Wojciech Hellwing - ICC, Durham and ICM, Warsaw

Wojciech Hellwing
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Name
Wojciech Hellwing
Affiliation
ICC, Durham and ICM, Warsaw
City
Warsaw
Country
Poland

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Cosmology and Nongalactic Astrophysics (41)
 
Astrophysics of Galaxies (11)
 
High Energy Physics - Phenomenology (4)
 
General Relativity and Quantum Cosmology (3)
 
Instrumentation and Methods for Astrophysics (3)
 
Astrophysics (2)
 
High Energy Physics - Theory (1)
 
Physics - History of Physics (1)
 
Physics - Physics and Society (1)

Publications Authored By Wojciech Hellwing

The cosmic web is one of the most striking features of the distribution of galaxies and dark matter on the largest scales in the Universe. It is composed of dense regions packed full of galaxies, long filamentary bridges, flattened sheets and vast low density voids. The study of the cosmic web has focused primarily on the identification of such features, and on understanding the environmental effects on galaxy formation and halo assembly. Read More

We use a set of N-body simulations employing a modified gravity (MG) model with Vainshtein screening to study matter and halo hierarchical clustering. As test-case scenarios we consider two normal branch Dvali-Gabadadze-Porrati (nDGP) gravity models with mild and strong growth rate enhancement. We study higher-order correlation functions $\xi_n(R)$ up to $n=9$ and associated hierarchical amplitudes $S_n(R)\equiv\xi_n(R)/\sigma(R)^{2n-2}$. Read More

We elucidate the importance of the consistent treatment of gravity-model specific non-linearities when estimating the growth of cosmological structures from redshift space distortions (RSD). Within the context of standard perturbation theory (SPT), we compare the predictions of two theoretical templates with redshift space data from N-body simulations in the normal branch of DGP gravity (nDGP) and General Relativity (GR). The two templates correspond to the standard general relativistic perturbation equations and those same equations modelled within nDGP. Read More

We use a pair of high resolution N-body simulations implementing two dark matter models, namely the standard cold dark matter (CDM) cosmogony and a warm dark matter (WDM) alternative where the dark matter particle is a 1.5keV thermal relic. We combine these simulations with the GALFORM semi-analytical galaxy formation model in order to explore differences between the resulting galaxy populations. Read More

We present two-point correlation function statistics of the mass and the halos in the chameleon $f(R)$ modified gravity scenario using a series of large volume N-body simulations. Three distinct variations of $f(R)$ are considered (F4, F5 and F6) and compared to a fiducial $\Lambda$CDM model in the redshift range $z \in [0,1]$. We find that the matter clustering is indistinguishable for all models except for F4, which shows a significantly steeper slope. Read More

2016Nov
Affiliations: 1ICC, Durham, 2ICC, Durham, 3MPA, Garching, 4ICC, Durham, 5ICG, Portsmouth, 6ICG, Portsmouth, 7ICC, Durham, 8NAO, Beijing, ICG, Portsmouth

We describe and demonstrate the potential of a new and very efficient method for simulating certain classes of modified gravity theories, such as the widely studied $f(R)$ gravity models. High resolution simulations for such models are currently very slow due to the highly nonlinear partial differential equation that needs to be solved exactly to predict the modified gravitational force. This nonlinearity is partly inherent, but is also exacerbated by the specific numerical algorithm used, which employs a variable redefinition to prevent numerical instabilities. Read More

2016Oct
Affiliations: 1MPIA, UvA, Leiden, 2Durham, 3Leiden, 4LJMU, 5Durham, 6ICG Portsmouth, 7Durham, 8Victoria, 9Copenhagen, EPFL, 10Helsinki, 11Durham, 12Leiden, 13Durham

We study galaxy formation in sterile neutrino dark matter models that differ significantly from both cold and from `warm thermal relic' models. We use the EAGLE code to carry out hydrodynamic simulations of the evolution of pairs of galaxies chosen to resemble the Local Group, as part of the APOSTLE simulations project. We compare cold dark matter (CDM) with two sterile neutrino models with 7 keV mass: one, the warmest among all models of this mass (LA120) and the other, a relatively cold case (LA10). Read More

