gds6

https://tritonstation.wordpress.com/2016/10/21/la-fin-de-quoi/

B.W. Keller, J.W. Wadsley

Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond {\Lambda}CDM . In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 {\Lambda}CDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.

Mordehai Milgrom

Keller and Wadsley (2016) have smugly suggested, recently, that the end of MOND may be in view. This is based on their claim that their highly-restricted sample of $\Lambda$CDM-simulated galaxies are "consistent" with the observed MOND mass-discrepancy-acceleration relation (MDAR), in particular, with its recent update by McGaugh et al. (2016), based on the SPARC sample. From this they extrapolate to "$\Lambda$CDM is fully consistent" with the MDAR. I explain why these simulated galaxies do not show that $\Lambda$CDM accounts for the MDAR. a. Their sample of simulated galaxies contains only 18 high-mass galaxies, within a narrow range of one order of magnitude in baryonic mass, at the very high end of the observed, SPARC sample, which spans 4.5 orders of magnitude in mass. More importantly, the simulated sample has none of the low-mass, low-acceleration galaxies -- abundant in SPARC -- which encapsulate the crux and the nontrivial aspects of the predicted and observed MDAR. The low-acceleration part of the simulated MDAR is achieved, rather trivially, from the flattish-velocity-curve regions of the simulated high-mass galaxies. b. Half of the simulated galaxies have "wrong" rotation curves that differ greatly from any observed ones. This, does not prevent these wrong galaxies from lying on the observed MDAR (for trivial reasons, again). They, in fact, define the high-acceleration branch of the simulated MDAR. c. To boot, even if $\Lambda$CDM were made "consistent" with the MDAR through the elaborate adjustments that the simulations allow, this would not obviate MOND, which predicts much more than the MDAR.

Alexandra Terrana, Mary-Jean Harris, Matthew C. Johnson

Due to cosmic variance we cannot learn any more about large-scale inhomogeneities from the primary cosmic microwave background (CMB) alone. More information on large scales is essential for resolving large angular scale anomalies in the CMB. Here we consider cross correlating the large-scale kinetic Sunyaev Zel'dovich (kSZ) effect and probes of large-scale structure, a technique known as kSZ tomography. The statistically anisotropic component of the cross correlation encodes the CMB dipole as seen by free electrons throughout the observable Universe, providing information about long wavelength inhomogeneities. We compute the large angular scale power asymmetry, constructing the appropriate transfer functions, and estimate the cosmic variance limited signal to noise for a variety of redshift bin configurations. The signal to noise is significant over a large range of power multipoles and numbers of bins. We present a simple mode counting argument indicating that kSZ tomography can be used to estimate more modes than the primary CMB on comparable scales. This paper motivates a more systematic investigation of how close to the cosmic variance limit it will be possible to get with future observations.

Jeppe Trøst Nielsen, Alberto Guffanti, Subir Sarkar

The "standard" model of cosmology is founded on the basis that the expansionrate of the universe is accelerating at present --- as was inferred originallyfrom the Hubble diagram of Type Ia supernovae. There exists now a much biggerdatabase of supernovae so we can perform rigorous statistical tests to checkwhether these "standardisable candles" indeed indicate cosmic acceleration.Taking account of the empirical procedure by which corrections are made totheir absolute magnitudes to allow for the varying shape of the light curve andextinction by dust, we find, rather surprisingly, that the data are still quiteconsistent with a constant rate of expansion.

http://www.nature.com/articles/srep35596

Joel D. Green, Johannes Burge, John A. Stansberry, Bonnie Meinke

The two most powerful optical/IR telescopes in history -- NASA's Hubble and James Webb Space Telescopes -- will be in space at the same time. We have a unique opportunity to leverage the 1.5 million kilometer separation between the two telescopic nodal points to obtain simultaneously captured stereoscopic images of asteroids, comets, moons and planets in our Solar System. Given the recent resurgence in stereo-3D movies and the recent emergence of VR-enabled mobile devices, these stereoscopic images provide a unique opportunity to engage the public with unprecedented views of various Solar System objects. Here, we present the technical requirements for acquiring stereoscopic images of Solar System objects, given the constraints of the telescopic equipment and the orbits of the target objects, and we present a handful of examples.