1811.09070
The dark matter deficit galaxies in hydrodynamical simulations
Jing, et al
Low mass galaxies are expected to be DM dominated even with their centrals. Recently two observations reported two dwarf galaxies in group environment with very little dark matter in their centrals. Explore the population and origins of DM deficit galaxies (DMDGs) in 2 state-of-the-art hydro sims, the EAGLE and Illustris projects. For all satellite galaxies with M*>1e9 Msun in groups with M200>1e13 Msun, find that about 5.0% of them in the EAGLE, and 3.2 % in the Illlustris are DMDGs with DM fractions below 50% inside 2x half-stellar-mass radii. Demonstrate the DMDGs are highly tidal disrupted galaxies; and because DM has higher binding energy than stars, mass loss of the DM is much more rapid than stars in DMDGs during tidal interactions. If DMDGs were confirmed in observations, they are expected in current galaxy formation models.
1811.09598
KiDS+GAMA: intrinsic alignment model constraints for current and future weak lensing cosmology
Johnston, et al
Directly constrain the NLA model of galaxy IA, analyzing the most representative and compete flux-limited sample of spectroscopic galaxies available for cosmic shear surveys. Measure the projected galaxy position-intrinsic shear correlations and the projected galaxy clustering signal using high- resolution imaging from KiDS overlapping with GAMA, and data from SDSS. Separating samples by color, make no significant detection of blue galaxy alignments, constraining the blue galaxy NLA amplitude A_IA^B=0.2±0.4 to be consistent with zero. Make robust detections (~9sigma) for red galaxies, with A_IA^R=3.4±0.5, corresponding to a net radial alignment with the galaxy density field. Provide informative priors for current and future WL surveys, and improvement over de facto wide priors that allow for unrealistic levels of IA contamination. For a color-split cosmic shear analysis of the final KiDS survey area, forecast that the priors will improve the constraining power on S_8 and the DE equation of state w_0, by up to 62% and 51%, respectively. The results indicate, however, that the modeling of red/blue-split galaxy alignments may be insufficient to describe samples with variable central/satellite galaxy fractions.
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