@article{2644, abstract = {The release of GABA in synapses is modulated by presynaptic metabotropic glutamate receptors (mGluRs). We tested whether GABA release to identified hippocampal neurons is influenced by group III mGluR activation using the agonist L-(+)-2-amino-4-phosphonobutyric acid (L-AP4) on inhibitory postsynaptic currents (IPSCs) evoked in CA1 interneurons and pyramidal cells. In interneurons, characterized with biocytin and immunolabelling for somatostatin, evoked IPSCs were depressed by 50 μM L-AP4 (activating mGluR4 and 8) to 68±6% of control, but they were rarely depressed in pyramidal cells (96±4% of control). At 300-500 μM concentration (activating mGluR4, 7 and 8), L-AP4 depressed IPSCs in both interneurons (to 70±6%) and pyramidal cells (to 67±4%). The change in trial-to-trial variability and in paired-pulse depression indicated a presynaptic action. In interneurons, the degree of IPSC depression was variable (to 9-87%), and a third of IPSCs were not affected by L-AP4. The L-AP4-evoked IPSC depression was blocked by LY341495. The depression of IPSCs was similar in O-LM cells and other interneurons. The lack of cell-type selectivity and the similar efficacy of different concentrations of L-AP4 suggest that several group III mGluRs are involved in the depression of IPSCs. Electron microscopic immunocytochemistry confirmed that mGluR4, mGluR7a and mGluR8a occur in the presynaptic active zone of GABAergic terminals on interneurons, but not on those innervating pyramidal cells. The high variability of L-AP4-evoked IPSC suppression is in line with the selective expression of presynaptic mGluRs by several distinct types of GABAergic neuron innervating each interneuron type.}, author = {Kogo, Naoki and Dalezios, Yannis and Capogna,Marco and Ferraguti, Francesco and Ryuichi Shigemoto and Somogyi, Péter}, journal = {European Journal of Neuroscience}, number = {10}, pages = {2727 -- 2740}, publisher = {Wiley-Blackwell}, title = {{Depression of GABAergic input to identified hippocampal neurons by group III metabotropic glutamate receptors in the rat}}, doi = {10.1111/j.0953-816X.2004.03394.x}, volume = {19}, year = {2004}, } @article{11762, abstract = {In this paper, we describe six algorithmic problems that arise in web search engines and that are not or only partially solved: (1) Uniformly sampling of web pages; (2) modeling the web graph; (3) finding duplicate hosts; (4) finding top gainers and losers in data streams; (5) finding large dense bipartite graphs; and (6) understanding how eigenvectors partition the web.}, author = {Henzinger, Monika H}, issn = {1944-9488}, journal = {Internet Mathematics}, number = {1}, pages = {115--123}, publisher = {Internet Mathematics}, title = {{Algorithmic challenges in web search engines}}, doi = {10.1080/15427951.2004.10129079}, volume = {1}, year = {2004}, } @article{17725, abstract = {A 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 at wavelengths approaching and shorter than that corresponding to the Stromgren sphere's boundary along the line of sight. We show here that simultaneously considering the measured absorption in two or more hydrogen Lyman lines can provide the dynamical range required to detect this feature. We model broad and robust features of the Lyman alpha and Lyman beta regions of the spectrum of the z=6.28 quasar SDSS J1030+0524, using a hydrodynamical simulation. From the steep wavelength-dependence of the inferred absorption opacity, we detect the boundary of the Stromgren sphere at a proper distance of 6.0 +/- 0.2 Mpc away from the source redshift. From the spectrum alone, we also find that beyond this distance, cosmic hydrogen turns nearly neutral, with a neutral fraction of x_HI > 0.2, and that the ionizing luminosity of this quasar is in the range (5.2 +/- 2.5) times 10^{56} photons/sec. The method presented here, when applied to future quasars, can probe the complex topology of overlapping ionized regions, and can be used to study the details of the reionization process.