Transcript Upper limits on neutrino masses from cosmology: new results

Upper limits on neutrino
masses from cosmology:
new results
Øystein Elgarøy
(Institute of theoretical astrophysics,
University of Oslo)
Collaborator: Ofer Lahav (UCL, London)
SNOW06
Room for neutrinos?
NASA/WMAP Science Team
Absolute Masses of
Neutrinos
E & Lahav, NJP 05
What do we mean by
‘systematic uncertainties’?
• Cosmological (parameters and priors)
• Astrophysical (e.g. Galaxy biasing)
• Instrumental (e.g. ‘seeing’)
Neutrinos decoupled when they were still
relativistic, hence they wiped out structure
on small scales
k > knr = 0.026 (m /1 eV)1/2 m1/2 h/Mpc
Colombi, Dodelson, &
Widrow 1995
CDM+HDM
WDM
Massive neutrinos mimic
a smaller source term
CDM
P(k)=A kn T2(k)
Neutrino Free Streaming
DP(k)/P(k) = -8  /m
(Hu et al. 1998)
Neutrino mass from Cosmology
Data
Authors
2dF (P01)
WMAP+2dF+…
2dF (C05)+CMB
BAO+CMB+LSS
+SNIa
Ly- + SDSS+
WMAP (3 year)
WMAP (1 year)
alone
Elgaroy et al. 02
Spergel et al. 03
Sanchez et al. 05
Goobar et al. 06
M = S mi
< 1.8 eV
< 0.7 eV
< 1.2 eV
< 0.5 eV
Seljak et al. 06
< 0.17eV
Ichikawa et al. 04
< 2.0 eV
All upper limits 95% CL, but different assumed priors !
Example of “model”
systematics: Dark energy
• Most cosmological neutrino mass limits
have assumed that the dark energy is a
cosmological constant
• There are (too!) many alternatives
• Common parameterization:
p = w
where w is a constant (can be < -1)
Hannestad, PRL95 (2005) 221301
Why this degeneracy?
• P(k) sensitive to the combination
f=/m
• But m=h2 eV
• If one allows for w <-1, SNIa data allow
large values of m
• The degeneracy is indirect, the effect of
varying w on P(k) corresponds roughly
to varying the amplitude
Modified gravity
TeVeS vs LCDM (D. F. Mota et al., in preparation)
Primordial power spectrum
The 2dF Galaxy Redshift
Survey
•
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APM selected
Magnitude bJ < 19.45
Median z  0.1
230 K measured
All public
• Cosmology
• Galaxy properties
The 2dFGRS Team Members
I.J. Baldry, C.M. Baugh, J. Bland-Hawthorn,
T.J. Bridges, R.D. Cannon, S. Cole, C.A. Collins,
M. Colless (PI),W.J. Couch, N.G.J. Cross, G.B. Dalton, R.
DePropris, S.P. Driver, G. Efstathiou, R.S. Ellis,
C.S. Frenk, K. Glazebrook, E. Hawkins, C.A. Jackson,
O. Lahav, I.J. Lewis, S.L. Lumsden, S. Maddox (PI),
D.S. Madgwick, S. Moody, P. Norberg, J.A. Peacock (PI),
B.A. Peterson, W. Sutherland, K. Taylor
http://www.mso.anu.edu.au/2dFGRS/
The 2dFGRS Power Spectrum
l=200
50 Mpc/h
l=1500
7 Mpc/h
• 160 K (Percival et
al.)
• Redshift space
• Convolved
• Good fit to CDM
• Wiggles ?
Empirical test of bias
• Red galaxies are more common in the
centres of rich clusters than blue
galaxies
• The opposite is the case in the rest of
the universe
• Can get a feeling of the significance of
bias for m limits by splitting the 2dF
sample into red and blue galaxies
From Cole et al. 2005
Preliminary results
• Fix mh=0.18, fb=0.17, n=1
• Vary f, marginalize over amplitude and
non-linear correction parameter Q (see
Cole 2005)
• Look at various cuts in k
• Gives an idea of the importance of bias
ØE,OL,Percival, Cole & Peacock (in preparation)
ØE, OL, Percival, Cole & Peacock (in preparation)
Summary
• Cosmological neutrino mass limits start to
probe the sub-eV range
• Need to focus on systematics
• No data set can do the job alone
• Dark energy: degeneracy with w understood
and can be dealt with, but not much has been
done on “weird” models
• Bias: red and blue galaxies cluster differently,
is it taken properly into account?