R. Allison - Oxford

R. Allison
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Name
R. Allison
Affiliation
Oxford
City
Oxford
Country
United Kingdom

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Cosmology and Nongalactic Astrophysics (21)
 
Astrophysics of Galaxies (12)
 
Instrumentation and Methods for Astrophysics (5)
 
High Energy Physics - Phenomenology (3)
 
General Relativity and Quantum Cosmology (2)
 
Solar and Stellar Astrophysics (1)
 
High Energy Physics - Theory (1)

Publications Authored By R. Allison

2017Apr
Authors: C. Burigana, C. S. Carvalho, T. Trombetti, A. Notari, M. Quartin, G. De Gasperis, A. Buzzelli, N. Vittorio, G. De Zotti, P. de Bernardis, J. Chluba, M. Bilicki, L. Danese, J. Delabrouille, L. Toffolatti, A. Lapi, M. Negrello, P. Mazzotta, D. Scott, D. Contreras, A. Achucarro, P. Ade, R. Allison, M. Ashdown, M. Ballardini, A. J. Banday, R. Banerji, J. Bartlett, N. Bartolo, S. Basak, M. Bersanelli, A. Bonaldi, M. Bonato, J. Borrill, F. Bouchet, F. Boulanger, T. Brinckmann, M. Bucher, P. Cabella, Z. -Y. Cai, M. Calvo, G. Castellano, A. Challinor, S. Clesse, I. Colantoni, A. Coppolecchia, M. Crook, G. D'Alessandro, J. -M. Diego, A. Di Marco, E. Di Valentino, J. Errard, S. Feeney, R. Fernandez-Cobos, S. Ferraro, F. Finelli, F. Forastieri, S. Galli, R. Genova-Santos, M. Gerbino, J. Gonzalez-Nuevo, S. Grandis, J. Greenslade, S. Hagstotz, S. Hanany, W. Handley, C. Hernandez-Monteagudo, C. Hervias-Caimapo, M. Hills, E. Hivon, K. Kiiveri, T. Kisner, T. Kitching, M. Kunz, H. Kurki-Suonio, L. Lamagna, A. Lasenby, M. Lattanzi, J. Lesgourgues, M. Liguori, V. Lindholm, M. Lopez-Caniego, G. Luzzi, B. Maffei, N. Mandolesi, E. Martinez-Gonzalez, C. J. A. P. Martins, S. Masi, D. McCarthy, A. Melchiorri, J. -B. Melin, D. Molinari, A. Monfardini, P. Natoli, A. Paiella, D. Paoletti, G. Patanchon, M. Piat, G. Pisano, L. Polastri, G. Polenta, A. Pollo, V. Poulin, M. Remazeilles, M. Roman, J. -A. Rubino-Martin, L. Salvati, A. Tartari, M. Tomasi, D. Tramonte, N. Trappe, C. Tucker, J. Valiviita, R. Van de Weijgaert, B. van Tent, V. Vennin, P. Vielva, K. Young, M. Zannoni, for the CORE Collaboration

We discuss the effects on the CMB, CIB, and thermal SZ effect due to the peculiar motion of an observer with respect to the CMB rest frame, which induces boosting effects. We investigate the scientific perspectives opened by future CMB space missions, focussing on the CORE proposal. The improvements in sensitivity offered by a mission like CORE, together with its high resolution over a wide frequency range, will provide a more accurate estimate of the CMB dipole. Read More

