Reionization with Multi-Frequency Datasets

FD 5 (AlbaNova University Centre)

FD 5

AlbaNova University Centre

Roslagstullsbacken 21, Stockholm
Axel Brandenburg (NORDITA), Garrelt Mellema (Dept. of Astronomy, Stockholm University), Göran Östlin (Dept. of Astronomy, Stockholm University), Saleem Zaroubi (kapteyn Institute, University of Groningen)

A workshop around the theme of combining different datasets relevant for the epoch of reionization.

Several different types of surveys are currently aiming at detecting signatures from the era beyond redshift 6, which is when the reionization of the Universe happened. Each of these surveys is at the cutting edge of what is possible, and detecting the desired signatures will be challenging. However, by comparing or cross-correlating the same areas on the sky between different data sets, a clearer detection may be possible.

In this workshop we want to explore the possibilities of combining and/or cross-correlating future redshifted 21cm data with other observables from the epoch of reionization. The main ones that have been considered are galaxy probes such as Ly-a emitters and high redshift QSOs, and CMB data from Planck and groundbased CMB experiments. Other data sets that could potentially be useful are the near-infrared and x-ray backgrounds, as well as the distribution of Ly-a absorption towards QSOs.

The idea of the meeting is both to present current or upcoming observational datasets relevant for epoch of reionization studies, as well as get an overview of how combining these multi-frequency datasets can help improve our understanding of this important epoch in the history of the Universe. (mostly based on theoretical/numerical explorations). The workshop could also be a meeting place for starting collaborations which could lead to such combined studies.

Programme outline
  1. Overview of 21cm experiments
  2. Simulations of the reionization process and the 21cm signal
  3. Overview of Galaxy & QSO surveys
  4. Combining Galaxy/QSO data with 21cm
  5. Overview of CMB experiments
  6. CMB and reionization
  7. Other data sets

Invited Speakers
  • Ger de Bruijn
  • Miguel Morales
  • Nobunari Kashikawa
  • Matt Jarvis
  • Adam Lidz
  • Antony Lewis
  • Gil Holder
  • Jochen Weller
  • Ilian Iliev

  • Chris Carilli
  • Olivier Doré
  • Steve Furlanetto
  • Johan Fynbo
  • Martin Haehnelt
  • Toru Yamada
  • Saleem Zaroubi

  • Garrelt Mellema
  • Göran Östlin
  • Angela Adamo
  • Martina Friedrich
  • Fabio del Sordo
  • Sandra Åberg


Sponsored by NORDITA, Vetenskapsrådet, the Oskar Klein Centre and the Nordic Network of Astrophysics and Cosmology

