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.)? shal

lower Adiabatic Contraction by cooling gas (Blumenthal et al., Gn

edin 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 u

ncertain), 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• LCDM (WMAP parameters), Box ： 100 Mpc/h• Gadget-v2 (Springel 2005)• A set of simulations using the same IC and all st

arted from z=120, softening 4.5kpc (if not indicated)

1. Pure DM simulation 5123 (as reference)2. Non-radiative (A4) 5123 DM + 5123 Gas3. Non-radiative (A3) 5123 DM + 2563 Gas4. Non-radiative (A2) 2563 DM + 2563 Gas(9kpc)5. Non-radiative (A1) 2563 DM + 2563 Gas6. 5123 DM + 5123 Gas with cooling, SF, SNFB(9k

pc/h)The simulations were done at Shanghai supercomputer cent

er.

Halo mass distributionThe influence of gas on the mass distribution in hal

os, first stage: non-radiative caseExpectation: gas components are more extended

because of pressure• It is not clear if kinetic energy of DM can be trans

ferred 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 two-body 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 Navarro-Frenk-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

A4(5123)Gadget-v2

Results

High resolution

Main results for non-radiative case• 3% increase in halo concentration of total mass in non-radi

ative 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 an

d 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 cluster

s 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 With Cooling, SF, FB

Adiabatic

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 non-radiative 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!