Results for "J. Stuart B. Wyithe"

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Realistic Event Rates for Detection of Supermassive Black Hole Coalescence by LISAMar 09 2005The gravitational waves generated during supermassive black hole (SMBH) coalescence are prime candidates for detection by the satellite LISA. We use the extended Press-Schechter formalism combined with empirically motivated estimates for the SMBH--dark ... More
Modification of the 21-cm power spectrum by quasars during the epoch of reionisationApr 21 2009We assess the effect of a population of high-redshift quasars on the 21-cm power spectrum during the epoch of reionisation. Our approach is to implement a semi-numerical scheme to calculate the three-dimensional structure of ionised regions surrounding ... More
Reionization and Cosmology with 21 cm FluctuationsOct 16 2009Measurement of the spatial distribution of neutral hydrogen via the redshifted 21 cm line promises to revolutionize our knowledge of the epoch of reionization and the first galaxies, and may provide a powerful new tool for observational cosmology from ... More
Detecting the redshifted 21cm forest during reionizationJan 28 2011Oct 25 2011The 21cm forest -- HI absorption features in the spectra of high-redshift radio sources -- can potentially provide a unique probe of the largely neutral intergalactic medium (IGM) during the epoch of reionization. We present simulations of the 21cm forest ... More
Testing the Copernican Principle via Cosmological ObservationsJul 18 2008Jan 14 2009Observations of distances to Type-Ia supernovae can be explained by cosmological models that include either a gigaparsec-scale void, or a cosmic flow, without the need for Dark Energy. Instead of invoking dark energy, these inhomogeneous models instead ... More
Low-Frequency Gravitational Waves from Massive Black Hole Binaries: Predictions for LISA and Pulsar Timing ArraysNov 26 2002Apr 11 2003The coalescence of massive black hole (BH) binaries due to galaxy mergers provides a primary source of low-frequency gravitational radiation detectable by pulsar timing measurements and by the proposed LISA (Laser Interferometry Space Antenna) observatory. ... More
Polarised foreground removal at low radio frequencies using rotation measure synthesis: uncovering the signature of hydrogen reionisationNov 10 2010Jul 27 2011Measurement of redshifted 21-cm emission from neutral hydrogen promises to be the most effective method for studying the reionisation history of hydrogen and, indirectly, the first galaxies. These studies will be limited not by raw sensitivity to the ... More
Measurement of the baryonic acoustic oscillation scale in 21 cm intensity fluctuations during the reionisation eraMar 19 2008Jan 13 2009It has recently been suggested that the power spectrum of redshifted 21cm fluctuations could be used to measure the scale of baryonic acoustic oscillations (BAOs) during the reionisation era. The resulting measurements are potentially as precise as those ... More
The Multi-Band Magnification Bias for Gravitational LensesAug 29 2002We present a generalization of the concept of magnification bias for gravitationally-lensed quasars, in which the quasars are selected by flux in more than one wavelength band. To illustrate the principle, we consider the case of two-band selection, in ... More
Fast, large volume, GPU enabled simulations for the Ly-alpha forest: power spectrum forecasts for baryon acoustic oscillation experimentsMay 24 2011Aug 15 2011High redshift measurements of the baryonic acoustic oscillation scale (BAO) from large Ly-alpha forest surveys represent the next frontier of dark energy studies. As part of this effort, efficient simulations of the BAO signature from the Ly-alpha forest ... More
Searching for MACHOs in Galaxy ClustersAug 10 2000If cluster dark matter is in the form of compact objects it will introduce fluctuations into the light curves of distant sources. Current searches for MACHOs in clusters of galaxies focus on monitoring quasars behind nearby systems. This paper considers ... More
Photometric Variability in Earthshine ObservationsApr 06 2009The identification of an extrasolar planet as Earth-like will depend on the detection of atmospheric signatures or surface non-uniformities. In this paper we present spatially unresolved flux light curves of Earth for the purpose of studying a prototype ... More
The impact of temperature fluctuations on the large-scale clustering of the Ly$α$ forestNov 06 2014Jan 22 2015We develop a semi-analytic method for assessing the impact of the large-scale IGM temperature fluctuations expected following He${\rm\,{\scriptstyle II}}$ reionization on three-dimensional clustering measurements of the Ly$\alpha$ forest. Our methodology ... More