    • Detecting the 21cm signal from the epoch of reionization
    • 1
      Reionization with the MWA
      I will review the design and status of the Murchison Widefield Array and its capabilities for observing the Epoch of Reionization. In addition I will discuss the challenges of instrumental calibration and foreground subtraction facing all 21 cm EoR observatories; the constraints these observational and astrophysical effects place on the measurements; and how these constraints affect efforts to cross-correlate 21 cm observations with measurements in other wave bands.
      Speaker: Prof. Miguel Morales (University of Washington)
    • 2
      LOFAR: Finding an EoR Needle in a 1500 Pbyte Haystack
      The LOFAR EoR KSP will produce around 1500 PByte of raw data in the coming years. This data will first be processed and calibrated in real time, compressed to 1.5 Pbyte and stored, and subsequently reprocessed several times, before ultimately being analyzed in detail. I will describe the LOFAR EoR data model, the computational challenges that are faced by the LOFAR EoR KSP and how we plan to overcome these issues using graphics processor units.
      Speaker: Prof. Leon Koopmans (Kapteyn Astronomical Institute)
    • 3
      Power spectrum analysis of the LOFAR EoR data
      We present a power spectrum analysis of the simulation LOFAR data. The simulated data include cosmological signal, foreground contamination, instrument response (UV coverage, observational time, etc...) and system noise. The foregrounds are fitted out using the Wp method and the power spectrum analysis is performed on the residuals. We show that after 400 hundred hours of observations with multiple beams we can reconstruct the input power spectrum reasonably well. We show also that within the first 3 years we will be able to constrain the power spectrum with a high accuracy.
      Speaker: Prof. Saleem Zaroubi (Kapteyn Astronomical Institute)
    • 4
      Simulating the 21 cm signal in absorption during the early EoR
      It has been recognized from the start that the high redshift 21 cm signal from the neutral IGM during the Epoch of Reionization may been seen as a strong absorption against the CMB early on as long as the IGM has undergone little heating from X-ray sources. The difficulty with simulating this stage of the Reionization is that the strength of the signal depends on an accurate computation of the spin temperature of neutral hydrogen including a proper modeling of the Wouthuysen-Field effect. We will present results from simulations combining the full radiative transfer of both the ionizing continuum and Lyman alpha photons, allowing us to model the 21cm signal during the early absorption regime. We find a strong (>100 mK) absorption signal during a limited period even if we take into account a reasonable contribution from X-ray sources.
      Speaker: Dr Benoit Semelin (Obs de Paris)
    • 5
      Cosmological reionization simulations: all halos great and small
      Simulations of the early structure formation and the Epoch of Reionization have now reached sufficient volume, dynamic range and resolution to make reliable predictions for the fundamental features and observable signatures of these epochs. I will review recent progress we have made in this area, which include performing the largest and most detailed early structure formation and EoR simulations. I will discuss the various observational signatures we predict, with a particular focus on the best observational strategies. I will also present some of our recent results on the reionization history of the Local Group of galaxies using constrained simulations of its formation.
      Speaker: Dr Ilian Iliev (University of Sussex)
    • 6
      Cosmological Reionization Simulations for LOFAR
      The redshifted 21-cm cosmological signal emanating from the "dark ages of the universe" as it transitions into the Epoch of Reionization (EoR) began to be intensely investigated in the last decade. The studies became all the more urgent as a result of unprecedented possibilities in signal extraction offered by large upcoming radio telescope arrays like LOFAR, MWA and SKA. From a theoretical perspective, challenges in predicting the 21(1+z) signal stem from the inadequacies of our understanding of the astrophysical processes that dominated the Universe before redshift 6. Apart from the nature of the first sources (Pop III stars, mini-quasars, dark matter annihilation) that ionized the Universe, there is a plethora of unknown entities that affect the signal as it traverses the Universe, impinges on the ionosphere, and ultimately enters the observation window of the telescope. The focus of the research reported in this thesis was the development of a fast and efficient radiative transfer (RT) scheme able to accurately predict the 21-cm cosmological signal, modulo the detection capability of the LOFAR telescope. The fast and novel scheme we propose here facilitates the spanning of large parameter spaces dictated by the astrophysical unknowns. The simulations that form part of the scheme provide the starting point for the LOFAR-EoR simulation pipeline. These mock datacubes will subsequently be used in conjunction with datasets of other measurements like the CMB and deep near-IR to test our calibration and signal extraction schemes and to extract more information about the "dark ages".
      Speaker: Dr Rajat Mani Thomas (Institute of Physics and Mathematics of the Universe)