2017Apr
Authors: M. Remazeilles, A. J. Banday, C. Baccigalupi, S. Basak, A. Bonaldi, G. De Zotti, J. Delabrouille, C. Dickinson, H. K. Eriksen, J. Errard, R. Fernandez-Cobos, U. Fuskeland, C. Hervías-Caimapo, M. López-Caniego, E. Martinez-González, M. Roman, P. Vielva, I. Wehus, A. Achucarro, P. Ade, R. Allison, M. Ashdown, M. Ballardini, R. Banerji, N. Bartolo, J. Bartlett, D. Baumann, M. Bersanelli, M. Bonato, J. Borrill, F. Bouchet, F. Boulanger, T. Brinckmann, M. Bucher, C. Burigana, A. Buzzelli, Z. -Y. Cai, M. Calvo, C. -S. Carvalho, G. Castellano, A. Challinor, J. Chluba, S. Clesse, I. Colantoni, A. Coppolecchia, M. Crook, G. D'Alessandro, P. de Bernardis, G. de Gasperis, J. -M. Diego, E. Di Valentino, S. Feeney, S. Ferraro, F. Finelli, F. Forastieri, S. Galli, R. Genova-Santos, M. Gerbino, J. González-Nuevo, S. Grandis, J. Greenslade, S. Hagstotz, S. Hanany, W. Handley, C. Hernandez-Monteagudo, M. Hills, E. Hivon, K. Kiiveri, T. Kisner, T. Kitching, M. Kunz, H. Kurki-Suonio, L. Lamagna, A. Lasenby, M. Lattanzi, J. Lesgourgues, A. Lewis, M. Liguori, V. Lindholm, G. Luzzi, B. Maffei, C. J. A. P. Martins, S. Masi, D. McCarthy, J. -B. Melin, A. Melchiorri, D. Molinari, A. Monfardini, P. Natoli, M. Negrello, A. Notari, A. Paiella, D. Paoletti, G. Patanchon, M. Piat, G. Pisano, L. Polastri, G. Polenta, A. Pollo, V. Poulin, M. Quartin, J. -A. Rubino-Martin, L. Salvati, A. Tartari, M. Tomasi, D. Tramonte, N. Trappe, T. Trombetti, C. Tucker, J. Valiviita, R. Van de Weijgaert, B. van Tent, V. Vennin, N. Vittorio, K. Young, for the CORE collaboration

We demonstrate that, for the baseline design of the CORE satellite mission, the polarized foregrounds can be controlled at the level required to allow the detection of the primordial cosmic microwave background (CMB) $B$-mode polarization with the desired accuracy at both reionization and recombination scales, for tensor-to-scalar ratio values of $r\gtrsim 5\times 10^{-3}$. Under the assumption of perfect control of lensing effects, CORE would measure an unbiased estimate of $r=5\times 10^{-3}$ with an uncertainty of ${\sigma(r=5\times 10^{-3})=0.4\times 10^{-3}}$ after foreground cleaning. Read More

2017Mar
Authors: J. -B. Melin, A. Bonaldi, M. Remazeilles, S. Hagstotz, J. M. Diego, C. Hernández-Monteagudo, R. T. Génova-Santos, G. Luzzi, C. J. A. P. Martins, S. Grandis, J. J. Mohr, J. G. Bartlett, J. Delabrouille, S. Ferraro, D. Tramonte, J. A. Rubiño-Martín, J. F. Macìas-Pérez, A. Achúcarro, P. Ade, R. Allison, M. Ashdown, M. Ballardini, A. J. Banday, R. Banerji, N. Bartolo, S. Basak, J. Baselmans, K. Basu, R. A. Battye, D. Baumann, M. Bersanelli, M. Bonato, J. Borrill, F. Bouchet, F. Boulanger, T. Brinckmann, M. Bucher, C. Burigana, A. Buzzelli, Z. -Y. Cai, M. Calvo, C. S. Carvalho, M. G. Castellano, A. Challinor, J. Chluba, S. Clesse, S. Colafrancesco, I. Colantoni, A. Coppolecchia, M. Crook, G. D'Alessandro, P. de Bernardis, G. de Gasperis, M. De Petris, G. De Zotti, E. Di Valentino, J. Errard, S. M. Feeney, R. Fernández-Cobos, F. Finelli, F. Forastieri, S. Galli, M. Gerbino, J. González-Nuevo, J. Greenslade, S. Hanany, W. Handley, C. Hervias-Caimapo, M. Hills, E. Hivon, K. Kiiveri, T. Kisner, T. Kitching, M. Kunz, H. Kurki-Suonio, L. Lamagna, A. Lasenby, M. Lattanzi, A. M. C. Le Brun, J. Lesgourgues, A. Lewis, M. Liguori, V. Lindholm, M. Lopez-Caniego, B. Maffei, E. Martinez-Gonzalez, S. Masi, D. McCarthy, A. Melchiorri, D. Molinari, A. Monfardini, P. Natoli, M. Negrello, A. Notari, A. Paiella, D. Paoletti, G. Patanchon, M. Piat, G. Pisano, L. Polastri, G. Polenta, A. Pollo, V. Poulin, M. Quartin, M. Roman, L. Salvati, A. Tartari, M. Tomasi, N. Trappe, S. Triqueneaux, T. Trombetti, C. Tucker, J. Väliviita, R. van de Weygaert, B. Van Tent, V. Vennin, P. Vielva, N. Vittorio, J. Weller, K. Young, M. Zannoni, for the CORE collaboration

