The Dipole Anisotropy of the 2MASS Redshift Survey

The Dipole Anisotropy of the The Dipole Anisotropy of the 2MASS Redshift Survey2MASS Redshift Survey

Pirin ErdoPirin Erdoğğdudu

(University of Nottingham)(University of Nottingham)

and the 2MRS Teamand the 2MRS Team

MNRAS, in pressMNRAS, in press

OUTLINEOUTLINE

What is the 2MASS Redshift Survey?What is the 2MASS Redshift Survey? What is the acceleration on our Local What is the acceleration on our Local

Group of galaxies?Group of galaxies? Why do I think I am right?Why do I think I am right?

Main AssumptionsMain Assumptions

CMB dipole is due to the motion of the CMB dipole is due to the motion of the Sun. Sun.

Linear theory of density perturbations Linear theory of density perturbations is acceptable.is acceptable.

The 2MASS has constant mass-to-light The 2MASS has constant mass-to-light ratio and linear bias.ratio and linear bias.

The 2MASS Redshift Survey

z ≤ 0.01 0.01 < z ≤ 0.025 0.025 < z < 0.05 0.05 ≤ z

If we have a perfect 3-dimensional If we have a perfect 3-dimensional galaxy catalogue with same mass, with no selection galaxy catalogue with same mass, with no selection

effects, no z-distortions and with linear biasing then effects, no z-distortions and with linear biasing then

i i

im

r

r

b

G

r

rrrdGg 23

0

3 ˆ0

Linear theory:

b

gG

Hv

m6.0

0 04

0

Linear theory:

From CMB: vLG = 627 km/sec towards l=273o and b=29o

From galaxy cat.

Number Weighting Technique

The 2MRS Redshift Distribution

The Rocket EffectThe Rocket Effect(Kaiser, 1987)(Kaiser, 1987)

cz=Hcz=H00r + (r + (vvpecpec- v- v(0))(0))..((rr/r)/r)

LG

Gal 1 with d=100 km/sec v pec = 20 km/secThus calculated distance=120 km/secThus calculated dipole= 44% less than the real dipole

Gal 2 with d = 100 km/sec v pec= -20 km/sec Thus calculated distance=80 km/secThus calculated dipole = 64 % more than the Real dipole

Net effect: A spurious contribution to the LG dipole from

All the galaxies.

If we have a perfect 2-dimensional If we have a perfect 2-dimensional galaxy catalogue with no selection effects, constant mass-to-galaxy catalogue with no selection effects, constant mass-to-

light ratio and with linear biasing thenlight ratio and with linear biasing then

22

ˆˆ)0(

i

i

ii

i

i

ii r

rL

L

MG

r

rMGg

ii

irSL

MG ˆ4

since24 r

LS

Flux Weighting Technique

Luminosity Weighting Function

Notice the Zone of AvodianceNotice the Zone of Avodiance

ShapleyCentaurus

Hydra

Star: CMBTriangle: 2MRS – Lum WeightedTriangle: 2MRS-Num WeightedCircle: 2MASS by Maller etal 2003Upside down Triangle: IRAS PSCz DipoleUpside down Triangle: 2MASS dipole of PSCz galaxiesTriangle: 2MRS – Lum Weighted without Maffei 1, 2, Dwingeloo 1, IC342, M87Blue square: Dipole from X-Ray Clusters (Kocevski & Ebeling 2005)

To summarise…To summarise…

The flux weighted galaxy dipoles are better.The flux weighted galaxy dipoles are better. Most of the LG dipole is caused by the tug-of-war Most of the LG dipole is caused by the tug-of-war

between the GA and Per-Pis. The dipole between the GA and Per-Pis. The dipole converges by ~ 60 Mpc/h.converges by ~ 60 Mpc/h.

If dipole converged If dipole converged ββ2mrs2mrs = 0.4 = 0.4±0.1±0.1

Small discrepancy between LG and CMB dipoles Small discrepancy between LG and CMB dipoles are due to ZoA, 2nd and 3rd assumptions are due to ZoA, 2nd and 3rd assumptions mentioned in the earlier slide and structure mentioned in the earlier slide and structure beyond. But no big deal! beyond. But no big deal!