Massive Neutrinos and Cosmology Ofer Lahav University College London * Brief history of ‘Hot Dark Matter’ * Limits on the total Neutrino mass from redshift surveys: M < eV * The CMB alone is not sensitive to M. * Mixed Dark Matter?  Paris

SDSS: Galaxy images and Redshifts

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%): room for HDM? e.g. Primack, astro-ph/

The model 95% of cosmologists favour today

The Cosmic Budget (Post-WMAP) * Reality or ‘Epicycles’? * More components? - e.g. neutrinos?

Density Fluctuations vs. Scale Tegmark

Precision Cosmology? Not Just Yet … Bridle, OL, Ostriker & Steinhardt 2003 OL & Liddle 2003

The 2dF Galaxy Redshift Survey  APM selected  Magnitude b J <  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 On 2dF Sociology see OL, astro-ph/

The 2dF Redshift Machine 400 fibres in 2 deg Field

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

2dF vs SDSS 50 Mpc/h Pope et al Tegmark et al. 2003

Neutrino properties  The number of neutrino species N affects the expansion rate of the universe, hence BBN. the expansion rate of the universe, hence BBN. BBN constraints N between 1.7 and 3 (95% CL) (e.g. Barger et al. 2003). We shall assume N  =3 and no annihilation (cf. Beacom et al. 2004)   h    eV  

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)

Weighing Neutrinos with 2dFGRS  Free streaming effect:   /  m  < 0.13 Total mass M< 1.8 eV    (Oscillations) (2dF)  a Four-Component Universe ? Elgaroy, Lahav & 2dFGRS team, astro-ph/ , PRL   =

Absolute Masses of Neutrinos Based on measured squared mass differences from solar and atmospheric oscillations Assuming m 1 < m 2 < m 3

2dF limits on the neutrino mass n= 0.9 n= 1.1 n=1.0 Prior 0<  m <0.5

Galaxy biasing

Galaxy Biasing

To b or not to b ?

Biasing from halo occupation + redshift distortion models Seljak 2001 Total neutrino mass

Biasing vs. neutrino mass Elgaroy & Lahav astro-ph/ SAM for L>0.75 L* P g (k) = b 2 (k) P m (k) b(k) = a log(k) + c a Total neutrino mass

The History of CMB observations Discovery COBE WMAP

WMAP Results T-T power spectrum Polarisation T-E power spectrum Bennett et al. 2003

Neutrinos and the CMB The CMB alone in NOT sensitive to massive neutrinos. The WMAP result (Spergel at al. 2003) of M < 0.69 eV (95% CL) is based on WMAP+2dF+Ly-   * 2dF is sensitive to  /  m * WMAP constrains  m (and other parameters)

X-ray galaxy clusters + CMB Allen, Schmidt & Bridle (2003) Claimed a preferred value M = eV * But it depends on the M-L x relation for clusters. * This really illustrates the degeneracy between the amplitude of fluctuations and the neutrino mass. The idea: Connecting  small and large scales (Fukugita et al. 2000)

Mixed Dark Matter?   m =1,  =0.2, h=0.45 * Consistent with 2dF. * To fit WMAP, a break is required in the Primordial power-spectrum (e.g. Blanchard et al. 2003). * Also at odds with HST’s H 0, SNIa, cluster evolution and baryon fraction. Elgaroy & Lahav, JCAP 2003 Astro-ph/ P(k) 2dF WMAP

Neutrino mass from Cosmology DataAuthors M  m i 2dFGRSElgaroy et al. 02 < 1.8 eV WMAP+2dF+…Spergel et al. 03 < 0.7 eV WMAP+2dFHannestad 03 < 1.0 eV SDSS+WMAPTegmark et al. 04 < 1.7 eV WMAP+2dF+ SDSS Crotty et al. 04 < 1.0 eV Clusters +WMAPAllen et al eV All upper limits 95% CL, but different assumed priors !

Summary * Redshift surveys (supplemented by the CMB) constrain M < eV within the  -CDM scenarios, subject to priors. * Alternatives - MDM? * Future: errors down to 0.1 eV using SDSS+Planck, and weak gravitational lensing of background galaxies and of the CMB.