We examine the cosmological constraints that can be achieved with a galaxy cluster survey with the future CORE space mission. Using realistic simulations of the millimeter sky, produced with the latest version of the Planck Sky Model, we characterize the CORE cluster catalogues as a function of the main mission performance parameters. We pay particular attention to telescope size, key to improved angular resolution, and discuss the comparison and the complementarity of CORE with ambitious future ground-based CMB experiments that could be deployed in the next decade. Read More

2016Dec
Authors: CORE Collaboration, Fabio Finelli, Martin Bucher, Ana Achúcarro, Mario Ballardini, Nicola Bartolo, Daniel Baumann, Sébastien Clesse, Josquin Errard, Will Handley, Mark Hindmarsh, Kimmo Kiiveri, Martin Kunz, Anthony Lasenby, Michele Liguori, Daniela Paoletti, Christophe Ringeval, Jussi Väliviita, Bartjan van Tent, Vincent Vennin, Rupert Allison, Frederico Arroja, Marc Ashdown, A. J. Banday, Ranajoy Banerji, James G. Bartlett, Soumen Basak, Jochem Baselmans, Paolo de Bernardis, Marco Bersanelli, Anna Bonaldi, Julian Borril, François R. Bouchet, François Boulanger, Thejs Brinckmann, Carlo Burigana, Alessandro Buzzelli, Zhen-Yi Cai, Martino Calvo, Carla Sofia Carvalho, Gabriella Castellano, Anthony Challinor, Jens Chluba, Ivan Colantoni, Martin Crook, Giuseppe D'Alessandro, Guido D'Amico, Jacques Delabrouille, Vincent Desjacques, Gianfranco De Zotti, Jose Maria Diego, Eleonora Di Valentino, Stephen Feeney, James R. Fergusson, Raul Fernandez-Cobos, Simone Ferraro, Francesco Forastieri, Silvia Galli, Juan García-Bellido, Giancarlo de Gasperis, Ricardo T. Génova-Santos, Martina Gerbino, Joaquin González-Nuevo, Sebastian Grandis, Josh Greenslade, Steffen Hagstotz, Shaul Hanany, Dhiraj K. Hazra, Carlos Hernández-Monteagudo, Carlos Hervias-Caimapo, Matthew Hills, Eric Hivon, Bin Hu, Ted Kisner, Thomas Kitching, Ely D. Kovetz, Hannu Kurki-Suonio, Luca Lamagna, Massimiliano Lattanzi, Julien Lesgourgues, Antony Lewis, Valtteri Lindholm, Joanes Lizarraga, Marcos López-Caniego, Gemma Luzzi, Bruno Maffei, Nazzareno Mandolesi, Enrique Martínez-González, Carlos J. A. P. Martins, Silvia Masi, Darragh McCarthy, Sabino Matarrese, Alessandro Melchiorri, Jean-Baptiste Melin, Diego Molinari, Alessandro Monfardini, Paolo Natoli, Mattia Negrello, Alessio Notari, Filippo Oppizzi, Alessandro Paiella, Enrico Pajer, Guillaume Patanchon, Subodh P. Patil, Michael Piat, Giampaolo Pisano, Linda Polastri, Gianluca Polenta, Agnieszka Pollo, Vivian Poulin, Miguel Quartin, Andrea Ravenni, Mathieu Remazeilles, Alessandro Renzi, Diederik Roest, Matthieu Roman, Jose Alberto Rubiño-Martin, Laura Salvati, Alexei A. Starobinsky, Andrea Tartari, Gianmassimo Tasinato, Maurizio Tomasi, Jesús Torrado, Neil Trappe, Tiziana Trombetti, Carole Tucker, Marco Tucci, Jon Urrestilla, Rien van de Weygaert, Patricio Vielva, Nicola Vittorio, Karl Young