2016Oct
Authors: DESI Collaboration, Amir Aghamousa, Jessica Aguilar, Steve Ahlen, Shadab Alam, Lori E. Allen, Carlos Allende Prieto, James Annis, Stephen Bailey, Christophe Balland, Otger Ballester, Charles Baltay, Lucas Beaufore, Chris Bebek, Timothy C. Beers, Eric F. Bell, José Luis Bernal, Robert Besuner, Florian Beutler, Chris Blake, Hannes Bleuler, Michael Blomqvist, Robert Blum, Adam S. Bolton, Cesar Briceno, David Brooks, Joel R. Brownstein, Elizabeth Buckley-Geer, Angela Burden, Etienne Burtin, Nicolas G. Busca, Robert N. Cahn, Yan-Chuan Cai, Laia Cardiel-Sas, Raymond G. Carlberg, Pierre-Henri Carton, Ricard Casas, Francisco J. Castander, Jorge L. Cervantes-Cota, Todd M. Claybaugh, Madeline Close, Carl T. Coker, Shaun Cole, Johan Comparat, Andrew P. Cooper, M. -C. Cousinou, Martin Crocce, Jean-Gabriel Cuby, Daniel P. Cunningham, Tamara M. Davis, Kyle S. Dawson, Axel de la Macorra, Juan De Vicente, Timothée Delubac, Mark Derwent, Arjun Dey, Govinda Dhungana, Zhejie Ding, Peter Doel, Yutong T. Duan, Anne Ealet, Jerry Edelstein, Sarah Eftekharzadeh, Daniel J. Eisenstein, Ann Elliott, Stéphanie Escoffier, Matthew Evatt, Parker Fagrelius, Xiaohui Fan, Kevin Fanning, Arya Farahi, Jay Farihi, Ginevra Favole, Yu Feng, Enrique Fernandez, Joseph R. Findlay, Douglas P. Finkbeiner, Michael J. Fitzpatrick, Brenna Flaugher, Samuel Flender, Andreu Font-Ribera, Jaime E. Forero-Romero, Pablo Fosalba, Carlos S. Frenk, Michele Fumagalli, Boris T. Gaensicke, Giuseppe Gallo, Juan Garcia-Bellido, Enrique Gaztanaga, Nicola Pietro Gentile Fusillo, Terry Gerard, Irena Gershkovich, Tommaso Giannantonio, Denis Gillet, Guillermo Gonzalez-de-Rivera, Violeta Gonzalez-Perez, Shelby Gott, Or Graur, Gaston Gutierrez, Julien Guy, Salman Habib, Henry Heetderks, Ian Heetderks, Katrin Heitmann, Wojciech A. Hellwing, David A. Herrera, Shirley Ho, Stephen Holland, Klaus Honscheid, Eric Huff, Timothy A. Hutchinson, Dragan Huterer, Ho Seong Hwang, Joseph Maria Illa Laguna, Yuzo Ishikawa, Dianna Jacobs, Niall Jeffrey, Patrick Jelinsky, Elise Jennings, Linhua Jiang, Jorge Jimenez, Jennifer Johnson, Richard Joyce, Eric Jullo, Stéphanie Juneau, Sami Kama, Armin Karcher, Sonia Karkar, Robert Kehoe, Noble Kennamer, Stephen Kent, Martin Kilbinger, Alex G. Kim, David Kirkby, Theodore Kisner, Ellie Kitanidis, Jean-Paul Kneib, Sergey Koposov, Eve Kovacs, Kazuya Koyama, Anthony Kremin, Richard Kron, Luzius Kronig, Andrea Kueter-Young, Cedric G. Lacey, Robin Lafever, Ofer Lahav, Andrew Lambert, Michael Lampton, Martin Landriau, Dustin Lang, Tod R. Lauer, Jean-Marc Le Goff, Laurent Le Guillou, Auguste Le Van Suu, Jae Hyeon Lee, Su-Jeong Lee, Daniela Leitner, Michael Lesser, Michael E. Levi, Benjamin L'Huillier, Baojiu Li, Ming Liang, Huan Lin, Eric Linder, Sarah R. Loebman, Zarija Lukić, Jun Ma, Niall MacCrann, Christophe Magneville, Laleh Makarem, Marc Manera, Christopher J. Manser, Robert Marshall, Paul Martini, Richard Massey, Thomas Matheson, Jeremy McCauley, Patrick McDonald, Ian D. McGreer, Aaron Meisner, Nigel Metcalfe, Timothy N. Miller, Ramon Miquel, John Moustakas, Adam Myers, Milind Naik, Jeffrey A. Newman, Robert C. Nichol, Andrina Nicola, Luiz Nicolati da Costa, Jundan Nie, Gustavo Niz, Peder Norberg, Brian Nord, Dara Norman, Peter Nugent, Thomas O'Brien, Minji Oh, Knut A. G. Olsen, Cristobal Padilla, Hamsa Padmanabhan, Nikhil Padmanabhan, Nathalie Palanque-Delabrouille, Antonella Palmese, Daniel Pappalardo, Isabelle Pâris, Changbom Park, Anna Patej, John A. Peacock, Hiranya V. Peiris, Xiyan Peng, Will J. Percival, Sandrine Perruchot, Matthew M. Pieri, Richard Pogge, Jennifer E. Pollack, Claire Poppett, Francisco Prada, Abhishek Prakash, Ronald G. Probst, David Rabinowitz, Anand Raichoor, Chang Hee Ree, Alexandre Refregier, Xavier Regal, Beth Reid, Kevin Reil, Mehdi Rezaie, Constance M. Rockosi, Natalie Roe, Samuel Ronayette, Aaron Roodman, Ashley J. Ross, Nicholas P. Ross, Graziano Rossi, Eduardo Rozo, Vanina Ruhlmann-Kleider, Eli S. Rykoff, Cristiano Sabiu, Lado Samushia, Eusebio Sanchez, Javier Sanchez, David J. Schlegel, Michael Schneider, Michael Schubnell, Aurélia Secroun, Uros Seljak, Hee-Jong Seo, Santiago Serrano, Arman Shafieloo, Huanyuan Shan, Ray Sharples, Michael J. Sholl, William V. Shourt, Joseph H. Silber, David R. Silva, Martin M. Sirk, Anze Slosar, Alex Smith, George F. Smoot, Debopam Som, Yong-Seon Song, David Sprayberry, Ryan Staten, Andy Stefanik, Gregory Tarle, Suk Sien Tie, Jeremy L. Tinker, Rita Tojeiro, Francisco Valdes, Octavio Valenzuela, Monica Valluri, Mariana Vargas-Magana, Licia Verde, Alistair R. Walker, Jiali Wang, Yuting Wang, Benjamin A. Weaver, Curtis Weaverdyck, Risa H. Wechsler, David H. Weinberg, Martin White, Qian Yang, Christophe Yeche, Tianmeng Zhang, Gong-Bo Zhao, Yi Zheng, Xu Zhou, Zhimin Zhou, Yaling Zhu, Hu Zou, Ying Zu