    • 7
      Fast Simulations of the High Redshift 21cm Signal
      I present a fast and powerful tool for calculating full 3D realizations of the high-redshift 21cm signal. We compare our semi-numerical techniques against cosmological hydrodynamic simulations with radiative transfer, and find good agreement in the nonlinear density, ionization, peculiar velocity, and the resulting 21cm emission fields, especially on scales relevant to upcoming 21cm experiments. Interestingly, we also find that peculiar velocities have a complex impact on the mean and power spectrum of the 21cm emission, which varies with scale and the global ionized fraction. We also include prescriptions for computing inhomogenous X-ray heating and Lyman alpha pumping. Our simulation boxes can be of arbitrary size and can be run on ordinary computers in a matter of minutes. Thus they can rapidly explore wide swaths of parameter space, and be invaluable in interpreting upcoming 21cm observations.
      Speaker: Dr Andrei Mesinger (Princeton Univerisity)
    • 8
      The large scale structure of the high redshift 21-cm background
      We use high resolution three-dimensional simulations of reionization to develop a framework for interpreting upcoming 21-cm observations. These simulations have a dynamic range in excess of 3,000 at all points in the volume, on comoving (angular) scales from ~1 Mpc (arcminute) to several Gpc (tens of degrees). At these scales, first generation 21-cm experiments are expected to be sufficiently sensitive to detect the fluctuating signal from reionization. Because our simulations are highly-optimized using spectral filtering techniques, we can efficiently survey parameter space to distinguish between different reionization histories, source populations, and IGM absorption models. In order to maximize the constraints of the observations on theory, we present several new diagnostics that should be applied to the first generation of large-scale 21-cm measurements.
      Speaker: Dr Marcelo Alvarez (Stanford University)
    • 9
      High-z galaxies at the reionization epoch
      The large statistical sample of galaxies beyond z=6 explore the very early stage of the most fundamental observables in both star formation history and structure formation process. These observations also put critical constraints on the cosmic reionization. I will review the current status of several high-z galaxy surveys and future prospects.
      Speaker: Prof. NOBUNARI Kashikawa (NAOJ)
    • 10
      Detections of Ionizing Radiation from High-z Galaxies
      Ionizing radiation from young star-forming galaxies are thought to be a dominat source of ionizing background at z>3 and to have played a primary role in the cosmic reionization. So knowning the amount of ionizing photons from galaxies has particular importance on understanding of the cosmic reionization process. Since ionizing photons are easily absorbed by intervening neutral hydrogen clouds, direct observation of ionizing radiation at z>6 is virtually impossible. Even at z~3 where there is a significant possibility of relatively transparent line of sight, very deep observation is required and escape fraction of ionizing photons remains highly uncertain. Here we report the results of our searches for Lyman continuum from high-z galaxies through deep narrow-band imaging. We made a special filter for Subaru / Suprime-Cam to optimally trace ionizing radiation from galaxies in the SSA22 proto-cluster at z=3.1. The unique wide field-of-view of Suprime-Cam enabled us to search ionizing photons from ~200 spectroscopically confirmed galaxies. We detected ionizing radiation for 17 galaxies, and found that some of them - especially Ly-alpha emitters which are less luminous in non-ionizing UV compared to Lyman Break Galaxies - have surprisingly large ionizing to non-ionizing UV radiation ratios, which are difficult to be explained with population synthesis models with standard initial mass functions. We also made another narrow- band imaging search with VLT / FORS in a blank field and detected three strong Lyman continuum sources at z=3.2. This supports the idea that the strong ionizing sources are ubiquitous in the early universe. We discuss the implications of these findings on process of the cosmic reionization, as well as on galaxy formation in the early universe.
      Speaker: Dr Ikuru Iwata (National Astronomical Observatory of Japan)
    • 11
      AGN in the epoch of reionization from multi-wavelength surveys
      The combination of multi-wavelength large area, shallow surveys and smaller area deep surveys will allow us to determine the space density of AGN within the epoch of reionization. Furthermore, follow-up of these surveys at radio wavelengths may provide the best way of measuring the density of HI at these earl;y epochs. I will present an overview of current and future surveys that will be crucial in enabling us to explore the AGN population within the epoch of reionization.
      Speaker: Dr Jarvis Matt (University of Hertfordshire)
    • 12
      Constraints on Star Forming Galaxies at z>6.5
