Galaxy alignment and the physical origin Kang Xi （ PMO, China) � � � In collaboration with � Wang Peng （ PhD Student), Lin Weipeng, Yang Xiaohu, Dong X, Wang Y (SHAO) Quy Nhon, Vietnam, July 4 2016
How to describe galaxy distribution in space? Two-point correlation ? 2PCF widely used in 1980,great wall for 2dFGRS/SDSS • Correlation function: 2-points, 3-points etc (1980, Peebles) � • 2PCF describes how galaxies are biased with dark matter distribution � • 2PCF etc can well constrain the cosmological parameters
Galaxy alignment is seen on different scales Several types of galaxy alignment Galaxy alignment One halo term Two halo term • satellite-satellite • satellite-central • central-central • central-LSS Small scales
In addition to galaxy clustering, Why do we care galaxy alignment? On small scale (one-halo term) � •Infer dark matter halo shape from galaxy alignment •alignment to infer galaxy formation? •primordial anisotropic accretion or evolution (Nature vs Nurture?) On large scales (two-halo term) � •Interaction of halo shape to cosmic tidal field •intrinsic alignment of galaxies (crucial to weak lensing) •formation of cosmic web? •dependence on DM/DE properties?
1,satellite-satellite: The great circle （ co-rotated plane) Kroupa 2005 Satellite galaxy in the Milky Way • 2005:Milky Way satellites are in a thin disc � • 2007:The same is true in M31, but weaker � • 2013: Satellites in the disc are co- rotated ! MW and M31 are special? need large galaxy sample
3, Central-Central alignment Angular scale at z=1 (arcmins) 10 1 10 2 10 -1 10 -2 c 11 (r) 10 -3 10 -4 0.01 c 22 (r) 0 -0.01 10 100 r (h -1 Mpc) Jing+ 2009 Li+ 2015 Galaxy(Halo) intrinsic alignment is crucial for Weak Lensing cosmology
2,satellite-central alignment group galaxy Brainerd 05, Yang+06 From 2dFGRS and SDSS � • satellite galaxies are aligned with the major axis of central galaxy • stronger alignment for red centrals • strong alignment for red satellites
Modeling the satellite-central alignment Halo is triaxial Kang et al. 07 using SAM N-body study is limited results as its difficult to properly � determine the shape of • if central galaxy follow major axis of DM halo central galaxy (inside virial radius): signal too strong � • need some mis-alignment (inner DM halo, or spin) signal is OK, but no color dependence
Modeling the satellite-central alignment Using hydro-dynamical simulation: star formation, SN feedback (no AGN feedback) alignment with radius alignment: dependence on color 44 1 . 3 < θ > model = 42 . 1 ± 0 . 1 < θ > model = 42 . 4 ± 0 . 3 < θ > model = 42 . 1 ± 0 . 1 50 2 D : 2 D : 3D: 3D: 3D: 0 . 1 R : < θ > = 20 . 2 ± 0 . 6 Red Satellites < θ > obs = 42 . 2 ± 0 . 2 < θ > obs = 43 . 3 ± 0 . 3 < θ > obs = 41 . 5 ± 0 . 3 1 . 6 Blue Satellites 0 . 3 R : < θ > = 28 . 6 ± 0 . 6 All Sample 1 . 2 All Sample Blue SGs Red SGs Metal Rich Satellites 43 1 . 0 R : < θ > = 39 . 7 ± 0 . 7 1 . 4 Metal poor Satellites 40 1 . 1 p ( θ ) < θ CG , Halo > P ( r / r 200 ) 42 1 . 0 1 . 2 < θ > 30 0 . 9 41 1 . 0 0 . 8 20 0 . 8 40 1 . 3 < θ > model = 42 . 0 ± 0 . 1 < θ > model = 43 . 2 ± 0 . 2 M h < 2 ∗ 10 11 M � r < 0 . 1 R < θ > obs = 44 . 5 ± 0 . 5 < θ > obs = 41 . 5 ± 0 . 2 r < 0 . 3 R M h < 10 12 M � 0 . 6 r < 1 . 0 R 1 . 2 10 Blue CGs Red CGs M h > 2 ∗ 10 11 M � 39 0 . 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 0 . 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 10 12 10 13 10 14 10 15 M h > 10 12 M � 1 . 1 r / r 200 r / r 200 M Halo [ M � ] p ( θ ) nel: radial distribution of red and blue, metal-rich (top 30% by order ranking), and metal poor (bottom 30% by order ranki 1 . 0 Dong X, Kang X et al. 2014 0 . 9 CGs Defined By Halo Mass 0 . 8 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 θ θ θ Result ★ There is mis-alignment between shape of central galaxy and DM halo ★ Their misalignment is a function of halo mass (color dependence of central) ★ misalignment is a function of radial distance (red satellites in inner halo,blues at outer region )
4: Alignment with LSS: I. define the LSS environment Zel’dovich approximation for Λ CDM, z=0 formation of cosmic web x ( t ) = q + D ( t ) r ψ ( q ) , ρ ¯ ρ ( x ) = [1 � D λ 1 ( q )] [1 � D λ 2 ( q )] [1 � D λ 3 ( q )] ƛ ~ eig of ( ∂ i ∂ j ɸ ) Sheet—>Filament—>Node 100 h -1 Mpc Following Zeldovich, Hahn+2007. c p M define the LSS environment: 1 - h • smooth the density field 0 8 1 • compute the potential • compute eigenvector of tidal field ∂ 2 φ T ij ( x ) = , ∂ x i ∂ x j Hahn, Porciani, Carollo, Dekel (2007a), MNRAS 375, 489 • number of +- eigenvalue determine: voids, sheet, filament, nodes
I. Halo-LSS alignment from simulation Halo spin -LSS Halo major axis-LSS Hahn+ 2007,Codis+12 M_flip~10 12 M sun *(1+z) -2.5 These correlation are widely confirmed by many others using simulations (Aragon-Calvo+08, Codis+12, Libeskind+14 ， Kang & Wang 15 …..)
