Effects of galaxy formation on dark matter haloes Susana Pedrosa Patricia Tissera, Cecilia Scannapieco Chile 2010

Introduction Cuspy inner profiles obtained from simulations: not consistent with the observational results found for the rotation velocity of low surface brightness and dwarf galaxies (Flores & Primac 1994; Moore 1994; Dutton et al. 2008; Gnedin & Zao 2002)‏ Overabundance of small DM subhaloes. The universality of the profiles (Navarro et al. 2004; Merrit et al. 2006; Gao et al. 2008; Navarro et al. 2008,N08)‏ Theoretical model for the contraction when baryons are present, Adiabatic Contraction (Blumenthal et al. 1986; Gnedin et al. 2004; Sellwood et al. 2005)‏ Numerical results for the contraction of DM haloes when baryons are present, Tissera & Dominguez Tenreiro (1998); Gnedin et al. (2004); Romano-D í az et al. (2008).

Simulations Set of 6 simulations from the Aquarius project (Springel et al. 2008), Haloes extracted from a cosmological box of 100 Mpc and resimulated with very high resolution (Scannapieco et al. 2009, S09) using GADGET-3, total mass: 5-11x10 11 h -1 M ⊙, Cosmological parameters: Ω Λ =0.75, Ω m =0.25, σ 8 =0.9 and H 0 = 100 h k s -1 Mpc -1, con h=0.73.  1x10 6 particles within r vir with masses of: 10 6 h -1 M ⊙ for the DM and 2x10 5 h -1 M ⊙.for the gas; e g = h -1 kpc. Set of 6 simulations, (Scannapieco et al. 2008, S08) haloes of ~ h -1 M ⊙, resimulated with higher resolution using GADGET-2 (Scannapieco et al y S06)‏. Cosmological parameters: Ω Λ =0.7, Ω m =0.3, Ω b =0.04, σ 8 =0.9 and H 0 = 100 h km s -1 Mpc -1, h=0.7.  10 5 particles within r vir ; Particles masses: DM = 1.6x 10 7 h -1 M ⊙ y gas = 2.4x10 6 h -1 M ⊙.; e g =0.8 h -1 kpc.

Simulations Aquarius Set : Different initial conditions, aprox same baryonic physics: variety of structures and star formation histories. Dominated by stellar populations older than ~ 8 Gyr. Some galaxies have centrifugally supported disks (Aq-C-5, Aq-D-5, Aq- E-5), and one spheroid (Aq-F-5) Results are compared with purely dynamical runs (DMo) of Navarro et al Set S08: All experiments have the same initial conditions while the baryonic physics were varied: they all share the same underlying merger tree, differences are due to the different hydrodynamic evolution of baryons. Varied resulting morphology: NF, C-001: espheroids; E-07, F- 09: important disk component; E-03: thick disk; E3: extreme case with very high E SN, DM dominated.

Density Profiles Spherically averaged within the virial radius. CM: Shrinking Sphere (Power et al. 2003)‏ Better fit by Einasto, 3 parameters n y r _2, y ρ _2. In S08 set ρ _2 fixed with the total mass as constrain. Profiles always more concentrated than the DMo case. NF E07 F09 C001 E03 E3 S08 The level of concentration can be correlated to the formation history. Galaxies that were able to develop a disk: more concentrated profiles, although the ones hosting spheroids are more massive. Key: feedback regulation acting on the galaxy but also on the satellites.

Interaction with satellites Δ v/2 Parameter All haloes increase their concentration with time and the DMo is always less concentrated. NF, C-001: flattened curve -> close approching of satellites E-07, F09 y E3: feedback regulation action: less massive satellites. NF E07 F09 C001 E03 E3 Satellites cumulative mass vs r Feedback regulates the SF in both, the central galaxy and the satellites: spheroids have more massive satellites and they are able to survive further in the halo.

Aquarius density profiles Density increases in the central regions. Baryonic runs: below DMo for large r and above for the inner regions. Inside the peak, aproximately isothemal.

Velocity Dispersion S08: In agreement with Aq, increases in the central regions Systems with higher stellar masses → steeper inner profiles. ti is also lost, except for the DM dominated run, E3 Dependence with z: the inversion is never at place. NF E07 F09 C001 E03 E3 The DM velocity dispersion profiles are strongly affected by baryons: increase in the central regions. Decrease monotonically with radius. The DMo characteristic “temperature inversion” is not present. S08 Aq

The presence of baryons modify the anisotropy. Trend: spheroids tend to have lower levels of anisotropy than their DMo, while disks higher. Aq: baryons affect  in a complicated way: some cases similar shape to the DMo and others result less dominated by radial movements. Velocity Anisotropy Parameter Measure of the internal velocity structure of the haloes. S08 Aq

Pseudo Phase Space Density DMo, follow Bertschinger. With baryons: lower values of α. Larger residuals: espheroids, weaker effects: disks the universality is lost all runs flatten with respect to Bertschinger solution, different levels of discrepancy. changes: mass and velocity redistribution in the central regions. Related with the entropy. Taylor & Navarro (2001): Bertschinger (1985): α ~ Haloes contraction has not been adiabatic S08 Aq

Rotation Velocity Problem in  CDM: inability to reproduce observed rotation curves: enormous concentration of baryons in the central regions. Important disk component at place: total velocity gets flatter within the baryonic dominated region. S08: V max /V vir between 1.15 and 1.5, in better agreement with observations.

Adiabatic Contraction Blumenthal et al. (1986): overstimate the level of concentration in the central regions. Gnedin et al. (2004) and Abadi et al. (2009), better agreement but still overpredict. Discrepancy: haloes contraction depend on the way baryons were collected during galaxy assembly. DMo SPH B86 Gne04 S08 Aq

Conclusions When baryons are present DM density profile become more concentrated than their DMo counterpart. The amount of baryons collected within the inner regions does not by itself determine the response of the DM haloes. Central regions, profiles nearly isothermal. Best fit: Einasto model. Formation history S08: haloes hosting galaxies that were able to develop an important disk structure: profiles more concentrated. Evolution with redshift: all haloes increase their concentration in time. Flattening in the relation: close approach of satellites. Satellite system, spheroids have more massive satellites and survive further in the halo, stars more gravitational bounded. Presence of baryons increase the velocity dispersion within the central regions. No “ temperature inversion ”. For S08, slope increase with increasing baryonic mass.

Conclusions II The phase space density in presence of baryons does not follow Bertschinger; Not consistent with a purely adiabatic contraction of the DM halo. The rotation velocity curves flatten in systems that developed a disk structure: lower the maximum to virial velocity ratio. Comparison with the predicted contraction for different AC models: neither of them provides a good prediction of the contraction, they don't account for the formation history of the galaxy. All our findings indicate that the response of the DM halo to the presence of baryons is the result of the joint evolution of baryons and DM during the assembly of the galaxy.

General trend between  and β. Aquarius: some haloes have linear relation in the central zones, 2e g < r < r _2. For r > r -2 this relation is lost. S08: also the linear relation keep only for the central zones. Hansen & Moore relation

HR Cosmological simulation with DM mass iresolution of 5.93x 10 6 h -1 M ⊙ and 9.12x10 5 h -1 M ⊙ ; factor 4 in particle number. Δ v/2 : get more concentrated with time; where the curve flattens → correlate with the interaction with satellites; Δ v/2 for the spheroid is flatter The general trends agree with the S08 results