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Environmental Effect on Mock Galaxy Quantities
Juhan Kim, Yun-Young Choi, & Changbom Park
Korea Institute for Advanced StudyKorea Institute for Advanced Study
2007/02/21
Content
• A model to make mock galaxies from N-body simulation
• Model test & Justification• Model prediction
A Roadmap for Galaxy World
Luminosity FunctionChoi & Park
Spin DistributionChoi & Park
Velocity CorrelationsPark & Park
Topology of LRG & Galaxy
Choi & Park
Morphology/Velocity dispersion
Park & Park
Cosmological Model
Halo-to-galaxy model
How to build Mock Galaxies
• • Directly implements algorithms & parameters for hydrodynamics.
• (SAM)• Uses merging tree built by random realizations
• Merging mass growth : M(t) M’(t’)• Uses galaxy formation recipe
• mass growth star-formationL & chemical evolution• Parameters: IMF, SF rate, metal enrichment….
• (HOD)• P(N|M): probability number of galaxies in an FoF halo of mass M• Galaxy distribution inside a halo to satisfy observed gg
• (MOC)• Subhalo galaxy: every subhalo can host a galaxy• Subhalo Mass galaxy Luminosity
Pros & Cons• Direct Hydro Simulation
• Can directly follow complex nonlinear evolution of gas particles.• But uses ambiguous parameters for complicated nonlinear phenomena (IMF,SF).• Lack in resolution needs much more computer resources than currently available
(Small-scale phenomena in Large-scale environments).• SAM
• Can reproduce observables by introducing parameters. • But needs too many parameters.• Some parameter values can be degenerated in parameter space.
• HOD• Can parameterize the spatial distribution of galaxies in clusters.• Is a kind of descriptive methods and, therefore, restricted. • Cannot predict phase-space distributions inside clusters.
• MOC• Is simple & straightforward: very few parameters are needed.• Because recently developed, it is not seriously tested in various fields.
MOC implementation to PSB halos
• Two (simple & reasonable) assumptions• One subhalo may host only one galaxy
• One-to-one correspondence • A more massive subhalo has a more luminous galaxy
• Luminosity of a galaxy is a monotonic function of its host subhalo mass
• If halo mass is given, the luminosity of the inside galaxy is obtained.
• SDSS :
• PSB :
€
φ(M ')dM '−∞
M
∫ = Φ(mh )dmhm
∞
∫
€
φ(M) = 0.4 ln10φ*10−0.4(M −M * )(α +1) exp[−10−0.4(M −M * )]
€
M* − 5log10 h = −20.22,φ* =1.847 ×10−2h3Mpc−3,α = −0.81
€
f (ν ) = Aa
2π1+
1
aν
⎛
⎝ ⎜
⎞
⎠ ⎟p ⎡
⎣ ⎢
⎤
⎦ ⎥1
νexp −
aν
2
⎛
⎝ ⎜
⎞
⎠ ⎟
€
a = 0.923, p = 0.0121,A = 0.368
€
cf .a = 0.707, p = 0.3,A = 0.322
Subhalos in a halo
• Cloud in Cloud
Mass Function of Dark Halos
Press & Schechter
Sheth & Tormen
Mass-to-light relation
€
Υ=Mh
L= Ψml
Mh
M*
⎛
⎝ ⎜
⎞
⎠ ⎟
γ
expM*
M
⎛
⎝ ⎜
⎞
⎠ ⎟
Ψml = 31.3,M* = 2.07 ×1011,γ = 0.690
M<-18
M<-20
Model Test
• Local density distribution• -21<Mr<-20 galaxies are used for density seeds.• Variable size Spline kernel is used to measure local
density.• Luminosity functions of various sub-samples
divided by local density criteria
M<-21
M<-20€
Ξ(Δ) = Ae−(ln Δ−μ )2 / 2σ 2
2πσ
Luminosity FunctionTotal
Void
crowded
Schechter Parameters with Local Density
Spin Distributions• Spin parameter:
=1(rotation-supported)=0(pressure-supported)
• Spin distribution• Log-normal
• Gamma
€
=J −E
GM 5 / 2
€
Pl =1
λ 2πσ λexp[−
ln2(λ /λ 0)
2σ λ2
]
€
PG =(λ /θ)k−1
θΓ(k)exp(−λ /θ),
k : shape parameter
θ : shift parameter
Universality of
the Spin Shape
€
PGθ =(λ /θ)k−1
Γ(k)exp(−λ /θ),
€
M < −19.8
M < −20.3
M < −20.6
M < −21.0
M < −21.3
€
PG =(λ /θ)k−1
θΓ(k)exp(−λ /θ),
k : shape parameter
θ : shift parameter
Characteristics of Spin distributions
• Shape (k) of spin distributions: nearly constant• Origin of spins: off-center impact & inhomogeneous infall
• Depends on the number of local filament branches• More massive halo: smaller spin• In more crowded region: higher spin
€
M < −19.8
M < −20.3
M < −20.6
M < −21.0
M < −21.3
Spin Dependence on Galaxy Mass
Less massive galaxies: more anisotropic merging
more massive galaxies: more isotropic merging
Spin Dependence on Local Density
•Under dense region: accretion dominated
•Overdense region: merging dominated
Summary
• MOC is more powerful than other traditional methods.• Simple implementation to create mock galaxies• A model with less parameters is more powerful!!!!!!
• SDSS density distributions & LF’s are well recovered.• Spin distributions of mock galaxies
• Distribution shape is constant and shift parameter depends on local & merging environments. hints at a possible statistical explanation on the spin & merging history of halos?