Results for "Andrei Mesinger"

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Was reionization complete by z ~ 5-6?Oct 22 2009It is generally taken for granted that reionization has completed by z=6, due to the detection of flux in the Lyman alpha forest at redshifts z<6. However, since reionization is expected to be highly inhomogeneous, much of the spectra pass through just ... More
Reionization and Cosmic Dawn: theory and simulationsJan 08 2018We highlight recent progress in the sophistication and diversification of cosmic dawn and reionization simulations. The application of these modeling tools to current observations has allowed us narrow down the timing of reionization, which we now know ... More
Probing Reionization with the Cosmological Proximity Effect and High-Redshift Supernovae RatesSep 26 2005We develop and assess the potential of several powerful techniques, designed to investigate the details of reionization. First, we present a procedure to probe the neutral fraction, x_HI, using the Lyman alpha transmission statistics of high-redshift ... More
How the first generations of luminous baryons established the X-ray and UV backgroundsJan 21 2011The first generations of astrophysical objects made a substantial impact on our Universe with their radiation. X-rays from the first sources, with large mean free paths, likely quickly heated the intergalactic medium (IGM). The second generation of 21cm ... More
Reionisation & Cosmic Dawn Astrophysics from the Square Kilometre Array: Impact of Observing StrategiesJun 19 2019Interferometry of the cosmic 21-cm signal is set to revolutionise our understanding of the Epoch of Reionisation (EoR) and the Cosmic Dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography ... More
The depletion of gas in high-redshift dwarf galaxies from an inhomogeneous reionizationJan 28 2013The reionization of the intergalactic medium (IGM) was likely inhomogeneous and extended. By heating the IGM and photo-evaporating gas from the outskirts of galaxies, this process can have a dramatic impact on the growth of structures. Using a suite of ... More
Evidence for a Cosmological Stromgren Surface and for Significant Neutral Hydrogen Surrounding the Quasar SDSS J1030+0524Jun 07 2004Jul 12 2004A bright quasar residing in a dense and largely neutral intergalactic medium (IGM) at high redshifts (z > 6) will be surrounded by a large cosmological Stromgren sphere. The quasar's spectrum will then show a sharp increase in resonant Lyman line absorption ... More
Constraints on Reionization and Source Properties from the Absorption Spectra of z>6.2 QuasarsOct 10 2006Jan 30 2007We make use of hydrodynamical simulations of the intergalactic medium (IGM) to create model quasar absorption spectra. We compare these model spectra with the observed Keck spectra of three z>6.2 quasars with full Gunn-Peterson troughs: SDSS J1148+5251 ... More
The Global History of ReionisationMay 17 2016Feb 28 2018Using a Bayesian framework, we quantify what current observations imply about the history of the epoch of reionisation (EoR). We use a popular, three-parameter EoR model, flexible enough to accommodate a wide range of physically-plausible reionisation ... More
Lyman-alpha Damping Wing Constraints on Inhomogeneous ReionizationOct 01 2007One well-known way to constrain the hydrogen neutral fraction, x_H, of the high-redshift intergalactic medium (IGM) is through the shape of the red damping wing of the Lya absorption line. We examine this method's effectiveness in light of recent models ... More
The clustering of Lyman alpha emitters at z=7: implications for reionization and host halo massesMay 11 2015Sep 09 2015The Ly$\alpha$ line of high-redshift galaxies has emerged as a powerful probe of both early galaxy evolution and the epoch of reionization (EoR). Motivated by the upcoming wide-field survey with the Subaru Hyper Suprime-Cam (HSC), we study the angular ... More
How does radiative feedback from a UV background impact reionization?Jan 28 2013An ionizing UV background (UVB) inhibits gas accretion and photo-evaporates gas from the shallow potential wells of small, dwarf galaxies. During cosmological reionization, this effect can result in negative feedback: suppressing star-formation inside ... More