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1. Read More

2016Oct
Authors: DESI Collaboration, Amir Aghamousa, Jessica Aguilar, Steve Ahlen, Shadab Alam, Lori E. Allen, Carlos Allende Prieto, James Annis, Stephen Bailey, Christophe Balland, Otger Ballester, Charles Baltay, Lucas Beaufore, Chris Bebek, Timothy C. Beers, Eric F. Bell, José Luis Bernal, Robert Besuner, Florian Beutler, Chris Blake, Hannes Bleuler, Michael Blomqvist, Robert Blum, Adam S. Bolton, Cesar Briceno, David Brooks, Joel R. Brownstein, Elizabeth Buckley-Geer, Angela Burden, Etienne Burtin, Nicolas G. Busca, Robert N. Cahn, Yan-Chuan Cai, Laia Cardiel-Sas, Raymond G. Carlberg, Pierre-Henri Carton, Ricard Casas, Francisco J. Castander, Jorge L. Cervantes-Cota, Todd M. Claybaugh, Madeline Close, Carl T. Coker, Shaun Cole, Johan Comparat, Andrew P. Cooper, M. -C. Cousinou, Martin Crocce, Jean-Gabriel Cuby, Daniel P. Cunningham, Tamara M. Davis, Kyle S. Dawson, Axel de la Macorra, Juan De Vicente, Timothée Delubac, Mark Derwent, Arjun Dey, Govinda Dhungana, Zhejie Ding, Peter Doel, Yutong T. Duan, Anne Ealet, Jerry Edelstein, Sarah Eftekharzadeh, Daniel J. Eisenstein, Ann Elliott, Stéphanie Escoffier, Matthew Evatt, Parker Fagrelius, Xiaohui Fan, Kevin Fanning, Arya Farahi, Jay Farihi, Ginevra Favole, Yu Feng, Enrique Fernandez, Joseph R. Findlay, Douglas P. Finkbeiner, Michael J. Fitzpatrick, Brenna Flaugher, Samuel Flender, Andreu Font-Ribera, Jaime E. Forero-Romero, Pablo Fosalba, Carlos S. Frenk, Michele Fumagalli, Boris T. Gaensicke, Giuseppe Gallo, Juan Garcia-Bellido, Enrique Gaztanaga, Nicola Pietro Gentile Fusillo, Terry Gerard, Irena Gershkovich, Tommaso Giannantonio, Denis Gillet, Guillermo Gonzalez-de-Rivera, Violeta Gonzalez-Perez, Shelby Gott, Or Graur, Gaston Gutierrez, Julien Guy, Salman Habib, Henry Heetderks, Ian Heetderks, Katrin Heitmann, Wojciech A. Hellwing, David A. Herrera, Shirley Ho, Stephen Holland, Klaus Honscheid, Eric Huff, Timothy A. Hutchinson, Dragan Huterer, Ho Seong Hwang, Joseph Maria Illa Laguna, Yuzo Ishikawa, Dianna Jacobs, Niall Jeffrey, Patrick Jelinsky, Elise Jennings, Linhua Jiang, Jorge Jimenez, Jennifer Johnson, Richard Joyce, Eric Jullo, Stéphanie Juneau, Sami Kama, Armin Karcher, Sonia Karkar, Robert Kehoe, Noble Kennamer, Stephen Kent, Martin Kilbinger, Alex G. Kim, David Kirkby, Theodore Kisner, Ellie Kitanidis, Jean-Paul Kneib, Sergey Koposov, Eve Kovacs, Kazuya Koyama, Anthony Kremin, Richard Kron, Luzius Kronig, Andrea Kueter-Young, Cedric G. Lacey, Robin