Planck intermediate results - XLVII. Planck constraints on reionization history
R. AdamN. AghanimM. AshdownJ. AumontC. BaccigalupiM. BallardiniA. J. BandayR. B. BarreiroN. BartoloS. BasakRichard A. BattyeK. BenabedJ.-P. BernardM. BersanelliP. BielewiczJ. J. BockA. BonaldiL. BonaveraJ. R. BondJ. BorrillF. R. BouchetF. BoulangerM. BucherC. BuriganaE. CalabreseJ.-F. CardosoJ. CarronH. C. ChiangL. P. L. ColomboC. CombetB. ComisF. CouchotA. CoulaisB. P. CrillA. CurtoF. CuttaiaR. J. DavisP. de BernardisA. de RosaG. de ZottiJ. DelabrouilleEleonora Di ValentinoC. DickinsonJ. M. DiegoJ. M. DiegoM. DouspisA. DucoutX. DupacF. ElsnerT. A. EnßlinH. K. EriksenE. FalgaroneY. FantayeF. Finelli⋆F. ForastieriM. FrailisA. A. FraisseE. FranceschiA. FrolovS. GaleottaS. GalliK. GangaR. T. Génova-SantosM. GerbinoT. GhoshJ. González-NuevoK. M. GórskiA. GruppusoJ. E. GudmundssonF. K. HansenG. HélouS. Henrot–VersilléD. HerranzE. HivonZhiqi HuangS. IlićA. H. JaffeW. C. JonesE. KeihänenR. KeskitaloTheodore KisnerL. KnoxN. KrachmalnicoffM. KunzH. Kurki‐SuonioG. LagacheA. LähteenmäkiJ.‐M. LamarreM. LangerA. LasenbyM. LattanziC. R. LawrenceM. Le JeuneF. LevrierAntony LewisM. LiguoriP. B. LiljeM. López-CaniegoYin-Zhe MaJ. F. Macías–PérezG. MaggioA. MangilliM. MarisP. G. MartinE. Martínez-GonzálezS. MatarreseN. MauriJ.D. McEwenP. R. MeinholdA. MelchiorriA. MennellaM. MigliaccioM.-A. Miville-DeschênesD. MolinariA. MonetiL. MontierG. MorganteAdam MossP. NaselskyP. NatoliC. A. OxborrowL. PaganoD. PaolettiB. PartridgeG. PatanchonL. PatriziiO. PerdereauL. PerottoV. PettorinoF. PiacentiniS. PlaszczynskiL. PolastriG. PolentaJ.-L. PugetJ.P. RachenB. RacineM. ReineckeM. RemazeillesA. RenziG. RochaM. RossettiG. RoudierJ. A. Rubiño-MartínB. Ruiz-GranadosL. SalvatiM. SandriМ. СавелайненD. ScottG. SirriR. SunyaevA.-S. Suur-UskiJ.A. TauberM. TentiL. ToffolattiM. TomasiM. TristramT. TrombettiJ. VäliviitaF. Van TentP. VielvaF. VillaN. VittorioB.D. WandeltI. K. WehusMartin WhiteA. ZaccheiA. Zonca
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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.Keywords:
South Pole Telescope
We introduce a powerful semi-numeric modeling tool, 21cmFAST, designed to efficiently simulate the cosmological 21-cm signal. Our code generates 3D realizations of evolved density, ionization, peculiar velocity, and spin temperature fields, which it then combines to compute the 21-cm brightness temperature. Although the physical processes are treated with approximate methods, we compare our results to a state-of-the-art large-scale hydrodynamic simulation, and find good agreement on scales pertinent to the upcoming observations (>~ 1 Mpc). The power spectra from 21cmFAST agree with those generated from the numerical simulation to within 10s of percent, down to the Nyquist frequency. We show results from a 1 Gpc simulation which tracks the cosmic 21-cm signal down from z=250, highlighting the various interesting epochs. Depending on the desired resolution, 21cmFAST can compute a redshift realization on a single processor in just a few minutes. Our code is fast, efficient, customizable and publicly available, making it a useful tool for 21-cm parameter studies.