21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signalJan 26 2015Mar 30 2015We introduce 21CMMC: a parallelized, Monte Carlo Markov Chain analysis tool, incorporating the epoch of reionization (EoR) seminumerical simulation 21CMFAST. 21CMMC estimates astrophysical parameter constraints from 21 cm EoR experiments, accommodating ... More
21CMMC with a 3D light-cone: the impact of the co-evolution approximation on the astrophysics of reionisation and cosmic dawnJan 05 2018We extend 21CMMC, a Monte Carlo Markov Chain sampler of 3D reionisation simulations, to perform parameter estimation directly on 3D light-cones of the cosmic 21cm signal. This brings theoretical analysis closer to the tomographic 21-cm observations achievable ... More
Efficient Simulations of Early Structure Formation and ReionizationApr 09 2007We present a method to construct semi-numerical ``simulations'', which can efficiently generate realizations of halo distributions and ionization maps at high redshifts. Our procedure combines an excursion-set approach with first-order Lagrangian perturbation ... More
UV Radiative Feedback During the Advanced Stages of ReionizationJun 19 2008The ionizing ultraviolet background (UVB) during reionization can suppress the gas content of low-mass galaxies, even those capable of efficient atomic cooling, and thus lead to an extended reionization epoch. In this work, we explore the importance of ... More
Inhomogeneous recombinations during cosmic reionizationFeb 10 2014By depleting the ionizing photon budget available to expand cosmic HII regions, recombining systems (or Lyman limit systems) can have a large impact during (and following) cosmic reionization. Unfortunately, directly resolving such structures in large-scale ... More
Simultaneously constraining the astrophysics of reionisation and the epoch of heating with 21CMMCMay 09 2017Feb 28 2018The cosmic 21 cm signal is set to revolutionise our understanding of the early Universe, allowing us to probe the 3D temperature and ionisation structure of the intergalactic medium (IGM). It will open a window onto the unseen first galaxies, showing ... More
The Inhomogeneous Ionizing Background Following ReionizationJun 17 2009We study the spatial fluctuations in the hydrogen ionizing background in the epoch following reionization (z ~ 5--6). The rapid decrease with redshift in the photon mean free path (m.f.p.), combined with the clustering of increasingly rare ionizing sources, ... More
The Global History of ReionisationMay 17 2016Using a Bayesian framework, we quantify what current observations imply about the history of the epoch of reionisation (EoR). We use a popular, three-parameter EoR model, flexible enough to accommodate a wide range of physically-plausible reionisation ... More
Lyman-alpha Emitters During the Early Stages of ReionizationJul 31 2007Jan 30 2008We investigate the potential of exploiting Lya Emitters (LAEs) to constrain the volume-weighted mean neutral hydrogen fraction of the IGM, x_H, at high redshifts (specifically z~9). We use "semi-numerical'' simulations to efficiently generate density, ... More
The ionizing background at the end of overlapSep 25 2008One of the most sought-after signatures of reionization is a rapid increase in the ionizing background (usually measured through the Lyman-alpha optical depth toward distant quasars). Conventional wisdom associates this with the "overlap" phase when ionized ... More
Probing the Reionization History Using the Spectra of High-Redshift SourcesJan 08 2004Jun 07 2004We quantify and discuss the footprints of neutral hydrogen in the intergalactic medium (IGM) on the spectra of high-redshift (z ~ 6) sources, using mock spectra generated from hydrodynamical simulations of the IGM. We show that it should be possible to ... More
Implications of the Lyman alpha Emission Line from a Candidate z=10 GalaxyMar 17 2004Mar 29 2004The recently discovered z=10 galaxy (Pello et al 2004) has a strong Lyman alpha emission line that is consistent with being surprisingly symmetric, even given the relatively poor quality of its spectrum. The blue wing of a Lyman alpha line originating ... More