      We present the results of our search for high redshift Lyman-break galaxies over the GOODS-South field. We use ACS HST data in B, V, i' & z', VLT ISAAC J and Ks, Spitzer 3.6, 4.5, 5.8 and 8.0 micron data in conjunction with the new HAWK-I Y-band science verification data to search for dropout galxies in the 6<z<9 redshift range. Candidates were selected on the basis of a colour cut of (Y-J)AB>0.75 and (z'-Y)AB>1.0 for Y and z' drops respectively. We find no robust Y-drops (z~9) brighter than J(AB)<26.4. In our search for z'-band dropouts (z~6.5-7.5), we identify two previously-known Galactic T-dwarf stellar contaminants with these colours, and two likely supernovae seen in the Y-band data. We also identify 2 galaxies with z'-drop colours and bright Spitzer/IRAC fluxes which are likely z>6.5 galaxies.The implications if all or none of our candidates are real on the Ultra-Violet luminosity functions at z>6.5 are explored. We find our number of z'-drop candidates to be inconsistent with the expected number of z' drops in a simple no-evolution scenario from the z=3 Lyman-break galaxy luminosity function but we are marginally consistent with the observed luminosity function at z approx. 6 (if all our candidates are real). However, it is possible that one or both of our z'-drop candidates are not z>6.5 galaxies, which would demand evolution of the luminosity function at early epochs, in the sense that the number density of UV-luminous star-forming galaxies at z>7 is less than at z=3-6.
      Speaker: Ms Samantha Hickey (University of Hertfordshire)
    • 13
      Probing Reionisation with UKIDSS
      The UKIRT Infra-red Deep Sky Survey (UKIDSS) is the next generation deep sky survey. The Large Area Survey (LAS), within UKIDSS, aims to observe 4000 deg2 in Y, J, H and K, and provide near-ir counterparts to SDSS which are 3 magnitudes deeper than 2MASS. We present two z>6 quasar discovered by UKIDSS-LAS. We perform a detailed study of the Lyman alpha forest and find that this object has similar Lyman alpha absorption properties as other high-redshift quasars found in optical surveys, in particular the suggestion that the effective optical depth increases significantly at z > 5.5. This suggests that subsequent high-redshift quasars discovered in near-IR surveys like UKIDSS will be accurate probes of cosmological reionization to a redshift of 7 and beyond.
      Speaker: Mr Mitesh Patel (Imperial College London)
    • 14
      Probing Reionization with Lyman Alpha Emitters
      The present talk will focus on recently obtained results concerning the nature and properties of Lyman Alpha Emitters (LAEs) and their use as a probe to investigate cosmic reionization history. Based on state-of-art hydrodynamical simulations we discuss how the LAE Lya luminosity functions observed at various redshifts might be affected by the presence of intergalactic neutral gas and clarify the role of dust grains and clustering of sources. For the first time a coherent picture is developed in which the nature and global properties (stellar mass, star formation rate, metallicity, gas mass and temperature) of the emitters are linked to their visibility. We also test our model by reproducing the SED of specific high-z LAEs, as observed by Lai et al. 2007, for which Spitzer data are available. I will discuss the remaining puzzles and possible strategies to overcome them.
      Speaker: Ms Pratika Dayal (SISSA / International School for Advanced Studies)
    • 15
      Observational constraints on the Lyman alpha escape fraction from galaxies
      I will present results from our ongoing studies of Lyman alpha escape fraction at redsfhifts z=0, 0.3, and 2.2
      Speaker: Prof. Göran Östlin (Department of Astronomy, Stockholm University)
    • 16
      WISH [Wide-field Imaging Surveyor for High-redshift] upon the first galaxies
      WISH is a space science mission whose primary goal is to reveal the first- generation galaxies in the early young universe. We launch a 1.5m-aperture telescope equipped with 0.5-degree-diameter wide-field NIR camera by middle of 2010's in order to conduct ultra-deep and wide-area sky survey with the depth that cannot have been achieved by previous ground-base telescopes. WISH should be a very powerful and unique facility not only for the search for first-generation objects but also for study of dark energy and many other fields in astronomy.
      Speaker: Prof. Toru Yamada (Astronomical Institute Tohoku University)
    • 17
      Probing reionization with the 21cm galaxy cross-power spectrum
      No abstract submitted
      Speaker: Prof. Adam Lidz (Univ of Pennsylvania)
    • 18
      CMB studies with PLANCK
      I review the status of the Planck satellite and what it should be able to tell us about cosmology. I discuss the constraints on cosmological parameters, the role of degeneracies, uses of CMB polarization including constraints on the optical depth and the prospects for detecting primordial graviational waves. I will also discuss secondard signals, weak lensing of the CMB and SZ, as well as prospects for improving cosmological constraints by using Planck in combination with other data sets.
      Speaker: Dr Antony Lewis (IoA, Cambridge)
    • 19
      Fingerprints in the CMB from Reionization
      Free electrons liberated by the reionization process scatter CMB photons and lead to additonal temperature and polarization anisotropies. Along with a large scale polarization feature there are both temperature and polarization anisotropies on arcminute scales. The signals are small, but have a lot of information about both reionization and large scale structure, especially when combined with future measurements of the 21cm signal. The currently deepest CMB experiment on arcminute scales is the South Pole Telescope; I'll report on the current status and prospects for reionization studies.
