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  • 1
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    Clumps and streams in the local dark matter distribution (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-08-08
    Description: In cold dark matter cosmological models, structures form and grow through the merging of smaller units. Numerical simulations have shown that such merging is incomplete; the inner cores of haloes survive and orbit as 'subhaloes' within their hosts. Here we report a simulation that resolves such substructure even in the very inner regions of the Galactic halo. We find hundreds of very concentrated dark matter clumps surviving near the solar circle, as well as numerous cold streams. The simulation also reveals the fractal nature of dark matter clustering: isolated haloes and subhaloes contain the same relative amount of substructure and both have cusped inner density profiles. The inner mass and phase-space densities of subhaloes match those of recently discovered faint, dark-matter-dominated dwarf satellite galaxies, and the overall amount of substructure can explain the anomalous flux ratios seen in strong gravitational lenses. Subhaloes boost gamma-ray production from dark matter annihilation by factors of 4 to 15 relative to smooth galactic models. Local cosmic ray production is also enhanced, typically by a factor of 1.4 but by a factor of more than 10 in one per cent of locations lying sufficiently close to a large subhalo. (These estimates assume that the gravitational effects of baryons on dark matter substructure are small.).〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Diemand, J -- Kuhlen, M -- Madau, P -- Zemp, M -- Moore, B -- Potter, D -- Stadel, J -- England -- Nature. 2008 Aug 7;454(7205):735-8. doi: 10.1038/nature07153.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉University of California, Department of Astronomy and Astrophysics, Santa Cruz, California 95064, USA. diemand@ucolick.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18685701" 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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  • 2
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    Rapid formation of supermassive black hole binaries in galaxy mergers with gas (2007)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2007-06-09
    Description: Supermassive black holes (SMBHs) are a ubiquitous component of the nuclei of galaxies. It is normally assumed that after the merger of two massive galaxies, a SMBH binary will form, shrink because of stellar or gas dynamical processes, and ultimately coalesce by emitting a burst of gravitational waves. However, so far it has not been possible to show how two SMBHs bind during a galaxy merger with gas because of the difficulty of modeling a wide range of spatial scales. Here we report hydrodynamical simulations that track the formation of a SMBH binary down to scales of a few light years after the collision between two spiral galaxies. A massive, turbulent, nuclear gaseous disk arises as a result of the galaxy merger. The black holes form an eccentric binary in the disk in less than 1 million years as a result of the gravitational drag from the gas rather than from the stars.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mayer, L -- Kazantzidis, S -- Madau, P -- Colpi, M -- Quinn, T -- Wadsley, J -- New York, N.Y. -- Science. 2007 Jun 29;316(5833):1874-7. Epub 2007 Jun 7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Theoretical Physics, University of Zurich, Winterthurestrasse 190, CH-8057 Zurich, Switzerland. lucio@phys.ethz.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17556550" 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
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  • 3
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    A cosmic web filament revealed in Lyman-alpha emission around a luminous high-redshift quasar (2014)
    Nature Publishing Group (NPG)
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    Publication Date: 2014-01-28
    Description: Simulations of structure formation in the Universe predict that galaxies are embedded in a 'cosmic web', where most baryons reside as rarefied and highly ionized gas. This material has been studied for decades in absorption against background sources, but the sparseness of these inherently one-dimensional probes preclude direct constraints on the three-dimensional morphology of the underlying web. Here we report observations of a cosmic web filament in Lyman-alpha emission, discovered during a survey for cosmic gas fluorescently illuminated by bright quasars at redshift z approximately 2.3. With a linear projected size of approximately 460 physical kiloparsecs, the Lyman-alpha emission surrounding the radio-quiet quasar UM 287 extends well beyond the virial radius of any plausible associated dark-matter halo and therefore traces intergalactic gas. The estimated cold gas mass of the filament from the observed emission-about 10(12.0 +/- 0.5)/C(1/2) solar masses, where C is the gas clumping factor-is more than ten times larger than what is typically found in cosmological simulations, suggesting that a population of intergalactic gas clumps with subkiloparsec sizes may be missing in current numerical models.