Evidence of Gunn-Peterson damping wings in high-z quasar spectra: strengthening the case for incomplete reionizationApr 12 2012Nov 04 2012The spectra of several high-redshift (z>6) quasars have shown evidence for a Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However, previous analyses assumed ... More
Focusing on Warm Dark Matter with Lensed High-redshift GalaxiesMay 31 2013Jul 17 2013We propose a novel use of high-redshift galaxies, discovered in deep Hubble Space Telescope (HST) fields around strong lensing clusters. These fields probe small comoving volumes (about 1000 cubic Mpc) at high magnification ({\mu} > 10), and can detect ... More
Model-independent evidence in favor of an end to reionization by z~6Nov 19 2014We present new upper limits on the volume-weighted neutral hydrogen fraction, <xHI>, 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 ... More
The Redshift Distribution of Distant Supernovae and its Use in Probing ReionizationMay 06 2005Sep 26 2005We model the number of detectable supernovae (SNe) as a function of redshift at different flux thresholds, making use of the observed properties of local SNe, such as their lightcurves, fiducial spectra, and peak magnitude distributions. We obtain a rate ... More
Unveiling the nature of dark matter with high redshift 21 cm line experimentsAug 05 2014Nov 19 2014Observations of the redshifted 21 cm line from neutral hydrogen will open a new window on the early Universe. By influencing the thermal and ionization history of the intergalactic medium (IGM), annihilating dark matter (DM) can leave a detectable imprint ... More
Constraints on reionisation from the z=7.5 QSO ULASJ1342+0928Jul 04 2018The recent detection of ULASJ1342+0928, a bright QSO at $z=7.54$, provides a powerful probe of the ionisation state of the intervening intergalactic medium, potentially allowing us to set strong constraints on the epoch of reionisation (EoR). Here we ... More
The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a parameter space studyDec 08 2011Feb 28 2012[ABRIDGED] Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev-Zel'dovich (kSZ) effect. Observational efforts with the Atacama Cosmology ... More
The first (nearly) model-independent constraint on the neutral hydrogen fraction at z~5--6Jan 17 2011Cosmic reionization is expected to be complex, extended and very inhomogeneous. Existing constraints at z~6 on the volume-averaged neutral hydrogen fraction, <x_HI>, are highly model-dependent and controversial. Constraints at z<6, suggesting that the ... More
Early galaxy formation in warm dark matter cosmologiesAug 05 2014May 07 2015We present a framework for high-redshift ($z \geq 7$) galaxy formation that traces their dark matter (DM) and baryonic assembly in four cosmologies: Cold Dark Matter (CDM) and Warm Dark Matter (WDM) with particle masses of $m_x =$ 1.5, 3 and 5 ${\rm keV}$. ... More
The Detectability of Lyman Alpha Emission from Galaxies during the Epoch of ReionizationJan 26 2011Nov 30 2011We study the visibility of the Lyman Alpha (Lya) emission line during the Epoch of Reionization (EoR). Combining galactic outflow models with large-scale semi-numeric simulations of reionization, we quantify the probability distribution function (PDF) ... More
Cross-correlation of the cosmic 21-cm signal and Lyman Alpha Emitters during reionizationFeb 15 2016Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the Epoch of Reionization (EoR), eventually providing 3D maps of the early Universe. Initial detections however will be low signal-to-noise, limited by systematics. ... More
Constraints on the temperature of the intergalactic medium at z=8.4 with 21-cm observationsSep 07 2015Nov 24 2015We compute robust lower limits on the spin temperature, $T_{\rm S}$, of the $z=8.4$ intergalactic medium (IGM), implied by the upper limits on the 21-cm power spectrum recently measured by PAPER-64. Unlike previous studies which used a single epoch of ... More
Constraints on the small-scale power spectrum of density fluctuations from high-redshift gamma-ray burstsJan 12 2005Apr 01 2005Cosmological models that include suppression of the power spectrum of density fluctuations on small scales exhibit an exponential reduction of high-redshift, non-linear structures, including a reduction in the rate of gamma ray bursts (GRBs). Here we ... More
