O : Recap - University of Maryland Observatory · 2016-12-08 · 1 Class 23 : Dark Matter Halos n...

of 4 /4
1 Class 23 : Dark Matter Halos n This class l Dark matter halos; the “skeleton” of a galaxy l Halo over-density factor Δ V l Applications of Virial Theorem O : Recap n Last class : Linear theory of structure formation l Gravitational Instability l Evolution of perturbations, from big bang to present day l Find “preferred scale” corresponding to the particle horizon at matter-radiation equality l Beautiful agreement between observed and predicted power-spectrum

Embed Size (px)

Transcript of O : Recap - University of Maryland Observatory · 2016-12-08 · 1 Class 23 : Dark Matter Halos n...

  • 1

    Class 23 : Dark Matter Halos

    n  This class l  Dark matter halos; the “skeleton” of a galaxy l  Halo over-density factor ΔV l  Applications of Virial Theorem

    O : Recap

    n  Last class : Linear theory of structure formation l  Gravitational Instability l  Evolution of perturbations, from big bang to

    present day l  Find “preferred scale” corresponding to the

    particle horizon at matter-radiation equality l  Beautiful agreement between observed and

    predicted power-spectrum

  • 2

    I : Dark Matter Halos

    n  On small scales, the dark matter collapses to form well defined bound objects (halos!)

    n  Dark Matter in the halos obeys the virial theorem (i.e. the system is in virial equilibrium)…

    n  In order to settle down to this state, the Dark Matter has to dissipate excess energy.

    n  How does collisionless dark matter dissipate energy???

  • 3

    Galaxies

    Groups and clusters of galaxies

    Jenkins et al. (2001)

    Properties of a DM halo

    n  Definition… let Δ(r) be average density within radius r of a dark matter halo in units where the overall cosmological density is unity.

    n  It turns out that the “virial radius” rv of a DM halo corresponds to a pretty universal value of Δ , often assume Δv=200.

    n  Suppose that a DM halo has a mass Mv with the virial radius. If σ is velocity of an average DM particle, Virial theorem gives

  • 4

    n  By definition we have

    n  Combining with the virial theorem…

    n  For illustrative purposes, evaluating at z=1…