Lafever, Ofer Lahav, Andrew Lambert, Michael Lampton, Martin Landriau, Dustin Lang, Tod R. Lauer, Jean-Marc Le Goff, Laurent Le Guillou, Auguste Le Van Suu, Jae Hyeon Lee, Su-Jeong Lee, Daniela Leitner, Michael Lesser, Michael E. Levi, Benjamin L'Huillier, Baojiu Li, Ming Liang, Huan Lin, Eric Linder, Sarah R. Loebman, Zarija Lukić, Jun Ma, Niall MacCrann, Christophe Magneville, Laleh Makarem, Marc Manera, Christopher J. Manser, Robert Marshall, Paul Martini, Richard Massey, Thomas Matheson, Jeremy McCauley, Patrick McDonald, Ian D. McGreer, Aaron Meisner, Nigel Metcalfe, Timothy N. Miller, Ramon Miquel, John Moustakas, Adam Myers, Milind Naik, Jeffrey A. Newman, Robert C. Nichol, Andrina Nicola, Luiz Nicolati da Costa, Jundan Nie, Gustavo Niz, Peder Norberg, Brian Nord, Dara Norman, Peter Nugent, Thomas O'Brien, Minji Oh, Knut A. G. Olsen, Cristobal Padilla, Hamsa Padmanabhan, Nikhil Padmanabhan, Nathalie Palanque-Delabrouille, Antonella Palmese, Daniel Pappalardo, Isabelle Pâris, Changbom Park, Anna Patej, John A. Peacock, Hiranya V. Peiris, Xiyan Peng, Will J. Percival, Sandrine Perruchot, Matthew M. Pieri, Richard Pogge, Jennifer E. Pollack, Claire Poppett, Francisco Prada, Abhishek Prakash, Ronald G. Probst, David Rabinowitz, Anand Raichoor, Chang Hee Ree, Alexandre Refregier, Xavier Regal, Beth Reid, Kevin Reil, Mehdi Rezaie, Constance M. Rockosi, Natalie Roe, Samuel Ronayette, Aaron Roodman, Ashley J. Ross, Nicholas P. Ross, Graziano Rossi, Eduardo Rozo, Vanina Ruhlmann-Kleider, Eli S. Rykoff, Cristiano Sabiu, Lado Samushia, Eusebio Sanchez, Javier Sanchez, David J. Schlegel, Michael Schneider, Michael Schubnell, Aurélia Secroun, Uros Seljak, Hee-Jong Seo, Santiago Serrano, Arman Shafieloo, Huanyuan Shan, Ray Sharples, Michael J. Sholl, William V. Shourt, Joseph H. Silber, David R. Silva, Martin M. Sirk, Anze Slosar, Alex Smith, George F. Smoot, Debopam Som, Yong-Seon Song, David Sprayberry, Ryan Staten, Andy Stefanik, Gregory Tarle, Suk Sien Tie, Jeremy L. Tinker, Rita Tojeiro, Francisco Valdes, Octavio Valenzuela, Monica Valluri, Mariana Vargas-Magana, Licia Verde, Alistair R. Walker, Jiali Wang, Yuting Wang, Benjamin A. Weaver, Curtis Weaverdyck, Risa H. Wechsler, David H. Weinberg, Martin White, Qian Yang, Christophe Yeche, Tianmeng Zhang, Gong-Bo Zhao, Yi Zheng, Xu Zhou, Zhimin Zhou, Yaling Zhu, Hu Zou, Ying Zu

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution $R= \lambda/\Delta\lambda$ between 2000 and 5500, depending on wavelength. Read More