}, author = {Mesinger, Andrei and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {L69--L72}, publisher = {American Astronomical Society}, title = {{Evidence of a cosmological Strömgren surface and of significant neutral hydrogen surrounding the quasar SDSS J1030+0524}}, doi = {10.1086/423935}, volume = {611}, year = {2004}, } @article{17743, abstract = {We use a physically motivated semi-analytic model, based on the mass function of dark matter halos, to predict the number of radio-loud quasars as a function of redshift and luminosity. Simple models in which the central BH mass scales with the velocity dispersion of its host halo as M(bh) sigma(halo)^5 have been previously found to be consistent with a number of observations, including the optical and X-ray quasar luminosity functions. We find that similar models, when augmented with an empirical prescription for radio emission, overpredict the number of faint (10 micro-Jy) radio sources by 1-2 orders of magnitude. This translates into a more stringent constraint on the low-mass end of the quasar black hole mass function than is available from the Hubble and Chandra Deep Fields. We interpret this discrepancy as evidence that black holes with masses below 10^7 Msun are either rare or are not as radio-loud as their more massive counterparts. Models that exclude BHs with masses below 10^7 Msun are in agreement with the deepest existing radio observations, but still produce a significant tail of high-redshift objects. In the 1-10GHz bands, at the sensitivity of 10 micro-Jy, we find surface densities of 100, 10, and 0.3 deg^-2 for sources located at z>6, 10, and 15, respectively. The discovery of these sources with instruments such as the Allen Telescope Array (ATA), Extended Very Large Array (EVLA), and the Square Kilometer Array (SKA) would open a new window for the study of supermassive BHs at high redshift. We also find surface densities of 0.1 deg^-2 at z > 6 for mJy sources that can be used to study 21 cm absorption from the epoch of reionization. We suggest that, although not yet optically identified, the FIRST survey may have already detected 10^3-10^4 such sources.}, author = {Haiman, Zoltán and Quataert, Eliot and Bower, Geoffrey C.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {698--705}, publisher = {American Astronomical Society}, title = {{Modeling the counts of faint radio‐loud quasars: Constraints on the supermassive black hole population and predictions for high redshift}}, doi = {10.1086/422834}, volume = {612}, year = {2004}, } @article{17745, abstract = {We 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 extract relevant parameters, including the mean neutral fraction in the IGM and the radius of the local cosmological Strömgren region, from the flux distribution in the observed spectra of distant sources. We focus on quasars, but a similar analysis is applicable to galaxies and gamma-ray burst (GRB) afterglows. We explicitly include uncertainties in the spectral shape of the assumed source template near the Lyα line. Our results suggest that a mean neutral hydrogen fraction, xH, of unity can be statistically distinguished from xH ≈ 10^-2 by combining the spectra of tens of bright (M ≈ -27) quasars. Alternatively, the same distinction can be achieved using the spectra of several hundred sources that are ~100 times fainter. Furthermore, if the radius of the Strömgren sphere can be independently constrained to within ~10%, this distinction can be achieved using a single source. The information derived from such spectra will help in settling the current debate as to what extent the universe was reionized at redshifts near z ~ 6.}, author = {Mesinger, Andrei and Haiman, Zoltán and Cen, Renyue}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {23--35}, publisher = {American Astronomical Society}, title = {{Probing the reionization history using the spectra of high‐redshift sources}}, doi = {10.1086/422898}, volume = {613}, year = {2004}, } @article{17763, abstract = {Recent studies have suggested that during their coalescence, binary supermassive black holes (SMBHs) experience typical gravitational recoil velocities that may be as large as ≳100 km s^-1. These velocities exceed the escape velocity vesc from typical dark matter (DM) halos at high redshift (z ≳ 6), and therefore put constraints on scenarios in which early SMBHs grow at the centers of DM halos. Here we quantify these constraints for the most distant known SMBH, with an inferred mass in excess of 10^9 M☉, powering the bright quasar SDSS J1148+5251 discovered in the Sloan Digital Sky Survey at z = 6.43. We assume that this SMBH grew via a combination of accretion and mergers between preexisting seed BHs in individual progenitor halos, and that mergers between progenitors with vesc < vkick disrupt the BH growth process. Our results suggest that under these assumptions, the z ≈ 6 SMBHs had a phase during which they gained mass vary rapidly. In particular, typical z ≈ 3 quasars with luminosities similar to that of SDSS J1148+5251 have recently been inferred to have an average radiative efficiency of epsilon ≈ 20%. The growth rate of the SMBH in SDSS J1148+5251 must have significantly exceeded the Eddington accretion rate with this efficiency.}, author = {Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {36--40}, publisher = {American Astronomical Society}, title = {{Constraints from gravitational recoil on the growth of supermassive black holes at high redshift}}, doi = {10.1086/422910}, volume = {613}, year = {2004}, } @article{17775, abstract = {We discuss a simple model for the growth of supermassive black holes (BHs) at the center of spheroidal stellar systems. In particular, we assess the hypotheses that (1) star formation in spheroids and BH fueling are proportional to one another, and (2) the BH accretion luminosity stays near the Eddington limit during luminous quasar phases. With the aid of this simple model, we are able to interpret many properties of the QSO luminosity function, including the puzzling steep decline of the characteristic luminosity from redshift z=2 to to z=0: indeed the residual star formation in spheroidal systems is today limited to a small number of bulges, characterized by stellar velocity dispersions a factor of 2-3 smaller those of the elliptical galaxies hosting QSOs at z > 2. A simple consequence of our hypotheses is that the redshift evolution of the QSO emissivity and of the star formation history in spheroids should be roughly parallel. We find this result to be broadly consistent with our knowledge of the evolution of both the global star formation rate, and of the evolution of the QSO emissivity, but we identify interesting discrepancies at both low and high redshifts, to which we offer tentative solutions. Finally, our hypotheses allow us to present a robust method to derive the duty cycle of QSO activity, based on the observed QSO luminosity function, and on the present-day relation between the masses of supermassive BHs and those of their spheroidal host stellar systems. The duty cycle is found to be substantially less than unity, with characteristic values in the range (3-6)x10^(-3), and we compute that the average bolometric radiative efficiency is epsilon=0.07. Finally, we find that the growth in mass of individual black holes at high redshift (z>2) can be dominated by mergers, and is therefore not necessarily limited by accretion.}, author = {Haiman, Zoltán and Ciotti, Luca and Ostriker, Jeremiah P.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {763--773}, publisher = {American Astronomical Society}, title = {{Reasoning from fossils: Learning from the local black hole population about the evolution of quasars}}, doi = {10.1086/383022}, volume = {606}, year = {2004}, } @article{17790, abstract = {Over the last few years, the Sloan Digital Sky Survey (SDSS) has discovered several hundred quasars with redshift between 4.0 and 6.4. Including the effects of magnification bias, one expects a priori that an appreciable fraction of these objects are gravitationally lensed. We have used the Advanced Camera for Surveys on the Hubble Space Telescope to carry out a snapshot imaging survey of high-redshift SDSS quasars to search for gravitationally split lenses. This paper, the first in a series reporting the results of the survey, describes snapshot observations of four quasars at z = 5.74, 5.82, 5.99, and 6.30, respectively. We find that none