Cosmology from clustering of Lyman-alpha galaxies: breaking non-gravitational Lyman-alpha radiative transfer degeneracies using the bispectrumDec 05 2012Large surveys for Lyman-alpha emitting (LAE) galaxies have been proposed as a new method for measuring clustering of the galaxy population at high redshift with the goal of determining cosmological parameters. However, Lyman-alpha radiative transfer effects ... More
Constraining reionization using 21 cm observations in combination with CMB and Lyman-alpha forest dataAug 26 2009In this paper, we explore the constraints on the reionization history that are provided by current observations of the Lyman-alpha forest and the CMB. Rather than using a particular semi-analytic model, we take the novel approach of parametrizing the ... More
A Method to Measure the Mass of Damped Ly-alpha Absorber Host Galaxies Using Fluctuations in 21cm EmissionApr 10 2008Observations of damped Ly-alpha absorbers (DLA) indicate that the fraction of hydrogen in its neutral form (HI) is significant by mass at all redshifts. This gas represents the reservoir of material that is available for star formation at late times. ... More
Redshifted 21cm Observations of High Redshift Quasar Proximity ZonesApr 03 2008The introduction of low-frequency radio arrays is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21cm emission between a large HII region and the surrounding neutral inter-galactic medium (IGM) ... More
The shallow slope of the z~6 quasar luminosity function: limits from the lack of multiple image gravitational lensesAug 18 2003We place a limit on the logarithmic slope of the luminous quasar luminosity function at z~6 of beta>-3.0 (90%) using gravitational lensing constraints to build on the limit of beta>-3.3 (90%) derived from an analysis of the luminosity distribution (Fan ... More
A Log-Quadratic Relation Between the Nuclear Black-Hole Masses and Velocity Dispersions of GalaxiesMar 21 2005Jul 17 2006We demonstrate that a log-linear relation does not provide an adequate description of the correlation between the masses of Super-Massive Black-Holes (SMBH, M_bh) and the velocity dispersions of their host spheroid (sigma). An unknown relation between ... More
Low-mass galaxy formation and the ionizing photon budget during reionizationMay 29 2014Jul 20 2014We use high-resolution simulations of cosmological volumes to model galaxy formation at high-redshift, with the goal of studying the photon budget for reionization. We demonstrate that galaxy formation models that include a strong, thermally coupled supernovae ... More
The Halo Occupation Distribution of HI from 21cm Intensity Mapping at Moderate RedshiftsDec 11 2009The spatial clustering properties of HI galaxies can be studied using the formalism of the halo occupation distribution (HOD). The resulting parameter constraints describe properties like gas richness verses environment. Unfortunately, clustering studies ... More
The growth of disks and bulges during hierarchical galaxy formation. II: metallicity, stellar populations and dynamical evolutionJun 20 2016We investigate the properties of the stellar populations of model galaxies, using the new semi-analytic model presented in Tonini et al. (2016a). This new model follows the angular momentum evolution of gas and stars, providing the base for a new star ... More
The growth of disks and bulges during hierarchical galaxy formation. I: fast evolution vs secular processesApr 07 2016Apr 20 2016We present a theoretical model for the evolution of mass, angular momentum and size of galaxy disks and bulges, and we implement it into the semi-analytic galaxy formation code SAGE. The model follows both secular and violent evolutionary channels, including ... More
Convergence properties of halo merger trees; halo and substructure merger rates across cosmic historySep 05 2017We introduce gbpTrees: an algorithm for constructing merger trees from cosmological simulations, designed to identify and correct for pathological cases introduced by errors or ambiguities in the halo finding process. gbpTrees is built upon a halo matching ... More
The Structure of Reionization in Hierarchical Galaxy Formation ModelsMar 16 2012Oct 15 2012Understanding the epoch of reionization and the properties of the first galaxies represents an important goal for modern cosmology. The structure of reionization, and hence the observed power spectrum of redshifted 21cm fluctuations are known to be sensitive ... More
Dark Matter Annihilation in the First Galaxy HalosNov 14 2014May 13 2015We investigate the impact of energy released from self-annihilating dark matter on heating of gas in the small, high-redshift dark matter halos thought to host the first stars. A SUSY neutralino like particle is implemented as our dark matter candidate. ... More
The accretion history of dark matter halos I: The physical origin of the universal functionSep 18 2014Aug 03 2015Understanding the universal accretion history of dark matter halos is the first step towards determining the origin of their structure. We use the extended Press-Schechter formalism to derive the halo mass accretion history from the growth rate of initial ... More
