1505.05158
Strong ultraviolet pulse from a newborn type Ia supernova
Cao, et al
Type Ia SNe: although they are used empirically to measure cosmo distances, the nature of their progenitors remains mysterious. One of the leading progenitor models, called the single degenerate channel, hypothesizes that a WD accrete matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Report observations of strong but declining UV emission from a Type Ia SN within 4 days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the SN and a companion star, and therefore provides evidence that some Type Ia SNe arise from the single degenerate model.
1505.05470
The offsets between galaxies and their dark matter in {\Lambda}CDM
Schaller, Robertson, Massey, Bower, Eke
Use the EAGLE suite of hydro cosmo sims to measure offsets between the centers of stellar and DM components of galaxies. Find that the vast majority (>95%) of the simulated galaxies display an offset smaller than the gravitational softening length of the simulations (700pc), both for field galaxies and satellites in clusters and groups. Also find no systematic trailing or leading of the DM along a galaxy's direction ofmostion. The offsets are consistent with being randomly drawn from a Maxwellian distribution with a sigma=196pc. Since astrophysical effects produce no feasible analogues for the 1.62±0.48 kpc offset recently observed in Abell 3827, this observational result is in tension with the collisionless CDM assumed in the sims.
1505.03468
Galaxy cluster lensing masses in modified lensing potentials
Barreira, et al
Determine the concentration-mass relation of 19 X-ray selected galaxy clusters from the CLASH survey in theories of gravity that directly modify the lensing potential. Model the clusters as NFW haloes and fit their lensing signal, in the Cubic Galileon and Nonlocal gravity models, to the lensing convergence profiles of the clusters. Discuss a number of important issues that need to be taken into account, associated with the use of nonparametric and parametric lensing methods, as well as assumptions about the background cosmology. Results show that the concentration and mass estimates in the modified gravity models are, within the error bars, the same as in LCDM. This result demonstrates that, for the Nonlocal model, the modifications to gravity are too weak at the cluster redshifts, and for the Galileon model, the screening mechanism is very difficult inside the cluster radius. However, at distances ~[2-20]Mpc/h from the cluster center, find that the surrounding force profiles are enhanced by ~20-40% in the Cubic Galileon model. This has an impact on dynamical mass estimates, which means that tests of gravity based on comparisons between lensing and dynamical masses can also be applied to the Cubic Galileon model.
1505.03592
Precipitation-regulated star formation in galaxies
Voit, Bryan, O'Shea, Donahue
Galaxy growth depends critically on the interplay between radiative cooling of cosmic gas and the resulting energetic feedback that cooling triggers. This interplay has proven exceedingly difficult to model, even with large supercomputer simulations, because of its complexity. Nevertheless, real galaxies are observed to obey simple scaling relations among their primary observable characteristics. Show that a generic emergent property of the interplay between cooling and feedback can explain the observed scaling relationships between a galaxy's stellar mass, its total mass, and its chemical enrichment level, as well as the relationship between the average orbital velocity of its stars and the mass of its central black hole. These relationships naturally result from any feedback mechanism that strongly heats a galaxy's circumgalactic gas in response to precipitation of colder clouds out of that gas, because feedback then suspends the gas in a marginally precipitating state.
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