of these objects has a lensed companion within 5 mag with a separation larger than 0farcs3; within 2.5 mag we can rule out companions within 0farcs1. Based on the nondetection of strong lensing in these four systems, we constrain the z ∼ 6 luminosity function to a slope of β > -4.63 (3 σ), assuming a break in the quasar luminosity function at M = -24.1. We discuss the implications of this constraint on the ionizing background due to quasars in the early universe. Given that these quasars are not highly magnified, estimates of the masses of their central engines by the Eddington argument must be taken seriously, possibly challenging models of black hole formation.}, author = {Richards, Gordon T. and Strauss, Michael A. and Pindor, Bartosz and Haiman, Zoltán and Fan, Xiaohui and Eisenstein, Daniel and Schneider, Donald P. and Bahcall, Neta A. and Brinkmann, J. and Brunner, Robert}, issn = {0004-6256}, journal = {The Astronomical Journal}, number = {3}, pages = {1305--1312}, publisher = {American Astronomical Society}, title = {{A snapshot survey for gravitational lenses among z ≥ 4.0 quasars. I. The z >5.7 sample}}, doi = {10.1086/381906}, volume = {127}, year = {2004}, } @article{17806, abstract = {A population of black holes (BHs) at high redshifts (z ≳ 6) that contributes significantly to the ionization of the intergalactic medium (IGM) would be accompanied by the copious production of hard (≳10 keV) X-ray photons. The resulting hard X-ray background would redshift and be observed as a present-day soft X-ray background (SXB). Under the hypothesis that BHs are the main producers of reionizing photons in the high-redshift universe, we calculate their contribution to the present-day SXB. We find that accreting BHs with a hard spectrum (be it luminous quasars or their lower mass "miniquasar" counterparts) could not fully reionize the universe without saturating the unresolved component of the 0.5-2 keV SXB at the ≥2 σ level. Distant miniquasars that produce enough X-rays to only partially ionize the IGM to a level of at most xe ~ 50% saturate the unresolved SXB by ≲1 σ. Improved determinations of the unresolved component of the SXB can provide a powerful constraint on the contribution of accreting BHs to partial or full reionization.}, author = {Dijkstra, Mark and Haiman, Zoltán and Loeb, Abraham}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {2}, pages = {646--654}, publisher = {American Astronomical Society}, title = {{A limit from the X‐ray background on the contribution of quasars to reionization}}, doi = {10.1086/422167}, volume = {613}, year = {2004}, } @article{4256, abstract = {Artificial Life models may shed new light on the long-standing challenge for evolutionary biology of explaining the origins of complex organs. Real progress on this issue, however, requires Artificial Life researchers to take seriously the tools and insights from population genetics.}, author = {Barton, Nicholas H and Zuidema, Willem}, issn = {0960-9822}, journal = {Current Biology}, number = {16}, pages = {R649 -- R651}, publisher = {Cell Press}, title = {{The erratic path towards complexity}}, doi = {10.1016/S0960-9822(03)00573-6}, volume = {13}, year = {2003}, } @article{3150, abstract = {Tripartite G-protein-coupled receptors (GPCRs) represent one of the largest groups of signal transducers, transmitting signals from hormones, neuropeptides, odorants, food and light. Ligand-bound receptors catalyse GDP/GTP exchange on the G-protein α-subunit (Gα), leading to α-GTP separation from the βγ subunits and pathway activation. Activating mutations in the receptors or G proteins underlie many human diseases, including some cancers, dwarfism and premature puberty. Regulators of G-protein signalling (RGS proteins) are known to modulate the level and duration of ligand-induced signalling by accelerating the intrinsic GTPase activity of the Gα subunit, and thus reformation of the inactive GDP-bound Gα. Here we find that even in the absence of receptor, mutation of the RGS family member Sst2 (refs 6-9) permits spontaneous activation of the G-protein-coupled mating pathway in Saccharomyces cerevisiae at levels normally seen only in the presence of ligand. Our work demonstrates the occurence of spontaneous tripartite G-protein signalling in vivo and identifies a requirement for RGS proteins in preventing such receptor-independent activation.