The Star Formation Rate in the Reionization Era as Indicated by Gamma-ray BurstsJun 02 2009Sep 18 2009High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to study aspects of the early Universe, including the cosmic star formation rate (SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and GRB 090423 at z = 8.1, ... More
Thermal constraints on the reionisation of hydrogen by population-II stellar sourcesJan 24 2012Measurements of the intergalactic medium (IGM) temperature provide a potentially powerful constraint on the reionisation history due to the thermal imprint left by the photo-ionisation of neutral hydrogen. However, until recently IGM temperature measurements ... More
On the significance of the excess number of strong MgII absorbers observed towards Gamma-ray burstsJan 03 2013The number of strong (equivalent width > 1A) MgII absorbers observed towards Gamma-ray bursts (GRBs) has been found to be statistically larger than the number of strong absorbers towards quasi-stellar objects (QSOs). We formalize this "MgII problem" and ... More
Clustering of Ly-alpha emitters around luminous quasars at z = 2-3: an alternative probe of reionization on galaxy formationMay 18 2011Narrowband observations have detected no Ly-alpha emission within a 70 pMpc^3 volume centered on the z = 2.168 quasar PKS 0424-131. This is in contrast to surveys of Ly-alpha emitters in the field at similar redshifts and flux limits, which indicate that ... More
The accretion history of dark matter halos II: The connections with the mass power spectrum and the density profileJan 19 2015Aug 03 2015We explore the relation between the structure and mass accretion histories of dark matter halos using a suite of cosmological simulations. We confirm that the formation time, defined as the time when the virial mass of the main progenitor equals the mass ... More
The accretion history of dark matter halos III: A physical model for the concentration-mass relationFeb 02 2015Aug 03 2015We present a semi-analytic, physically motivated model for dark matter halo concentration as a function of halo mass and redshift. The semi-analytic model combines an analytic model for the halo mass accretion history (MAH), based on extended Press Schechter ... More
A distortion of very--high--redshift galaxy number counts by gravitational lensingJan 12 2011The observed number counts of high-redshift galaxy candidates have been used to build up a statistical description of star-forming activity at redshift z >~ 7, when galaxies reionized the Universe. Standard models predict that a high incidence of gravitational ... More
The cross-power spectrum between 21cm emission and galaxies in hierarchical galaxy formation modelsSep 13 2013The correlation between 21cm fluctuations and galaxies is sensitive to the astrophysical properties of the galaxies that drove reionization. Thus, detailed measurements of the cross-power spectrum and its evolution could provide a powerful measurement ... More
Variation in the escape fraction of ionising photons from galaxies and the redshifted 21-cm power spectrum during reionizationMar 12 2013The observed power spectrum of redshifted 21cm fluctuations is known to be sensitive to the astrophysical properties of the galaxies that drove reionization. Thus, detailed measurements of the 21cm power spectrum and its evolution could lead to measurements ... More
Determination of the transverse velocity of Q2237+0305Sep 21 1999The largest systematic uncertainty present in the analysis of gravitationally microlensed quasar light curves is that of the galactic transverse velocity. We describe a method for determining the transverse velocity as well as its application to published ... 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
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 - 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
A hybrid multi resolution scheme to efficiently model the structure of reionization on the largest scalesNov 10 2015Redshifted 21cm measurements of the structure of ionised regions that grow during reionization promise to provide a new probe of early galaxy and structure formation. One of the challenges of modelling reionization is to account both for the sub-halo ... More
Testing the gravitational lensing explanation for the MgII problem in GRBsAug 26 2011Jun 04 2012Sixty percent of gamma-ray bursts (GRBs) reveal strong MgII absorbing systems, which is a factor of ~2 times the rate seen along lines-of-sight to quasars. The discrepancy in the covering factor is most likely to be the result of either quasars being ... More
Very Massive Stars in High-Redshift GalaxiesApr 12 2007Jun 27 2007A significant fraction of Lyman Alpha (Lya) emitting galaxies (LAEs) at z> 5.7 have rest-frame equivalent widths (EW) greater than ~100 Angstrom. However only a small fraction of the Lya flux produced by a galaxy is transmitted through the IGM, which ... More
