The influence of baryons on the
matter distribution and shape of
dark matter halos
Weipeng Lin， Yipeng Jing
（Shanghai Astronomical Observatory，CAS
Joint Institute for Galaxy and Cosmology of SHAO & USTC）
Shude Mao (U.Manchester),
Liang Gao, Ian G. McCarthy (Durham)
Outline
• Problems: The inner slop of halos of clusters and groups of
galaxies, flat (Sand et al. 2004) or cuspy (many works)?
Dynamic Friction by sinking galaxies (El-Zant et al.)?
shallower
Adiabatic Contraction by cooling gas (Blumenthal et al.,
Gnedin et al.)? steeper M(<ri ) ri =M(< rf) rf
Observationally, NO AC effect for clusters?
The influence of gas on the mass distribution of halos?
(WMAP: gas fraction ~16%)
Before considering gas cooling, SF, Feedback, etc (more
uncertain), we study non-radiative case to set a benchmark
of baryon effect.
• The influence of gas on the shape of halos
tri-axial halos? How elliptical?
Brief of simulations
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1.
2.
3.
4.
5.
6.
LCDM (WMAP parameters), Box：100 Mpc/h
Gadget-v2 (Springel 2005)
A set of simulations using the same IC and all
started from z=120, softening 4.5kpc (if not
indicated)
Pure DM simulation 5123 (as reference)
Non-radiative (A4) 5123 DM + 5123 Gas
Non-radiative (A3) 5123 DM + 2563 Gas
Non-radiative (A2) 2563 DM + 2563 Gas(9kpc)
Non-radiative (A1) 2563 DM + 2563 Gas
5123 DM + 5123 Gas with cooling, SF,
SNFB(9kpc/h)
The simulations were done at Shanghai supercomputer
center.
Halo mass distribution
The influence of gas on the mass distribution in
halos, first stage: non-radiative case
Expectation: gas components are more extended
because of pressure
• It is not clear if kinetic energy of DM can be
transferred to non-radiative gas and thus
increase concentration of DM and total mass
• Rasia et al. (2004) reported briefly that in
adiabatic simulations halo concentration of total
mass can be 10% higher than those in pure DM
simulation.
• We will investigate resolution and spurious twobody heating effects (Steinmetz & White 1997).
Methods
• Selecting about 400 halos with mass larger
than 1013 h-1M⊙
• Because of the same IC, massive halos
have one-to-one correspondence in all the
simulations.
• Fitting halo mass profiles with NavarroFrenk-White (NFW) form to get halo
concentration for DM & total mass
(DM+Gas).
1283
P3M
Mgas=2.4E9M
Mdm=2.2E10M
2563
Gadget-v1
Mgas=3.0E8M
Mdm=2.8E9M
Results
High
resolution
A4(5123)
Gadget-v2
Main results for non-radiative case
• 3% increase in halo concentration of total mass in nonradiative SPH simulations comparing with those in PDM
simulation.
The total mass density profile is little affected by the gas
component in the non-radiative simulations.
• 10% increase in halo concentration of DM
• For the 400 massive halos (with mass of galaxy groups
and clusters) in run A4, two-body heating effect is
negligible (halos with more than 4000 particles).
• The difference in A1/A2/A3 with A4 is due to the resolution
of SPH component (gas).
• In the inner part of halos, as the SPH resolution increases,
the gas density becomes higher, but both the entropy and
temperature decrease.
The case with Cooling, SF & FB
Fitting from 2%
Virial radius
Results depend on
the inner fitting
radii
(the amount of star
components, mass
dependence)
Preliminary conclusions
• Stellar mass dominate center part of
clusters and groups of galaxies.
• Inner slops of halos become very steep, due
to the contribution of stars in cD galaxies.
These central galaxies are too bright to
compare with observations (AGN feedback
is necessary to suppress star formation rate).
• The distributions of dark matter and total
mass become more concentrated, due to
the effect of adiabatic contraction.
But Over-cooling!
Influence of baryons on halo shape
• Non-radiative case
• The case with star formation (cooling, SN
feedback)
• Two-ways:
1. Inertia tensor in radius bin
2. Tri-axial model （Jing & Suto 2002)
Pure-DM
Adiabatic
With Cooling,
SF, FB
Methods
• Problems of using radii bins:
affected by sub-structures?
presumption of spherical shell?
• We use tri-axial model (Jing & Suto 2002)
to calculate halo shapes
 3D-SPH density of gas, stars & DM
 remove substructures
 fitting iso-density ellipsoid
Non-radiative case (iso-density)
a≤b≤c
Over-density
2360-2650
100
halos
The case with star formation and
feedback (iso-density)
a≤b≤c
summary
• The halos in simulations with gas cooling
and star formation become significantly
more spherical than those in N-body
simulation, while the effect by nonradiative gas is less significant.
• To do: the shape of DM part of halos in
SPH simulations?
• Problems: over-cooling effect on the halo
shape?
Thank you very much!