We forecast the scientific capabilities to improve our understanding of cosmic inflation of CORE, a proposed CMB space satellite submitted in response to the ESA fifth call for a medium-size mission opportunity. The CORE satellite will map the CMB anisotropies in temperature and polarization in 19 frequency channels spanning the range 60-600 GHz. CORE will have an aggregate noise sensitivity of $1. Read More

2016Nov
Authors: Eleonora Di Valentino, Thejs Brinckmann, Martina Gerbino, Vivian Poulin, François R. Bouchet, Julien Lesgourgues, Alessandro Melchiorri, Jens Chluba, Sebastien Clesse, Jacques Delabrouille, Cora Dvorkin, Francesco Forastieri, Silvia Galli, Deanna C. Hooper, Massimiliano Lattanzi, Carlos J. A. P. Martins, Laura Salvati, Giovanni Cabass, Andrea Caputo, Elena Giusarma, Eric Hivon, Paolo Natoli, Luca Pagano, Simone Paradiso, Jose Alberto Rubino-Martin, Ana Achucarro, Peter Ade, Rupert Allison, Frederico Arroja, Marc Ashdown, Mario Ballardini, A. J. Banday, Ranajoy Banerji, Nicola Bartolo, James G. Bartlett, Soumen Basak, Jochem Baselmans, Daniel Baumann, Paolo de Bernardis, Marco Bersanelli, Anna Bonaldi, Matteo Bonato, Julian Borrill, François Boulanger, Martin Bucher, Carlo Burigana, Alessandro Buzzelli, Zhen-Yi Cai, Martino Calvo, Carla Sofia Carvalho, Gabriella Castellano, Anthony Challinor, Ivan Charles, Ivan Colantoni, Alessandro Coppolecchia, Martin Crook, Giuseppe D'Alessandro, Marco De Petris, Gianfranco De Zotti, Josè Maria Diego, Josquin Errard, Stephen Feeney, Raul Fernandez-Cobos, Simone Ferraro, Fabio Finelli, Giancarlo de Gasperis, Ricardo T. Génova-Santos, Joaquin González-Nuevo, Sebastian Grandis, Josh Greenslade, Steffen Hagstotz, Shaul Hanany, Will Handley, Dhiraj K. Hazra, Carlos Hernández-Monteagudo, Carlos Hervias-Caimapo, Matthew Hills, Kimmo Kiiveri, Ted Kisner, Thomas Kitching, Martin Kunz, Hannu Kurki-Suonio, Luca Lamagna, Anthony Lasenby, Antony Lewis, Michele Liguori, Valtteri Lindholm, Marcos Lopez-Caniego, Gemma Luzzi, Bruno Maffei, Sylvain Martin, Enrique Martinez-Gonzalez, Silvia Masi, Darragh McCarthy, Jean-Baptiste Melin, Joseph J. Mohr, Diego Molinari, Alessandro Monfardini, Mattia Negrello, Alessio Notari, Alessandro Paiella, Daniela Paoletti, Guillaume Patanchon, Francesco Piacentini, Michael Piat, Giampaolo Pisano, Linda Polastri, Gianluca Polenta, Agnieszka Pollo, Miguel Quartin, Mathieu Remazeilles, Matthieu Roman, Christophe Ringeval, Andrea Tartari, Maurizio Tomasi, Denis Tramonte, Neil Trappe, Tiziana Trombetti, Carole Tucker, Jussi Väliviita, Rien van de Weygaert, Bartjan Van Tent, Vincent Vennin, Gérard Vermeulen, Patricio Vielva, Nicola Vittorio, Karl Young, Mario Zannoni, for the CORE collaboration

We forecast the main cosmological parameter constraints achievable with the CORE space mission which is dedicated to mapping the polarisation of the Cosmic Microwave Background (CMB). CORE was recently submitted in response to ESA's fifth call for medium-sized mission proposals (M5). Here we report the results from our pre-submission study of the impact of various instrumental options, in particular the telescope size and sensitivity level, and review the great, transformative potential of the mission as proposed. Read More

We report a measurement of the power spectrum of cosmic microwave background (CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter (ACTPol) CMB data. The CMB lensing power spectrum is extracted from both temperature and polarization data using quadratic estimators. We obtain results that are consistent with the expectation from the best-fit Planck LCDM model over a range of multipoles L=80-2100, with an amplitude of lensing A_lens = 1. Read More