}, author = {Siekhaus, Daria E and Drubin, David}, issn = {1476-4679}, journal = {Nature Cell Biology}, number = {3}, pages = {231 -- 235}, publisher = {Springer Nature}, title = {{Spontaneous receptor-independent heterotrimeric G-protein signalling in an RGS mutant}}, doi = {10.1038/ncb941}, volume = {5}, year = {2003}, } @inproceedings{3210, abstract = {Luby and Rackoff showed how to construct a (super-)pseudo-random permutation {0,1}2n→ {0,1}2n from some number r of pseudo-random functions {0,1}n → {0,1}n. Their construction, motivated by DES, consists of a cascade of r Feistel permutations. A Feistel permutation 1for a pseudo-random function f is defined as (L, R) → (R,L ⊕ f (R)), where L and R are the left and right part of the input and ⊕ denotes bitwise XOR or, in this paper, any other group operation on {0,1}n. The only non-trivial step of the security proof consists of proving that the cascade of r Feistel permutations with independent uniform random functions {0,1}n → {0,1}n, denoted Ψ2nr is indistinguishable from a uniform random permutation {0,1}2n → {0,1}2n by any computationally unbounded adaptive distinguisher making at most O(2cn) combined chosen plaintext/ciphertext queries for any c < α, where a is a security parameter. Luby and Rackoff proved α = 1/2 for r = 4. A natural problem, proposed by Pieprzyk is to improve on α for larger r. The best known result, α = 3/4 for r = 6, is due to Patarin. In this paper we prove a = 1 -O(1/r), i.e., the trivial upper bound α = 1 can be approached. The proof uses some new techniques that can be of independent interest. }, author = {Maurer, Ueli and Pietrzak, Krzysztof Z}, isbn = {9783540140399}, location = {Warschau, Polen}, pages = {544 -- 561}, publisher = {Springer Nature}, title = {{The security of many round Luby Rackoff pseudo random permutations}}, doi = {10.1007/3-540-39200-9_34}, volume = {2656}, year = {2003}, } @article{3536, abstract = {Genetic engineering of the mouse brain allows investigators to address novel hypotheses in vivo. Because of the paucity of information on the network patterns of the mouse hippocampus, we investigated the electrical patterns in the behaving animal using multisite silicon probes and wire tetrodes. Theta (6-9 Hz) and gamma (40-100 Hz) oscillations were present during exploration and rapid eye movement sleep. Gamma power and theta power were comodulated and gamma power varied as a function of the theta cycle. Pyramidal cells and putative interneurons were phase-locked to theta oscillations. During immobility, consummatory behaviors and slow-wave sleep, sharp waves were present in cornu ammonis region CA1 of the hippocampus stratum radiatum associated with 140-200-Hz “ripples” in the pyramidal cell layer and population burst of CA1 neurons. In the hilus, large-amplitude “dentate spikes” occurred in association with increased discharge of hilar neurons. The amplitude of field patterns was larger in the mouse than in the rat, likely reflecting the higher neuron density in a smaller brain. We suggest that the main hippocampal network patterns are mediated by similar pathways and mechanisms in mouse and rat. }, author = {Buzsáki, György and Buhl, Derek and Harris, Kenneth and Csicsvari, Jozsef L and Czéh, Boldizsár and Morozov, Alexei}, issn = {1873-7544}, journal = {Neuroscience}, number = {1}, pages = {201 -- 211}, publisher = {Elsevier}, title = {{Hippocampal network patterns of activity in the mouse}}, doi = {10.1016/S0306-4522(02)00669-3}, volume = {116}, year = {2003}, } @article{2631, abstract = {Cyclic ADP-ribose (cADP-ribose) is a putative second messenger or modulator. However, the role of cADP-ribose in the downstream signals of the metabotropic glutamate receptors (mGluRs) is unclear. Here, we show that glutamate stimulates ADP-ribosyl cyclase activity in rat or mouse crude membranes of retina via group III mGluRs or in superior cervical ganglion via group I mGluRs. The retina