Upper limits on neutrino masses from cosmology: new results Øystein Elgarøy (Institute of theoretical astrophysics, University of Oslo) Collaborator: Ofer Lahav (UCL, London) SNOW06

NASA/WMAP Science Team Room for neutrinos?

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 > k nr = (m  /1 eV) 1/2  m 1/2 h/Mpc Colombi, Dodelson, & Widrow 1995  WDMCDM+HDM CDM Massive neutrinos mimic a smaller source term

P(k)=A k n T 2 (k) Neutrino Free Streaming  P(k)/P(k) = -8    m (Hu et al. 1998)  P(k)/P(k) = -8    m (Hu et al. 1998)

Neutrino mass from Cosmology DataAuthors M  m i 2dF (P01)Elgaroy et al. 02 < 1.8 eV WMAP+2dF+…Spergel et al. 03 < 0.7 eV 2dF (C05)+CMBSanchez et al. 05 < 1.2 eV BAO+CMB+LSS +SNIa Goobar et al. 06 < 0.5 eV Ly-  + SDSS+ WMAP (3 year) Seljak et al. 06 < 0.17eV WMAP (1 year) alone 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)

Why this degeneracy? P(k) sensitive to the combination f   m But m  h 2 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 APM selected Magnitude b J < Median z  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

Galaxy Biasing

To b or not to b ?

The 2dFGRS Power Spectrum 160 K (Percival et al.) Redshift space Convolved Good fit to  CDM Wiggles ? l=200l= Mpc/h7 Mpc/h

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  m h=0.18, f b =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)

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?