackson: L ~ σ4 E’s occupy a plane in re, σ, μe space re ~ σAμB (A~1.3, B~-0.8) virial theorem: <re> = <σ2><μe>-1<M/L>-1 Observed fit: log re = 0.36(<I>e/μB)+1.4logσ Why the discrepancy? M/L is not constant? Es are really anisotropic? Hot Gas and Dark Matter:  Hot Gas and Dark Matter T  velocity dispersion  mass distribution Let’s assume hydrostatic equilibrium d/dr(ρgaskT/μmp) = (GM(<r)/r2)ρgas Direct measure of elliptical mass from X-ray data; also works in galaxy clusters Gas temp > stellar kinetic temp μmp<σ>2/k<T> ~ 0.5  this alone suggest some dark matter; Tgas/T* ratio increases for low velocity dispersion X-ray Emission:  X-ray Emission Hot Gas and Dark Matter:  Hot Gas and Dark Matter T  velocity dispersion  mass distribution Let’s assume hydrostatic equilibrium d/dr(ρgaskT/μmp) = (GM(<r)/r2)ρgas Direct measure of elliptical mass from X-ray data; also works in galaxy clusters Gas temp > stellar kinetic temp μmp<σ>2/k<T> ~ 0.5  this alone suggest some dark matter; Tgas/T* ratio increases for low velocity dispersion Stellar Kinematics and DM:  Stellar Kinematics and DM Apply something like the CBE Jeans equation for spherical, isotropic stellar system d(ρσ2)/dr = -GM(r)ρ/r2 + ρV2/r Adopt a mass model e.g. isothermal sphere, NFW halo This is only for the dark matter e.g. Hernquist: ρ(r)=(Mla/2π)(1/r(r+a)2) This is only for the luminous matter For N5128, this yields M/L ~ 12-15 Central Regions:  Central Regions Again, it’s the photometry game  try to fit some function to the observed light distribution  looking for deviations from “R1/4” law I(r)=Ib2(β-γ)/α(rb/r)γ[1+(r/rb)α](γ-β)/α rb = “break” radius γ = inner logarithmic slope (r < rb)  γ = - dlogI/dlogr β = outer slope α = sharpness of break “core” galaxies (γ > 0) “power law” galaxies – steep surface brightness profile with luminosity densities in center brighter than “core” galaxies – tend to be less luminous, smaller galaxies Two families of early-type galaxies Mergers/BH increase vel dispersion and flatten light profile Gas dissipation increases nuclear luminosity Central Black Holes:  Central Black Holes Not just a problem for ellipticals, but that’s where we’ll start… How do you tell? Central Black Holes:  Central Black Holes Ellipticals Central surface brightness Velocity dispersions MBH/σ relationship Spirals Rotational velocities VLBA measurement of masers in NGC 4258 Case Study: N821:  Case Study: N821 Central Black Holes:  Central Black Holes Ellipticals Central surface brightness Velocity dispersions MBH/σ relationship Spirals Rotational velocities VLBA measurement of masers in NGC 4258 Formation of Elliptical Galaxies:  Formation of Elliptical Galaxies Mergers Tails and bridges result of tidal forces Two galaxies approach on parabolic orbits Systems pass, turn around, but leave tails behind them Ultimately the systems merge Simulated merger remnants follow r1/4 law Observationally…. E+A galaxies look like merger remnants Ellipticals reside in high density environments Interactions Gallery:  Interactions Gallery HI Rogues Gallery J. Hibbard What is this thing?:  What is this thing? Zabludoff et al. Galactic Cannibalism:  Galactic Cannibalism “dynamical friction” induced cannibalism turns a normal elliptical into a cD giant  several Es have multiple nuclei Dynamical friction = braking of some massive body via large numbers of weak gravitational interactions with a distribution of smaller masses (i.e. stars)  satellite, M, deflects stars into building a trailing concentration of stars, increasing the gravitational drag, slowing down the satellite Cannibalism:  Cannibalism Consider: Satellite with mass, M Stars with mass, m Relative velocity, v0 Impact parameter, b Angle of deflection, θ “reduced particle”; μ=mM/(m+M) Change in velocity parallel to the initial motion Δv = (2mv0/M+m)[1+(b2v04/G2(M+m)2]-12πbdb Then you integrate over impact parameter and some velocity distribution Applications:  Applications Growth of elliptical galaxies Milky Way is swallowing a number of its satellites – could the halo be comprised entirely of tidally stripped stars? Growth of the Milky Way?:  Growth of the Milky Way? Majewski – real data Johnston - simulation

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