2016Oct
Authors: Demitri Muna, Michael Alexander, Alice Allen, Richard Ashley, Daniel Asmus, Ruyman Azzollini, Michele Bannister, Rachael Beaton, Andrew Benson, G. Bruce Berriman, Maciej Bilicki, Peter Boyce, Joanna Bridge, Jan Cami, Eryn Cangi, Xian Chen, Nicholas Christiny, Christopher Clark, Michelle Collins, Johan Comparat, Neil Cook, Darren Croton, Isak Delberth Davids, Éric Depagne, John Donor, Leonardo A. dos Santos, Stephanie Douglas, Alan Du, Meredith Durbin, Dawn Erb, Daniel Faes, J. G. Fernández-Trincado, Anthony Foley, Sotiria Fotopoulou, Søren Frimann, Peter Frinchaboy, Rafael Garcia-Dias, Artur Gawryszczak, Elizabeth George, Sebastian Gonzalez, Karl Gordon, Nicholas Gorgone, Catherine Gosmeyer, Katie Grasha, Perry Greenfield, Rebekka Grellmann, James Guillochon, Mark Gurwell, Marcel Haas, Alex Hagen, Daryl Haggard, Tim Haines, Patrick Hall, Wojciech Hellwing, Edmund Christian Herenz, Samuel Hinton, Renee Hlozek, John Hoffman, Derek Holman, Benne Willem Holwerda, Anthony Horton, Cameron Hummels, Daniel Jacobs, Jens Juel Jensen, David Jones, Arna Karick, Luke Kelley, Matthew Kenworthy, Ben Kitchener, Dominik Klaes, Saul Kohn, Piotr Konorski, Coleman Krawczyk, Kyler Kuehn, Teet Kuutma, Michael T. Lam, Richard Lane, Jochen Liske, Diego Lopez-Camara, Katherine Mack, Sam Mangham, Qingqing Mao, David J. E. Marsh, Cecilia Mateu, Loïc Maurin, James McCormac, Ivelina Momcheva, Hektor Monteiro, Michael Mueller, Roberto Munoz, Rohan Naidu, Nicholas Nelson, Christian Nitschelm, Chris North, Juan Nunez-Iglesias, Sara Ogaz, Russell Owen, John Parejko, Vera Patrício, Joshua Pepper, Marshall Perrin, Timothy Pickering, Jennifer Piscionere, Richard Pogge, Radek Poleski, Alkistis Pourtsidou, Adrian M. Price-Whelan, Meredith L. Rawls, Shaun Read, Glen Rees, Hanno Rein, Thomas Rice, Signe Riemer-Sørensen, Naum Rusomarov, Sebastian F. Sanchez, Miguel Santander-García, Gal Sarid, William Schoenell, Aleks Scholz, Robert L. Schuhmann, William Schuster, Peter Scicluna, Marja Seidel, Lijing Shao, Pranav Sharma, Aleksandar Shulevski, David Shupe, Cristóbal Sifón, Brooke Simmons, Manodeep Sinha, Ian Skillen, Bjoern Soergel, Thomas Spriggs, Sundar Srinivasan, Abigail Stevens, Ole Streicher, Eric Suchyta, Joshua Tan, O. Grace Telford, Romain Thomas, Chiara Tonini, Grant Tremblay, Sarah Tuttle, Tanya Urrutia, Sam Vaughan, Miguel Verdugo, Alexander Wagner, Josh Walawender, Andrew Wetzel, Kyle Willett, Peter K. G. Williams, Guang Yang, Guangtun Zhu, Andrea Zonca

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Read More

2016Sep

We assess the effect of the local large scale structure on the estimation of two-point statistics of the observed radial peculiar velocities of galaxies. A large N-body simulation is used to examine these statistics from the perspective of random observers as well as "Local Group (LG)-like" observers conditioned to reside in an environment resembling the observed universe within 20 Mpc. The local environment systematically distorts the shape and amplitude of velocity statistics with respect to ensemble-averaged measurements made by a Copernican (random) observer. Read More

2016Apr
Affiliations: 1ICC, Durham, 2ICG, Portsmouth, 3ICC, Durham, 4ICC, Durham, 5GRAPPA, Amsterdam, 6ICC, Durham, 7ICC, Durham, 8ICG, Portsmouth, 9NAOC & ICC, Durham

We use the Copernicus Complexio (COCO) high resolution $N$-body simulations to investigate differences in the properties of small-scale structures in the standard cold dark matter (CDM) model and in a model with a cutoff in the initial power spectrum of density fluctuations consistent with both a thermally produced warm dark matter (WDM) particle or a sterile neutrino with mass 7 keV and leptogenesis parameter $L_6=8.7$. The latter corresponds to the "coldest" model with this sterile neutrino mass compatible with the identification of the recently detected 3. Read More

We use the EAGLE galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales $k{\stackrel{>}{{}_\sim}} 4{h\,{\rm Mpc}^{-1}}$ the effect of baryons on the amplitude of the total matter power spectrum is greater than $1\%$. The back-reaction of baryons affects the density field of the dark matter at the level of $\sim3\%$ on scales of $1\leq k/({h\,{\rm Mpc}^{-1}})\leq 5$. Read More

We use a suite of cosmological simulations to study the mass-concentration-redshift relation, $c({\rm M},z)$, of dark matter halos. Our simulations include standard $\Lambda$-cold dark matter (CDM) models, and additional runs with truncated power spectra, consistent with a thermal warm dark matter (WDM) scenario. We find that the mass profiles of CDM and WDM halos are self-similar and well approximated by the Einasto profile. Read More

The cold dark matter (CDM) cosmological model unambigously predicts that a large number of haloes should survive as subhaloes when they are accreted into a larger halo. The CDM model would be ruled out if such substructures were shown not to exist. By contrast, if the dark matter consists of warm particles (WDM), then below a threshold mass that depends on the particle mass far fewer substructures would be present. Read More