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cantalupo, Sebastiano -- Arrigoni-Battaia, Fabrizio -- Prochaska, J Xavier -- Hennawi, Joseph F -- Madau, Piero -- England -- Nature. 2014 Feb 6;506(7486):63-6. doi: 10.1038/nature12898. Epub 2014 Jan 19.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, California 95064, USA [2] University of California Observatories, Lick Observatory, 1156 High Street, Santa Cruz, California 95064, USA. ; Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg, Germany. ; 1] Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, California 95064, USA [2] University of California Observatories, Lick Observatory, 1156 High Street, Santa Cruz, California 95064, USA [3] Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg, Germany. ; Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, California 95064, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24463517" 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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  • 4
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    Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-02-25
    Description: For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Governato, F -- Brook, C -- Mayer, L -- Brooks, A -- Rhee, G -- Wadsley, J -- Jonsson, P -- Willman, B -- Stinson, G -- Quinn, T -- Madau, P -- England -- Nature. 2010 Jan 14;463(7278):203-6. doi: 10.1038/nature08640.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astronomy Department, University of Washington, Seattle, Washington 98195, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20075915" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
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    Exploring dark matter with Milky Way substructure (2009)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2009-07-18
    Description: The unambiguous detection of dark matter annihilation in our Galaxy would unravel one of the most outstanding puzzles in particle physics and cosmology. Recent observations have motivated models in which the annihilation rate is boosted by the Sommerfeld effect, a nonperturbative enhancement arising from a long-range attractive force. We applied the Sommerfeld correction to Via Lactea II, a high-resolution N-body simulation of a Milky Way-sized galaxy, to investigate the phase-space structure of the galactic halo. We found that the annihilation luminosity from kinematically cold substructure could be enhanced by orders of magnitude relative to previous calculations, leading to the prediction of gamma-ray fluxes from as many as several hundred dark clumps that should be detectable by the Fermi satellite.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kuhlen, Michael -- Madau, Piero -- Silk, Joseph -- New York, N.Y. -- Science. 2009 Aug 21;325(5943):970-3. doi: 10.1126/science.1174881. Epub 2009 Jul 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540, USA. mqk@ias.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19608862" 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
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  • 6
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    The photoheating of the intergalactic medium in synthesis models of the UV background (2015)
    Oxford University Press
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    Publication Date: 2015-05-22
    Description: We compare cosmological hydrodynamical simulations combined with the homogeneous metagalactic UV background (UVB) of Haardt & Madau (hereafter HM2012 ) to observations of the Lyman α forest that are sensitive to the thermal and ionization state of the intergalactic medium (IGM). The transition from optically thick to thin photoheating predicted by the simple one-zone, radiative transfer model implemented by HM2012 predicts a thermal history that is in remarkably good agreement with the observed rise of the IGM temperature at z  ~ 3 if we account for the expected evolution of the volume filling factor of He iii . Our simulations indicate that there may be, however, some tension between the observed peak in the temperature evolution and the rather slow evolution of the He ii opacities suggested by recent Hubble Space Telescope /Cosmic Origins Spectrograph measurements. The HM2012 UVB also underpredicts the metagalactic hydrogen photoionization rate required by our simulations to match the observed opacity of the forest at z  〉 4 and z  〈 2.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Evidence of patchy hydrogen reionization from an extreme Ly{alpha} trough below redshift six (2015)
    Oxford University Press
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    Publication Date: 2015-01-24
    Description: We report the discovery of an extremely long (~110 Mpc h –1 ) and dark ( eff   7) Lyα trough extending down to z ~= 5.5 towards the z em ~= 6.0 quasar ULAS J0148+0600. We use these new data in combination with Lyα forest measurements from 42 quasars at 4.5 ≤  z em  ≤ 6.4 to conduct an updated analysis of the line-of-sight variance in the intergalactic Lyα opacity over 4 ≤  z  ≤ 6. We find that the scatter in transmission among lines of sight near z  ~ 6 significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near z ~= 5.6–5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone. We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by z ~= 5.6, however, a large fraction of the data are consistent with a uniform UVB, and by z  ~ 5 the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at z  ~ 6, it has fully completed by z  ~ 5.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Faint dwarfs as a test of DM models: WDM versus CDM (2015)