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. Read More

2016Sep
Authors: G. De Zotti, J. Gonzalez-Nuevo, M. Lopez-Caniego, M. Negrello, J. Greenslade, C. Hernandez-Monteagudo, J. Delabrouille, Z. -Y. Cai, M. Bonato, A. Achucarro, P. Ade, R. Allison, M. Ashdown, M. Ballardini, A. J. Banday, R. Banerji, J. G. Bartlett, N. Bartolo, S. Basak, M. Bersanelli, M. Biesiada, M. Bilicki, A. Bonaldi, J. Borrill, F. Bouchet, F. Boulanger, T. Brinckmann, M. Bucher, C. Burigana, A. Buzzelli, M. Calvo, C. S. Carvalho, M. G. Castellano, A. Challinor, J. Chluba, D. L. Clements, S. Clesse, S. Colafrancesco, I. Colantoni, A. Coppolecchia, M. Crook, G. D'Alessandro, P. de Bernardis, G. de Gasperis, J. M. Diego, E. Di Valentino, J. Errard, S. M. Feeney, R. Fernandez-Cobos, S. Ferraro, F. Finelli, F. Forastieri, S. Galli, R. T. Genova-Santos, M. Gerbino, S. Grandis, S. Hagstotz, S. Hanany, W. Handley, C. Hervias-Caimapo, M. Hills, E. Hivon, K. Kiiveri, T. Kisner, T. Kitching, M. Kunz, H. Kurki-Suonio, G. Lagache, L. Lamagna, A. Lasenby, M. Lattanzi, A. Le Brun, J. Lesgourgues, A. Lewis, M. Liguori, V. Lindholm, G. Luzzi, B. Maffei, N. Mandolesi, E. Martinez-Gonzalez, C. J. A. P. Martins, S. Masi, M. Massardi, D. McCarthy, A. Melchiorri, J. -B. Melin, D. Molinari, A. Monfardini, P. Natoli, A. Notari, A. Paiella, D. Paoletti, R. B. Partridge, G. Patanchon, M. Piat, G. Pisano, L. Polastri, G. Polenta, A. Pollo, V. Poulin, M. Quartin, M. Remazeilles, M. Roman, G. Rossi, B. F. Roukema, J. -A. Rubino-Martin, L. Salvati, D. Scott, S. Serjeant, A. Tartari, L. Toffolatti, M. Tomasi, N. Trappe, S. Triqueneaux, T. Trombetti, M. Tucci, C. Tucker, J. Valiviita, R. van de Weygaert, B. Van Tent, V. Vennin, P. Vielva, N. Vittorio, K. Young, for the CORE collaboration

We discuss the potential of a next generation space-borne Cosmic Microwave Background (CMB) experiment for studies of extragalactic sources. Our analysis has particular bearing on the definition of the future space project, CORE, that has been submitted in response to ESA's call for a Medium-size mission opportunity as the successor of the Planck satellite. Even though the effective telescope size will be somewhat smaller than that of Planck, CORE will have a considerably better angular resolution at its highest frequencies, since, in contrast with Planck, it will be diffraction limited at all frequencies. Read More

Measurements of cosmic microwave background (CMB) anisotropies provide strong evidence for the existence of dark matter and dark energy. They can also test its composition, probing the energy density and particle mass of different dark-matter and dark-energy components. CMB data have already shown that ultra-light axions (ULAs) with mass in the range $10^{-32}~{\rm eV} \to 10^{-26}~{\rm eV}$ compose a fraction $< 0. Read More

Current constraints on spatial curvature show that it is dynamically negligible: $|\Omega_{\rm K}| \lesssim 5 \times 10^{-3}$ (95% CL). Neglecting it as a cosmological parameter would be premature however, as more stringent constraints on $\Omega_{\rm K}$ at around the $10^{-4}$ level would offer valuable tests of eternal inflation models and probe novel large-scale structure phenomena. This precision also represents the "curvature floor", beyond which constraints cannot be meaningfully improved due to the cosmic variance of horizon-scale perturbations. Read More

