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NEUTRINOS FROM THE LYMAN-a FOREST
MYTH or REALITY ?
Trieste
MATTEO VIEL
OUTLINE
- What is the Lyman-a forest ? Is it a
cosmological probe ? - Constraints on sterile
neutrinos - Constraints on active neutrinos
NOW 2006 - Conca Specchiulla (Italy) 12th
September 2006
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Physics of the simulations is simple dark
matter, Gas cooling, photoionization heating,
star formation
80 of the baryons at z3 are in the
Lyman-a forest
Bi Davidsen (1997), Rauch (1998)
baryons as tracer of the dark matter density
field d IGM d DM at scales
larger than the Jeans length 1 com
Mpc t (dIGM )1.6 T -0.7
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GOAL the primordial dark matter power spectrum
from the observed flux spectrum
CMB physics z 1100 dynamics
Continuum fitting
Lya physics z lt 6 dynamics
termodynamics
Temperature, metals, noise
Tegmark Zaldarriaga 2002
CMB Lyman a
Long lever arm
Relation P FLUX (k) - P MATTER (k) ??
Constrain spectral index and shape
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SDSS vs LUQAS
McDonald et al. astro-ph/0405013
Kim, Viel et al. 2004, MNRAS,
347, 355
SDSS
LUQAS
3000 LOW RESOLUTION LOW S/N 30
HIGH RESOLUTION HIGH S/N
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Lyman-a forest CMB - I
VHS(LUQAS) high res Ly-a from Viel, Haehnelt,
Springel 2004 SDSS low res Ly-a from McDonald et
al. 2005
Ly-a WMAP1
Ly-a WMAP3
VHSWMAP1
POWER SPECTRUM AMPLITUDE
SDSSWMAP1
POWER SPECTRUM SLOPE
Viel , Haehnelt, Lewis, 2006, MNRAS Lett., 370, 51
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RESULTS STERILES
Warm dark matter
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Lyman-a and Warm Dark Matter - I
WDM 0.5 keV
LCDM
30 comoving Mpc/h z3
See Bode, Ostriker, Turok 2001 Abazajian,
Fuller, Patel 2001
In general

k FS 5 Tv/Tx (m x/1keV) Mpc-1

Set by relativistic degrees of freedom at
decoupling
Viel, Lesgourgues, Haehnelt, Matarrese, Riotto,
PRD, 2005, 71, 063534
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Lyman-a and Warm Dark Matter - II
WDM
LCWDM (gravitinos)
neutrinos
m WDM gt 550 eV thermal
gt 2keV sterile
neutrino

Viel et al. (2005)from high-res z2.1 sample
Seljak et al. 2006, astro-ph/0602430
m WDM gt 2 keV thermal
gt 14 keV sterile
neutrino

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Lya-WDM III analysis with flux derivatives
z lt 4.2
z lt 3.2
z lt 3.8
L n 0
Viel, Lesgourgues, Haehnelt, Matarrese, Riotto,
Phys.Rev.Lett., 2006, 97, 071301
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Decaying channel into photons and active
neutrinos line with Ems/2 (X-band)
Perseus Cluster (Jeremy Sanders)
5.66 keV
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COLD
(a bit) WARM sterile 7 keV
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RESULTS ACTIVE
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• S m n 0.138 eV
• m n 1.38 eV

Lyman-a forest
Lesgourgues Pastor 2006
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Active neutrinos -II
WDM
neutrinos

• mn (eV) lt 1 eV (95 C.L.)
• WMAP1 2dF LYa

Good agreement with the latest Tegmark et al.
results..
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Active neutrinos - III
Seljak, Slosar. McDonald, 2006, a-ph/0604335
normal
3
1,2
inverted
2
3
1
Tight constraints because data Are not
compatible!!!!

• mn (eV) lt 0.17 (95 C.L.)
• r lt 0.22 (95 C.L.)
• running -0.020 0.12
• CMB SN SDSS gal SDSS Ly-a

Goobar et al. (aph/0602155) get upper limits 2-3
times larger
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Hydro-simulations what can we learn? Many
uncertainties which contribute more or less
equally (statistical
error seems not to be an issue!)
VERY CONSERVATIVE ERRORS

