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  • 1
    Electronic Resource
    Electronic Resource
    Hierarchical N-body methods
    Amsterdam : Elsevier
    Computer Physics Communications 48 (1988), S. 107-115 
    Details
    ISSN: 0010-4655
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0010-4655(88)90028-8
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of Interacting Galaxies (1992)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 30 (1992), S. 705-742 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.30.090192.003421
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  • 3
    Electronic Resource
    Electronic Resource
    Vectorization of tree traversals
    Amsterdam : Elsevier
    Journal of Computational Physics 87 (1990), S. 137-147 
    Details
    ISSN: 0021-9991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0021-9991(90)90230-X
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  • 4
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    Empirical covariance modeling for 21 cm power spectrum estimation: A method demonstration and new limits from early Murchison Widefield Array 128-tile data (2015)
    American Physical Society
    Details
    Publication Date: 2015-06-19
    Print ISSN: 1550-7998
    Electronic ISSN: 1550-2368
    Topics: Physics
    Published by American Physical Society
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  • 5
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    Hydrogen reionization in the Illustris universe (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-11
    Description: Hydrodynamical simulations of galaxy formation such as the Illustris simulations have progressed to a state where they approximately reproduce the observed stellar mass function from high to low redshift. This in principle allows self-consistent models of reionization that exploit the accurate representation of the diffuse gas distribution together with the realistic growth of galaxies provided by these simulations, within a representative cosmological volume. In this work, we apply and compare two radiative transfer algorithms implemented in a GPU-accelerated code to the 106.5-Mpc-wide volume of Illustris in post-processing in order to investigate the reionization transition predicted by this model. We find that the first generation of galaxies formed by Illustris is just about able to reionize the universe by redshift z  ~ 7, provided quite optimistic assumptions about the escape fraction and the resolution limitations are made. Our most optimistic model finds an optical depth of ~= 0.065, which is in very good agreement with recent Planck 2015 determinations. Furthermore, we show that moment-based approaches for radiative transfer with the M1 closure give broadly consistent results with our angular-resolved radiative transfer scheme. In our favoured fiducial model, 20 per cent of the hydrogen is reionized by redshift z  = 9.20, and this rapidly climbs to 80 per cent by redshift z  = 6.92. It then takes until z  = 6.24 before 99 per cent of the hydrogen is ionized. On average, reionization proceeds ‘inside-out’ in our models, with a size distribution of reionized bubbles that progressively features regions of ever larger size while the abundance of small bubbles stays fairly constant.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    On the assembly of dwarf galaxies in clusters and their efficient formation of globular clusters (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-25
    Description: Galaxy clusters contain a large population of low-mass dwarf elliptical galaxies whose exact origin is unclear: their colours, structural properties and kinematics differ substantially from those of dwarf irregulars in the field. We use the Illustris cosmological simulation to study differences in the assembly histories of dwarf galaxies (3 x 10 8 〈 M * /M 〈 10 10 ) according to their environment. We find that cluster dwarfs achieve their maximum total and stellar mass on average ~8 and ~4.5 Gyr ago (or redshifts z  = 1.0 and 0.4, respectively), around the time of infall into the clusters. In contrast, field dwarfs not subjected to environmental stripping reach their maximum mass at z  = 0. These different assembly trajectories naturally produce a colour bimodality, with blue isolated dwarfs and redder cluster dwarfs exhibiting negligible star formation today. The cessation of star formation happens over median times 3.5–5 Gyr depending on stellar mass, and shows a large scatter (~1–8 Gyr), with the lower values associated with starburst events that occur at infall through the virial radius or pericentric passages. We argue that such starbursts together with the early assembly of cluster dwarfs can provide a natural explanation for the higher specific frequency of globular clusters (GCs) in cluster dwarfs, as found observationally. We present a simple model for the formation and stripping of GCs that supports this interpretation. The origin of dwarf ellipticals in clusters is, therefore, consistent with an environmentally driven evolution of field dwarf irregulars. However, the z  = 0 field analogues of cluster dwarf progenitors have today stellar masses a factor of ~3 larger – a difference arising from the early truncation of star formation in cluster dwarfs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The mass profile of the Milky Way to the virial radius from the Illustris simulation (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-21
