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  • 1
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    A free-form mass model of the Hubble Frontier Fields cluster AS1063 (RXC J2248.7-4431) with over one hundred constraints (2016)
    Oxford University Press
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    Publication Date: 2016-05-12
    Description: We derive a free-form mass distribution for the massive cluster AS1063 ( z = 0.348) using the completed optical imaging from the Hubble Frontier Fields programmme. Based on a subset of 11 multiply lensed systems with spectroscopic redshift, we produce a lens model that is accurate enough to secure new multiply lensed systems, totalling over a 100 arclets, and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using only the subset of lensed sources with spectroscopically measured redshifts. Although a relatively large elongation of the mass distribution is apparent relative to the X-ray map, no significant offset is found between the centroid of our mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster. For the well-resolved lensed images, we provide detailed model comparisons to illustrate the precision of our model and hence the reliability of our de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example of jet-induced star formation, at redshift z 3.1.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Detecting the cosmological recombination signal from space (2015)
    Oxford University Press
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    Publication Date: 2015-07-03
    Description: Spectral distortions of the cosmic microwave background (CMB) have recently experienced an increased interest. One of the inevitable distortion signals of our cosmological concordance model is created by the cosmological recombination process, just a little before photons last scatter at redshift z ~= 1100. These cosmological recombination lines, emitted by the hydrogen and helium plasma, should still be observable as tiny deviation from the CMB blackbody spectrum in the cm–dm spectral bands. In this paper, we present a forecast for the detectability of the recombination signal with future satellite experiments. We argue that serious consideration for future CMB experiments in space should be given to probing spectral distortions and, in particular, the recombination line signals. The cosmological recombination radiation not only allows determination of standard cosmological parameters, but also provides a direct observational confirmation for one of the key ingredients of our cosmological model: the cosmological recombination history. We show that, with present technology, such experiments are futuristic but feasible. The potential rewards won by opening this new window to the very early universe could be considerable.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Using galaxy pairs to probe star formation during major halo mergers (2015)
    Oxford University Press
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    Publication Date: 2015-04-28
    Description: Currently-proposed galaxy quenching mechanisms predict very different behaviours during major halo mergers, ranging from significant quenching enhancement (e.g. clump-induced gravitational heating models) to significant star formation enhancement (e.g. gas starvation models). To test real galaxies’ behaviour, we present an observational galaxy pair method for selecting galaxies whose host haloes are preferentially undergoing major mergers. Applying the method to central L * (10 10 M  〈  M *  〈 10 10.5 M ) galaxies in the Sloan Digital Sky Survey at z  〈 0.06, we find that major halo mergers can at most modestly reduce the star-forming fraction, from 59 to 47 per cent. Consistent with past research, however, mergers accompany enhanced specific star formation rates for star-forming L * centrals: ~10 per cent when a paired galaxy is within 200 kpc (approximately the host halo's virial radius), climbing to ~70 per cent when a paired galaxy is within 30 kpc. No evidence is seen for even extremely close pairs (〈30 kpc separation) rejuvenating star formation in quenched galaxies. For galaxy formation models, our results suggest: (1) quenching in L * galaxies likely begins due to decoupling of the galaxy from existing hot and cold gas reservoirs, rather than a lack of available gas or gravitational heating from infalling clumps, (2) state-of-the-art semi-analytic models currently overpredict the effect of major halo mergers on quenching, and (3) major halo mergers can trigger enhanced star formation in non-quenched central galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Effect of primordial non-Gaussianities on the far-UV luminosity function of high-redshift galaxies: implications for cosmic reionization (2014)
    Oxford University Press
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    Publication Date: 2014-12-07
    Description: Understanding how the intergalactic medium (IGM) was reionized at z 6 is one of the big challenges of current high-redshift astronomy. It requires modelling the collapse of the first astrophysical objects (Pop III stars, first galaxies) and their interaction with the IGM, while at the same time pushing current observational facilities to their limits. The observational and theoretical progress of the last few years have led to the emergence of a coherent picture in which the budget of hydrogen-ionizing photons is dominated by low-mass star-forming galaxies, with little contribution from Pop III stars and quasars. The reionization history of the Universe therefore critically depends on the number density of low-mass galaxies at high redshift. In this work, we explore how changes in the cosmological model, and in particular in the statistical properties of initial density fluctuations, affect the formation of early galaxies. Following Habouzit et al. ( 2014 ), we run five different N -body simulations with Gaussian and (scale-dependent) non-Gaussian initial conditions, all consistent with Planck constraints. By appealing to a phenomenological galaxy formation model and to a population synthesis code, we compute the far-UV galaxy luminosity function down to M FUV = -14 at redshift 7 ≤ z ≤ 15. We find that models with strong primordial non-Gaussianities on  Mpc scales show a far-UV luminosity function significantly enhanced (up to a factor of 3 at z  = 14) in low-mass galaxies. We adopt a reionization model calibrated from state-of-the-art hydrodynamical simulations and show that such scale-dependent non-Gaussianities leave a clear imprint on the Universe reionization history and electron Thomson scattering optical depth e . Although current uncertainties in the physics of reionization and on the determination of e still dominate the signatures of non-Gaussianities, our results suggest that e could ultimately be used to constrain the statistical properties of initial density fluctuations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Blowing cold flows away: the impact of early AGN activity on the formation of a brightest cluster galaxy progenitor (2013)