Possibility of Precise Measurement of the Cosmological Power Spectrum With a Dedicated 21cm Survey After ReionizationJan 10 2008Mar 21 2008Measurements of the 21cm line emission by residual cosmic hydrogen after reionization can be used to trace the power spectrum of density perturbations through a significant fraction of the observable volume of the Universe. We show that a dedicated 21cm ... More
The 21cm Power Spectrum After ReionizationAug 18 2008Jul 24 2009We discuss the 21cm power spectrum (PS) following the completion of reionization. In contrast to the reionization era, this PS is proportional to the PS of mass density fluctuations, with only a small modulation due to fluctuations in the ionization field ... More
Fluctuations in 21cm Emission After ReionizationAug 26 2007The fluctuations in the emission of redshifted 21cm photons from neutral inter-galactic hydrogen will provide an unprecedented probe of the reionization era. Conventional wisdom assumes that this 21cm signal disappears as soon as reionization is complete, ... More
Gravitational lenses magnify up to one third of the most distant quasarsMar 07 2002May 01 2002Exceptionally bright quasars with redshifts up to z=6.28 have recently been discovered. Quasars are thought to be powered by the accretion of gas onto supermassive black holes at the centres of galaxies. Their maximum (Eddington) luminosity is proportional ... More
Undetected Sources Allow Transmission of the Lyman-alpha Line From Galaxies Prior to ReionizationJul 08 2004Jul 09 2004The discovery of Lyman-alpha emission from galaxies at redshifts beyond z~6.5 should not be naively interpreted as implying that the intergalactic medium (IGM) had been reionized at higher redsifts. We show that a cluster of faint undetected sources around ... More
Redshifted 21cm Signatures Around the Highest Redshift QuasarsJan 26 2004The Ly-alpha absorption spectrum of the highest redshift quasars indicates that they are surrounded by giant HII regions, a few Mpc in size. The neutral gas around these HII regions should emit 21cm radiation in excess of the Cosmic Microwave Background, ... More
A suppressed contribution of low mass galaxies to reionization due to supernova feedbackSep 11 2012Motivated by recent observations of the star formation rate density function out to z~7, we describe a simple model for the star formation rate density function at high redshift based on the extended Press-Schechter formalism. This model postulates a ... More
A Physical Model for the Luminosity Function of High-Redshift QuasarsJun 10 2002We provide a simple theoretical model for the quasar luminosity function at high redshifts that naturally reproduces the statistical properties of the luminous SDSS quasar sample at redshifts z~4.3 and z>5.7. Our model is based on the assumptions that ... More
Gravitational Lensing of the SDSS High-Redshift QuasarsMar 08 2002May 23 2002We predict the effects of gravitational lensing on the color-selected flux-limited samples of z~4.3 and z>5.8 quasars, recently published by the Sloan Digital Sky Survey (SDSS). Our main findings are: (i) The lensing probability should be 1-2 orders of ... More
A first direct measurement of the intergalactic medium temperature around a quasar at z=6Jan 19 2010Mar 25 2010The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the HI and HeII reionisation epochs. Current constraints on the IGM temperature from the Lya forest are restricted to the redshift range 2<z<4.5, limiting the ability ... More
The Extended Starformation History of the First Generation of Stars, and the Reionization of Cosmic HydrogenFeb 23 2006Population-III (Pop-III) starformation (SF) is thought to be quenched when the metallicity of the star-forming gas reaches a critical level. At high z, when the general intergalactic medium (IGM) was enriched with metals, the fraction of primordial gas ... More
Properties of High Redshift Quasars-II: What does the quasar luminosity function tell us about super-massive black-hole evolution?Mar 14 2006In the local universe, the masses of Super-Massive Black-Holes (SMBH) appear to correlate with the physical properties of their hosts, including the mass of the dark-matter halo. Using these clues as a starting point many studies have produced models ... More
Extrapolating the Evolution of Galaxy Sizes to the Epoch of ReionizationNov 14 2010We use data on the high-redshift evolution of the size distribution and luminosity function of galaxies to constrain the relationship between their star formation efficiency and starburst lifetime. Based on the derived scaling relations, we predict the ... More
The Imprint of Cosmic Reionization on Galaxy ClusteringJun 26 2007We consider the effect of reionization on the clustering properties of galaxy samples at intermediate redshifts (z~0.3-5.5). Current models for the reionization of intergalactic hydrogen predict that overdense regions will be reionized early, thus delaying ... More
