missing satellite problem final? - cwru astronomyastroweb.case.edu/ssm/333f13/class20.pdf · mtot...
TRANSCRIPT
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missing satellite problem
Scaling relations
final?
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Need non-linear mapping between properties of dark matter halos and observed, luminous galaxies
Feedback
It does not work to make the obvious assumptionM
tot
/ L
One infers the presence of numerous dark sub-halos
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Not all sub-halos host proportionately luminous galaxies
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CDM is scale freeMoore et al. (1999)
Density of dark matter within a cluster halo of mass 5 × 1014 M (top). The edge of the box is the virial radius, 2000 kpc for the cluster (with peak circular velocity1100 km s-1).
Density of dark matter within a galaxy halo of mass 2 × 1012 M
(bottom). The edge of the box is the virial radius, 300 kpc (with peak circular velocity of 200 km s-1).
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Missing satellite problem
Moore et al. (1999)
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dwarf Spheroidal galaxies (satellites of the Milky Way)
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Tully-Fisher (disks)
Tully-Fisher (
disks)
dSph galaxiesMW satellitesM31 satellites
ultrafaint dwarfsall MW satellites
105 < L < 107 L�
L < 105 L�
“Classical” dSph galaxies
ultrafaint dSph galaxies
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Ultrafaint dwarf satellite galaxies discovered by SDSS
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Tollerud et al. (2008)
Ultrafaint dwarfsdiscovered in SDSS
}
Correction: SDSSdidn’t cover full sky
Correction: SDSSless sensitive to fainter dwarfs
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SelectionLimits
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Pawlowski et al. (2012)
Is sky coverage correction appropriate?dwarf satellites appear primarily to reside in a polar plane.
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CDM
WDM
Benson et al (2013)
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Slopes are mismatched everywhere,so it isn’t obvious that WDM helps
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Too Big to Fail?
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Many models can be invoked to suppress galaxy formation in small dark matter halos; is harder to prevent in mid-size halos.
e.g., Reionization models illustrated here are good for explaining the smallest galaxies, but not ~40 km/s halos, which are too big to fail.
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Velocity dispersions of dwarfs spheroidal galaxies measured from velocities of individual stars.
Walker et al. (2007)
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Velocity dispersionprofiles of dwarfs spheroidal galaxies approximately flat.
Walker et al. (2007)
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Wolf et al. (2010)
M(r) =r�2
r
G(�⇤ + �� � 2�)
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Walker & Panarrubia (2011)find that dSph galaxies sufferthe same cusp-core problemas found in rotating low surfacebrightness galaxies
⇢ ⇠ r��
� = 0.39
� = 0.05
Fornax
Sculptor
� = 1
� = 0
cusp
core[ ]
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Dwarf spheroidals problematic for CDM in two distinct ways:
- there should be thousands of them rather than dozens
(missing satellite problem)
- they have cored dark matter halos(cusp/core problem)