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Sanders R.H.,NOVA Kapteyn Astronomical Institute
Monthly Notices of the Royal Astronomical Society | Year: 2014

show that the lensing masses of the Sloan Lens Advanced Camera Surveys sample of strong gravitational lenses are consistent with the stellar masses determined from population synthesis models using the Salpeter initial mass function. This is true in the context of both General Relativity and modified Newtonian dynamics (MOND), and is in agreement with the expectation of MOND that there should be little classical discrepancy within the high surface brightness regions probed by strong gravitational lensing. There is also dynamical evidence from this sample supporting the claim that the mass-to-light ratio of the stellar component increases with the velocity dispersion. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Sanders R.H.,NOVA Kapteyn Astronomical Institute
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

I argue that, despite repeated claims of Ibata et al., the globular cluster NGC 2419 does not pose a problem for modified Newtonian dynamics (MOND). I present a new polytropic model with a running polytropic index. This model provides an improved representation of the radial distribution of surface brightness while maintaining a reasonable fit to the velocity dispersion profile. Although it may be argued that the differences with these observations remain large compared to the reported random errors, there are several undetectable systematic effects which render a formal likelihood analysis irrelevant. I comment generally upon these effects and upon the intrinsic limitations of pressure-supported objects as tests of gravity. © 2012 The Author. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source


Sanders R.H.,NOVA Kapteyn Astronomical Institute
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

I show that, in the context of modified Newtonian dynamics (MOND), non-isothermal models, approximated by high-order polytropic spheres, are consistent with the observations of the radial distribution of the line-of-sight velocity dispersion in the distant globular cluster, NGC 2419. This calls into question the claim by Ibata et al. that the object constitutes a severe challenge for MOND. In general, the existence and properties of globular clusters are more problematic for LCDM than for MOND. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Bekenstein J.D.,Hebrew University of Jerusalem | Sanders R.H.,NOVA Kapteyn Astronomical Institute
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

Wojtak, Hansen & Hjorth have recently claimed to confirm general relativity (GR) and to rule out the tensor-vector-scalar (TeVeS) gravitational theory based on an analysis of the gravitational redshifts of galaxies in 7800 clusters. However, their ubiquitous modelling of the sources of cluster gravitational fields with Navarro-Frenk-White mass profiles is neither empirically justified out to the necessary radii in clusters, nor germane in the case of TeVeS. Using MONDian (whereMONDstands for MOdified Newtonian Dynamics) isothermal sphere models consistently constructed within MOND (equivalent to TeVeS models), we can fit the determined redshifts no worse than does GR with dark haloes. Moreover, Wojtak, Hansen & Hjorth have inappropriately used the simple MOND interpolating function for the μ function of the scalar field of TeVeS; the consequent MOND effective interpolating function turns out to enhance the gravitational potential, and so contributes to the discrepancy which forms the basis of their claims. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source


Salvadori S.,NOVA Kapteyn Astronomical Institute | Ferrara A.,Normal School of Pisa
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

In order to characterize damped Lyα aborption systems (DLAs) potentially hosting first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf galaxies. The merger tree method previously developed is extended to include inhomogeneous reionization and metal mixing, and it is validated by matching both the metallicity distribution function of Galactic halo stars and the Fe-luminosity relation of dwarf spheroidal galaxies. The model explains the observed N HI-Fe relation of DLAs along with the chemical abundances of [Fe/H] <-2 systems. In this picture, the recently discovered z abs ≈ 2.34 C-enhanced DLA pertains to a new class of absorbers hosting first stars along with second-generation long-living lowmass stars. These 'Population III DLAs' are the descendants of H 2-cooling minihaloes with M h ≈ 10 7M ⊙, which virialize at z > 8 in neutral, primordial regions of the MW environment and passively evolve after a short initial period of star formation. The gas in these systems is warm T g ≈ (40-1000) K, and strongly C-enriched by long-living, extremely metal-poor stars of total mass M * ≈ 10 2.-10 4M ⊙. © 2011 The Authors Monthly Notices of the Royal Astronomical Society. © 2011 RAS. Source

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