Advanced ACTPol is a polarization-sensitive upgrade for the 6 m aperture Atacama Cosmology Telescope (ACT), adding new frequencies and increasing sensitivity over the previous ACTPol receiver. In 2016, Advanced ACTPol will begin to map approximately half the sky in five frequency bands (28-230 GHz). Its maps of primary and secondary cosmic microwave background (CMB) anisotropies -- imaged in intensity and polarization at few arcminute-scale resolution -- will enable precision cosmological constraints and also a wide array of cross-correlation science that probes the expansion history of the universe and the growth of structure via gravitational collapse. Read More

Mass calibration uncertainty is the largest systematic effect for using clusters of galaxies to constrain cosmological parameters. We present weak lensing mass measurements from the Canada-France-Hawaii Telescope Stripe 82 Survey for galaxy clusters selected through their high signal-to-noise thermal Sunyaev-Zeldovich (tSZ) signal measured with the Atacama Cosmology Telescope (ACT). For a sample of 9 ACT clusters with a tSZ signal-to-noise greater than five the average weak lensing mass is $\left(4. Read More

Amongst standard model parameters that are constrained by cosmic microwave background (CMB) observations, the optical depth $\tau$ stands out as a nuisance parameter. While $\tau$ provides some crude limits on reionization, it also degrades constraints on other cosmological parameters. Here we explore how 21 cm cosmology---as a direct probe of reionization---can be used to independently predict $\tau$ in an effort to improve CMB parameter constraints. Read More

Future cosmological measurements should enable the sum of neutrino masses to be determined indirectly through their effects on the expansion rate of the Universe and the clustering of matter. We consider prospects for the gravitationally lensed Cosmic Microwave Background anisotropies and Baryon Acoustic Oscillations in the galaxy distribution, examining how the projected uncertainty of $\approx15$ meV on the neutrino mass sum (a 4$\sigma$ detection of the minimal mass) might be reached over the next decade. The current 1$\sigma$ uncertainty of $\approx 103$ meV (Planck-2015+BAO-15) will be improved by upcoming 'Stage-3' CMB experiments (S3+BAO-15: 44 meV), then upcoming BAO measurements (S3+DESI: 22 meV), and planned next-generation 'Stage 4' CMB experiments (S4+DESI: 15-19 meV, depending on angular range). Read More

Galaxy shapes are subject to distortions due to the tidal field of the Universe. The cross-correlation of galaxy lensing with the lensing of the Cosmic Microwave Background (CMB) cannot easily be separated from the cross-correlation of galaxy intrinsic shapes with CMB lensing. Previous work suggested that the intrinsic alignment contamination can be $15\%$ of this cross-spectrum for the CFHT Stripe 82 (CS82) and Atacama Cosmology Telescope surveys. Read More

In this paper we consider the issue of paradigm evaluation by applying Bayes' theorem along the following nested hierarchy of progressively more complex structures: i) parameter estimation (within a model), ii) model selection and comparison (within a paradigm), iii) paradigm evaluation. In such a hierarchy the Bayesian evidence works both as the posterior's normalization at a given level and as the likelihood function at the next level up. Whilst raising no objections to the standard application of the procedure at the two lowest levels, we argue that it should receive a considerable modification when evaluating paradigms, when testability and fitting data are equally important. Read More

We correlate the positions of radio galaxies in the FIRST survey with the CMB lensing convergence estimated from the Atacama Cosmology Telescope over 470 square degrees to determine the bias of these galaxies. We remove optically cross-matched sources below redshift $z=0.2$ to preferentially select Active Galactic Nuclei (AGN). Read More

We present a measurement of the gravitational lensing of the Cosmic Microwave Background (CMB) temperature and polarization fields obtained by cross-correlating the reconstructed convergence signal from the first season of ACTPol data at 146 GHz with Cosmic Infrared Background (CIB) fluctuations measured using the Planck satellite. Using an overlap area of 206 square degrees, we detect gravitational lensing of the CMB polarization by large-scale structure at a statistical significance of 4.5 sigma. Read More

We present evidence of the gravitational lensing of the cosmic microwave background by $10^{13}$ solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12,000 optically-selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles, and is favored over a null signal at 3. Read More

We report on measurements of the cosmic microwave background (CMB) and celestial polarization at 146 GHz made with the Atacama Cosmology Telescope Polarimeter (ACTPol) in its first three months of observing. Four regions of sky covering a total of 270 square degrees were mapped with an angular resolution of $1.3'$. Read More

