Ofer Lahav

Large Scale Structure
at Low Redshift
The interface between Cosmology
and Galaxy Formation
Ofer Lahav
University College London

Redshift Surveys

LSS at low z
• 2MRS/6dF The LG dipole revisited,
density and velocity fields
• SDSS “Baryonic” Faber-Jackson
• 2dF Neutrino masses,
Testing the halo model
• DES Photo-z, Dark Energy
“Nearly Normal Galaxies”, BFP@60, Santa Cruz, Aug 2005

Great
Attractor
Greatness in the Cosmic Web
SDSS
CfA Great Wall
2dFGRS

2MASS Galactic chart
F

Spectral PCA types in 2MASS
62% E’s in 2MASS
35% E’s in 2dF
Madgwick, OL et al.

2MASS and follow-ups
• 2MASS: 1.5M galaxies (K s < 13.5)
• 6dF (Southern hemisphere):
150K redshifts (K s < 12.75)
and 15K Dn-sigma distances
* 2MRS: 25K redshifts (K s

A brief history of the LG dipole
• LG motion wrt to the CMB
based on WMAP (1 st year)
v LG = 627 +/- 22 km/sec
towards
(l,b) = (273 +/- 3 , 29 +/- 3) deg
* IRAS dipole
(Yahil, Rowan-Robinson, Davis,
Strauss, …)
* Optical dipole
(Lynden-Bell, Lahav, Hudson,…)
* Cluster dipole
(Scaramella, Plionis, Tully,…)
* 2MASS
(Maller,…)

Dipole – weighting schemes
by Number
by Flux
ρ L = (7.67+- 1.02) x 10 8 L_sun h Mpc -3
β=Ω m 0.6 /b
g / L/ (4 π r 2 )

Dipoles in the Local Group Frame
Number weighed Flux weighted
Erdogdu, Huchra, Lahav et al.,
Astro-ph/0507166
Ω m 0.6 /bL < 0.55+- 0.20
15 o @ 50 Mpc/h
24 o @ 130 Mpc/h

Kocevski, Mullis
& Ebeling,
astro-ph/0403275
Dipole from X-ray clusters
Shapley

2MRS Dipole directions
Erdogdu et al. 2005

The expected rms bulk motion
h V 2 (R *) i / Ω m 1.2 s dk P(k) W 2 (kR*)
almost independent of the Cosmological Constant
(Lahav, Lilje, Primack & Rees 91)
Or Dark Energy (Wang & Steinhardt 98)
In low density CDM smaller amplitude (σ 8 Ω m 0.6 ),
larger coherence length (smaller Ω m h)
than in SCDM

Wiener Filter 2MRS velocity field
(CMB frame)
Erdogdu
et al.

The revival of peculiar velocities
15,000 Dn - σ measurements out to 15,000 km/sec
δσ /σ » 10%
δR /R» 20%
Campbell et al.

“Baryonic” Faber-Jackson relation
M dyn
M dyn ¼ 1.02 M star 1.03
M star
M star ¼ 10 11 M sun (σ/195) 4.05
M star
SDSS data from Bernardi et al Lintott, Ferreras, Lahav
σ

7 Abell clusters
77 groups (>8)
20 Abell clusters
93 groups (>8)
Baugh et al., Erdogdu et al.
2dFGRS

A Nearly Normal Universe
Are Dark Matter & Dark Energy
the new epicycles?
More components?

From 2dF+CMB (6 parameter fit):
Cole et al. 2005
Ω m =0.23 §0.02

Baryonic wiggles – SDSS LRG
Eisenstein et al 2005.

Brief History of
‘Hot Dark Matter’
* 1970s : Top-down scenario with massive neutrinos (HDM) –
Zeldovich Pancakes
* 1980s: HDM - Problems with structure formation
* 1990s: Mixed CDM (80%) + HDM (20% )
* 2000s: Baryons (4%) + CDM (26%) +Lambda (70%):
But now we know HDM exists!
How much?

