RESEARCH AND PUBLICATIONS

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1) Wyithe, J.S.B., Yan, H.J., Windhorst, R., Mao, S., A Distortion of Very-High-Redshift Galaxy Number Counts by Gravitational Lensing, 2011, Nature 7329, 181


This paper recognized the importance of gravitational lensing for observations of the most distant galaxies, and presented evidence for this in the Hubble Ultra-Deep Field. This realization resolves a controversy regarding the findings of different groups studying the Hubble Ultra Deep field, one of the highest profile data sets in astronomy. One of the important motivations for constructing the James Webb Space Telescope (successor to the Hubble Space Telescope) is the study of the buildup of stellar mass in the early Universe and the discovery of the earliest galaxies. This paper illustrates that high redshift surveys do not provide an unbiased census of the build up of stellar mass, but suggests that gravitational lensing could be used in the future to probe galaxy luminosities that are otherwise unreachable. The gravitational lensing already seen by Hubble Space Telescope will be of critical importance to these future studies. The paper reinforces the importance of the James Webb Space Telescope.



2) Wyithe, J.S.B., Loeb, A., Geil, P.M. Baryonic Acoustic Oscillations in 21-cm Emission: A Probe of Dark Energy Out to High Redshifts, 2008, Monthly Notices of the Royal Astronomical Society, 383, 1195-1209


Baryonic acoustic oscillations in the mass-density of the Universe on the largest scales can be used as a standard ruler, providing the most promising method to infer the evolution of the equation of state for the dark energy. This paper showed that low frequency telescopes being built to detect the end of reionization from the redshifted 21cm emission line of hydrogen could be used to study the evolution of this acoustic scale over the first half of cosmic time where it is not accessible to the traditional method of galaxy clustering. It demonstrated that first generation of low-frequency experiments such as the Murchison Widefield Array will be able to constrain the acoustic scale to within a few per cent both prior to and after reionization, comparable to the best current measurements from galaxy redshift surveys, but at much higher redshifts. The paper further showed that future extensions of the first-generation experiments could reach sensitivities below 1 per cent in several redshift windows and could be used to study the dark energy in the unexplored redshift regime of 3.5<z<12.



3) Dijkstra, M., Wyithe, J.S.B., Haiman, Z., Constraints on Reionization of Cosmic Hydrogen from the Ly-alpha Luminosity function of Galaxies, 2007, Monthly Notices of the Royal Astronomical Society, 379, 253-259


High redshift galaxies can be found either by searching for absorption at wavelengths shorter than the Lyman limit of hydrogen in broad-band photometry, or by searching for Ly-alpha emission in a narrow band. Significant observational effort on the world’s largest telescopes has been invested in both approaches. The epoch when the first galaxies finished ionizing all of the hydrogen in the inter-galactic medium remains a sought after observational prize. Because the Ly-alpha radiation can be absorbed by the neutral inter-galactic hydrogen, these galaxies are often suggested as probes of when the reionization era was ended. In this paper we constructed the first model of the luminosity function of Ly-alpha emitters, including both a physical model for transmission of Ly-alpha photons through the inter-galactic medium and the growth of galaxies. Using this model we showed that the observed evolution of the luminosity function does not constrain reionization, as was claimed in the literature.



4) Wyithe, J.S.B., A Log-Quadratic Relation Between the Nuclear Super-Massive Black-Hole Masses and Velocity Dispersions of Galaxies, 2006, Monthly Notices of the Royal Astronomical Society, 365, 1082-1098


The origin tight relation between Super-Massive Black-Holes and their host galaxies remains a great mystery for galaxy formation models, but arguably provides the best evidence for the mechanisms that regulate star-formation and quasar activity. The relation between black-hole mass and galaxy velocity dispersion in particular has received much attention, and is traditionally parameterized by a power-law relation. This paper showed that the relation between the mass of a central black hole and the velocity dispersion of galaxies departs from a pure powerlaw. This  eparture is not predicted by simple models, and indicates that there is an additional physical effect at play beyond the hypothesized modes of feedback. Subsequent studies have investigated the origin of the third parameter in this relation.



5) Wyithe, J.S.B., Loeb, A., A Characteristic Size of ~10Mpc for the Ionized Bubbles at the End of Reionization, 2004, Nature, 432, 194-196


Early galaxies are thought to have filled the Universe with ionized bubbles, the size and distribution of which provide a signature for studying the first galaxies. The aim of telescopes like the Murchison Widefield Array (MWA), currently under construction in Western Australia is to measure this ionization structure. However these radio telescopes have only a limited range of angular scales over which they are sensitive to the reionization fluctuations. As a result, the size of the ionized bubbles is a critical (unknown) input into the design of the MWA and other similar instruments. This paper presented the first calculation of the maximum size of the ionized regions at the end of reionization from very general considerations of the standard Cold-Dark Matter Model model. We found that the maximum size of bubbles that can be observed is limited to around half a degree, which sets the largest size of the smallest baselines that are required in the radio array in order to ensure sensitivity to the crucial final stages of reionization.