Cosmic Variance In the Transparency of the Intergalactic Medium After ReionizationAug 29 2005Jan 30 2006Following the completion of cosmic reionization, the mean-free-path of ionizing photons was set by a population of Ly-limit absorbers. As the mean-free-path steadily grew, the intensity of the ionizing background also grew, thus lowering the residual ... More
The escape fraction of ionizing photons from high redshift galaxiesJul 30 2008The fraction of ionizing photons which escape their host galaxy and so are able to ionize hydrogen in the inter-galactic medium (IGM) is a critical parameter in studies of the reionization era and early galaxy formation. In this paper we combine observations ... More
An Empirical Study of the Relationship between Lyα and UV selected Galaxies: Do Theorists and Observers `Select' the Same Objects?Aug 18 2011Nov 30 2011Lyman Alpha Emitters (LAEs) are galaxies that have been selected on the basis of a strong Ly{\alpha} emission line in their spectra. Observational campaigns have dramatically increased the sample of known LAEs, which now extends out to z=7. These discoveries ... More
Seeing Through the Trough: Outflows and the Detectability of Lyman Alpha Emission from the First GalaxiesApr 14 2010The next generation of telescopes aim to directly observe the first generation of galaxies that initiated the reionization process in our Universe. The Lyman Alpha (Lya) emission line is robustly predicted to be the most prominent intrinsic spectral feature ... More
Smooth Boundaries to Cosmological HII Regions from Galaxy ClusteringJul 12 2006The HII regions around quasars and galaxies at redshifts beyond the epoch of reionisation will provide prime targets for upcoming 21cm campaigns using a new generation of low-frequency radio observatories. Here we show that the boundaries of these HII ... More
Dwarf Galaxy Formation Was Suppressed By Cosmic ReionizationMar 21 2006Mar 22 2006A large number of faint galaxies, born less than a billion years after the big bang, have recently been discovered. The fluctuations in the distribution of these galaxies contributed to a scatter in the ionization fraction of cosmic hydrogen on scales ... More
Constraining the Quasar Contribution to the Reionisation of Cosmic HydrogenOct 11 2006Absorption spectra of high redshift quasars suggest that the reionisation of cosmic hydrogen was complete near z~6. The dominant sources of ionising photons responsible for this reionisation are generally thought to be stars and quasars. In this paper ... More
Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He-II reionisation at z~6Oct 03 2011We present measurements of the intergalactic medium (IGM) temperature within ~5 proper Mpc of seven luminous quasars at z~6. The constraints are obtained from the Doppler widths of Lyman-alpha absorption lines in the quasar near-zones and build upon our ... More
The spatial distribution of neutral hydrogen as traced by low HI mass galaxiesMar 08 2016The formation and evolution of galaxies with low neutral atomic hydrogen (HI) masses, M$_{\rm HI}$$<$10$^{8}h^{-2}$M$_{\odot}$, are affected by host dark matter halo mass and photoionisation feedback from the UV background after the end of reionization. ... More
The spatial distribution of neutral hydrogen as traced by low HI mass galaxiesMar 08 2016Nov 08 2016The formation and evolution of galaxies with low neutral atomic hydrogen (HI) masses, M$_{\rm HI}$$<$10$^{8}h^{-2}$M$_{\odot}$, are affected by host dark matter halo mass and photoionisation feedback from the UV background after the end of reionization. ... More
Non-Gravitational Contributions to the Clustering of Ly-alpha Selected Galaxies: Implications for Cosmological SurveysApr 04 2011We show that the dependence of Ly-alpha absorption on environment leads to significant non-gravitational features in the redshift space power-spectrum of Ly-alpha selected galaxies. We derive a physically motivated fitting formula that can be included ... More
Lyman Alpha Constraints on Very Low Luminosity AGNJun 14 2006Sep 21 2006Recent surveys have detected Lya emission from z=4.5-6.5 at luminosities as low as 10^41 erg/s. There is good evidence that low numbers of AGN are among observed faint Lya emitters. Combining these observations with an empirical relation between the intrinsic ... More
Biased Reionisation and Non-Gaussianity in Redshifted 21cm Intensity Maps of the Reionisation EpochMar 05 2007Spatial dependence in the statistics of redshifted 21cm fluctuations promises to provide the most powerful probe of the reionisation epoch. In this paper we consider the second and third moments of the redshifted 21cm intensity distribution using a simple ... More
Photon Trapping Enables Super-Eddington Growth of Black-Hole Seeds in Galaxies at High RedshiftNov 23 2011We identify a physical mechanism that would have resulted in rapid, obscured growth of seed super-massive black-holes in galaxies at z>6. Specifically, we find that the density at the centre of typical high redshift galaxies was at a level where the Bondi ... More