      Speaker: Dr Gil Holder (McGill University)
    • 20
      Reconstructing the Reionization History with the Cosmic Microwave Background
      I will discuss how we can learn from cosmic microwave background polarization data about the reionization history of the Universe. In particular I will compare different parameterizations and how well they can be constrained.
      Speaker: Prof. Jochen Weller (Ludwigs-Maximilians-University Munich)
    • 21
      CMB secondary anisotropies from re-ionization
      Using N-bopdy simulations we compute different effects from the reionization time affecting the CMB phtons and/or distortinmg the obserevd emission at mm/sub-mm wavelenf\gths. Some of these effects include the Sunyaev-Zel'dovich effect, Ostriker-Vishniac effect, lensing by galaxy clusters and other effects that will be persenetd during this talk. All these mechanisms introduce secondary anisotropies that could be observed by facilities such as ALMA and SKA.
    • 22
      kSZ effect from patchy reionization
      I will review the current state of the predictions for the kSZ signatures from reionization. I will discuss the origin of this signal, its expected magnitude and features and the possibilities for its detection and for using it to discriminate between different reionization models.
      Speaker: Dr Ilian Iliev (University of Sussex)
    • 23
      The cross-correlation between CMB and 21-cm fluctuations during the epoch of reionisation
      The cosmic microwave background (CMB) and the 21-cm line fluctuations are powerful probes for cosmological reionisation. We study the potential of the cross-correlation between the CMB anisotropy and the 21 cm line fluctuations to obtain further understanding of the reionisation history. We calculate a signal-to-noise ratio for 21-cm surveys, LOFAR, MWA and SKA, with the CMB observation, Planck. For the cross-correlation between 21-cm fluctuations and the CMB temperature, the cross-correlation signal from the instant reionisation can be detected with a significant level; SN ratio $\sim 1$ for LOFAR and SN ratio $\sim 10$ for SKA. On the other hand, the detection of the 21-cm cross-correlation with CMB polarisation is difficult for current observation plans.
      Speaker: Dr Hiroyuki Tashiro (Institut d'Astrophysique Spatiale, University of Paris-Sud 11)
    • 24
      Cross-correlation Study between the Cosmological 21-cm Signal and the kinetic Sunyaev-Zel’dovich effect
      The Universe’s Epoch of Reionization (EoR) could be studied using a number of observational probes that provide complementary or corroborating information. Since each of these probes suffer from its own systematic and statistical uncer tainties, it is useful to consider the mutual information that these data sets contain. In this talk we will present a cross-correlation study between the kinetic Sunyaev-Zel’dovich effect (kSZ)– produced by the scattering of CMB photons off free electrons produced during the reioniza tion process – and the cosmological 21 cm signal– which reflects instead the neutral hydrogen content of the Universe, as a function of redshift. The study is carried out using simulated reionization history in 100/h Mpc scale N-body simulations with radiative transfer. In essence we find that the two probes anti-correlate. The significance of the anti-correlation signal depends on the extent of the reionization process, wherein extended histories result in a much stronger signal compared to instantaneous cases. Unfortunately however, the primary CMB fluctuations once folded in serve as a source of large correlated noise that ren ders the cross-correlation signal insignificant, regardless of the reionization scenario in focus. Obviously, this conclusion is modulo the simulation box size and reionization scenarios considered in this study and does not mean that a cross-correlation signal is absent at all scales and reionization histories.
      Speaker: Mr Vibor Jelic (Kapteyn Astronomical Institute, RUG)
    • 25
      Constraining reionization using 21 cm experiments in combination with CMB and Lyman alpha forest data
      It is hoped that 21 cm experiments will measure the neutral fraction at redshifts z=6-10 in the near future. We look at what current constraints from the CMB and the Lyman alpha forest tell us about reionization. The existing data is used to constrain different parametrizations for the sources that drive reionization via a likelihood analysis. In this talk, I will discuss how this allows us to quantify our uncertainty in the ionization history. The resulting histories are then used to make predictions for what 21 cm experiments will observe and how their observations will feed back on our understanding of reionization.
      Speaker: Dr Jonathan Pritchard (Harvard)
    • 26
      Cosmic Infrared Background and the Search for Reionization EBL
      In this talk I will update the ongoing sounding rocket experiment CIBER related to an absolute EBL measurement since DIRBE and related measurements with Spitzer etc to search for fluctuations in the background light. The main science goals are: total EBL as a constraint on galaxy formation, EBL component at z > 6 associated with first-light sources, and composition and distribution of zodiacal dust in the solar system. I will also update the status of an EBL explorer making measurements at 5 AU outside the zodiacal cloud.
      Speaker: Prof. Asantha Cooray (UC Irvine)