0.01
0.00
Weighing Neutrinos with
Ω ν = 0.05
Elgaroy , Lahav & 2dFGRS team,
astro-ph/0204152 , PRL
2dFGRS
Free streaming effect:
Ω ν /Ω m < 0.13
Total ν mass M< 1.8 eV
0.001 < Ω ν < 0.04
(Oscillations) (2dF)
a Four-Component
Universe ?

Data
2dFGRS
Neutrino mass from Cosmology
WMAP+2dF+…
WMAP+2dFnew
SDSS+WMAP
Ly-α + SDSS+
WMAP
WMAP alone
Authors
Elgaroy et al. 02
Spergel et al. 03
Sanchez et al. 05
Tegmark et al. 04
Seljak et al. 04
Ichikawa et al. 04
All upper limits 95% CL, but different assumed priors !
Mν = Σ mi < 1.8 eV
< 0.7 eV
< 1.2 eV
< 1.7 eV
< 0.4 eV
< 2.0 eV

Halo model for LSS
Picture credit: Cooray & Sheth (2002)

The halo model – the ‘new biasing’
P(k) = P lin +P halo
Truncates NFW fit with C=2.4§ 0.2
Using 2dF Groups
Collister & Lahav, astro-ph/0412516

Clustering of Red vs. Blue 2dF
galaxies
Madgwick, Hawkins, Lahav & 2dFGRS team, astro-ph/0303668

Correlation Function per Type
dP / n [1+ξ(r)] dV
ξ(r) = (r/r 0 ) -γ
Why a power law?
different slopes for blue
and red explained by
different halo
Occupation numbers

Probing Dark Energy
• Probe dark energy through the history of the expansion rate:
H 2 (z) = H 2 0 [Ω M (1+z) 3 + Ω DE (1+z) 3 (1+w) ] (flat Universe)
matter dark energy (constant w)
P = w ρ
• Comoving distance r(z) = ∫ dz/H(z)
• Standard Candles d L(z) = (1+z) r(z)
• Standard Rulers d A(z) = (1+z) −1 r(z)
• Standard Population (volume) dV/dzdΩ = r 2 (z)/H(z)
• The rate of growth of structure also determined by H(z) and by
any modifications of gravity on large scales

Imaging CFHTLS
Supernovae
SDSS
Spectroscopy
SDSS
Clusters AMI
Surveys to measure Dark Energy
2005 2010
CSP
CFHTLS
SZA
FMOS KAOS
ATLAS
APEX
AMIBA
SPT
ACT
CMB WMAP 2/3 WMAP 6 yr
2005
SUBARU
ATLAS KIDS
DES
VISTA JDEM/
Pan-STARRS
SNAP
DES LSST
Pan-STARRS
DES
JDEM/
SNAP
Planck Planck 4yr
2010
LSST SKA
SKA
2015
2015

The Dark Energy Survey
300,000,000 photometric redshifts
• 4 complementary techniques:
* Cluster counts & clustering
* Weak lensing
* Galaxy angular clustering
* SNe Ia distances
A new 3 deg 2 camera
on the CTIO Blanco 4m
Construction 2005-2009
Survey 2009-2014 (~525 nights)
5000 deg 2 g, r, i, z
Goal: error bar of few % on W=P/ρ

Input:
magnitudes
ANNz
Collister & Lahav 2004
Output:
redshift

DES
griz filters
10σ Limiting Magnitudes
g 24.6
r 24.1
i 24.0
z 23.9
Field Galaxy Photo-z Results

DES + VISTA
griz+YJHKs filters
10σ 10 Limiting Magnitudes
Y 22.45
J 22.15
H 21.65
Ks 21.15
Field Galaxy Photo-z Results

Mock Dark Energy Survey data
DES (griz) 5-yr alone DES + VISTA (YJHKs)
σ z = 0.13 σ z =0.08

Conclusions - in the Trio’s own words…
● “Although a spherically symmetric Great
Attractor model fits the present data well…it is
dangerous to use it for cosmology.” (Faber &
Burstein 1988)
● “CDM still does the best job, but there are many,
many unresolved issues.” (Blumenthal 1987)
● “The total neutrino mass could be comparable to
that of the visible stars in the universe, or perhaps
even larger.” (Primack 2001)