    Oxford University Press
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    Publication Date: 2013-01-03
    Description: Supermassive black holes (BH) are powerful sources of energy that are already in place at very early epochs of the Universe (by z  = 6). Using hydrodynamical simulations of the formation of a massive M vir  = 5  x 10 11 M halo by z  = 6 (the most massive progenitor of a cluster of M vir  = 2  x 10 15 M at z  = 0), we evaluate the impact of active galactic nuclei (AGN) on galaxy mass content, BH self-regulation and gas distribution inside this massive halo. We find that supernova feedback has a marginal influence on the stellar structure, and no influence on the mass distribution on large scales. In contrast, AGN feedback alone is able to significantly alter the stellar-bulge mass content by quenching star formation when the BH is self-regulating, and by depleting the cold gas reservoir in the centre of the galaxy. The growth of the BH proceeds first by a rapid Eddington-limited period fed by direct cold filamentary infall. When the energy delivered by the AGN is sufficiently large to unbind the cold gas of the bulge, the accretion of gas on to the BH is maintained by both smooth gas inflow and clump migration through the galactic disc triggered by merger-induced torques. The feedback from the AGN has also a severe consequence on the baryon mass content within the halo, producing large-scale hot superwinds, able to blow away some of the cold filamentary material from the centre and reduce the baryon fraction by more than 30 per cent within the halo’s virial radius. Thus, in the very young universe, AGN feedback is likely to be a key process, shaping the properties of the most massive galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Interpretative problems [Social Sciences] (2013)
    National Academy of Sciences
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    Publication Date: 2013-08-14
    Description: In an effort to compare fairness preferences in chimpanzees and children, Proctor et al. (1) have devised experiments aimed at replicating the essential features of two common experiments, the dictator game (DG) and the ultimatum game (UG). Here, we present both methodological concerns and broader interpretative issues. In order for...
    Keywords: Letters
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Unbound geodesics from the ergosphere and potential observability of debris from ultrahigh energy particle collisions (2014)
    American Physical Society (APS)
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    Publication Date: 2014-09-05
    Description: Author(s): J. Gariel, N. O. Santos, and J. Silk Particle collisions in black hole ergoregions may result in extremely high center-of-mass energies that could probe new physics if escape to infinity were possible. Here we show that some geodesics at high inclinations to the equatorial plane may be unbound. Hence a finite flux of annihilation debri... [Phys. Rev. D 90, 063505] Published Thu Sep 04, 2014
    Keywords: Cosmology
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 8
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    Extracting primordial density fluctuations (1998)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1998-06-05
    Description: The combination of detections of anisotropy in cosmic microwave background radiation and observations of the large-scale distribution of galaxies probes the primordial density fluctuations of the universe on spatial scales varying by three orders of magnitude. These data are found to be inconsistent with the predictions of several popular cosmological models. Agreement between the data and the cold + hot dark matter model, however, suggests that a significant fraction of the matter in the universe may consist of massive neutrinos.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gawiser -- Silk -- New York, N.Y. -- Science. 1998 May 29;280(5368):1405-11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉E. Gawiser is at the Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA. E-mail: gawiser@astron. berkeley.edu. J. Silk is at the Departments of Physics and Astronomy and the Center for Particle Astrophysics, Univ.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9603724" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Interstellar Processes. David J. Hollenbach and Harley A. Thronson, Jr., Eds. Reidel, Dordrecht, 1987 (U.S. distributor, Kluwer, Norwell, MA). xiv, 807 pp., illus. $139. Astrophysics and Space Science Library, vol. 134. From a symposium, Grand Teton National Park, WY, July 1986; Physical Processes In Interstellar Clouds. G. E. Morfill and M. Scholer, Eds. Reidel, Dordrecht, 1987 (U.S. distributor, Kluwer, Norwell, MA). x, 554 pp., illus. $92. NATO Advanced Science Institutes Series C, vol. 210. From an institute, Irsee, F.R.G., Aug. 1986 (1988)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1988-02-12
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Silk, J -- New York, N.Y. -- Science. 1988 Feb 12;239(4841):802-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17832946" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    The role of black holes in galaxy formation and evolution (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-07-10
    Description: Virtually all massive galaxies, including our own, host central black holes ranging in mass from millions to billions of solar masses. The growth of these black holes releases vast amounts of energy that powers quasars and other weaker active galactic nuclei. A tiny fraction of this energy, if absorbed by the host galaxy, could halt star formation by heating and ejecting ambient gas. A central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies, which typically have little cold gas and few young stars, unlike spiral galaxies.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cattaneo, A -- Faber, S M -- Binney, J -- Dekel, A -- Kormendy, J -- Mushotzky, R -- Babul, A -- Best, P N -- Bruggen, M -- Fabian, A C -- Frenk, C S -- Khalatyan, A -- Netzer, H -- Mahdavi, A -- Silk, J -- Steinmetz, M -- Wisotzki, L -- England -- Nature. 2009 Jul 9;460(7252):213-9. doi: 10.1038/nature08135.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany. acattaneo@aip.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19587763" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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