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Planck intermediate results. XLVII. Planck constraints on reionization history

Planck Collaboration; Adam, R.; Aghanim, N.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S.; Battye, R.; Benabed, K.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Calabrese, E.; Cardoso, J.-F.; Carron, J.; Chiang, H. C.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Di Valentino, E.; Dickinson, C.; Diego, J. M.; Dor?, O.; Douspis, M.; Ducout, A.; Dupac, X.; Elsner, F.; En?lin, T. A.; Eriksen, H. K.; Falgarone, E.; Fantaye, Y.; Finelli, F.; Forastieri, F.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frolov, A.; Galeotta, S.; Galli, S.; Ganga, K.; G?nova-Santos, R. T.; Gerbino, M.; Ghosh, T.; Gonz?lez-Nuevo, J.; G?rski, K. M.; Gruppuso, A.; Gudmundsson, J. E.; Hans...


Planck Collaboration

R. Adam

N. Aghanim

M. Ashdown

J. Aumont

C. Baccigalupi

M. Ballardini

A. J. Banday

R. B. Barreiro

N. Bartolo

S. Basak

R. Battye

K. Benabed

J.-P. Bernard

M. Bersanelli

P. Bielewicz

J. J. Bock

A. Bonaldi

L. Bonavera

J. R. Bond

J. Borrill

F. R. Bouchet

F. Boulanger

M. Bucher

C. Burigana

E. Calabrese

J.-F. Cardoso

J. Carron

H. C. Chiang

L. P. L. Colombo

C. Combet

B. Comis

F. Couchot

A. Coulais

B. P. Crill

A. Curto

F. Cuttaia

R. J. Davis

P. de Bernardis

A. de Rosa

G. de Zotti

J. Delabrouille

E. Di Valentino

C. Dickinson

J. M. Diego


M. Douspis

A. Ducout

X. Dupac

F. Elsner

T. A.

H. K. Eriksen

E. Falgarone

Y. Fantaye

F. Finelli

F. Forastieri

M. Frailis

A. A. Fraisse

E. Franceschi

A. Frolov

S. Galeotta

S. Galli

K. Ganga

R. T.

M. Gerbino

T. Ghosh


K. M.

A. Gruppuso

J. E. Gudmundsson

F. K. Hansen

G. Helou


D. Herranz

E. Hivon

Z. Huang

S. Ili?

A. H. Jaffe

W. C. Jones


R. Keskitalo

T. S. Kisner

L. Knox

N. Krachmalnicoff

M. Kunz

H. Kurki-Suonio

G. Lagache


J.-M. Lamarre

M. Langer

A. Lasenby

M. Lattanzi

C. R. Lawrence

M. Le Jeune

F. Levrier

A. Lewis

M. Liguori

P. B. Lilje


Y.-Z. Ma


G. Maggio

A. Mangilli

M. Maris

P.G. Martin


S. Matarrese

N. Mauri

J.D. McEwen

P.R. Meinhold

A. Melchiorri

A. Mennella

M. Migliaccio


D. Molinari

A. Moneti

L. Montier

G. Morgante

Associate Professor

P. Naselsky

P. Natoli

C.A. Oxborrow

L. Pagano

D. Paoletti

B. Partridge

G. Patanchon

L. Patrizii

O. Perdereau

L. Perotto

V. Pettorino

F. Piacentini

S. Plaszczynski

L. Polastri

G. Polenta

J.-L. Puget

J.P. Rachen

B. Racine

M. Reinecke

M. Remazeilles

A. Renzi

G. Rocha

M. Rossetti

G. Roudier


B. Ruiz-Granados

L. Salvati

M. Sandri

M. Savelainen

D. Scott

G. Sirri

R. Sunyaev

A.-S. Suur-Uski

J.A. Tauber

M. Tenti

L. Toffolatti

M. Tomasi

M. Tristram

T. Trombetti

J. Valiviita

F. Van Tent

P. Vielva

F. Villa

N. Vittorio

B.D. Wandelt

I.K. Wehus

M. White

A. Zacchei

A. Zonca


We investigate constraints on cosmic reionization extracted from the Planck cosmic microwave background (CMB) data. We combine the Planck CMB anisotropy data in temperature with the low-multipole polarization data to fit ΛCDM models with various parameterizations of the reionization history. We obtain a Thomson optical depth τ = 0.058 ± 0.012 for the commonly adopted instantaneous reionization model. This confirms, with data solely from CMB anisotropies, the low value suggested by combining Planck 2015 results with other data sets, and also reduces the uncertainties. We reconstruct the history of the ionization fraction using either a symmetric or an asymmetric model for the transition between the neutral and ionized phases. To determine better constraints on the duration of the reionization process, we also make use of measurements of the amplitude of the kinetic Sunyaev-Zeldovich (kSZ) effect using additional information from the high-resolution Atacama Cosmology Telescope and South Pole Telescope experiments. The average redshift at which reionization occurs is found to lie between z = 7.8 and 8.8, depending on the model of reionization adopted. Using kSZ constraints and a redshift-symmetric reionization model, we find an upper limit to the width of the reionization period of Δz < 2.8. In all cases, we find that the Universe is ionized at less than the 10% level at redshifts above z ≃ 10. This suggests that an early onset of reionization is strongly disfavoured by the Planck data. We show that this result also reduces the tension between CMB-based analyses and constraints from other astrophysical sources.


Planck Collaboration, Adam, R., Aghanim, N., Ashdown, M., Aumont, J., Baccigalupi, C., …Zonca, A. (2016). Planck intermediate results. XLVII. Planck constraints on reionization history. Astronomy and Astrophysics, 596, Article A108.

Journal Article Type Article
Acceptance Date Jul 23, 2016
Online Publication Date Dec 12, 2016
Publication Date 2016-12
Deposit Date Apr 28, 2017
Publicly Available Date Jul 30, 2018
Journal Astronomy & Astrophysics
Electronic ISSN 1432-0746
Publisher EDP Open
Peer Reviewed Peer Reviewed
Volume 596
Article Number A108
Keywords cosmic background radiation; dark ages, reionization, first stars; polarization
Public URL
Publisher URL


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