The Growth of the Earliest Supermassive Black Holes and Their Contribution to ReionizationSep 04 2004We discuss currently available observational constraints on the reionization history of the intergalactic medium (IGM), and the extent to which accreting black holes (BHs) can help explain these observations. We show new evidence, based on the combined ... More
UV Radiative Feedback on High-Redshift Proto-GalaxiesApr 07 2006We use three-dimensional hydrodynamic simulations to investigate the effects of a transient photoionizing ultraviolet (UV) flux on the collapse and cooling of pregalactic clouds. These clouds have masses in the range 10^5 -10^7 M_sun, form at high redshifts ... More
The Evolution of 21-cm Structure (EOS): public, large-scale simulations of Cosmic Dawn and ReionizationFeb 24 2016We introduce the Evolution of 21-cm Structure (EOS) project: providing periodic, public releases of the latest cosmological 21-cm simulations. 21-cm interferometry is set to revolutionize studies of the Cosmic Dawn (CD) and epoch of reionization (EoR), ... More
Gas in Simulations of High Redshift Galaxies and MinihalosJun 01 2009We study the gas content of halos in the early universe using high resolution hydrodynamical simulations. We extract from the simulations and also predict based on linear theory the halo mass for which the enclosed baryon fraction equals half of the mean ... More
21cmFAST: A Fast, Semi-Numerical Simulation of the High-Redshift 21-cm SignalMar 19 2010We 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 ... More
Feedback-regulated Super Massive Black Hole Seed FormationMay 26 2014The nature of the seeds of high-redshift supermassive black holes (SMBHs) is a key question in cosmology. Direct collapse black holes (DCBH) that form in pristine, atomic-line cooling halos, illuminated by a Lyman-Werner (LW) UV flux exceeding a critical ... More
Radiative Feedback in Relic HII Regions at High-RedshiftDec 15 2008Sep 13 2009UV radiation from early astrophysical sources could have a large impact on subsequent star formation in nearby protogalaxies. Here we study the radiative feedback from the first, short-lived stars using hydrodynamical simulations with transient UV backgrounds ... More
Signatures of X-rays in the early UniverseOct 27 2012Apr 17 2013[abridged] With their long mean free paths and efficient heating of the intergalactic medium (IGM), X-rays could have a dramatic impact on the thermal and ionization history of the Universe. We explore this in various signals: (i) Reionization history: ... More
Upper Limits on the 21 cm Power Spectrum at z = 5.9 from Quasar Absorption Line SpectroscopyAug 03 2016We present upper limits on the 21 cm power spectrum at $z = 5.9$ calculated from the model-independent limit on the neutral fraction of the intergalactic medium of $x_{\rm H{\small I }} < 0.06 + 0.05\ (1\sigma)$ derived from dark pixel statistics of quasar ... More
Reionization and Beyond: detecting the peaks of the cosmological 21cm signalOct 01 2013Apr 05 2014[ABRIDGED] The cosmological 21cm signal is set to become the most powerful probe of the early Universe, with first generation interferometers aiming to make statistical detections of reionization. There is increasing interest also in the pre-reionization ... More
Fluctuations in the High-Redshift Lyman-Werner Background: Close Halo Pairs as the Origin of Supermassive Black HolesOct 01 2008The earliest generation of stars and black holes must have established an early 'Lyman-Werner' background (LWB) at high redshift, prior to the epoch of reionization. Because of the long mean free path of photons with energies E<13.6 eV, the LWB was nearly ... More
Optimal core baseline design and observing strategy for probing the astrophysics of reionization with the SKASep 10 2015With the first phase of the Square Kilometre Array (SKA1) entering into its final pre-construction phase, we investigate how best to maximise its scientific return. Specifically, we focus on the statistical measurement of the 21 cm power spectrum (PS) ... More
Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signalSep 24 2018Jan 23 2019The properties of the first galaxies, expected to drive the Cosmic Dawn (CD) and the Epoch of Reionization (EoR), are encoded in the 3D structure of the cosmic 21-cm signal. Parameter inference from upcoming 21-cm observations promises to revolutionize ... More