of mGluR6-deficient mice showed no increase in the ADP-ribosyl cyclase level in response to glutamate. GTP enhanced the initial rate of basal and glutamate-stimulated cyclase activity. GTP-γ-S also stimulated basal activity. To determine whether the coupling mode of mGluRs to ADP-ribosyl cyclase is a feature common to individual cloned mGluRs, we expressed each mGluR subtype in NG108-15 neuroblastoma x glioma hybrid cells. The glutamate-induced stimulation of the cyclase occurs preferentially in NG108-15 cells over-expressing mGluRs1, 3, 5, and 6. Cells expressing mGluR2 or mGluRs4 and 7 exhibit inhibition or no coupling, respectively. Glutamate-induced activation or inhibition of the cyclase activity was eliminated after pre-treatment with cholera or pertussis toxin, respectively. Thus, the subtype-specific coupling of mGluRs to ADP-ribosyl cyclase via G proteins suggests that some glutamate-evoked neuronal functions are mediated by cADP-ribose.}, author = {Higashida, Haruhiro and Zhang, Jia and Mochida, Sumiko and Chen, Xiao and Shin, Yeonsook and Noda, Mami and Hossain, Kazi and Hoshi, Naoto and Hashii, Minako and Shigemoto, Ryuichi and Nakanishi, Shigetada and Fukuda, Yutaka and Yokoyama, Shigeru}, issn = {1471-4159}, journal = {Journal of Neurochemistry}, number = {5}, pages = {1148 -- 1158}, publisher = {Wiley-Blackwell}, title = {{Subtype-specific coupling with ADP-ribosyl cyclase of metabotropic glutamate receptors in retina, cervical superior ganglion and NG108-15 cells}}, doi = {10.1046/j.1471-4159.2003.01751.x}, volume = {85}, year = {2003}, } @article{11122, abstract = {Nuclear pore complexes (NPCs) are large multiprotein assemblies that allow traffic between the cytoplasm and the nucleus. During mitosis in higher eukaryotes, the Nuclear Envelope (NE) breaks down and NPCs disassemble. How NPCs reassemble and incorporate into the NE upon mitotic exit is poorly understood. We demonstrate a function for the conserved Nup107-160 complex in this process. Partial in vivo depletion of Nup133 or Nup107 via RNAi in HeLa cells resulted in reduced levels of multiple nucleoporins and decreased NPC density in the NE. Immunodepletion of the entire Nup107-160 complex from in vitro nuclear assembly reactions produced nuclei with a continuous NE but no NPCs. This phenotype was reversible only if Nup107-160 complex was readded before closed NE formation. Depletion also prevented association of FG-repeat nucleoporins with chromatin. We propose a stepwise model in which postmitotic NPC assembly initiates on chromatin via early recruitment of the Nup107-160 complex.}, author = {Walther, Tobias C. and Alves, Annabelle and Pickersgill, Helen and Loı̈odice, Isabelle and HETZER, Martin W and Galy, Vincent and Hülsmann, Bastian B. and Köcher, Thomas and Wilm, Matthias and Allen, Terry and Mattaj, Iain W. and Doye, Valérie}, issn = {0092-8674}, journal = {Cell}, keywords = {General Biochemistry, Genetics and Molecular Biology}, number = {2}, pages = {195--206}, publisher = {Elsevier}, title = {{The conserved Nup107-160 complex is critical for nuclear pore complex assembly}}, doi = {10.1016/s0092-8674(03)00235-6}, volume = {113}, year = {2003}, } @article{11766, abstract = {This paper studies the multicast routing and admission control problem on unit-capacity tree and mesh topologies in the throughput model. The problem is a generalization of the edge-disjoint paths problem and is NP-hard both on trees and meshes. We study both the offline and the online version of the problem: In the offline setting, we give the first constant-factor approximation algorithm for trees, and an -factor approximation algorithm for meshes. In the online setting, we give the first polylogarithmic competitive online algorithm for tree and mesh topologies. No polylogarithmic-competitive algorithm is possible on general network topologies (Lower bounds for on-line graph problems with application to on-line circuits and optical routing, in: Proceedings of the 28th ACM Symposium on Theory of Computing, 1996, pp. 531–540) and there exists a polylogarithmic lower bound on the competitive ratio of any online algorithm on tree topologies (Making commitments in the face of uncertainity: how to pick a winner almost every time, in: Proceedings of the 28th Annual ACM Symposium on Theory of Computing, 1996, pp. 519–530). We prove the same lower bound for meshes.