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Register a new userThe cold dark matter content of Galactic dwarf spheroidals: no cores, no failures, no problem
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We examine the dark matter content of satellite galaxies in Lambda-CDM cosmological hydrodynamical simulations of the Local Group from the APOSTLE project. We find excellent agreement between simulation results and estimates for the 9 brightest Galactic dwarf spheroidals (dSphs) derived from their stellar velocity dispersions and half-light radii. Tidal stripping plays an important role by gradually removing dark matter from the outside in, affecting in particular fainter satellites and systems of larger-than-average size for their luminosity. Our models suggest that tides have significantly reduced the dark matter content of Can Ven I, Sextans, Carina, and Fornax, a prediction that may be tested by comparing them with field galaxies of matching luminosity and size. Uncertainties in observational estimates of the dark matter content of individual dwarfs have been underestimated in the past, at times substantially. We use our improved estimates to revisit the `too-big-to-fail problem highlighted in earlier N-body work. We reinforce and extend our previous conclusion that the APOSTLE simulations show no sign of this problem. The resolution does not require `cores in the dark mass profiles, but, rather, relies on revising assumptions and uncertainties in the interpretation of observational data and accounting for `baryon effects in the theoretical modelling.
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The NGC 1052 group, and in particular the discovery of two ultra diffuse galaxies with very low internal velocity dispersions, has been the subject of much attention recently. Here we present radial velocities for a sample of 77 globular clusters associated with NGC 1052 obtained on the Keck telescope. Their mean velocity and velocity dispersion are consistent with that of the host galaxy. Using a simple tracer mass estimator, we infer the enclosed dynamical mass and dark matter fraction of NGC 1052. Extrapolating our measurements with an NFW mass profile we infer a total halo mass of 6.2 ($pm$0.2) $times$ 10$^{12}$ M$_{odot}$. This mass is fully consistent with that expected from the stellar mass--halo mass relation, suggesting that NGC 1052 has a normal dark matter halo mass (i.e. it is not deficient in dark matter in contrast to two ultra diffuse galaxies in the group). We present a phase space diagram showing the galaxies that lie within the projected virial radius (390 kpc) of NGC 1052. Finally, we briefly discuss the two dark matter deficient galaxies (NGC 1052--DF and DF4) and consider whether MOND can account for their low observed internal velocity dispersions.
Can normal science-in the Kuhnian sense-add something substantial to the discussion about the measurement problem? Does an extended Wigners-friend Gedankenexperiment illustrate new issues? Or a new quality of known issues? Are we led to new interpretations, new perspectives, or do we iterate the previously known? The recent debate does, as we argue, neither constitute a turning point in the discussion about the measurement problem nor fundamentally challenge the legitimacy of quantum mechanics. Instead, the measurement problem asks for a reflection on fundamental paradigms of doing physics.
For successful deployment of deep neural networks on highly--resource-constrained devices (hearing aids, earbuds, wearables), we must simplify the types of operations and the memory/power resources used during inference. Completely avoiding inference-time floating-point operations is one of the simplest ways to design networks for these highly-constrained environments. By discretizing both our in-network non-linearities and our network weights, we can move to simple, compact networks without floating point operations, without multiplications, and avoid all non-linear function computations. Our approach allows us to explore the spectrum of possible networks, ranging from fully continuo
Using ultra-deep imaging ($mu_g = 30.4$ mag/arcsec$^2$; 3$sigma$, 10x10), we probed the surroundings of the first galaxy lacking dark matter KKS2000[04] (NGC 1052-DF2). Signs of tidal stripping in this galaxy would explain its claimed low content of dark matter. However, we find no evidence of tidal tails. In fact, the galaxy remains undisturbed down to a radial distance of 80 arcsec. This radial distance triples previous spatial explorations of the stellar distribution of this galaxy. In addition, the distribution of its globular clusters (GCs) is not extended in relation to the bulk of the galaxy (the radius containing half of the GCs is 21 arcsec). We also found that the surface brightness radial profiles of this galaxy in the g and r bands decline exponentially from 35 to 80 arcsec. That, together with a constant ellipticity and position angle in the outer parts of the galaxy strongly suggests the presence of a low-inclination disk. This is consistent with the evidence of rotation found for this object. This finding implies that the dynamical mass of this galaxy is a factor of 2 higher than previously reported, bringing the dark matter content of this galaxy in line with galaxies of similar stellar mass.
Since 2013 IceCube cascade showers sudden overabundance have shown a fast flavor change above 30-60 TeV up to PeV energy. This flavor change from dominant muon tracks at TeVs to shower events at higher energies, has been indebted to a new injection of a neutrino astronomy. However the recent published 54 neutrino HESE, high energy starting events, as well as the 38 external muon tracks made by trough going muon formed around the IceCube, none of them are pointing to any expected X-gamma or radio sources: no one in connection to GRB, no toward active BL Lac, neither to AGN source in Fermi catalog. No clear correlation with nearby mass distribution (Local Group), nor to galactic plane. Moreover there have not been any record (among a dozen of 200 TeV energetic events) of the expected double bang due to the tau neutrino birth and decay. An amazing and surprising unfair distribution in flavor versus expected democratic one. Finally there is not a complete consistence of the internal HESE event spectra and the external crossing muon track ones. Moreover the apparent sudden astrophysical neutrino flux rise at 60 TeV might be probably also suddenly cut at a few PeV in order to hide the (unobserved , yet) Glashow resonance peak at 6.3 PeV. A more mondane prompt charmed atmospheric neutrino component may explain most of the IceCube puzzles. If this near future, 2017-2018, it does not shine tau neutrino signals somewhere (by tau airshowers in AUGER, TA, ASHRA or double bang in IceCube) there are a list of consequences to face. These missing correlations and in particular the tau signature absence force us to claim : No Tau? No neutrino Astronomy.
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