2015Jul
Affiliations: 1ICC, Durham, 2ICC, Durham and ICM, Warsaw, 3ICC, Durham, 4ICC, Durham, 5GRAPPA, Amsterdam, 6ICC, Durham, 7ICC, Durham

The recent detection of a 3.5 keV X-ray line from the centres of galaxies and clusters by Bulbul et al. (2014a) and Boyarsky et al. Read More

Self-consistent ${\it N}$-body simulations of modified gravity models are a key ingredient to obtain rigorous constraints on deviations from General Relativity using large-scale structure observations. This paper provides the first detailed comparison of the results of different ${\it N}$-body codes for the $f(R)$, DGP, and Symmetron models, starting from the same initial conditions. We find that the fractional deviation of the matter power spectrum from $\Lambda$CDM agrees to better than $1\%$ up to $k \sim 5-10~h/{\rm Mpc}$ between the different codes. Read More

2015Jun
Affiliations: 1ICC Durham, 2ICC Durham, 3ICC Durham, 4NAO Beijing, 5ICC Durham, 6ICC Durham, 7ICC Durham, 8ICC Durham

The detection of planar structures within the satellite systems of both the Milky Way (MW) and Andromeda (M31) has been reported as being in stark contradiction to the predictions of the standard cosmological model ($\Lambda$CDM). Given the ambiguity in defining a planar configuration, it is unclear how to interpret the low incidence of the MW and M31 planes in $\Lambda$CDM. We investigate the prevalence of satellite planes around galactic mass haloes identified in high resolution cosmological simulations. Read More

We introduce Copernicus Complexio (COCO), a high-resolution cosmological N-body simulation of structure formation in the $\Lambda{\rm CDM}{}$ model. COCO follows an approximately spherical region of radius $\sim 17.4h^{-1}\,{\rm Mpc}$ embedded in a much larger periodic cube that is followed at lower resolution. Read More

We apply a semi-analytic galaxy formation model to two high resolution cosmological N-body simulations to investigate analogues of the Milky Way system. We select these according to observed properties of the Milky Way rather than by halo mass as in most previous work. For disk-dominated central galaxies with stellar mass (5--7) x 10d10Msun, the median host halo mass is 1. Read More

2015Mar
Affiliations: 1ICC, Durham, 2ICC, Durham, 3ICC, Durham, 4NAOC & ICC, Durham, 5ICC, Durham

We investigate the properties of dark matter haloes and subhaloes in an $f(R)$ gravity model with $|f_{R0}|=10^{-6}$, using a very high-resolution N-body simulation. The model is a borderline between being cosmologically interesting and yet still consistent with current data. We find that the halo mass function in this model has a maximum 20% enhancement compared with the $\Lambda$CDM predictions between $z=1$ and $z=0$. Read More

We present results of analysis of the dark matter (DM) pairwise velocity statistics in different Cosmic Web environments. We use the DM velocity and density field from the Millennium 2 simulation together with the NEXUS+ algorithm to segment the simulation volume into voxels uniquely identifying one of the four possible environments: nodes, filaments, walls or cosmic voids. We show that the PDFs of the mean infall velocities $v_{12}$ as well as its spatial dependence together with the perpendicular and parallel velocity dispersions bear a significant signal of the large-scale structure environment in which DM particle pairs are embedded. Read More

Numerical simulations in modified gravity have commonly been performed under the quasi-static approximation -- that is, by neglecting the effect of time derivatives in the equation of motion of the scalar field that governs the fifth force in a given modified gravity theory. To test the validity of this approximation, we analyse the case of $f(R)$ gravity beyond this quasi-static limit, by considering effects, if any, these terms have in the matter and velocity divergence cosmic fields. To this end, we use the adaptive mesh refinement code ECOSMOG to study three variants ($|f_{R}|= 10^{-4}[$F4$], 10^{-5}[$F5$]$ and $10^{-6}[$F6$]$) of the Hu-Sawicki $f(R)$ gravity model, each of which refers to a different magnitude for the scalar field that generates the fifth force. Read More

2014Aug
Affiliations: 1ICC and IPPP, Durham, 2ICC, Durham, 3ICC, Durham, ICM, Warsaw, 4ICC, Durham, 5IPPP, Durham

We study the nonlinear growth of structure in nonlocal gravity models with the aid of N-body simulation and the spherical collapse and halo models. We focus on a model in which the inverse-squared of the d'Alembertian operator acts on the Ricci scalar in the action. For fixed cosmological parameters, this model differs from $\Lambda{\rm CDM}$ by having a lower late-time expansion rate and an enhanced and time-dependent gravitational strength ($\sim 6\%$ larger today). Read More