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We report the discovery of an extremely long ($\sim$110 Mpc/$h$) and dark ($\tau_{\rm eff} \gtrsim 7$) Ly$\alpha$ trough extending down to $z \simeq 5.5$ towards the $z_{\rm em} \simeq 6.0$ quasar ULAS J0148+0600. We use these new data in combination with Ly$\alpha$ forest measurements from 42 quasars at $4.5 \le z_{\rm em} \le 6.4$ to conduct an updated analysis of the line-of-sight variance in the intergalactic Ly$\alpha$ opacity over $4 \le z \le 6$. We find that the scatter in transmission among lines of sight near $z \sim 6$ significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near $z \simeq 5.6$-5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone. We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by $z \simeq 5.6$, however, a large fraction of the data are consistent with a uniform UVB, and by $z \sim 5$ the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at $z \sim 6$, it has fully completed by $z \sim 5$.
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Recently, there has been a great deal of interest in understanding the reionization of hydrogen in the intergalactic medium (IGM). One of the major outstanding questions is how this event proceeds on large scales. Motivated by numerical simulations, we develop a model for the growth of HII regions during the reionization era. We associate ionized regions with large-scale density fluctuations and use the excursion set formalism to model the resulting size distribution. We then consider ways in which to characterize the morphology of ionized regions. We show how to construct the power spectrum of fluctuations in the neutral hydrogen field. The power spectrum contains definite features from the HII regions that should be observable with the next generation of low-frequency radio telescopes through surveys of redshifted 21 cm emission from the reionization era. Finally, we also consider statistical descriptions beyond the power spectrum and show that our model of reionization qualitatively changes the distribution of neutral gas in the IGM.
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We present new upper limits on the volume-weighted neutral hydrogen fraction, , at z~5-6 derived from spectroscopy of bright quasars. The fraction of the Lyman-alpha and Lyman-beta forests that is "dark" (with zero flux) provides the only model-independent upper limit on , requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed UV continuum. In this work we update our previous results using a larger sample (22 objects) of medium-depth (~ few hours) spectra of high-redshift quasars obtained with the Magellan, MMT, and VLT. This significantly improves the upper bound on derived from dark pixel analysis to <= 0.06 + 0.05 (1{\sigma}) at z=5.9, and <= 0.04 + 0.05 (1{\sigma}) at z=5.6. These results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z~6.
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We present Lya luminosity function (LF), clustering measurements, and Lya line profiles based on the largest sample, to date, of 207 Lya emitters (LAEs) at z=6.6 on the 1-deg^2 sky of Subaru/XMM-Newton Deep Survey (SXDS) field. Our z=6.6 Lya LF including cosmic variance estimates yields the best-fit Schechter parameters of phi*=8.5 +3.0/-2.2 x10^(-4) Mpc^(-3) and L*(Lya)=4.4 +/-0.6 x10^42 erg s^(-1) with a fixed alpha=-1.5, and indicates a decrease from z=5.7 at the >~90% confidence level. However, this decrease is not large, only =~30% in Lya luminosity, which is too small to be identified in the previous studies. A clustering signal of z=6.6 LAEs is detected for the first time. We obtain the correlation length of r_0=2-5 h^(-1) Mpc and bias of b=3-6, and find no significant boost of clustering amplitude by reionization at z=6.6. The average hosting dark halo mass inferred from clustering is 10^10-10^11 Mo, and duty cycle of LAE population is roughly ~1% albeit with large uncertainties. The average of our high-quality Keck/DEIMOS spectra shows an FWHM velocity width of 251 +/-16 km s^(-1). We find no large evolution of Lya line profile from z=5.7 to 6.6, and no anti-correlation between Lya luminosity and line width at z=6.6. The combination of various reionization models and our observational results about the LF, clustering, and line profile indicates that there would exist a small decrease of IGM's Lya transmission owing to reionization, but that the hydrogen IGM is not highly neutral at z=6.6. Our neutral-hydrogen fraction constraint implies that the major reionization process took place at z>~7.