Semi-numeric simulations of helium reionization and the fluctuating radiation backgroundJun 05 2013Recent He II Lyman-alpha forest observations from 2.0 < z < 3.2 show large fluctuations in the optical depth at z > 2.7. These results point to a fluctuating He-ionizing background, which may be due to the end of helium reionization of this era. We present ... More
The X-ray spectra of the first galaxies: 21cm signaturesMar 24 2014Jun 20 2014The cosmological 21cm signal is a physics-rich probe of the early Universe, encoding information about both the ionization and the thermal history of the intergalactic medium (IGM). The latter is likely governed by X-rays from star-formation processes ... More
Evolution in the Escape Fraction of Ionizing Photons and the Decline in Strong Lya Emission from z>6 GalaxiesJan 29 2014Mar 14 2014The rapid decline in the number of strong Lyman Alpha (Lya) emitting galaxies at z > 6 provides evidence for neutral hydrogen in the IGM, but is difficult to explain with plausible models for reionization. We demonstrate that the observed reduction in ... More
The Imprint of Warm Dark Matter on the Cosmological 21-cm SignalSep 30 2013Dec 10 2013We investigate the effects of warm dark matter (WDM) on the cosmic 21-cm signal. If dark matter exists as WDM instead of cold dark matter (CDM), its non-negligible velocities can inhibit the formation of low-mass halos that normally form first in CDM ... More
Are we witnessing the epoch of reionisation at $z=7.1$ from the spectrum of J1120+0641?Jun 01 2016We quantify the presence of Ly\alpha\ damping wing absorption from a partially-neutral intergalactic medium (IGM) in the spectrum of the $z=7.08$ QSO, ULASJ1120+0641. Using a Bayesian framework, we simultaneously account for uncertainties in: (i) the ... More
Probing First Galaxies and Their Impact on the Intergalactic Medium through the 21-cm Observation of the Cosmic Dawn with the SKAJan 17 2015Jan 21 2015We present an overview of the theory of high-redshift star and X-ray source formation, and how they affect the 21-cm background. Primary focus is given to Lyman alpha pumping and X-ray heating mechanisms at cosmic dawn, opening a new observational window ... More
The nature of dark matter from the global high redshift HI 21 cm signalSep 10 2012Nov 21 2012We study the imprint of dark matter (DM) annihilation on the global 21 cm signal from the Dark Ages to Cosmic Reionization. Motivated by recent observations, we focus on three DM candidates: (i) a 10 GeV Bino-like neutralino (ii) a 200 GeV Wino and (iii) ... More
Are we witnessing the epoch of reionisation at $z=7.1$ from the spectrum of J1120+0641?Jun 01 2016Feb 28 2018We quantify the presence of Ly\alpha\ damping wing absorption from a partially-neutral intergalactic medium (IGM) in the spectrum of the $z=7.08$ QSO, ULASJ1120+0641. Using a Bayesian framework, we simultaneously account for uncertainties in: (i) the ... More
Detecting the 21 cm Forest in the 21 cm Power SpectrumOct 29 2013Jun 02 2014We describe a new technique for constraining the radio loud population of active galactic nuclei at high redshift by measuring the imprint of 21 cm spectral absorption features (the 21 cm forest) on the 21 cm power spectrum. Using semi-numerical simulations ... More
Deep learning from 21-cm tomography of the Cosmic Dawn and ReionizationMay 07 2018Feb 04 2019The 21-cm power spectrum (PS) has been shown to be a powerful discriminant of reionization and cosmic dawn astrophysical parameters. However, the 21-cm tomographic signal is highly non-Gaussian. Therefore there is additional information which is wasted ... More
The distribution of Lyman-limit absorption systems during and after reionizationJul 30 2010Lyman-limit absorption systems can play many important roles during and after cosmological reionization. Unfortunately, due to the prohibitively large dynamic range required, it is impossible to self-consistently include these systems in cosmological ... More
Combining high-z galaxy luminosity functions with Bayesian evidenceJun 14 2019Galaxy formation during the first billion years of our Universe remains a challenging problem at the forefront of astrophysical cosmology. Although these $z \geq 6$ galaxies are likely responsible for the last major phase change of our Universe, the epoch ... More
