ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    The effect of tides on the Fornax dwarf spheroidal galaxy (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-15
    Description: Estimates of the mass distribution and dark-matter (DM) content of dwarf spheroidal galaxies (dSphs) are usually derived under the assumption that the effect of the tidal field of the host galaxy is negligible over the radial extent probed by kinematic data sets. We assess the implications of this assumption in the specific case of the Fornax dSph by means of N -body simulations of a satellite orbiting around the Milky Way. We consider observationally motivated orbits and tailor the initial distributions of the satellite's stars and DM to match, at the end of the simulations, the observed structure and kinematics of Fornax. In all our simulations the present-day observable properties of Fornax are not significantly influenced by tidal effects. The DM component is altered by the interaction with the Galactic field (up to 20 per cent of the DM mass within 1.6 kpc is lost.), but the structure and kinematics of the stellar component are only mildly affected even in the more eccentric orbit (more than 99 per cent of the stellar particles remain bound to the dwarf.). In the simulations that successfully reproduce Fornax's observables, the dark-to-luminous mass ratio within 1.6 kpc is in the range 5–6, and up to 16–18 if measured within 3 kpc.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    Action-based distribution functions for spheroidal galaxy components (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-16
    Description: We present an approach to the design of distribution functions that depend on the phase-space coordinates through the action integrals. The approach makes it easy to construct a dynamical model of a given stellar component. We illustrate the approach by deriving distribution functions that self-consistently generate several popular stellar systems, including the Hernquist, Jaffe, and Navarro, Frenk and White models. We focus on non-rotating spherical systems, but extension to flattened and rotating systems is trivial. Our distribution functions are easily added to each other and to previously published distribution functions for discs to create self-consistent multicomponent galaxies. The models this approach makes possible should prove valuable both for the interpretation of observational data and for exploring the non-equilibrium dynamics of galaxies via N -body simulations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    The imprint of dark matter haloes on the size and velocity dispersion evolution of early-type galaxies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-02
    Description: Early-type galaxies (ETGs) are observed to be more compact, on average, at z 2 than at z ~= 0, at fixed stellar mass. Recent observational works suggest that such size evolution could reflect the similar evolution of the host dark matter halo density as a function of the time of galaxy quenching. We explore this hypothesis by studying the distribution of halo central velocity dispersion ( 0 ) and half-mass radius ( r h ) as functions of halo mass M and redshift z , in a cosmological cold dark matter N -body simulation. In the range 0 z 2.5, we find 0 M 0.31-0.37 and r h M 0.28-0.32 , close to the values expected for homologous virialized systems. At fixed M in the range 10 11 M M 5.5 10 14 M we find 0   (1 + z ) 0.35 and r h   (1 + z ) –0.7 . We show that such evolution of the halo scaling laws is driven by individual haloes growing in mass following the evolutionary tracks 0    M 0.2 and r h    M 0.6 , consistent with simple dissipationless merging models in which the encounter orbital energy is accounted for. We compare the N -body data with ETGs observed at 0 z 3 by populating the haloes with a stellar component under simple but justified assumptions: the resulting galaxies evolve consistently with the observed ETGs up to z ~= 2, but the model has difficulty in reproducing the fast evolution observed at z 2. We conclude that a substantial fraction of the size evolution of ETGs can be ascribed to a systematic dependence on redshift of the dark matter haloes structural properties.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Early flattening of dark matter cusps in dwarf spheroidal galaxies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-24
    Description: Simulations of the clustering of cold dark matter yield dark matter haloes that have central density cusps, but observations of totally dark-matter-dominated dwarf spheroidal galaxies imply that they do not have cuspy central density profiles. We use analytic calculations and numerical modelling to argue that whenever stars form, central density cusps are likely to be erased. Gas that accumulates in the potential well of an initially cuspy dark matter halo settles into a disc. Eventually the surface density of the gas exceeds the threshold for fragmentation into self-gravitating clouds. The clouds are massive enough to transfer energy to the dark matter particles via dynamical friction on a short time-scale. The halo's central cusp is heated to form a core with central logarithmic density slope 0 before stellar feedback makes its impact. Since star formation is an inefficient process, the clouds are disrupted by feedback when only a small fraction of their mass has been converted to stars, and the dark matter dominates the final mass distribution.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    A fast and accurate method to compute the mass return from multiple stellar populations (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-19
    Description: The mass returned to the ambient medium by aging stellar populations over cosmological times sums up to a significant fraction (20–30 per cent or more) of their initial mass. This continuous mass injection plays a fundamental role in phenomena, such as galaxy formation and evolution, fuelling of supermassive black holes in galaxies and the consequent (negative and positive) feedback phenomena, and the origin of multiple stellar populations in globular clusters. In numerical simulations, the calculation of the mass return can be time consuming, since it requires at each time step the evaluation of a convolution integral over the whole star formation history, so the computational time increases quadratically with the number of time steps. The situation can be especially critical in hydrodynamical simulations, where different grid points are characterized by different star formation histories, and the gas cooling and heating times are shorter by orders of magnitude than the characteristic stellar lifetimes. In this paper, we present a fast and accurate method to compute the mass return from stellar populations undergoing arbitrarily complicated star formation histories. At each time step the mass return is calculated from its value at the previous time, and the star formation rate over the last time step only. Therefore, in the new scheme there is no need to store the whole star formation history, and the computational time increases linearly with the number of time steps.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Do globular clusters possess dark matter haloes? A case study in NGC 2419 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-01-03
