1507.03988
Observational consequences of turbulent pressure in the envelopes of massive stars
Grassitelli, Fossati, Simon-Diaz, Langer, Castro, Sanyal
The major mass fraction of the envelope of hot luminous stars is radiatively stable. However, the partial ionization of H, He and Fe gives rise to extended sub-surface convection zones in all of them. In this work, investigate the effect of the pressure induced by the turbulent motion in these zones based on the mixing length theory, and search for observable consequences. Find that the turbulent pressure fraction can amount up to ~5% in OB supergiants, and to ~30% in cooler supergiants. The resulting structural changes are, however, not significantly affecting the evolutionary tracks compared to previous calculations. Instead, a comparison of macro turbulent velocities derived from high quality spectra of OB stars with the turbulent pressure fraction obtained in corresponding stellar models reveals a strong correlation of these two quantities. Discuss a possible physical connection, and conclude that turbulent pressure fluctuations may drive high-order oscillations, which - as conjectured earlier - manifest themselves as macro turbulence in the photospheres of hot luminous stars.
1507.03992
Frontier Fields: Subary weak-lensing analysis of the merging galaxy cluster A2744
Medezinski, Umetsu, Okabe, Nonino, Molnar, Massey, Dupke, Merten
Present a WL analysis of the merging FF cluster A2744 using Suprime-cam imaging. The wide-field lensing mass distribution reveals this cluster is comprised of 4 distinct substructures. Simultaneously modeling the 2d reduced shear field using a combination of NFW model for the main core and truncated NFW models for the sub haloes, determine their masses and locations. The total mass of the system is constrained as M_200c=2.06±0.42e15 Msun. The most massive clump is the southern component with M_200c=7.7±3.4e14 Msun, followed by the western substructure M_200c=4.5±2.0e14 Msun and 2 smaller substructures to the NE M_200c=2.8±1.6e14Msun, and NW M_200c=1.9±1.2e14 Msun. The presence of the 4 substructures supports the picture of multiple mergers. Using a composite of hydrodynamical binary simulations explain this complicated system without the need for a "slingshot" effect to produce the northwest X-ray interloper, as previously proposed. The locations of the substructures appear to be offset from both the gas (87+34-28 arctic, 90%CL) and the galaxies (72+34-53 arctic, 90%CL) in the case of the NW and W subhalos. To confirm or refute these findings, high resolution space-based observations extending beyond the current FF limited coverage to the W and NW area are essential.
1507.04301
CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment
Schrabback, Hilbert, Hoekstra, Simon, van Uitert, Erben, Heymans, Hildebrandt, Kitching, Mellier, Miller, Van Waerbeke, Bett, Coupon, Fu, Hudson, Joachimi, Kilbinger, Kuijken
Present WL constrains on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment. Using data from CFHTLenS, measure the weighted-average ratio of the aligned projected ellipticity components of galaxy matter halos and their embedded galaxies, f_h, split by galaxy type. Then compare the observations to measurements taken from Millennium Sims, assuming different models of galaxy-halo misalignment. Using Millennium Sims verify that the statistical estimator used removes contamination from cosmic shear. Also detect an additional signal in the simulations, which is interpreted as the impact of inartistic shape-shear alignments between the lenses and their large-scale substructure environment. These alignments are likely to have caused some of the previous observational constraints on f_h to be biased high. From CFHTLenS, find f_h=-0.04±0.25 for early-type galaxies, which is consistent with current models for the galaxy-halo misalignment predicting f_h~0.20. For late-type galaxies, measure f_h=0.69±0.36 from CFHTLenS. This can be compared to the simulated results which yield f_h~0.02 for misaligned late-type models.
1507.04338
Analytical model for non-thermal pressure in galaxy clusters - II. removing the hydrostatic mass bias
Shi, Komatsu, Nagai, Lau
Non-thermal pressure in galaxy clusters leads to underestimation of the mass of galaxy clusters based on hydrostatic equilibrium with thermal gas pressure. This occurs even for dynamically relaxed clusters that are used for calibrating the mass-observable scaling relations. Show that the analytical model for non-thermal pressure developed in Shi+Komatsu 2014 can correct for this so-called 'hydrostatic mass bias', if most of the non-thermal pressure comes from bulk and turbulent motions of gas in the ICM. The correction works for the sample average irrespective of the mass estimation method, or the dynamical state of the clusters. This makes it possible to correct for the bias in the hydrostatic mass estimates from X-ray surface brightness and the SZ observations that will be available for clusters in a wide range of redshifts and dynamical states.
No comments:
Post a Comment