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  • 1
    Electronic Resource
    Electronic Resource
    Early gas stripping as the origin of the darkest galaxies in the Universe (2007)
    [s.l.] : Nature Publishing Group
    Nature 445 (2007), S. 738-740 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The known galaxies most dominated by dark matter (Draco, Ursa Minor and Andromeda IX) are satellites of the Milky Way and the Andromeda galaxies. They are members of a class of faint galaxies, devoid of gas, known as dwarf spheroidals, and have by far the highest ratio of dark to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05552
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    Paper (German National Licenses)
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  • 2
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    Cosmological galaxy evolution with superbubble feedback - I. Realistic galaxies with moderate feedback (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-11
    Description: We present the first cosmological galaxy evolved using the modern smoothed particle hydrodynamics (SPH) code gasoline2 with superbubble feedback. We show that superbubble-driven galactic outflows powered by Type II supernovae alone can produce L * galaxies with flat rotation curves with circular velocities ~ 200 km s – 1 , low bulge-to-disc ratios, and stellar mass fractions that match observed values from high redshift to the present. These features are made possible by the high mass loadings generated by the evaporative growth of superbubbles. Outflows are driven extremely effectively at high redshift, expelling gas at early times and preventing overproduction of stars before z  = 2. Centrally concentrated gas in previous simulations has often lead to unrealistically high bulge to total ratios and strongly peaked rotation curves. We show that supernova-powered superbubbles alone can produce galaxies that agree well with observed properties without the need for additional feedback mechanisms or increased feedback energy. We present additional results arising from properly modelled hot feedback.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Erratum: Probing the shape and history of the Milky Way halo with orbital spectral analysis (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-17
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Effects of galactic disc inclination and resolution on observed GMC properties and Larson's scaling relations (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-24
    Description: With ALMA (Atacama Large Millimeter/submillimeter Array) making it possible to resolve giant molecular clouds (GMCs) in other galaxies, it is becoming necessary to quantify the observational bias on measured GMC properties. Using a hydrodynamical simulation of a barred spiral galaxy, we compared the physical properties of GMCs formed in position–position–position (PPP) space to the observational position–position–velocity (PPV) space. We assessed the effect of disc inclination: face-on (PPV face ) and edge-on (PPV edge ), and resolution: 1.5 pc versus 24 pc, on GMC properties and the further implications of using Larson's scaling relations for mass–radius and velocity dispersion–radius. The low-resolution PPV data are generated by simulating ALMA Cycle 3 observations using the casa package. Results show that the median properties do not differ strongly between PPP and PPV face under both resolutions, but PPV edge clouds deviate from these two. The differences become magnified when switching to the lower, but more realistic resolution. The discrepancy can lead to opposite results for the virial parameter's measure of gravitational binding, and therefore the dynamical state of the clouds. The power-law indices for the two Larson's scaling relations decrease going from PPP, PPV edge to PPV face and decrease from high to low resolutions. We conclude that the relations are not entirely driven by the underlying physical origin and therefore have to be used with caution when considering the environmental dependence, dynamical state, and the extragalactic CO-to-H 2 conversion factor of GMCs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    NIHAO project II: halo shape, phase-space density and velocity distribution of dark matter in galaxy formation simulations (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-07
    Description: We use the NIHAO (Numerical Investigation of Hundred Astrophysical Objects) cosmological simulations to study the effects of galaxy formation on key properties of dark matter (DM) haloes. NIHAO consists of 90 high-resolution smoothed particle hydrodynamics simulations that include (metal-line) cooling, star formation, and feedback from massive stars and supernovae, and cover a wide stellar and halo mass range: 10 6 M * /M 10 11 (10 9.5 M halo /M 10 12.5 ). When compared to DM-only simulations, the NIHAO haloes have similar shapes at the virial radius, R vir , but are substantially rounder inside 0.1 R vir . In NIHAO simulations, c / a increases with halo mass and integrated star formation efficiency, reaching ~0.8 at the Milky Way mass (compared to 0.5 in DM-only), providing a plausible solution to the long-standing conflict between observations and DM-only simulations. The radial profile of the phase-space Q parameter (/ 3 ) is best fit with a single power law in DM-only simulations, but shows a flattening within 0.1 R vir for NIHAO for total masses M 〉 10 11 M . Finally, the global velocity distribution of DM is similar in both DM-only and NIHAO simulations, but in the solar neighbourhood, NIHAO galaxies deviate substantially from Maxwellian. The distribution is more symmetric, roughly Gaussian, with a peak that shifts to higher velocities for Milky Way mass haloes. We provide the distribution parameters which can be used for predictions for direct DM detection experiments. Our results underline the ability of the galaxy formation processes to modify the properties of DM haloes.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The anatomy of a star-forming galaxy: pressure-driven regulation of star formation in simulated galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-27