    Description: We use recently published measurements of the kinematics, surface brightness and stellar mass-to-light ratio of the globular cluster NGC 2419 to examine the possibility that this Galactic halo satellite is embedded in a low-mass dark matter halo. NGC 2419 is a promising target for such a study, since its extreme Galactocentric distance and large mass would have greatly facilitated the retention of dark matter. A Markov chain Monte Carlo approach is used to investigate composite dynamical models containing a stellar and a dark matter component. We find that it is unlikely that a significant amount of dark matter (6 per cent of the luminous mass inside the tidal limit of the cluster) can be present if the stars follow an anisotropic Michie model and the dark matter a double power-law model. However, we find that more general models, derived using a new technique we have developed to compute non-parametric solutions to the spherical Jeans equation, suggest the presence of a significant dark matter fraction (approximately twice the stellar mass). Thus, the presence of a dark matter halo around NGC 2419 cannot be fully ruled out at present, yet any dark matter within the 10 arcmin visible extent of the cluster must be highly concentrated and cannot exceed 1.1  x 10 6 M (99 per cent confidence), in stark contrast to expectations for a plausible progenitor halo of this structure.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    Relaxation of N-body systems with additive r-{alpha} interparticle forces (2013)
    Oxford University Press
    Details
    Publication Date: 2013-05-08
    Description: In Newtonian gravity the final states of cold dissipationless collapses are characterized by several structural and dynamical properties remarkably similar to those of observed elliptical galaxies. Are these properties a peculiarity of the Newtonian force or a more general feature of long-range forces? We study this problem by means of N -body simulations of dissipationless collapse of systems of particles interacting via additive r –α forces. We find that most of the results holding in Newtonian gravity are also valid for α != 2. In particular, the end-products are triaxial and never flatter than an E7 system, their surface density profiles are well described by the Sérsic law, the global density slope–anisotropy inequality is obeyed, the differential energy distribution is an exponential over a large range of energies (for α ≥ 1), and the pseudo-phase-space density is a power law of radius. In addition, we show that the process of virialization takes longer (in units of the system's dynamical time) for decreasing values of α, and becomes infinite for α = –1 (the harmonic oscillator). This is in agreement with the results of deep Modified Newtonian Dynamics collapses (qualitatively corresponding to α = 1) and it is due to the fact that the force becomes more and more similar to the α = –1 case, where, as well known, no relaxation can happen and the system oscillates forever.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    Gas rotation in galaxy clusters: signatures and detectability in X-rays (2013)
    Oxford University Press
    Details
    Publication Date: 2013-08-18
    Description: We study simple models of massive galaxy clusters in which the intracluster medium (ICM) rotates differentially in equilibrium in the cluster gravitational potential. We obtain the X-ray surface-brightness maps, evaluating the isophote flattening due to the gas rotation. Using a set of different rotation laws, we put constraint on the amplitude of the rotation velocity, finding that rotation curves with peak velocity up to ~600 km s –1 are consistent with the ellipticity profiles of observed clusters. We convolve each of our models with the instrument response of the X-ray Calorimeter Spectrometer on board the ASTRO-H to calculate the simulated X-ray spectra at different distance from the X-ray centre. We demonstrate that such an instrument will allow us to measure rotation of the ICM in massive clusters, even with rotation velocities as low as ~100 km s –1 .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Merger-driven evolution of the effective stellar initial mass function of massive early-type galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-15
    Description: The stellar initial mass function (IMF) of early-type galaxies is the combination of the IMF of the stellar population formed in situ and that of accreted stellar populations. Using as an observable the effective IMF α IMF , defined as the ratio between the true stellar mass of a galaxy and the stellar mass inferred assuming a Salpeter IMF, we present a theoretical model for its evolution as a result of dry mergers. We use a simple dry-merger evolution model, based on cosmological N -body simulations, together with empirically motivated prescriptions for the IMF to make predictions on how the effective IMF of massive early-type galaxies changes from z = 2 to z = 0. We find that the IMF normalization of individual galaxies becomes lighter with time. At fixed velocity dispersion, α IMF is predicted to be constant with redshift. Current dynamical constraints on the evolution of the IMF are in slight tension with this prediction, even though systematic uncertainties, including the effect of radial gradients in the IMF, prevent a conclusive statement. The correlation of α IMF with stellar mass becomes shallower with time, while the correlation between α IMF and velocity dispersion is mostly preserved by dry mergers. We also find that dry mergers can mix the dependence of the IMF on stellar mass and velocity dispersion, making it challenging to infer, from z = 0 observations of global galactic properties, what is the quantity that is originally coupled with the IMF.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    The volumetric star formation law in the Milky Way (2019)
    EDP Sciences
    Details
    Publication Date: 2019-12-01
    Description: Several open questions on galaxy formation and evolution have their roots in the lack of a universal star formation law that could univocally link the gas properties, such as its density, to the star formation rate (SFR) density. In a recent paper we used a sample of nearby disc galaxies to infer the volumetric star formation (VSF) law, a tight correlation between the gas and the SFR volume densities derived under the assumption of hydrostatic equilibrium for the gas disc. However, due to the dearth of information about the vertical distribution of the SFR in these galaxies, we could not find a unique slope for the VSF law, but two alternative values. In this paper, we use the scale height of the SFR density distribution in our Galaxy adopting classical Cepheids (age ≲200 Myr) as tracers of star formation. We show that this latter is fully compatible with the flaring scale height expected from gas in hydrostatic equilibrium. These scale heights allowed us to convert the observed surface densities of gas and SFR into the corresponding volume densities. Our results indicate that the VSF law ρSFR ∝ ραgas with α ≈ 2 is valid in the Milky Way as well as in nearby disc galaxies.
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...