}, author = {Henzinger, Monika H and Leonardi, Stefano}, issn = {0022-0000}, journal = {Journal of Computer and System Sciences}, number = {3}, pages = {567--611}, publisher = {Elsevier}, title = {{Scheduling multicasts on unit-capacity trees and meshes}}, doi = {10.1016/s0022-0000(03)00043-6}, volume = {66}, year = {2003}, } @article{17741, abstract = {The recent discovery of a Gunn-Peterson (GP) trough in the spectrum of the redshift 6.28 SDSS quasar has raised the tantalizing possibility that we have detected the reionization of the universe. However, a neutral fraction (of hydrogen) as small as 0.1% is sufficient to cause the GP trough; hence, its detection alone cannot rule out reionization at a much earlier epoch. The cosmic microwave background (CMB) polarization anisotropy offers an alternative way to explore the dark age of the universe. We show that for most models constrained by the current CMB data and by the discovery of a GP trough (showing that reionization occurred at z > 6.3), Microwave Anisotropy Probe (MAP) can detect the reionization signature in the polarization power spectrum. The expected 1 σ error on the measurement of the electron optical depth is around 0.03 with a weak dependence on the value of that optical depth. Such a constraint on the optical depth will allow MAP to achieve a 1 σ error on the amplitude of the primordial power spectrum of 6%. MAP with 2 yr (Planck with 1 yr) of observation can distinguish a model with 50% (6%) partial ionization between redshifts of 6.3 and 20 from a model in which hydrogen was completely neutral at redshifts greater than 6.3. Planck will be able to distinguish between different reionization histories even when they imply the same optical depth to electron scattering for the CMB photons.}, author = {Kaplinghat, Manoj and Chu, Mike and Haiman, Zoltán and Holder, Gilbert P. and Knox, Lloyd and Skordis, Constantinos}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {24--32}, publisher = {American Astronomical Society}, title = {{Probing the reionization history of the universe using the cosmic microwave background polarization}}, doi = {10.1086/344927}, volume = {583}, year = {2003}, } @article{17750, abstract = {We present the discovery of three new quasars at z>6 in 1300 deg^2 of SDSS imaging data, J114816.64+525150.3 (z=6.43), J104845.05+463718.3 (z=6.23) and J163033.90+401209.6 (z=6.05). The first two objects have weak Ly alpha emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate to 0.05 and could be affected by the presence of broad absorption line systems. The last object has a Ly alpha strength more typical of lower redshift quasars. Based on a sample of six quasars at z>5.7 that cover 2870 deg^2 presented in this paper and in Paper I, we estimate the comoving density of luminous quasars at z 6 and M_{1450} < -26.8 to be (8 +/- 3)x10^{-10} Mpc^{-3} (for H_0 = 50 km/s/Mpc, Omega = 1). HST imaging of two z>5.7 quasars and high-resolution ground-based images (seeing 0.4'') of three additional z>5.7 quasars show that none of them is gravitationally lensed. The luminosity distribution of the high-redshfit quasar sample suggests the bright end slope of the quasar luminosity function at z 6 is shallower than Psi L^{-3.5} (2-sigma), consistent with the absence of strongly lensed objects.}, author = {Fan, Xiaohui and Strauss, Michael A. and Schneider, Donald P. and Becker, Robert H. and White, Richard L. and Haiman, Zoltán and Gregg, Michael and Pentericci, Laura and Grebel, Eva K. and Narayanan, Vijay K. and Loh, Yeong-Shang and Richards, Gordon T. and Gunn, James E. and Lupton, Robert H. and Knapp, Gillian R. and Ivezić, Željko and Brandt, W. N. and Collinge, Matthew and Hao, Lei and Harbeck, Daniel and Prada, Francisco and Schaye, Joop and Strateva, Iskra and Zakamska, Nadia and Anderson, Scott and Brinkmann, Jon and Bahcall, Neta A. and Lamb, Don Q. and Okamura, Sadanori and Szalay, Alex and York, Donald G.