2014May
Affiliations: 1ICC, Durham, 2ICC, Durham, 3Kapteyn Astronomical Institute, Groningen, 4ICC, Durham, 5Kapteyn Astronomical Institute, Groningen

We use the distribution of maximum circular velocities, $V_{max}$, of satellites in the Milky Way (MW) to constrain the virial mass, $M_{200}$, of the Galactic halo under an assumed prior of a $\Lambda$CDM universe. This is done by analysing the subhalo populations of a large sample of halos found in the Millennium II cosmological simulation. The observation that the MW has at most three subhalos with $V_{max}\ge30 km/s$ requires a halo mass $M_{200}\le1. Read More

2014May
Affiliations: 1ICC, Durham, 2ICC, Durham, 3Kapteyn Astronomical Institute, Groningen, 4ICC, Durham, 5Kapteyn Astronomical Institute, Groningen, 6ICC, Durham

We study the substructure population of Milky Way (MW)-mass halos in the $\Lambda$CDM cosmology using a novel procedure to extrapolate subhalo number statistics beyond the resolution limit of N-body simulations. The technique recovers the mean and the variance of the subhalo abundance, but not its spatial distribution. It extends the dynamic range over which precise statistical predictions can be made by the equivalent of performing a simulation with 50 times higher resolution, at no additional computational cost. Read More

2014Jan
Affiliations: 1ICC and IPPP, Durham, 2ICC, Durham, 3ICC, Durham, ICM, Warsaw, 4IfA, Edinburgh, 5ICC, Durham, 6IPPP, Durham

We investigate the performance of semi-analytical modelling of large-scale structure in Galileon gravity cosmologies using results from N-body simulations. We focus on the Cubic and Quartic Galileon models that provide a reasonable fit to CMB, SNIa and BAO data. We demonstrate that the Sheth-Tormen mass function and linear halo bias can be calibrated to provide a very good fit to our simulation results. Read More

The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution, $v_{12}$, are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion, $\sigma_{12}(r)$, is very sensitive to the presence of modified gravity. Read More

We develop a numerical algorithm to solve the high-order nonlinear derivative-coupling equation associated with the quartic Galileon model, and implement it in a modified version of the RAMSES N-body code to study the effect of the Galileon field on the large-scale matter clustering. The algorithm is tested for several matter field configurations with different symmetries, and works very well. This enables us to perform the first simulations for a quartic Galileon model which provides a good fit to the cosmic microwave background (CMB) anisotropy, supernovae and baryonic acoustic oscillations (BAO) data. Read More

We present the relation between the genus in cosmology and the Betti numbers for excursion sets of three- and two-dimensional smooth Gaussian random fields, and numerically investigate the Betti numbers as a function of threshold level. Betti numbers are topological invariants of figures that can be used to distinguish topological spaces. In the case of the excursion sets of a three-dimensional field there are three possibly non-zero Betti numbers; $\beta_0$ is the number of connected regions, $\beta_1$ is the number of circular holes, and $\beta_2$ is the number of three-dimensional voids. Read More

We study the topology of the Megaparsec Cosmic Web in terms of the scale-dependent Betti numbers, which formalize the topological information content of the cosmic mass distribution. While the Betti numbers do not fully quantify topology, they extend the information beyond conventional cosmological studies of topology in terms of genus and Euler characteristic. The richer information content of Betti numbers goes along the availability of fast algorithms to compute them. Read More

2013Jun
Affiliations: 1ICC and IPPP, Durham, 2ICC, Durham, 3ICC, Durham, ICM, Warsaw, 4ICC, Durham, 5IPPP, Durham

We model the linear and nonlinear growth of large scale structure in the Cubic Galileon gravity model, by running a suite of N-body cosmological simulations using the {\tt ECOSMOG} code. Our simulations include the Vainshtein screening effect, which reconciles the Cubic Galileon model with local tests of gravity. In the linear regime, the amplitude of the matter power spectrum increases by $\sim 25%$ with respect to the standard $\Lambda$CDM model today. Read More

We use a suite of high resolution state-of-the-art N-body Dark Matter simulations of chameleon $f(R)$ gravity to study the higher order volume averaged correlation functions $\bar{\xi_n}$ together with the hierarchical $n$-th order correlation amplitudes $S_n=\bar{\xi}_n/\bar{\xi}_2^{n-1}$ and density distribution functions (PDF). We show that under the non-linear modifications of gravity the hierarchical scaling of the reduced cumulants is preserved. This is however characterised by significant changes of both the $\bar{\xi_n}$ and $S_n$'s values and their scale dependence with respect to General Relativity gravity (GR). Read More

2013Feb

In this contribution we present the preliminary results regarding the non-linear BAO signal in higher-order statistics of the cosmic density field. We use ensembles of N-body simulations to show that the non-linear evolution changes the amplitudes of the BAO signal, but has a negligible effect on the scale of the BAO feature. The latter observation accompanied by the fact that the BAO feature amplitude roughly doubles as one moves to higher orders, suggests that the higher-order correlation amplitudes can be used as probe of the BAO signal. Read More