6) Wyithe, J.S.B., Loeb, A., A Large Neutral Fraction of Cosmic Hydrogen a Billion Years After the Big Bang, 2004, Nature, 427, 815-817 (see news and Views, S.G. Djorgovski)


The epoch when the first galaxies finished ionizing all of the hydrogen in the inter-galactic medium remains an unknown milestone in the history of the Universe. One of the most robust methods for studying the ionization state of the inter-galactic medium in order to answer this question is absorption of Ly-alpha radiation from luminous high redshift quasars. Unfortunately only very low atomic fractions can be studied directly, so that the presence of large atomic fractions cannot be detected. This paper introduced a novel approach that used the size of the observed region of ionization around the quasar, combined with modelling of the quasars ionized bubble to constrain the ionized state of the general inter-galactic medium. We demonstrated that the hydrogen in the intergalactic medium was mostly atomic right up until the end of the reionization epoch. This paper motivated a very large number of follow up studies to model the Ly-alpha absorption in the vicinity of the quasar.



7) Wyithe, J.S.B., Loeb, A., Self Regulated Growth of Super-Massive Black-Holes in Galaxies as the Origin of the Optical and X-Ray Luminosity Functions of Quasars, 2003, Astrophysical Journal, 595, 614-623


In the local universe, the Hubble Space Telescope has been used to measure the mass of super-massive black-holes, which appear to be located in the cores of all galaxies. The masses of these black-holes correlate tightly with the properties of their host galaxies. This paper developed the first theory to include feedback in the growth mechanisms of the central Black Holes, to describe the formation and evolution of quasars. The model is based on the hierarchical growth of structure and successfully describes the luminosity functions of quasars, and the origin of quasar lifetimes at high redshift, as well as the local black-hole galaxy relation. This paper contributed to the foundation for the many successful subsequent studies of the hierarchical build up of super-massive black holes via quasar activity.



8) Wyithe, J.S.B., Loeb, A., The Reionization of Hydrogen and Helium by Early Stars and Quasars, 2003, Astrophysical Journal, 586, 693-708


This paper presented a model of the joint evolution of ionized structure in hydrogen and helium during reionization, including sources both from stars and quasars, as well as population-III stars. The paper made the point that reionization was not a rapid event, and that there was likely an early phase of reionisation by a population-III stars, followed by a period of recombination of the Hydrogen and Helium, and a second phase of reionisation at later times. We suggested that the Universe could have in fact have been reionized twice. In 2003, a major new measurement of the structure in the Cosmic Microwave Background by the Wilkinson Microwave Anisotropy Probe, suggested that the Epoch of Reionisation might have occurred at redshifts as high as 20. This was in sharp contrast to the evidence from absorption features in quasars, which suggested that the Universe was still neutral at a redshift of 6, a billion years after the Big Bang. Our paper provided the basis for the interpretation of this apparently contradictory result by modelling the implications for reionization by population-III stars within the observational constraints. The modelling showed that population-II stars could adequately explain the discrepancy, providing the extended era of reionization demanded by the data.



9) Wyithe, J.S.B., Loeb, A., Gravitational Lenses Magnify Up to One Third of the Most Distant Quasars, 2002, Nature, 417, 923-925 (see news and Views, E.L. Turner)


The existence of super-massive black holes within the first billion years of the Universes history poses a challenge to models for the formation of structures in the early Universe. This paper showed that up to one-third of the most distant quasars known were likely to have had their observed flux magnified by a factor of ten or more, as a consequence of gravitational lensing by galaxies along the line of sight. Based on knowledge of the quasar luminosity function at the time, this implied that their abundance, as well as their luminosity density, could have been substantially overestimated.



10) Wyithe J.S.B., Turner E.L., Spergel, D.N., Gravitational Lens Statistics for Generalized NFW Profiles: Parameter Degeneracy and Implications for Self-Interacting Cold Dark Matter, 2001, Astrophysical Journal, 555, 504-523


There is evidence that the cold dark matter model predicts cores that are denser than those observed in galaxies, groups, and clusters. One possible resolution of the discrepancy is that the dark matter has strong interactions, which leads to lower central densities. In this paper I demonstrated for the first time that gravitational lensing statistics provide a powerful test for the self-interacting dark matter model, since the lower density cores lead to many fewer gravitational cluster lenses. This paper showed that the number of cluster lenses place tight constraints on the interaction strength of dark matter.

A full list of publications is available from   ADShttp://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&qform=AST&arxiv_sel=astro-ph&arxiv_sel=cond-mat&arxiv_sel=cs&arxiv_sel=gr-qc&arxiv_sel=hep-ex&arxiv_sel=hep-lat&arxiv_sel=hep-ph&arxiv_sel=hep-th&arxiv_sel=math&arxiv_sel=math-ph&arxiv_sel=nlin&arxiv_sel=nucl-ex&arxiv_sel=nucl-th&arxiv_sel=physics&arxiv_sel=quant-ph&arxiv_sel=q-bio&sim_query=YES&ned_query=YES&adsobj_query=YES&aut_logic=OR&obj_logic=OR&author=Wyithe&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=&txt_logic=OR&text=&nr_to_return=200&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

Short descriptions of 10 of my most interesting papers are listed below

Image: Rogier Windhorst, Haojing Yan, HUDF