Large-scale structure from 2dFGRS
John Peacock IAU 216 Sydney July 2003
The distribution of the galaxies
1930s:
Hubble proves galaxies have a non-random distribution
1950s:
Shane & Wirtanen spend 10 years counting 1000,000 galaxies by eye
- filamentary patterns?
Results from the 2dF Galaxy Redshift Survey
Target: 250,000 redshifts to B<19.45
(median z = 0.11)
250 nights AAT 4m time
1997-2002
The 2dFGRS Team Australia
Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Warrick Couch Kathryn Deeley Roberto De Propris Karl Glazebrook Carole Jackson Ian Lewis Bruce Peterson Ian Price Keith Taylor
Britain Carlton Baugh Shaun Cole Chris Collins Nick Cross Gavin Dalton Simon Driver George Efstathiou Richard Ellis Carlos Frenk Ofer Lahav Stuart Lumsden Darren Madgwick Steve Maddox
Stephen Moody Peder Norberg John Peacock Will Percival Mark Seaborne Will Sutherland Helen Tadros
33 people at 11
institutions
2dF on the AAT
2dFGRS input catalogue Galaxies: bJ 19.45 from revised APM
Total area on sky ~ 2000 deg2
250,000 galaxies in total, 93% sampling rate Mean redshift <z> ~ 0.1, almost all with z < 0.3
2dFGRS geometry
NGP
SGP
NGP 75x7.5 SGP 75x15 Random 100x2Ø ~70,000 ~140,000 ~40,000
~2000 sq.deg.250,000 galaxies
Strips+random fields ~ 1x108 h-3 Mpc3
Volume in strips ~ 3x107 h-3 Mpc3
Final 2dFGRS Sky Coverage
NGP
SGP
Final redshift total: 221,283
2dFGRS Redshift distribution
N(z) Still shows significant clustering at z < 0.1
The median redshift of the survey is <z> = 0.11
Almost all objects have z < 0.3.
Cone diagram: 4-degree wedge
Spectrum of inhomogeneities
x
Primordial power-law spectrum (n=1?)
Transfer function
Transfer function Key scales:
* Horizon at zeq :
16 (mh2)-1 Mpc
(observe mh)
* Free-stream length : 80 (M/eV)-1 Mpc
(m h2 = M / 93.5 eV)
* Acoustic horizon : sound speed < c/31/2
* Silk damping
M sets damping scale - reduced power rather than cutoff if DM is mixed
Generally assume adiabatic
Parameters: d b v neutrino h w n M
2dFGRS power-spectrum results
Dimensionless power:
d (fractional variance in density) / d ln k
Percival et al. MNRAS 327, 1279 (2001)
Confidence limits
‘Prior’:
h = 0.7 ± 10%
&
n = 1
mh = 0.20 ± 0.03
Baryon fraction = 0.15 ± 0.07
Power spectrum: Feb 2001 vs ‘final’
Model fits: Feb 2001 vs ‘final’
mh = 0.20 ± 0.03
Baryon fraction = 0.15 ± 0.07
mh = 0.18 ± 0.02
Baryon fraction = 0.17 ± 0.06
if n = 1: or mh = 0.18 e1.3(n-1)
Conclusions from P(k)
• Lack of oscillations. Must have collisionless component
• CDM models work
• Low density if n=1 and h=0.7 apply
• possibilities for error:
• Isocurvature?
• =1 plus extra ‘radiation’?
• Massive neutrinos?
• Scale-dependent bias? (assumed gals mass)
Photometric recalibrationStart with SuperCosmos UKST scans
SDSS overlap in 33 equatorial plates: rms = 0.09 mag ( = SDSS-MGC
Force uniform optical and opt-2MASS colours: rms linearity and ZP corrections 1.4% and 0.15 mag
Calibration good to <1% and <0.03 mag
recalibrate APM (rms 0.14 mag)
2dFGRS in COLOUR
passive
active
R magnitudes from
SuperCosmos
Rest-frame colour gives same information as spectral type, but to higher z
Power spectrum and galaxy type
shape independent of galaxy type within error on spectrum
Relation to CMB results
Combining LSS & CMB breaks degeneracies:
LSS measures mh only if power index n is known
CMB measures n and mh3 (only if curvature is known)
curvature
total density
baryons
2dFGRS + CMB: Flatness
CMB alone has a geometrical degeneracy: large curvature is not ruled out
Adding 2dFGRS power spectrum forces flatness:
| 1 - tot | < 0.04
Efstathiou et al. MNRAS 330, L29 (2002)
The CMB peak degeneracy
Detailed constraints
for flat models
(CMB + 2dFGRS only: no priors)
Preferred model is scalar-dominated and very nearly scale-invariant
Percival et al. MNRAS 337, 1068 (2002)
Impact of WMAP
likelihood contours pre-WMAP + 2dFGRS 147024 galsscalar only, flat models
likelihood contours post-WMAP + 2dFGRS 147024 galsscalar only, flat models- WMAP reduces errors by factor 1.5 to 2
likelihood contours post-WMAP + 2dFGRS 213947galsscalar only, flat models
Vacuum equation of state (P = w c2)
w shifts present horizon, so different m
needed to keep CMB peak
location for given h
w < - 0.54
similar limit from
Supernovae: w < - 0.8 overall
2dFGRS
Extra relativistic components?
Matter-radiation horizon scale depends on matter density (mh2) and relativistic density (=1.68 CMB for 3 light neutrinos).
Suppose rel = X (1.68 CMB ) so apparent mh = mh X-1/2 and m=1 h=0.5 works if X=8
But extra radiation affects CMB too. Maintaining peak location needs h=0.5X1/2 if m=1
If w=-1, 2dFGRS+CMB measure h X-1/2 = 0.71 +- 5% with HST h = 0.72 +- 11%, hence
1.68X = 1.70 +- 0.24 (3.1 +- 1.1 neutrinos)
Summary >10 Mpc clustering in good accord with CDM
– power spectrum favours m h= 0.18 & 17% baryons
CMB + 2dFGRS implies flatness– CMB + Flatness measures m h3.4 = 0.078
– hence h = 0.71 ± 5%, m = 0.26 ± 0.04
No evidence for tilt (n = 0.96 +- 0.04) or tensors– But large tensor fractions not yet strongly excluded
Neutrino mass <0.6 eV if m =1 excluded
w < - 0.54 by adding HST data on h (agrees with SN) Boosted relativistic density cannot save m =1
– Neutrino background detected if w = -1
Data public: http://www.mso.anu.edu.au/2dFGRS/Public