Space configuration of Halo shape & Spin Filament Major axis of halo: M<M* M>M* Spin align with the least Major axis collapsed direction Spin Major axis � Minor axis of halo: align with the most Wall collapsed direction � Spin of halo : normal to the mass accretion direction Why there is a mass dependence?
II. Galaxy-LSS alignment from observation Galaxy Major axis-Filament Spin - Filament 1.2 e 3 -vector (filament axis) Spiral galaxies P(|cos θ |) 1 p KS = 2.8 ⋅ 10 -3 <cos( θ )> = 0.513 < σ > = 1.62 0.8 0 0.2 0.4 0.6 0.8 1 |cos( θ )| 1.2 e 3 -vector (filament axis) Elliptical galaxies P(|cos θ |) 1 p KS = 7.7 ⋅ 10 -9 <cos( θ )> = 0.479 < σ > = 3.38 0.8 0 0.2 0.4 0.6 0.8 1 |cos( θ )| Zhang Y+2013 Tempel & Libeskind 2014 Figure 4. Same as Figure 2, but for different sub-samples (“red” and “blue“) of Observations agree well with Theory ! Signal is weaker (galaxy-halo misalignment)
A common scenario for mass flow in cosmic web • mass flow from Voids —> Wall — >Filament —>Nodes • environment of halo changes as Wall—>Filament-Nodes • the velocity field around cosmic Codis+12, Cautun+14 web determines the spin-LSS original idea from Bond+96, van de Weygaert 96 correlation!
This scenario is basically right but details to be declared From this cosmic mass flow, we expect • in Wall, spin is parallel to wall. • In Filament, spin is perpendicular to filament But, simulations have found In Filament, there is still a mass dependence (spin flip) Any dependence on halo migrating time ? (from wall to filament) can we see the spin flip during the history of a massive halo?
tracing the evolution of halo mass accretion and spin N-body simulation • WMAP7 cosmology, LCDM • box: 200Mpc/h, 1024^3 particles • Full merger trees are constructed for every halo from z=10 to z=0 1) accretion along Halo major axis ( λ 1 ): Increasing time 2) accretion along e3 of LSS ( λ 3 ): The least compressed direction
subhalos accretion along halo major axis and e3 of LSS dependence on host halo mass (selected at z=0) black: along halo major axis halo mass dependence red: along e3 of LSS we find: Accretion along halo major axis: universal Accretion along e3 of LSS: not universal � Kang & Wang, 2015 ApJ � Libeskind+14, Universal along e3 of LSS (their mass bin is too wide)
The evolution of spin-LSS and mass accretion spin-e3 correlation mass accretion-e3 correlation black line: low-mass halo, red lines: massive halo There are evolution effects, at earlier times • mass accretion is perpendicular to Filament • Spin is parallel to Filament Wang & Kang, 2016 in prep
An useful parameter for anisotropic collapse Large FA: highly anisotropy � ( λ 1 − λ 3 ) 2 + ( λ 2 − λ 3 ) 2 + ( λ 1 − λ 2 ) 2 1 FA = , √ λ 2 1 + λ 2 2 + λ 2 Lower FA: collapse happen 3 3 ƛ ~ eig of ( ∂ i ∂ j ɸ ) on all directions Nodes: spin is normal to e3 Wang & Kang, 2016 in prep Filament: mass dependence
Dependence on time of formation and entering in Filament Spin-LSS: dependence on Z_formation and Z_filament • Later formed halo is more perpendicular to filament • Massive haloes: entering filament first, and then formed later (spin is build by mass accretion along filament) • Low-mass halo: forms early, but entering filament later (spin is build when they were in wall) Wang & Kang, 2016 in prep
Summary •Galaxies are distributed anisotropically on different scales On small scales On large scales • Halo spin-LSS is not universal •satellite-central alignment can be (subhalo accretion along LSS is ascribed to primordial anisotropy at not universal) accretion or the triaxial nature of DM � halo • Low-mass halo forms early, but •central galaxy is better aligned with enter filament later (spin is formed inner halo shape, and alignment in wall, so parallel to filament) increases with halo mass � � • High-mass halo enter filament •subhalo accretion along halo major early, but form later (spin is formed axis is universal, being strong in in filament by mass accretion massive haloes along it) Thank you !
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