    Description: We use particle data from the Illustris simulation, combined with individual kinematic constraints on the mass of the Milky Way (MW) at specific distances from the Galactic Centre, to infer the radial distribution of the MW's dark matter halo mass. Our method allows us to convert any constraint on the mass of the MW within a fixed distance to a full circular velocity profile to the MW's virial radius. As primary examples, we take two recent (and discrepant) measurements of the total mass within 50 kpc of the Galaxy and find that they imply very different mass profiles and stellar masses for the Galaxy. The dark-matter-only version of the Illustris simulation enables us to compute the effects of galaxy formation on such constraints on a halo-by-halo basis; on small scales, galaxy formation enhances the density relative to dark-matter-only runs, while the total mass density is approximately 20 per cent lower at large Galactocentric distances. We are also able to quantify how current and future constraints on the mass of the MW within specific radii will be reflected in uncertainties on its virial mass: even a measurement of M (〈50 kpc) with essentially perfect precision still results in a 20 per cent uncertainty on the virial mass of the Galaxy, while a future measurement of M (〈100 kpc) with 10 per cent errors would result in the same level of uncertainty. We expect that our technique will become even more useful as (1) better kinematic constraints become available at larger distances and (2) cosmological simulations provide even more faithful representations of the observable Universe.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Shock finding on a moving-mesh - II. Hydrodynamic shocks in the Illustris universe (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-30
    Description: Hydrodynamical shocks are a manifestation of the non-linearity of the Euler equations and play a fundamental role in cosmological gas dynamics. In this work, we identify and analyse shocks in the Illustris simulation, and contrast the results with those of non-radiative runs. We show that simulations with more comprehensive physical models of galaxy formation pose new challenges for shock finding algorithms due to radiative cooling and star-forming processes, prompting us to develop a number of methodology improvements. We find in Illustris a total shock surface area which is about 1.4 times larger at the present epoch compared to non-radiative runs, and an energy dissipation rate at shocks which is higher by a factor of around 7. Remarkably, shocks with Mach numbers above and below $\mathcal {M}\approx 10$ contribute about equally to the total dissipation across cosmic time. This is in sharp contrast to non-radiative simulations, and we demonstrate that a large part of the difference arises due to strong black hole radio-mode feedback in Illustris. We also provide an overview of the large diversity of shock morphologies, which includes complex networks of halo-internal shocks, shocks on to cosmic sheets, feedback shocks due to black holes and galactic winds, as well as ubiquitous accretion shocks. In high-redshift systems more massive than 10 12 M , we discover the existence of a double accretion shock pattern in haloes. They are created when gas streams along filaments without being shocked at the outer accretion shock, but then forms a second, roughly spherical accretion shock further inside.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Simulating the carbon footprint of galactic haloes (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-03
    Description: We compare simulations, including the Illustris simulations, to observations of C iv and C ii absorption at z  = 2–4. These are the C iv column density distribution function in the column density range 10 12 –10 15 cm –2 , the C iv equivalent width distribution at 0.1–2 Å, and the covering fractions and equivalent widths of C iv 1548 Å and C ii 1337 Å around damped Lyman α systems (DLAs). In the context of the feedback models that we investigate, all C iv observations favour the use of more energetic wind models, which are better able to enrich the gas surrounding haloes. We propose two ways to achieve this: an increased wind velocity and an increase in wind thermal energy. However, even our most energetic wind models do not produce enough absorbers with C iv equivalent width 〉0.6 Å, which in our simulations are associated with the most massive haloes. All simulations are in reasonable agreement with the C ii covering fraction and equivalent widths around damped Lyman α absorbers, although there is a moderate deficit in one bin 10–100 kpc from the DLA. Finally, we show that the C iv in our simulations is predominantly photoionized.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Discriminating topology in galaxy distributions using network analysis (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-06
    Description: The large-scale distribution of galaxies is generally analysed using the two-point correlation function. However, this statistic does not capture the topology of the distribution, and it is necessary to resort to higher order correlations to break degeneracies. We demonstrate that an alternate approach using network analysis can discriminate between topologically different distributions that have similar two-point correlations. We investigate two galaxy point distributions, one produced by a cosmological simulation and the other by a Lévy walk. For the cosmological simulation, we adopt the redshift z = 0.58 slice from Illustris and select galaxies with stellar masses greater than 10 8 M . The two-point correlation function of these simulated galaxies follows a single power law, ( r ) ~ r –1.5 . Then, we generate Lévy walks matching the correlation function and abundance with the simulated galaxies. We find that, while the two simulated galaxy point distributions have the same abundance and two-point correlation function, their spatial distributions are very different; most prominently, filamentary structures , absent in Lévy fractals. To quantify these missing topologies, we adopt network analysis tools and measure diameter, giant component, and transitivity from networks built by a conventional friends-of-friends recipe with various linking lengths. Unlike the abundance and two-point correlation function, these network quantities reveal a clear separation between the two simulated distributions; therefore, the galaxy distribution simulated by Illustris is not a Lévy fractal quantitatively. We find that the described network quantities offer an efficient tool for discriminating topologies and for comparing observed and theoretical distributions.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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