Evidence for Merger-Driven Activity in the Clustering of High Redshift QuasarsOct 20 2008Recently, a very large clustering length has been measured for quasars at a redshift of z~4. In combination with the observed quasar luminosity function we assess the implications of this clustering for the relationship between quasar luminosity and dark ... More
Detection of Gravitational Waves from the Coalescence of Population-III Remnants with Advanced LIGODec 03 2003The comoving mass density of massive black hole (MBH) remnants from pre-galactic star formation could have been similar in magnitude to the mass-density of supermassive black holes (SMBHs) in the present-day universe. We show that the fraction of MBHs ... More
Was the Universe Reionized by Massive Population-III Stars?Feb 17 2003Apr 10 2003The WMAP satellite has measured a large optical depth to electron scattering after cosmological recombination of 0.17+-0.04, implying significant reionization of the primordial gas only ~200 million years after the big bang. However, the most recent overlap ... More
Measuring the Size of Quasar Broad-Line Clouds Through Time Delay Light-Curve Anomalies of Gravitational LensesApr 30 2002Intensive monitoring campaigns have recently attempted to measure the time delays between multiple images of gravitational lenses. Some of the resulting light-curves show puzzling low-level, rapid variability which is unique to individual images, superimposed ... More
The HI mass function as a probe of photoionisation feedback on low mass galaxy formationJun 09 2015Aug 07 2015We explore the galaxy formation physics governing the low mass end of the HI mass function in the local Universe. Specifically, we predict the effects on the HI mass function of varying i) the strength of photoionisation feedback and the redshift of the ... More
Properties of High Redshift Quasars-I: Evolution of the super-massive black-hole to halo mass ratioJan 17 2005In the local universe, the masses of Super-Massive Black-Holes (SMBH) appear to correlate with physical properties of their hosts, including the mass of the dark-matter halos. At higher redshifts, we observe the growth of SMBHs indirectly through identification ... More
Calibrating the Galaxy Halo - Black Hole Relation Based on the Clustering of QuasarsMar 31 2004The observed number counts of quasars may be explained either by long-lived activity within rare massive hosts, or by short-lived activity within smaller, more common hosts. It has been argued that quasar lifetimes may therefore be inferred from their ... More
Cosmic Hydrogen Was Significantly Neutral a Billion Years After the Big BangJan 12 2004The ionization fraction of cosmic hydrogen, left over from the big bang, provides crucial fossil evidence for when the first stars and quasar black holes formed in the infant universe. Spectra of the two most distant quasars known show nearly complete ... More
Reionization of Hydrogen and Helium by Early Stars and QuasarsSep 03 2002Nov 14 2002We compute the reionization histories of hydrogen and helium due to the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function ... More
The correlation between the distribution of galaxies and 21cm emission at high redshiftsSep 27 2006Deep surveys have recently discovered galaxies at the tail end of the epoch of reionization. In the near future, these discoveries will be complemented by a new generation of low-frequency radio observatories that will map the distribution of neutral ... More
Constraints on the Process that Regulates the Growth of Supermassive Black Holes Based on the Intrinsic Scatter in the M_bh-sigma RelationJun 14 2005We show that the observed scatter in the relations between the mass of supermassive black holes (SMBHs), M_bh, and the velocity dispersion sigma or mass M_sph of their host spheroid, place interesting constraints on the process that regulates SMBH growth ... More
A Size of ~10 Mpc for the Ionized Bubbles at the End of Cosmic ReionizationSep 16 2004The first galaxies to appear in the universe at redshifts z>20 created ionized bubbles in the intergalactic medium of neutral hydrogen left over from the Big-Bang. It is thought that the ionized bubbles grew with time, surrounded clusters of dwarf galaxies ... More
Self-Regulated Growth of Supermassive Black Holes in Galaxies as the Origin of the Optical and X-ray Luminosity Functions of QuasarsApr 09 2003We postulate that supermassive black-holes grow in the centers of galaxies until they unbind the galactic gas that feeds them. We show that the corresponding self-regulation condition yields a correlation between black-hole mass (Mbh) and galaxy velocity ... 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
