Saturday.
1503.01116
Raising the bar: new constraints the Hubble parameter with cosmic chronometers at z$\sim$2
Moresco
One of the most compelling tasks of modern cosmology is to constraint the expansion history of the Universe, since this measurement can give insights on the nature of DE and help estimate cosmo parameters. Present two new measurements of the Hubble parameter H(z) obtained with the cosmic chronometer method up to z~2. Taking advantage of NIR spectroscopy of the few very massive and passive galaxies observed at z>1.4 available in literature, the differential evolution of this population is estimated and calibrated with different stellar population synthesis models to constrain H(z), including in the final error budget all possible sources of systematic uncertainties (SFH, stellar metallicity, model dependencies). This analysis is able to extend significantly the z range coverage with respect to present day constraints, crossing for the first time the limit at z~1.75. The new H(z) data are used to estimate the gain in accuracy on cosmo params with respect to previous measurements in two cosmo models, finding a small but detectable improvement (~5%) in particular on Omega_m and w_0. Finally, a simulation of a Euclid-like survey has been performed to forecast the expected improvement with future data. The provided constraints have been obtained just with the cosmic chronometers approach, without any additional data, and the results show the high potentiality of this method to constrain the expansion history of the Universe at these z.
1503.01117
Galactic angular moment in the Illustris Simulation: feedback and the Hubble sequence
Genel, Fall, Hernquist, Vogelsberger, Snyder, Rodriguez-Gomez, Sijacki, Springel
Study the angular momentum of galaxies in Illustris, which captures gravitational and gas dynamics within galaxies, as well as feedback from stars and BHs. Find that the angular momentum of the simulated galaxies matches observations well, and in particular two distinct relations are found for late-type vs early-type galaxies. The relation for late-type galaxies corresponds to the value expected from full conservation of the specific angular momentum generated by cosmo tidal torques. The relation for early-type galaxies corresponds to retention of only ~30% of that, but find that those early-type galaxies with low angular momentum at z=0 nevertheless reside at high z on the late-type relation. To gain further insight, explore the scaling relations in sims where the galaxy formation physics is modified wrt the fiducial model. Find that galactic winds with high mass-loading factors are essential for obtaining the high angular momentum relation typical for late-type galaxies, while AGN feedback largely operates in the opposite direction. Hence, feedback controls the angular momentum of galaxies, and appears to be instrumental for establishing the Hubble sequence.
1503.01125
Weak-lensing by the large scale structure in a spatially anisotropic universe: theory and predictions
Pitrou, Pereira, Uzan
Detail the computation of 2pt correlators for the convergence, E- and B-modes of the cosmic shear induced by the WL by LSS assuming that the BG spacetime is spatially homogeneous and anisotropic. After detailing the perturbation equations and the general theory of WL in an anisotropic universe, it develops a weak shear approximation scheme in which one can compute analytically the evolution of the Jacobi matrix. It allows one to compute the angular power spectrum of the E- and B-modes. In the linear regime, the existence of B-modes is a direct tracer of a late time anisotropy and their angular PS scales as the square of the shear. It is then demonstrated that there must also exist off-diagonal correlations between the E-modes, B-modes and convergence that are linear in the geometrical shear and allow one to reconstruct the eigen directions of expansion. These spectra can be measured in future large scale surveys, such as Euclid and SKA, and offer a new tool to test the isotropy of the expansion of the universe at low redshift.
1503.013333
The gender breakdown of the applicant pool for tenure-track faculty positions at a sample of north american research astronomy programs
Thompson
Find that the ratio of female applicants to the total number of applicants is ~0.2, with little dispersion and with no strong dependence on the total number of applicants.
1503.01482
Three-dimensional multi-probe analysis of A1689
Umetsu, et al
Perform a 3d multi-probe analysis of A1689 by combining improved WL data from new BVRi'z' Subaru/Suprime-Cam observations with SL, X-ray, and SZE data sets. Reconstruct the projected matter distribution from a joint WL analysis of 2d shear and azimuthally integrated magnification constraints, the combination that allows breaking of the mass-sheet degeneracy. The resulting mass distribution reveals elongation with axis ratio ~0.7 in projection. When assuming a spherical halo, the full WL analysis yields a projected concentration of 8.9pm1.1, consistent with and improved from earlier WL work. Find excellent consistency between WL and SL in the region of overlap. In a parametric triaxial framework, constrain the intrinsic structure and geometry of the matter and gas distributions, by combining WL/SL and X-ray/SZE data with minimal geometric assumptions. Show that the data favor a triaxial geometry with minor-major axis ratio 0.39±0.15 and major axis closely aligned with the LoS (22±10 deg). Obtain M_200c=(1.2±0.2)e15 Msun/h and c_200c=8.4±1.3, which overlaps with the >1sigma tail of the predicted distribution. The shape of the gas is rounder than the underlying matter but quite elongated with minor-major axis ratio 0.60±0.14. The gas mass fraction within 0.9 Mpc is 10+3-2%. The thermal gas pressure contributes to ~60% of the equilibrium pressure, indicating a significant level of non-thermal pressure support. When compared to Planck's hydrostatic mass estimate, the lensing measurements yield a spherical mass ratio of M_Planck/M_GL=0.70±0.15 and 0.58±0.10 with and without corrections for lensing projection effects, respectively.
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