Lyα emission line reconstruction for high-$z$ QSOsMay 30 2016Dec 19 2016We introduce an intrinsic Ly\alpha\ emission line profile reconstruction method for high-$z$ quasars (QSOs). This approach utilises a covariance matrix of emission line properties obtained from a large, moderate-$z$ ($2 \leq z \leq 2.5$), high signal ... More
High Mass X-ray Binaries and the Cosmic 21-cm Signal: Impact of Host Galaxy AbsorptionFeb 01 2017By heating the intergalactic medium (IGM) before reionization, X-rays are expected to play a prominent role in the early Universe. The cosmic 21-cm signal from this "Epoch of Heating" (EoH) could serve as a clean probe of high-energy processes inside ... More
Emulating Simulations of Cosmic Dawn for 21cm Power Spectrum Constraints on Cosmology, Reionization, and X-ray HeatingMay 12 2017Oct 24 2017Current and upcoming radio interferometric experiments are aiming to make a statistical characterization of the high-redshift 21cm fluctuation signal spanning the hydrogen reionization and X-ray heating epochs of the universe. However, connecting 21cm ... More
Constraints on Warm Dark Matter models from high-redshift long gamma-ray burstsMar 20 2013Apr 17 2013Structures in Warm Dark Matter (WDM) models are exponentially suppressed below a certain scale, characterized by the dark matter particle mass, $m_{\rm x}$. Since structures form hierarchically, the presence of collapsed objects at high-redshifts can ... More
Constraining High Redshift X-ray Sources with Next Generation 21 cm Power Spectrum MeasurementsNov 12 2015Apr 24 2016We use the Fisher matrix formalism and semi-numerical simulations to derive quantitative predictions of the constraints that power spectrum measurements on next-generation interferometers, such as the Hydrogen Epoch of Reionization Array (HERA) and the ... More
Bubble mapping with the Square Kilometer Array - I. Detecting galaxies with Euclid, JWST, WFIRST and ELT within ionized bubbles in the intergalactic medium at z>6May 01 2019The Square Kilometer Array is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z>6 and pinpoint the locations of individual ionized bubbles during the early stages of cosmic reionization. In scenarios ... More
Comparison Of Reionization Models: Radiative Transfer Simulations And Approximate, Semi-Numeric ModelsMar 17 2010We compare the predictions of four different algorithms for the distribution of ionized gas during the Epoch of Reionization. These algorithms are all used to run a 100 Mpc/h simulation of reionization with the same initial conditions. Two of the algorithms ... More
Can the intergalactic medium cause a rapid drop in Lyman alpha emission at z>6?Jun 24 2014The large cross-section of the Lyman alpha (Lya) line makes it a sensitive probe of the ionization state of the intergalactic medium (IGM). Here we present the most complete study to date of the IGM Lya opacity, and its application to the redshift evolution ... More
Lyα emission line reconstruction for high-$z$ QSOsMay 30 2016We introduce an intrinsic Ly\alpha\ emission line profile reconstruction method for high-$z$ quasars (QSOs). This approach utilises a covariance matrix of emission line properties obtained from a large, moderate-$z$ ($2 \leq z \leq 2.5$), high signal ... More
Dark-ages reionization and galaxy formation simulation--VII. The sizes of high-redshift galaxiesAug 02 2016We investigate high-redshift galaxy sizes using a semi-analytic model constructed for the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation project. Our fiducial model, including strong feedback from supernovae and photoionization ... More
Epoch of Reionization modelling and simulations for SKAJan 17 2015In this chapter we provide an overview of the current status of the simulations and modelling of the Cosmic Dawn and Epoch of Reionization. We discuss the modelling requirements as dictated by the characteristic scales of the problem and the SKA instrumental ... More
The Universe is Reionizing at z~7: Bayesian Inference of the IGM Neutral Fraction Using Ly$α$ Emission from GalaxiesSep 15 2017Feb 15 2018We present a new flexible Bayesian framework for directly inferring the fraction of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR, z~6-10) from detections and non-detections of Lyman Alpha (Ly$\alpha$) emission ... More
