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Register a new userFamilies of dynamically hot stellar systems over ten orders of magnitude in mass
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Dynamically hot stellar systems, whether star clusters or early-type galaxies, follow well-defined scaling relations over many orders of magnitudes in mass. These fundamental plane relations have been subject of several studies, which have been mostly confined to certain types of galaxies and/or star clusters so far. Here, we present a complete picture of hot stellar systems ranging from faint galaxies and star clusters of only a few hundred solar masses up to giant ellipticals (gEs) with 10^12 M_sun, in particular including large samples of compact ellipticals (cEs), ultra-compact dwarf galaxies (UCDs), dwarf ellipticals (dEs) of nearby galaxy clusters and Local Group ultra-faint dwarf spheroidals (dSphs). For all those stellar systems we show the effective radius-luminosity, effective radius-stellar mass, and effective mass surface density-stellar mass plane. Two families of hot stellar systems can be differentiated: the galaxian family, ranging from gEs over Es and dEs to dSphs, and the star cluster family, comprising globular clusters (GCs), UCDs and nuclear star clusters (NCs). Interestingly, massive ellipticals have a similar size-mass relation as cEs, UCDs and NCs, with a clear common boundary towards minimum sizes. No object of either family is located in the zone of avoidance beyond this limit. Even the majority of early-type galaxies at high redshift obeys this relation. The sizes of dEs and dSphs as well as GCs barely vary with mass over several orders of magnitude. We use the constant galaxy sizes to derive the distances of several local galaxy clusters. Both, galaxies and star clusters, do not exceed a surface density of Sigma_eff = 3.17*10^{10}*M^{-3/5} M_sun pc^{-2}, causing an orthogonal kink in the galaxy sequence for ellipticals more massive than 10^{11} M_sun. The densest stellar systems (within their effective radius) are nuclear star clusters. (abridged)
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Cosmological models in which dark matter consists of cold elementary particles predict that the dark halo population should extend to masses many orders of magnitude below those at which galaxies can form. Here we report a cosmological simulation of the formation of present-day haloes over the full range of observed halo masses (20 orders of magnitude) when dark matter is assumed to be in the form of weakly interacting massive particles of mass approximately 100 gigaelectronvolts. The simulation has a full dynamic range of 30 orders of magnitude in mass and resolves the internal structure of hundreds of Earth-mass haloes in as much detail as it does for hundreds of rich galaxy clusters. We find that halo density profiles are universal over the entire mass range and are well described by simple two-parameter fitting formulae. Halo mass and concentration are tightly related in a way that depends on cosmology and on the nature of the dark matter. For a fixed mass, the concentration is independent of the local environment for haloes less massive than those of typical galaxies. Haloes over the mass range of 10^3 to 10^11 solar masses contribute about equally (per logarithmic interval) to the luminosity produced by dark matter annihilation, which we find to be smaller than all previous estimates by factors ranging up to one thousand.
We use our recent electric dipole moment (EDM) measurement data to constrain the possibility that the HfF$^+$ EDM oscillates in time due to interactions with candidate dark matter axion-like particles (ALPs). We employ a Bayesian analysis method which accounts for both the look-elsewhere effect and the uncertainties associated with stochastic density fluctuations in the ALP field. We find no evidence of an oscillating EDM over a range spanning from 27 nHz to 400 mHz, and we use this result to constrain the ALP-gluon coupling over the mass range $10^{-22}-10^{-15}$ eV. This is the first laboratory constraint on the ALP-gluon coupling in the $10^{-17}-10^{-15}$ eV range, and the first laboratory constraint to properly account for the stochastic nature of the ALP field.
Most globular clusters have half-mass radii of a few pc with no apparent correlation with their masses. This is different from elliptical galaxies, for which the Faber-Jackson relation suggests a strong positive correlation between mass and radius. Objects that are somewhat in between globular clusters and low-mass galaxies, such as ultra-compact dwarf galaxies, have a mass-radius relation consistent with the extension of the relation for bright ellipticals. Here we show that at an age of 10 Gyr a break in the mass-radius relation at ~10^6 Msun is established because objects below this mass, i.e. globular clusters, have undergone expansion driven by stellar evolution and hard binaries. From numerical simulations we find that the combined energy production of these two effects in the core comes into balance with the flux of energy that is conducted across the half-mass radius by relaxation. An important property of this `balanced evolution is that the cluster half-mass radius is independent of its initial value and is a function of the number of bound stars and the age only. It is therefore not possible to infer the initial mass-radius relation of globular clusters and we can only conclude that the present day properties are consistent with the hypothesis that all hot stellar systems formed with the same mass-radius relation and that globular clusters have moved away from this relation because of a Hubble time of stellar and dynamical evolution.
We present clumps of dust emission from Herschel observations of the Large Magellanic Cloud (LMC) and their physical and statistical properties. We catalog cloud features seen in the dust emission from Herschel observations of the LMC, the Magellanic type irregular galaxy closest to the Milky Way, and compare these features with HI catalogs from the ATCA+Parkes HI survey. Using an automated cloud-finding algorithm, we identify clouds and clumps of dust emission and examine the cumulative mass distribution of the detected dust clouds. The mass of cold dust is determined from physical parameters that we derive by performing spectral energy distribution fits to 250, 350, and 500 micronm emission from SPIRE observations using DUSTY and GRASIL radiative transfer calculation with dust grain size distributions for graphite/silicate in low-metallicity extragalactic environments. The dust cloud mass spectrum follows a power law distribution with an exponent of gamma=-1.8 for clumps larger than 400 solar mass and is similar to the HI mass distribution. This is expected from the theory of ISM structure in the vicinity of star formation.
(Abridged) Objects with radii of 10 to 100 pc and masses in the range from 10^6 to 10^8 M_sun have been discovered during the past decade. These so-called ultra compact dwarf galaxies (UCDs) constitute a transition between classical star clusters and elliptical galaxies in terms of radii, relaxation times and V-band mass-to-light (M/L_V) ratios. Using new data, we find that the mass interval from 10^6 to 10^7 M_sun is of special interest, because within this range typical half-light radii and dynamical mass-to-light ratios begin to increase compared to globular clusters, the highest stellar densities are reached and typical median two-body relaxation times surpass a Hubble time. The M/L_V ratios of the UCDs turn out to be incompatible with the predictions from simple stellar population (SSP) models when using the canonical stellar initial mass function (IMF), although SSPs probably are good approximations to the real stellar populations in UCDs and the SSP models allow to account for metallicity effects on the M/L_V ratio. This provides evidence for the UCDs either having formed with an IMF different from the canonical one or containing dark matter. We emphasise that almost all pressure-supported stellar systems ranging from star clusters to massive elliptical galaxies have M/L_V ratios less than 10 M_sun/L_sun, and that only dSph satellite galaxies have M/L_V ratios greater than 100 M_sun/L_sun and therewith form exceptional systems.
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