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ASTRO 620 Spring 2007

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ASTRO 620 Spring 2007. The Missing Satellites. Am lie Saintonge. February 7, 2007 ... stay tuned for Brian's talk! Semi-analytical predictions. Kauffmann et al 1993: ... – PowerPoint PPT presentation

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Title: ASTRO 620 Spring 2007


1
ASTRO 620 Spring 2007
  • The Missing Satellites
  • Amélie Saintonge
  • February 7, 2007

2
The Missing Satellites Problem
  • Where are the missing satellites?

Klypin et al. 1999
3
What we learned last week
  • Perturbations collapse when
  • collapse from rmax to rmax/2
  • at Virial equilibrium

4
What we learned last week
  • the density of the virialised object should be at
    least
  • a galaxy with v300km/s and M10E12 zvirlt 10
  • a cluster with v1000km/s and M10E15 zvirlt 1

5
Dissipation
  • we need to introduce the loss of energy by
    radiation

Thermal bremsstrahlung
Longair, 1999
6
Dissipation
Blumenthal et al 1984
7
Initial power-spectrum
  • spectrum of initial fluctuations
  • the correlation function on scale r is
  • this can be written in terms of the mass within
    the fluctuations on the scale r

8
Press-Schechter mass function
  • first, assume that primordial density
    perturbations are Gaussian
  • the mean-squared fluctuation is

9
Press-Schechter mass function
  • The fraction of fluctuations of mass M that
    become bound have ? gt?c

where
10
Press-Schechter mass function
  • the amplitude of the perturbation grows as
  • the reference mass then grows as

11
Press-Schechter mass function
  • the space density of the masses that have
    collapsed is (assuming that in the linear regime
    M?V)

12
Press-Schechter mass function
  • two problems with this simple formulation
  • factor of 2 only the positive density
    fluctuations develop into bound systems
  • peaks-within-peaks in general, any perturbation
    is superimposed upon other longer wavelength
    perturbations

13
Press-Schechter mass function
Press Schechter, 1974
14
Schechter luminosity function
  • Schechter (1976) derives the LF from
    Press-Schechter but allows a free parameter
  • from best-fit results, Schechter suggests ?-1.24

15
Mass and luminosity functions
Zwaan et al. 2003
Blanton et al. 2001
16
Simulating structure formation
  • Numerical simulations predict the abundance of
    dark matter halos of with different masses
  • semi-analytical models
  • make predictions about observational properties
    of galaxies
  • parameter space can be explored quickly
  • accurate LFs for bright galaxies
  • BUT
  • faint-end slope of the LF is much steeper than
    observed
  • the overal normalization is off

more soon... stay tuned for Brian's talk!
17
Semi-analytical predictions
  • Kauffmann et al 1993

18
Direct numerical simulations
  • Klypin et al. 1999 Where are the missing
    galactic satellites?
  • use direct numerical simulations to predict the
    abundance of dwarf galaxies in the Local Group
  • investigate the survival of satellites in
    galaxy-size halos
  • are DM halos destroyed withn the virial radius of
    larger halos?
  • likelihood of a galactic satellite being
    destroyed is higher than for clusters

19
Case study the Local Group
  • about 40 satellites in the Local Group
  • most are dSphs and dEs
  • properties correlate with distance from MW and
    M31
  • hierarchical clustering the dwarfs should
    collappse earlier
  • slowly rotating galaxies have higher central
    densities
  • MW satellites formed before the MW itself

20
The sample of satellites
  • select satellites of MW and M31 with vrotgt10 km/s
  • 2 radii 200 and 400 h-1 kpc

21
Simulations
  • use two different cosmological scenarios
  • use the maximum circular velocity to define a
    halo
  • count the number of satellites within the same
    two radii of the large systems

22
Velocity distribution function
  • VDF number of halos in a given circular velocity
    intervl per unit volume

power law
halo catalog is incomplete
exponential term of PS is neglected
23
Results of simulations
  • example of simulated systems
  • vcirc 280, 205 km/s
  • M1.7E12, 7.9E11 h-1Msun within 100 h-1 kpc
  • Dhalos1.05 h-1 Mpc
  • 281 satellites with vgt10 km/s
  • but Msat 0.091 MDM

24
Characteristcs of the satellite systems
  • abundance and dynamics of the satallites depend
    on the host halo
  • predictions accurate for satellites with vgt50
    km/s
  • VFD significantly different at low v
  • the Galaxy should have about 50 satellites with
    vgt20km/s with Mgt3E8 and within 570kpc

25
Where are the missing satellites?
  • Several possible explanations
  • some of the missing DM satellites may be
    associated with high-velocity clouds
  • the satellites are invisible because they do not
    contain any luminous matter
  • early feedback by supernovae
  • heating of the gas by the intergalactic ionizing
    background...

more soon... stay tuned for Ann's talk!
26
HVCs as missing satellites?
  • some HVCs may be the counterparts of the missing
    satellites (Blitz et al. 1999)
  • some may be distant (gt100 kpc)
  • Blitz et al
  • diameters of 25kpc
  • masses 3E8 Msun

27
The Milky Way's HVCs
  • Wakker van Woerden (1991)
  • all-sky survey with 1deg resolution
  • 500 HVCs not associated with the Magellanic
    Stream (300 with FWHM gt 20 km/s)
  • total mass of 1.5E11 h-1Msun (0.05 of the mass of
    the Local Group)
  • Stark et al. 1992
  • 1312 clouds in northern hemisphere (444 resolved
    by the 2 deg beam)
  • 0.2-0.25 of the mass of the Local Group

28
The DM luminous matter connection
  • what determines the properties of a galaxy?
  • Park et al. 2006 Environmental dependence of
    properties of galaxies in SDSS
  • properties of galaxies depend on luminosity,
    morphology and environment

29
SDSS sample
  • 317,533 galaxies from SDSS DR5
  • magnitude limit 14.5ltrlt17.6 5195 bright
    galaxies
  • redshift limit 0.001ltzlt0.5

Park et al. 2006
30
morphology and environment
  • morphology determined by colours and
    concentration index
  • local density estimated using a smoothing kernel
    including a fixed number (20) of L galaxies

Park et al. 2006
31
morphology-density-luminosity relation
early-type fraction increases with luminosity, in
all environments
early-type fraction is lt20 in low density
environments
Park et al. 2006
32
morphology-density-luminosity relation
  • the local density dependence of the LF is due
    both to a change of the early-type fraction and
    of the shape of the LF
  • early-types are more sensitive to environment

Park et al. 2006
33
abundance of faint galaxies
  • very shallow slope for early types near the
    cosmic mean density

Park et al. 2006
Kauffmann et al. 1993
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