    Description: We explore the regulation of star formation in star-forming galaxies through a suite of high-resolution isolated galaxy simulations. We use the smoothed particle hydrodynamics code gasoline , including photoelectric heating and metal cooling, which produces a multi-phase interstellar medium (ISM). We show that representative star formation and feedback sub-grid models naturally lead to a weak, sub-linear dependence between the amount of star formation and changes to star formation parameters. We incorporate these sub-grid models into an equilibrium pressure-driven regulation framework. We show that the sub-linear scaling arises as a consequence of the non-linear relationship between scaleheight and the effective pressure generated by stellar feedback. Thus, simulated star formation regulation is sensitive to how well vertical structure in the ISM is resolved. Full galaxy discs experience density waves which drive locally time-dependent star formation. We develop a simple time-dependent, pressure-driven model that reproduces the response extremely well.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Uncovering mass segregation with galaxy analogues in dark-matter simulations (2016)
    Oxford University Press
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    Publication Date: 2016-08-07
    Description: We investigate mass segregation in group and cluster environments by identifying galaxy analogues in high-resolution dark-matter simulations. Subhaloes identified by the Amiga's Halo Finder ( ahf ) and rockstar halo finders have similar mass functions, independent of resolution, but different radial distributions due to significantly different subhalo hierarchies. We propose a simple way to classify subhaloes as galaxy analogues. The radial distributions of galaxy analogues agree well at large halocentric radii for both ahf and rockstar but disagree near parent halo centres where the phase-space information used by rockstar is essential. We see clear mass segregation at small radii (within 0.5 r vir ) with average galaxy analogue mass decreasing with radius. Beyond the virial radius, we find a mild trend where the average galaxy analogue mass increases with radius. These mass segregation trends are strongest in small groups and dominated by the segregation of low-mass analogues. The lack of mass segregation in massive galaxy analogues suggests that the observed trends are driven by the complex accretion histories of the parent haloes rather than dynamical friction.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Cosmological galaxy evolution with superbubble feedback - II. The limits of supernovae (2016)
    Oxford University Press
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    Publication Date: 2016-09-20
    Description: We explore when supernovae can (and cannot) regulate the star formation and bulge growth in galaxies based on a sample of 18 simulated galaxies. The simulations are the first to model feedback superbubbles including evaporation and conduction. These processes determine the mass loadings and wind speeds of galactic outflows. We show that for galaxies with virial masses 〉10 12 M , supernovae alone cannot prevent excessive star formation. This occurs due to a shutdown of galactic winds, with wind mass loadings falling from ~ 10 to 〈 1. In more massive systems, the ejection of baryons to the circumgalactic medium falters earlier on and the galaxies diverge significantly from observed galaxy scaling relations and morphologies. The decreasing efficiency is due to a deepening potential well preventing gas escape, and is unavoidable if mass-loaded outflows regulate star formation on galactic scales. This implies that non-supernova feedback mechanisms must become dominant for galaxies with stellar masses greater than ~4 x 10 10 M . The runaway growth of the central stellar bulge, strongly linked to black hole growth, suggests that feedback from active galactic nuclei is the likely mechanism. Below this mass, supernovae alone are able to produce a realistic stellar mass fraction, star formation history and disc morphology.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    How to bend galaxy disc profiles: the role of halo spin (2015)
    Oxford University Press
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    Publication Date: 2015-02-07
    Description: The radial density profiles of stellar galaxy discs can be well approximated as an exponential. Compared to this canonical form, however, the profiles in the majority of disc galaxies show downward or upward breaks at large radii. Currently, there is no coherent explanation in a galaxy formation context of the radial profile per se, along with the two types of profile breaks. Using a set of controlled hydrodynamic simulations of disc galaxy formation, we find a correlation between the host halo's initial angular momentum and the resulting radial profile of the stellar disc: galaxies that live in haloes with a low spin parameter 0.03 show an up-bending break in their disc density profiles, while galaxies in haloes of higher angular momentum show a down-bending break. We find that the case of pure exponential profiles (  0.035) coincides with the peak of the spin parameter distribution from cosmological simulations. Our simulations not only imply an explanation of the observed behaviours, but also suggest that the physical origin of this effect is related to the amount of radial redistribution of stellar mass, which is anticorrelated with .
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Faint dwarfs as a test of DM models: WDM versus CDM (2015)
    Oxford University Press
    Details
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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