1709.07881
The build up of the correlation between halo spin and the large scale structure
Wang, Kang
Both simulations and observations have confirmed that the spin of haloes/galaxies is correlated with the LSS with a mass dependence such that the spin of low-mass halos/galaxies tend to be parallel with the LSS, while that of massive halos/galaxies tend to be perpendicular with the LSS. It is still unclear how this mass dependence is built up over time. Use N-body sims to trace the evolution of the halo spin-LSS correlation and find that at early times the spin of all halo progenitors is parallel with the LSS. As time goes on, mass collapsing around massive halo is more isotropic, especially the recent mass accretion along the slowest collapsing direction is significant and it brings the halo spin to be perpendicular with the LSS. Adopting the fractional anisotropy (FA) parameter to describe the degree of anisotropy of the LSS, find that the spin-LSS correlation is a strong function of the environment such that a higher FA (more anisotropic environment) leads to an aligned signal, and a lower anisotropy leads to a misaligned signal. The results show in general that the spin-LSS correlation is a combined consequence of mass flow and halo growth within the cosmic web. The predicted environmental dependence between spin and large-scale structure can be further tested using galaxy surveys.
1709.08186
The effects of the WISE/GALEX photometry for the SED-Fitting with M31 star clusters and candidates
Fan, Wang
Conclude that the GALEX FUV/NUV bands are more crucial for the SED-fittting of ages and metallicities than the other bands [in UBVRIJHK], and high-quality UV data (with high photometry precision) are required.
1709.08437
How to confirm the existence of population III stars by observations of gravitational waves
Miyamoto, et al
Propose a method for confirmation of the existence of Pop III stars with massive BH binaries as GW15914 in gravitational wave (GW) observation. When there are enough number of events, want to determine which model is closer to reality, with and without Pop III stars. Need to prepare various "Pop I/II models" and various Pop I/II/III models" and investigate which model is consistent with the events. To demonstrate the analysis, simulate detections of GW events for some examples of population synthesis models with and without Pop III stars. Calculate the likelihood ratio with the realistic number of events and evaluate the probability of identifying the existence of Pop III stars. In typical cases, the analysis can distinguish between Pop I/II model and Pip I/II/III model with 90% probability by 22 GW signals from BH-BH binary mergers.
1709.08647
Comparing galaxy formation in semi-analytic models and hydrodynamical simulations
Mitchell, et al
It is now possible for hydro sims to reproduce a representative galaxy population. Accordingly, it is timely to assess critically some of the assumptions of traditional semi-analytic galaxy formation models. Use the Eagle sims to assess assumptions built into the Galform SAM, focussing on those relating to baryon cycling, angular momentum ad feedback. Show that the assumption in Galform that newly formed stars have the same specific angular momentum as the total disc leads to a significant overestimate of the total stellar specific angular momentum of disc galaxies. In Eagle, stars form preferentially out of low specific angular momentum gas in the ISM due to the assumed gas density threshold for stars to form, leading to more realistic galaxy sizes. Find that stellar mass assembly is similar between Galform and Eagle but that the evolution of gas properties is different, with various indications that the rate of baryon cycling in Eagle is slower than is assumed in Galform. Finally, by matching individual galaxies between Eagle and Galform, find that an artificial dependence of AGN feedback and gas infall rates on halo mass doubling events in Galform drives most of the scatter in stellar mass between individual objects. Put together the results suggest that the Galform SM can be significantly improved in light of recent advances.
1709.09371
Are redshift-space distortions actually a probe of growth of structure?
Kimura, et al
Present an impact of coupling between DM and a scalar field, which might be responsible for DE, son measurements of z-space distortions. Point out that, in the presence of conformal and/or disformal coupling, linearized continuity and Euler equations for total matter fluid significantly deviate from the standard ones even in the sub-horizon scales. In such a case, a peculiar velocity of total matter field is determined not only by a logarithmic time derivative of its density perturbation but also by density perturbations for both DM and baryon, leading to a large modification of the physical interpretation of observed data obtained by measurements of z-space distortions. Reformulate galaxy 2-pt correlation function in the space based on the modified continuity and Eulier equations. Conclude from the resultant formula that the true value of the linear growth rate of LSS cannot be necessarily constrained by single-z measurements of the z-space distortions, unless one observed the actual time-evolution of structure.
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