The posterior probability distribution for a set of model parameters encodes all that the data have to tell us in the context of a given model; it is the fundamental quantity for Bayesian parameter estimation. In order to infer the posterior probability distribution we have to decide how to explore parameter space. Here we compare three prescriptions for how parameter space is navigated, discussing their relative merits. Read More

We present a new hybrid Smoothed Particle Hydrodynamics (SPH)/N-body method for modelling the collisional stellar dynamics of young clusters in a live gas background. By deriving the equations of motion from Lagrangian mechanics we obtain a formally conservative combined SPH/N-body scheme. The SPH gas particles are integrated with a 2nd order Leapfrog, and the stars with a 4th order Hermite scheme. Read More

We present deep Hubble Space Telescope/Wide Field and Planetary Camera 2 photometry of the young HD 97950 star cluster in the giant H {\sc ii} region NGC 3603. The data were obtained in 1997 and 2007 permitting us to derive membership based on proper motions of the stars. Our data are consistent with an age of 1 Myr for the HD 97950 cluster. Read More

We investigate how the properties of escaping stars are related to the initial conditions of their birth clusters. We find that the number of escaping stars, their spatial distribution, and their kinematics show a dependence on the initial conditions of the host cluster (substructure and virial ratio). Thus the properties of escaping stars can be used to inform us of the initial conditions of star formation, and also provide a window into the dynamical history of star clusters. Read More

We investigate the formation of protostellar clusters during the collapse of dense molecular cloud cores with a focus on the evolution of potential and kinetic energy, the degree of substructure, and the early phase of mass segregation. Our study is based on a series of hydrodynamic simulations of dense cores, where we vary the initial density profile and the initial turbulent velocity. In the three-dimensional adaptive mesh refinement simulations, we follow the dynamical formation of filaments and protostars until a star formation efficiency of 20%. Read More

2011Aug
Affiliations: 1ETH Zurich, Switzerland, 2University of Sheffield, UK, 3ITA, Heidelberg, Germany

Observations and theory suggest that star clusters can form in a subvirial (cool) state and are highly substructured. Such initial conditions have been proposed to explain the level of mass segregation in clusters through dynamics, and have also been successful in explaining the origin of trapezium-like systems. In this paper we investigate, using N-body simulations, whether such a dynamical scenario is consistent with the observed binary properties in the Orion Nebula Cluster (ONC). Read More

We investigate the formation and evolution of high-order massive star multiples similar to the Trapezium in the Orion Nebula Cluster. We perform ensembles of N-body simulations of the evolution of N=1000 Orion-like clusters with initial conditions ranging from cool and clumpy to relatively smooth and relaxed. We find that trapezium-like systems are frequently formed in the first 2 Myr in initially cool and clumpy clusters and can survive for significant amounts of time in such clusters. Read More

We use the new minimum spanning tree (MST) method to look for mass segregation in the Taurus association. The method computes the ratio of MST lengths of any chosen subset of objects, including the most massive stars and brown dwarfs, to the MST lengths of random sets of stars and brown dwarfs in the cluster. This mass segregation ratio (Lambda_MSR) enables a quantitative measure of the spatial distribution of high-mass and low-mass stars, and brown dwarfs to be made in Taurus. Read More

Observations and theory both suggest that star clusters form sub-virial (cool) with highly sub-structured distributions. We perform a large ensemble of N-body simulations of moderate-sized (N=1000) cool, fractal clusters to investigate their early dynamical evolution. We find that cool, clumpy clusters dynamically mass segregate on a short timescale, that Trapezium-like massive higher-order multiples are commonly formed, and that massive stars are often ejected from clusters with velocities > 10 km/s (c. Read More

We discuss the observations and theory of star cluster formation to argue that clusters form dynamically cool (subvirial) and with substructure. We then perform an ensemble of simulations of cool, clumpy (fractal) clusters and show that they often dynamically mass segregate on timescales far shorter than expected from simple models. The mass segregation comes about through the production of a short-lived, but very dense core. Read More

We present a new method to detect and quantify mass segregation in star clusters. It compares the minimum spanning tree (MST) of massive stars with that of random stars. If mass segregation is present, the MST length of the most massive stars will be shorter than that of random stars. Read More