On 28th and 29th of January 2013 we held an international meeting in Zielona G\'ora (Poland) honouring the first anniversary of premature passing away^(1) of Professor Roman Juszkiewicz. We have celebrated an opening of a new seminar room at the University of Zielona G\'ora commemorated to the memory of Roman Juszkiewicz and we have shared our anecdotes and memories of this great scientist and friend. Here we want to present a limited and short memoir and obituary for Roman Juszkiewicz. Read More

Comparison of peculiar velocities of galaxies with their gravitational accelerations (induced by the density field) is one of the methods to constrain the redshift distortion parameter \beta=(\Omega_m^0.55)/b, where \Omega_m is the non-relativistic matter density parameter and b is the linear bias. In particular, one can use the motion of the Local Group (LG) for that purpose. Read More

We study the matter and velocity divergence power spectra in a f(R) gravity theory and their time evolution measured from several large-volume N-body simulations with varying box sizes and resolution. We find that accurate prediction of the matter power spectrum in f(R) gravity places stronger requirements on the simulation than is the case with LCDM, because of the nonlinear nature of the fifth force. Linear perturbation theory is shown to be a poor approximation for the f(R) models, except when the chameleon effect is very weak. Read More

In this study we show that the skewness S_3 of the cosmic density field contains a significant and potentially detectable and clean imprint of Baryonic Acoustic Oscillations. Although the BAO signal in the skewness has a lower amplitude than second order measures like the two-point correlation function and power spectrum, it has the advantage of a considerably lower sensitivity to systematic influences. Because it lacks a direct dependence on bias if this concerns simple linear bias, skewness will be considerably less beset by uncertainties due to galaxy bias. Read More

2011Nov

We investigate how long-range scalar interactions affect the properties of dark matter haloes. For doing so we employ the ReBEL model which implements an additional interaction between dark matter particles. On the phenomenological level this is equivalent to a modification of gravity. Read More

We introduce a new descriptor of the weblike pattern in the distribution of galaxies and matter: the scale dependent Betti numbers which formalize the topological information content of the cosmic mass distribution. While the Betti numbers do not fully quantify topology, they extend the information beyond conventional cosmological studies of topology in terms of genus and Euler characteristic used in earlier analyses of cosmological models. The richer information content of Betti numbers goes along with the availability of fast algorithms to compute them. Read More

In this work we investigate higher order statistics for the $\lcdm$ and ReBEL scalar-interacting dark matter models by analyzing $180\hmpc$ dark matter N-body simulation ensembles. The N-point correlation functions and the related hierarchical amplitudes, such as skewness and kurtosis, are computed using the Count-In-Cells method. Our studies demonstrate that the hierarchical amplitudes $S_n$ of the scalar-interacting dark matter model significantly deviate from the values in the $\lcdm$ cosmology on scales comparable and smaller then the screening length $r_s$ of a given scalar-interacting model. Read More

We investigate the effect of long-range scalar interactions in dark matter (DM) models of cosmic structure formation with a particular focus on the formation times of haloes. Utilising $N$-body simulations with $512^3$ DM particles we show that in our models dark matter haloes form substantially earlier: tracing objects up to redshift $z\sim6$ we find that the formation time, as characterised by the redshift $z_{1/2}$ at which the halo has assembled half of its final mass, is gradually shifted from $z_{1/2}\approx 1.83$ in the fiducial LCDM model to $z_{1/2}\approx 2. Read More

Based on a set of cosmological N-body simulations we analyze properties of the dark matter haloes (DM) in a galaxy mass range ($10^{11} - 10^{13} h^{-1}M_{\odot}$) in modified $\lcdm$ cosmology with additional dynamically screened scalar interactions in DM sector. Our simulations show that scalar interactions support picture of the Island Universe. Rapid structure formation processes are shifted into higher redshifts resulting in a much smaller accretion and merging rates for galactic haloes at low redshifts. Read More

We explore the possibility of improving the $\Lambda$CDM model at megaparsec scales by introducing a scalar interaction which increases the mutual gravitational attraction of dark matter particles. Using N-body simulations, we study the spatial distribution of dark matter particles and halos. We measure the effect of modifications in the Newton's gravity on properties of the two-point correlation function, the dark matter power spectrum, the cumulative halo mass function and density probability distribution functions. Read More

In this paper we present preliminary results from cosmological simulations of modified gravity in the dark matter sector. Our results show improvements over standard cold dark matter cosmology. The abundance of low-mass haloes in the modified gravity model fit observations better than the conventional theory, while the differences of the modified density fluctuation power spectrum differs from the standard, $\Lambda$CDM power spectrum are small enough to make these two models observationally indistinguishable at large scales. Read More