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 & galaxy formation simulation V: morphology and statistical signatures of reionizationDec 02 2015Aug 15 2016We use the Dark-ages, Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) framework to investigate the effect of galaxy-formation physics on the morphology and statistics of ionized hydrogen (HII) regions during the Epoch ... More
Dark-ages reionization and galaxy formation simulation - III. Modelling galaxy formation and the epoch of reionizationDec 02 2015Aug 18 2016We introduce Meraxes, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. Meraxes is the first model of its type to include a temporally and spatially coupled treatment of reionization and ... More
Dark-ages reionization & galaxy formation simulation VI: The origins and fate of the highest known redshift galaxyMay 25 2016Using Hubble data, including new grism spectra, Oesch et al. (2016) recently identified GN-z11, a $M_\textrm{UV}$=-21.1 galaxy at $z$=11.1 (just 400 Myr after the Big Bang). With an estimated stellar mass of $\sim$10$^9$M$_\odot$, this galaxy is surprisingly ... More
Dark-ages reionization and galaxy formation simulation - IX. Economics of reionizing galaxiesMay 20 2017Jun 19 2017Using a series of high-resolution hydrodynamical simulations we show that during the rapid growth of high-redshift (z > 5) galaxies, reserves of molecular gas are consumed over a time-scale of 300Myr, almost independent of feedback scheme. We find that ... More
Dark-ages Reionization & Galaxy Formation Simulation II: Spin and concentration parameters for dark matter haloes during the Epoch of ReionizationDec 02 2015We use high resolution N-Body simulations to study the concentration and spin parameters of dark matter haloes in the mass range $10^8\, {\rm M}_{\odot}\, h^{-1} < {\rm M} < 10^{11}\, {\rm M}_{\odot}\, h^{-1}$ and redshifts $5{<}z{<}10$, corresponding ... More
Dark-ages reionization and galaxy formation simulation--VII. The sizes of high-redshift galaxiesAug 02 2016Nov 08 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
Dark-ages Reionization & Galaxy Formation Simulation VIII. Suppressed growth of dark matter halos during the Epoch of ReionizationJan 13 2017Feb 21 2017We investigate how the hydrostatic suppression of baryonic accretion affects the growth rate of dark matter halos during the Epoch of Reionization. By comparing halo properties in a simplistic hydrodynamic simulation in which gas only cools adiabatically, ... More
A comparison of spectroscopic methods for detecting starlight scattered by transiting hot Jupiters, with application to Subaru data for HD 209458b and HD 189733bJun 29 2010Apr 29 2011The measurement of the light scattered from extrasolar planets informs atmospheric and formation models. With the discovery of many hot Jupiter planets orbiting nearby stars, this motivates the development of robust methods of characterisation from follow ... More
Dark-ages reionization & galaxy formation simulation IV: UV luminosity functions of high-redshift galaxiesDec 02 2015Apr 27 2016In this paper we present calculations of the UV luminosity function from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) project, which combines N-body, semi-analytic and semi-numerical modelling designed ... More
Near-zone sizes and the rest frame extreme ultra-violet spectral index of the highest redshift quasarsAug 06 2010The discovery of quasars with redshifts higher than six has prompted a great deal of discussion in the literature regarding the role of quasars, both as sources of reionization, and as probes of the ionization state of the IGM. However the extreme ultra-violet ... More
Dark-ages Reionization & Galaxy Formation Simulation I: The dynamical lives of high redshift galaxiesDec 02 2015Mar 21 2016We present the Dark-ages Reionization and Galaxy-formation Observables from Numerical Simulations (DRAGONS) program and Tiamat, the collisionless N-body simulation program upon which DRAGONS is built. The primary trait distinguishing Tiamat from other ... More
The clustering and halo occupation distribution of Lyman-break galaxies at $z\sim4$Nov 06 2015Jun 08 2016We investigate the clustering of Lyman-break galaxies (LBGs) at $z\sim4$. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular ... More
The Impact of a Percolating IGM on Redshifted 21 cm Observations of Quasar HII RegionsAug 28 2007Mar 04 2008We assess the impact of inhomogeneous reionization on detection of HII regions surrounding luminous high redshift quasars using planned low frequency radio telescopes. Our approach is to implement a semi-numerical scheme to calculate the 3-dimensional ... More
Cosmological Microlensing Statistics: Variability rates for Quasars and GRB Afterglows, and implications for macrolensing magnification bias and flux ratiosMar 13 2002The fraction of quasar's and gamma-ray burst (GRB) afterglows that vary due to microlensing by the stellar populations of intervening elliptical/S0 galaxies is computed by combining the joint distribution of effective microlensing convergence (kappa) ... More