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We discuss new constraints on the epoch of cosmic reionization and test the assumption that most of the ionizing photons responsible arose from high redshift star-forming galaxies. Good progress has been made in charting the end of reionization through spectroscopic studies of z~6-8 QSOs, gamma-ray bursts and galaxies expected to host Lyman-alpha emission. However, the most stringent constraints on its duration have come from the integrated optical depth, tau, of Thomson scattering to the cosmic microwave background. Using the latest data on the abundance and luminosity distribution of distant galaxies from Hubble Space Telescope imaging, we simultaneously match the reduced value tau=0.066 +/- 0.012 recently reported by the Planck collaboration and the evolving neutrality of the intergalactic medium with a reionization history within 6 <~ z <~ 10, thereby reducing the requirement for a significant population of very high redshift (z>>10) galaxies. Our analysis strengthens the conclusion that star-forming galaxies dominated the reionization process and has important implications for upcoming 21cm experiments and searches for early galaxies with James Webb Space Telescope.
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We study the evolution of the ionization state of the IGM at the end of the reionization epoch using spectra of a sample of nineteen quasars at 5.745.7: the optical depth evolution changes from tau ~ (1+z)^{4.3} to (1+z)^{>11}, and the average length of dark gaps with tau>3.5 increases from <10 to >80 comoving Mpc. The dispersion of IGM properties along different lines of sight also increases rapidly, implying fluctuations by a factor of >4 in the UV background at z>6, when the mean free path of UV photons is comparable to the correlation length of galaxies. The mean length of dark gaps shows the most dramatic increase at z~6, as well as the largest varianace. We suggest using dark gap statistics as a powerful probe of the ionization state of the IGM at yet higher redshift. The sizes of HII regions around quasars decrease rapidly towards higher redshift, suggesting that the neutral fraction of the IGM has increased by a factor of >10 from z=5.7 to 6.4. The mass-averaged neutral fraction is 1-4% at z~6.2 based on the GP optical depth and HII region sizes. The observations suggest that z~6 is the the end of the overlapping stage of reionization, and are inconsistent with a neutral IGM at z~6, as indicated by the finite length of dark absorption gaps.
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This paper describes the identification, modelling, and removal of previously unexplained systematic effects in the polarization data of the Planck High Frequency Instrument (HFI) on large angular scales, including new mapmaking and calibration procedures, new and more complete end-to-end simulations, and a set of robust internal consistency checks on the resulting maps. These maps, at 100, 143, 217, and 353 GHz, are early versions of those that will be released in final form later in 2016. The improvements allow us to determine the cosmic reionization optical depth τ using, for the first time, the low-multipole EE data from HFI, reducing significantly the central value and uncertainty, and hence the upper limit. Two different likelihood procedures are used to constrain τ from two estimators of the CMB E- and B-mode angular power spectra at 100 and 143 GHz, after debiasing the spectra from a small remaining systematic contamination. These all give fully consistent results. A further consistency test is performed using cross-correlations derived from the Low Frequency Instrument maps of the Planck 2015 data release and the new HFI data. For this purpose, end-to-end analyses of systematic effects from the two instruments are used to demonstrate the near independence of their dominant systematic error residuals. The tightest result comes from the HFI-based τ posterior distribution using the maximum likelihood power spectrum estimator from EE data only, giving a value 0.055 ± 0.009. In a companion paper these results are discussed in the context of the best-fit PlanckΛCDM cosmological model and recent models of reionization.
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We present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology we find a Hubble constant, H0= (67.8 +/- 0.9) km/s/Mpc, a matter density parameter Omega_m = 0.308 +/- 0.012 and a scalar spectral index with n_s = 0.968 +/- 0.006. (We quote 68% errors on measured parameters and 95% limits on other parameters.) Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a reionization optical depth of tau = 0.066 +/- 0.016. Combining Planck with other astrophysical data we find N_ eff = 3.15 +/- 0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to < 0.23 eV. Spatial curvature is found to be |Omega_K| < 0.005. For LCDM we find a limit on the tensor-to-scalar ratio of r <0.11 consistent with the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP data leads to a tighter constraint of r < 0.09. We find no evidence for isocurvature perturbations or cosmic defects. The equation of state of dark energy is constrained to w = -1.006 +/- 0.045. Standard big bang nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. We investigate annihilating dark matter and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.
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