Dark-Ages Reionisation & Galaxy Formation Simulation XVI: The Thermal Memory of ReionisationApr 12 2019Intergalactic medium temperature is a powerful probe of the epoch of reionisation, as information is retained long after reionisation itself. However, mean temperatures are highly degenerate with the timing of reionisation, with the amount heat injected ... More
Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshiftFeb 12 2018Aug 06 2018We study dwarf galaxy formation at high redshift ($z\ge5$) using a suite of high- resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant ... More
Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshiftFeb 12 2018We study dwarf galaxy formation at high redshift ($z\ge5$) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant ... More
The Silence of the Little StringsJun 17 2005Sep 28 2005We study the hydrodynamics of the high-energy phase of Little String Theory. The poles of the retarded two-point function of the stress energy tensor contain information about the speed of sound and the kinetic coefficients, such as shear and bulk viscosity. ... More
Counterexamples to Borsuk's conjecture on spheres of small radiiOct 03 2010In this work, the classical Borsuk conjecture is discussed, which states that any set of diameter 1 in the Euclidean space $ {\mathbb R}^d $ can be divided into $ d+1 $ parts of smaller diameter. During the last two decades, many counterexamples to the ... More
Dark ages reionization & galaxy formation simulation XII: Bubbles at dawnApr 18 2017Jul 21 2017Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, ... More
Dark-ages Reionization and Galaxy Formation Simulation - XV. Stellar evolution and feedback in dwarf galaxies at high redshiftAug 10 2018We directly compare predictions of dwarf galaxy properties in a semi-analytic model (SAM) with those extracted from a high-resolution hydrodynamic simulation. We focus on galaxies with halo masses of 1e9<Mvir/Msol<1e11 at high redshift ($z\ge5$). We find ... More
Dark-ages Reionization and Galaxy Formation Simulation - XIII. AGN quenching of high-redshift star formation in ZF-COSMOS-20115Apr 11 2017Aug 25 2017Massive quiescent galaxies (MQGs) are thought to have formed stars rapidly at early times followed by a long period of quiescence. The recent discovery of a MQG, ZF-COSMOS-20115 at $z\sim4$, only 1.5 Gyr after the big bang, places new constraints on galaxy ... More
Beacons into the Cosmic Dark Ages: Boosted transmission of Ly$α$ from UV bright galaxies at $z \gtrsim 7$Jan 05 2018Apr 12 2018Recent detections of Lyman alpha (Ly$\alpha$) emission from $z>7.5$ galaxies were somewhat unexpected given a dearth of previous non-detections in this era when the intergalactic medium (IGM) is still highly neutral. But these detections were from UV ... More
Results from EDGES High-Band: II. Constraints on Parameters of Early GalaxiesJun 20 2018We use the sky-average spectrum measured by EDGES High-Band ($90-190$ MHz) to constrain parameters of early galaxies independent of the absorption feature at $78$~MHz reported by Bowman et al. (2018). These parameters represent traditional models of cosmic ... More
Dark-ages reionization and galaxy formation simulation XI: Clustering and halo masses of high redshift galaxiesMar 15 2017Sep 15 2017We investigate the clustering properties of Lyman-break galaxies (LBGs) at $z\sim6$ - $8$. Using the semi-analytical model {\scshape Meraxes} constructed as part of the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation ... More
Dark-ages Reionization and Galaxy Formation Simulation - X. The small contribution of quasars to reionizationMar 15 2017Sep 26 2017Motivated by recent measurements of the number density of faint AGN at high redshift, we investigate the contribution of quasars to reionization by tracking the growth of central supermassive black holes in an update of the Meraxes semi-analytic model. ... More
Axiomatic Method and Category TheorySep 25 2012Lawvere's axiomatization of topos theory and Voevodsky's axiomatization of heigher homotopy theory exemplify a new way of axiomatic theory building, which goes beyond the classical Hibert-style Axiomatic Method. The new notion of Axiomatic Method that ... More
