Detection and extraction of signals from the epoch of reionization using higher-order one-point statistics     

Geraint J. A. Harker  Saleem Zaroubi  Rajat M. Thomas  Vibor Jeli&#;  Panagiotis Labropoulos  Garrelt Mellema  Ilian T. Iliev  Gianni Bernardi  Michiel A. Brentjens  A. G. de Bruyn  Benedetta Ciardi  Leon V. E. Koopmans  V. N. Pandey  reas H. Pawlik  Joop Schaye  Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,393(4):1449-1458

Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features – such as a dip at the onset of reionization, followed by a rise towards its later stages – may be generic, and give us a promising route to a statistical detection of reionization.  相似文献   

Keeping the Universe ionized: photoheating and the clumping factor of the high-redshift intergalactic medium     

Andreas H. Pawlik  Joop Schaye  Eveline van Scherpenzeel 《Monthly notices of the Royal Astronomical Society》2009,394(4):1812-1824

  相似文献   

The formation and survival of discs in a ΛCDM universe     

Cecilia Scannapieco  Simon D. M. White  Volker Springel  Patricia B. Tissera 《Monthly notices of the Royal Astronomical Society》2009,396(2):696-708

We study the formation of galaxies in a Λ cold dark matter (ΛCDM) universe using high-resolution hydrodynamical simulations with a multiphase treatment of gas, cooling and feedback, focusing on the formation of discs. Our simulations follow eight isolated haloes similar in mass to the Milky Way and extracted from a large cosmological simulation without restriction on spin parameter or merger history. This allows us to investigate how the final properties of the simulated galaxies correlate with the formation histories of their haloes. We find that, at   z = 0  , none of our galaxies contains a disc with more than 20 per cent of its total stellar mass. Four of the eight galaxies nevertheless have well-formed disc components, three have dominant spheroids and very small discs, and one is a spheroidal galaxy with no disc at all. The   z = 0  spheroids are made of old stars, while discs are younger and formed from the inside-out. Neither the existence of a disc at   z = 0  nor the final disc-to-total mass ratio seems to depend on the spin parameter of the halo. Discs are formed in haloes with spin parameters as low as 0.01 and as high as 0.05; galaxies with little or no disc component span the same range in spin parameter. Except for one of the simulated galaxies, all have significant discs at   z ≳ 2  , regardless of their   z = 0  morphologies. Major mergers and instabilities which arise when accreting cold gas is misaligned with the stellar disc trigger a transfer of mass from the discs to the spheroids. In some cases, discs are destroyed, while in others, they survive or reform. This suggests that the survival probability of discs depends on the particular formation history of each galaxy. A realistic ΛCDM model will clearly require weaker star formation at high redshift and later disc assembly than occurs in our models.  相似文献   

The nature and origin of low-redshift O vi absorbers     

Benjamin D. Oppenheimer  Romeel Davé 《Monthly notices of the Royal Astronomical Society》2009,395(4):1875-1904

  相似文献   

On the peculiar momentum of baryons after reionization     

Carlos Hernández-Monteagudo  Shirley Ho 《Monthly notices of the Royal Astronomical Society》2009,398(2):790-806

  相似文献   

Prompt optical emission and synchrotron self-absorption constraints on emission site of GRBs     

Rong-Feng Shen  Bing Zhang 《Monthly notices of the Royal Astronomical Society》2009,398(4):1936-1950

We constrain the distance of the gamma-ray burst (GRB) prompt emission site from the explosion centre R , by determining the location of the electron's self-absorption frequency in the GRB prompt optical-to-X/γ-ray spectral energy distribution, assuming that the optical and the γ-ray emissions are among the same synchrotron radiation continuum of a group of hot electrons. All possible spectral regimes are considered in our analysis. The method has only two assumed parameters, namely the bulk Lorentz factor of the emitting source Γ and the magnetic field strength B in the emission region (with a weak dependence). We identify a small sample of four bursts that satisfy the following three criteria: (1) they all have simultaneous optical and γ-ray detections in multiple observational time intervals, (2) they all show temporal correlations between the optical and γ-ray light curves and (3) the optical emission is consistent with belonging to the same spectral component as the γ-ray emission. For all the time intervals of these four bursts, it is inferred that   R ≥ 10¹⁴  (Γ/300)^3/4 ( B /10⁵ G)^1/4  cm. For a small fraction of the sample, the constraint can be pinned down to   R ≈ 10¹⁴–10¹⁵ cm  for  Γ∼ 300  . For a second sample of bursts with prompt optical non-detections, only upper limits on R can be obtained. We find no inconsistency between the R -constraints for this non-detection sample and those for the detection sample.  相似文献   

Dark matter annihilation at cosmological redshifts: possible relic signal from annihilation of weakly interacting massive particles     

A. N. Baushev 《Monthly notices of the Royal Astronomical Society》2009,398(2):783-789

We discuss the possibility of observing the products of the dark matter annihilation that was going on in the early Universe. Of all the particles that could be generated by this process, we consider only photons, as they are both uncharged and easily detectable. The younger the Universe was, the higher the dark matter concentration n and the annihilation rate (proportional to n ²) were. However, the emission from the very early Universe cannot reach us because of the opacity. The main part of the signal was generated at the moment the Universe had just become transparent for the photons produced by the annihilation. Thus, the dark matter annihilation in the early Universe should have created a sort of relic emission. We obtain its flux and the spectrum.
If weakly interacting massive particles (WIMPs) constitute dark matter, it is shown that we may expect an extragalactic gamma-ray signal in the energy range 0.5–20 MeV with a maximum near 8 MeV. We show that an experimentally observed excess in the gamma-ray background at 0.5–20 MeV could be created by the relic signal from the annihilation of WIMPs only if the dark matter structures in the Universe had appeared before the Universe became transparent for the annihilation products  ( z ≃ 300)  . We discuss in more detail physical conditions whereby this interpretation could be possible.  相似文献   

Relative clustering and the joint halo occupation distribution of red sequence and blue-cloud galaxies in COMBO-17     

P. Simon  M. Hetterscheidt  C. Wolf  K. Meisenheimer  H. Hildebrandt  P. Schneider  M. Schirmer  T. Erben 《Monthly notices of the Royal Astronomical Society》2009,398(2):807-831

  相似文献   

Large-scale non-Gaussian mass function and halo bias: tests on N-body simulations     

M. Grossi  L. Verde  C. Carbone  K. Dolag  E. Branchini  F. Iannuzzi  S. Matarrese  L. Moscardini 《Monthly notices of the Royal Astronomical Society》2009,398(1):321-332

  相似文献   

Gravitational wave backgrounds and the cosmic transition from Population III to Population II stars     

Stefania Marassi  Raffaella Schneider  Valeria Ferrari 《Monthly notices of the Royal Astronomical Society》2009,398(1):293-302

  相似文献