}, issn = {0004-6256}, journal = {The Astronomical Journal}, number = {4}, pages = {1649--1659}, publisher = {American Astronomical Society}, title = {{A survey of z > 5.7 quasars in the Sloan Digital Sky Survey. II. Discovery of three additional quasars at z > 6}}, doi = {10.1086/368246}, volume = {125}, year = {2003}, } @article{17754, abstract = {The recent discovery of a high optical depth tau to Thomson scattering from the WMAP data implies that significant reionization took place at redshifts z~15. This discovery has important implications for the sources of reionization, and allows, for the first time, constraints to be placed on physical reionization scenarios out to redshift z~20. Using a new suite of semi-analytic reionization models, we show that the high value of tau requires a surprisingly high efficiency epsilon of the first generation of UV sources for injecting ionizing photons into the intergalactic medium. We find that no simple reionization model can be consistent with the combination of the WMAP result with data from the z<6.5 universe. Satisfying both constraints requires either of the following: (i) H_2 molecules form efficiently at z~20, survive feedback processes, and allow UV sources in halos with virial temperatures below Tvir=10^4 K to contribute substantially to reionization, or (ii) the efficiency epsilon in halos with Tvir>10^4K decreased by a factor of ~ 30 between (z~20) and (z~6). We discuss the relevant physical issues to produce either scenario, and argue that both options are viable, and allowed by current data. In detailed models of the reionization history, we find that the evolution of the ionized fractions in the two scenarios have distinctive features that Planck can distinguish at 3 sigma significance. At the high WMAP value for tau, Planck will also be able to provide tight statistical constraints on reionization model parameters, and elucidate much of the physics at the end of the Dark Ages. The sources responsible for the high optical depth discovered by WMAP should be directly detectable out to z~15 by the James Webb Space Telescope.}, author = {Haiman, Zoltán and Holder, Gilbert P.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {1--12}, publisher = {American Astronomical Society}, title = {{The reionization history at high redshifts. I. Physical models and new constraints from cosmic microwave background polarization}}, doi = {10.1086/377337}, volume = {595}, year = {2003}, } @article{17796, abstract = {The recent measurement by WMAP of a large electron-scattering optical depth τe = 0.17 ± 0.04 is consistent with a simple model of reionization in which the intergalactic medium (IGM) is ionized at redshift z ~ 15 and remains highly ionized thereafter. Here we show that existing measurements of the IGM temperature from the Lyα forest at z ~ 2-4 rule out this "vanilla" model. Under reasonable assumptions about the ionizing spectrum, as long as the universe is reionized before z = 10 and remains highly ionized thereafter, the IGM reaches an asymptotic thermal state that is too cold compared to observations. To simultaneously satisfy the cosmic microwave background and Lyα forest constraints, the reionization history must be complex: reionization begins early at z ≳ 15, but there must have been significant (order-of-unity) changes in fractions of neutral hydrogen and/or helium at 6 < z < 10 and/or singly ionized helium at 4 < z < 10. We describe a physically motivated reionization model that satisfies all current observations. We also explore the impact of a stochastic reionization history and show that a late epoch of (He → He ) reionization induces a significant scatter in the IGM temperature, but the scatter diminishes with time quickly. Finally, we provide an analytic formula for the thermal asymptote and discuss possible additional heating mechanisms that might evade our constraints.}, author = {Hui, Lam and Haiman, Zoltán}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, pages = {9--18}, publisher = {American Astronomical Society}, title = {{The thermal memory of reionization history}}, doi = {10.1086/377229}, volume = {596}, year = {2003}, }