On non-markovian nature of stock tradingMar 18 2004Using a relationship between the moments of the probability distribution of times between the two consecutive trades (intertrade time distribution) and the moments of the distribution of a daily number of trades we show, that the underlying point process ... More
Geometry of optimal control problems and Hamiltonian systemsJun 10 2005These notes are based on the mini-course given in June 2004 in Cetraro, Italy, in the frame of a C.I.M.E. school. Of course, they contain much more material that I could present in the 6 hours course. The main goal is to give an idea of the general variational ... More
About the Mechanism of Volcanic EruptionsAug 02 2012A new approach to the volcanic eruption theory is proposed. It is based on a simple physical mechanism of the imbalance in the system "magma-crust-fluid". This mechanism helps to explain from unified positions the different types of volcanic eruptions. ... More
About the Mechanism of Geyser EruptionApr 06 2012Essentially new physical mechanism of geyser eruption based on instability in "water-vapor" system is proposed. Necessary and sufficient conditions of eruptions are received. For group of Kamchatka geysers a good accordance of theoretical model with empirical ... More
On periodic solutions of a Hamilton-Jacobi equation with periodic forcingJun 23 1999Feb 09 2001We prove that a Hamilton-Jacobi equation in 1D with periodic forcing has a set of generalized solutions such that each solution is a sum of linear and continuous periodic functions; we also give a condition of uniqueness of this solution in terms of Aubry-Mather ... More
Moduli spaces of PU(2)-monopolesFeb 07 1997Nov 12 2013The goal of this article was the S^1-equivariant transversality-problem and the compactification-problem for the moduli spaces of (perturbed) PU(2)-monopoles. A substantially improved version entitled "Moduli spaces of PU(2)-monopoles (revised version)" ... More
Non-abelian Seiberg-Witten theory and projectively stable pairsSep 26 1996Jun 02 1997We introduce the concept of Spin^G-structure in a SO-bundle, where $G\subset U(V)$ is a compact Lie group containing $-id_V$. We study and classify $Spin^G(4)$-structures on 4-manifolds, we introduce the G-Monopole equations associated with a $Spin^G$-structure. ... More
Nonspherical Giant Gravitons and Matrix TheoryAug 10 2002Apr 05 2003We consider the plane wave limit of the nonspherical giant gravitons. We compute the Poisson brackets of the coordinate functions and find a nonlinear algebra. We show that this algebra solves the supersymmetry conditions of the matrix model. This is ... More
Giant Gravitons from Holomorphic SurfacesOct 24 2000We introduce a class of supersymmetric cycles in spacetimes of the form AdS times a sphere or $T^{1,1}$ which can be considered as generalizations of the giant gravitons. Branes wrapped on these cycles preserve $1\over 2$, $1\over 4$ or $1\over 8$ of ... More
Anomalous dimension and local chargesNov 19 2004Sep 20 2005AdS space is the universal covering of a hyperboloid. We consider the action of the deck transformations on a classical string worldsheet in $AdS_5\times S^5$. We argue that these transformations are generated by an infinite linear combination of the ... More
Special contact Wilson loopsNov 24 2002Dec 05 2002Wilson loops in ${\cal N}=4$ supersymmetric Yang-Mills theory correspond at strong coupling to extremal surfaces in $AdS_5$. We study a class of extremal surfaces known as special Legendrian submanifolds. The "hemisphere" corresponding to the circular ... More
Polarization puzzle in B->phi K* and other B->VV at BABARSep 29 2004With a sample of about 227 million BB pairs recorded with the BABAR detector we perform a full angular analysis of the decay B0->phi K*0(892). Ten measurements include polarization, phases, and five CP asymmetries. We also observe the decay B0->phi K*0(1430). ... More
Propagation and interaction of extremely short electromagnetic pulses in non-linear mediaDec 25 2000Propagation of the extremely short electromagnetic pulse in non-linear dielectric media without the slowly varying envelope approximation is discussed. The models under consideration take into account both resonant and not-resonant excitations of non-linear ... More