CONTRIBUTION TO FLUCT. AMPL.
Statistical error 4
Systematic errors 15
t eff (z2.125)0.17 0.02 8
t eff (z2.72) 0.305 0.030 7
g 1.3 0.3 4
T0 15000 10000 K 3
Method 5
Numerical simulations 8
Further uncertainties 5
Mean flux
Thermal history
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SUMMARY
Lyman-a forest is a complementary measurement
of the matter power spectrum and can be use to
constrain cosmology together with the CMB There
are no other observables at the forest scales and
redshifts Tension for cosmological
parameters SDSSWMAP3 s80.86 0.03, n0.96
0.02 SDSSVHS s80.78 0.05, n
0.96 0.02 (not constraining anymore) Tight
constraints on neutrino mass fraction
Sterile neutrino probably ruled out in the
standard production mechanism

lt 0.9 eV
gt 10 keV
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Implementation of neutrino particles treated
self-consistently into GADGET-II
DM GAS
NEUTRINOS (1eV)
z 30 z 8 z 1
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Numerical modelling HydroParticleMesh
simulations of the forest
Full hydro 2003 part.
HPM NGRID600 HPM
NGRID400
MV, Haehnelt, Springel 2006
FLUX POWER
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Neutrinos
S mn (eV) 0.15
S mn (eV) 0.6
S mn (eV) 0.3
Neutrino mass effect on the CMB
3 massless 1 massive
S mn (eV) 0.9
Neutrino mass effect on P(k)
Seljak et al. 2004
Note that WMAP only has lt1 uncertainties at
l300!!! and Planck will improve this
especially at high l values
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Lyman-a forest CMB - II
SDSS McDonald et al. 2005, Seljak et al. 2005
Hydro Particle Mesh simulations SDSS-d
Viel Haehnelt 2006 analysis of SDSS flux power
using flux derivatives and full hydrodynamical
simulations
Flux power
P F (k, z p) P F (k, z p0) S i1,N ? P
F (k, z pi) (pi - pi0)

? pi
p p0

Best fit
p astro and cosmo param.
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Lyman-a forest CMB - II

• With WMAP3 like-priors
• M 0.235 0.035
• H 0 73 3 km/s/Mpc

SDSS amplitude and slope are 2s away WMAP3
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5.66 keV !!!
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Wm 0.26 WL 0.74 Wb0.0463 H0 72
km/sec/Mpc - 60 Mpc/h 2x4003 GASDM
2.5 com. kpc/h softening length GADGET
II code COSMOS computer DAMTP (Cambridge)
DM
GAS
STARS
NEUTRAL HYDROGEN
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Wm 0.26 WL 0.74 Wb0.0463 H0 72
km/sec/Mpc - 60 Mpc/h 2x4003 GASDM
2.5 com. kpc/h softening length GADGET
II code COSMOS computer DAMTP (Cambridge)
DM
GAS
STARS
NEUTRAL HYDROGEN
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LUQAS SDSS
DATA 27
high res z2.125 QSO spectra 3000 QSO spectra
zgt2.2 THEORY SIMULATIONS full hydro
simulations calibrated
simulations THEORY METHOD
3D flux inversion 1D flux
modelling ADVANTAGES band power
large redshift
range DRAWBACKS only
z2.1 (and 2.72) and 34 parameters
modelling larger error
bars RESULTS no
large running, scale invariant, high power
spectrum amplitude
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Fitting SDSS data with GADGET-2
this is SDSS Ly-a only !!
M sterile neutrino gt 10 KeV 95
C.L. SDSS data only s8 0.91 0.07 n
0.97 0.04
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Isocurvature perturbations
This is a model in agreement with WMAP3!
Beltran, Garcia-Bellido, Lesgourgues, Viel, 2005,
PRD, D72, 103515
Fully correlated
aisocurvature fraction at k0.05 Mpc-1
bquantifies correlation between ISO
and ADIABATIC modes
n iso1.9 1.0 95 C.L.
Anti correlated
No iso Only iso
n ad0.95 n iso 3
n ad 0.95 n iso 2
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Mean flux
Effective optical depth
Low resolution SDSS like spectra
High resolution UVES like spectra
ltFgt exp (- t eff) Power spectrum of
F/ltFgt
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Thermal state
T T0 ( 1 d) g-1
Thermal histories Flux
power fractional differences
Statistical SDSS errors on flux power
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Lack of power in the RSI model haloes form
later. Contrast with the large t
inferred (Yoshida et al. 2003)
Spergel et al. 2003
Peiris et al. 2003
Lyman-a does most of the job in constraining
running!!!
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The LUQAS sample
Large sample Uves Qso Absorption Spectra (LP-UVES
program P.I. J. Bergeron) high resolution 0.05
Angstrom, high S/N gt 50 low redshift, ltzgt2.25,
Dz 13.75
spectra
redshift
Kim, MV, Haehnelt, Carswell, Cristiani, 2004,
MNRAS, 347, 355