    Oxford University Press
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    Publication Date: 2015-02-08
    Description: We use high-resolution Hydro+ N -Body cosmological simulations to compare the assembly and evolution of a small field dwarf (stellar mass ~10 6–7  M , total mass 10 10  M ) in -dominated cold dark matter (CDM) and 2 keV warm dark matter (WDM) cosmologies. We find that star formation (SF) in the WDM model is reduced and delayed by 1–2 Gyr relative to the CDM model, independently of the details of SF and feedback. Independent of the dark matter (DM) model, but proportionally to the SF efficiency, gas outflows lower the central mass density through ‘dynamical heating’, such that all realizations have circular velocities 〈20 km s –1 at 500 pc, in agreement with local kinematic constraints. As a result of dynamical heating, older stars are less centrally concentrated than younger stars, similar to stellar population gradients observed in nearby dwarf galaxies. Introducing an important diagnostic of SF and feedback models, we translate our simulations into artificial colour–magnitude diagrams and star formation histories (SFHs) in order to directly compare to available observations. The simulated galaxies formed most of their stars in many ~10 Myr long bursts. The CDM galaxy has a global SFH, H i abundance and Fe/H and alpha-elements distribution well matched to current observations of dwarf galaxies. These results highlight the importance of directly including ‘baryon physics’ in simulations when (1) comparing predictions of galaxy formation models with the kinematics and number density of local dwarf galaxies and (2) differentiating between CDM and non-standard models with different DM or power spectra.
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    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Towards a unified description of the intergalactic medium at redshift z {approx} 2.5 (2014)
    Oxford University Press
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    Publication Date: 2014-01-16
    Description: We examine recent measurements of the z 2.5 intergalactic medium (IGM) which constrain the H  i frequency distribution $f(N_{\rm H\,{\small I}})$ and the mean free path $\lambda _{\rm mfp}^{912}$ to ionizing radiation. We argue that line-blending and the clustering of strong absorption-line systems have led previous authors to systematically overestimate the effective Lyman limit opacity, yielding too small of a $\lambda _{\rm mfp}^{912}$ for the IGM. We further show that recently published measurements of $f(N_{\rm H\,{\small I}})$ at $N_{\rm H\,{\small I}}\approx 10^{16} \, {\rm cm^{-2}}$ lie in strong disagreement, implying underestimated uncertainty from sample variance and/or systematics like line-saturation. Allowing for a larger uncertainty in the $f(N_{\rm H\,{\small I}})$ measurements, we provide a new cubic Hermite spline model for $f(N_{\rm H\,{\small I}})$ which reasonably satisfies all of the observational constraints under the assumption of randomly distributed absorption systems. We caution, however, that this formalism is invalid in the light of absorber clustering and use a toy model to estimate the effects. Future work must properly account for the non-Poissonian nature of the IGM.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Direct gravitational imaging of intermediate mass black holes in extragalactic haloes (2013)
    Oxford University Press
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    Publication Date: 2013-10-08
    Description: A galaxy halo may contain a large number of intermediate mass black holes (IMBHs) with masses in the range of 10 2 M    M BH   10 6 M . We propose to directly detect these IMBHs by observing multiply imaged QSO–galaxy or galaxy–galaxy strong lens systems in the submillimetre bands with high angular resolution. The silhouette of an IMBH in the lensing galaxy halo would appear as either a monopole-like or a dipole-like variation at the scale of the Einstein radius against the Einstein ring of the dust-emitting region surrounding the QSO. We use a particle tagging technique to dynamically populate a Milky Way-sized dark matter halo with black holes (BHs), and show that the surface mass density and number density of IMBHs have power-law dependences on the distance from the centre of the host halo if smoothed on a scale of ~ 1 kpc. Most of the BHs orbiting close to the centre are freely roaming as they have lost their dark matter hosts during infall due to tidal stripping. Next generation submillimetre telescopes with high angular resolution (0.3 mas) will be capable of directly mapping such off-nuclear freely roaming BHs with a mass of 10 6 M in a lensing galaxy that harbours an O (10 9 ) M supermassive black hole in its nucleus.
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    Topics: Physics
    Published by Oxford University Press
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