1604.00394
Mass segregation in star clusters is not energy equipartition
Parker et al
Mass segregation in star clusters is often thought to indicate the onset of energy equipartition, where the most massive stars impart kinetic energy to the lower-mass stars and brown dwarfs/free floating planets. The predicted net result of this is that the centrally concentrated massive stars should have significantly lower velocities thanfast-moving low-mass objects on the periphery of the cluster. Search for energy equipartition in initially spatially and kinematically substructures N-body simulations of star clusters with N-1500 stars, evolved for 100 Myr. In clusters that show significant mass segregation, find no differences in the proper motions or radial velocities as a function of mass. The kinetic energies of all stars decrease as the clusters relax, but the kinetic energies of the most massive stars do not decrease faster than those of lower-mass stars. These results suggest that dynamical mass segregation -- which is observed in many star clusters -- is not a signature of energy equipartition from 2-body relaxation.
1604.00435
Galaxy Zoo: Mergers - Dynamical models of interacting galaxies
Holincheck et al
With the use of a restricted 3-body simulation code and the help of Citizen Scientists, sample 1e5 points in parameter space for each system. Demonstrate a successful recreation of the morphologies of 62 pairs of interacting galaxies through the review of more than 3 million simulations. Examine the level of convergence and uniqueness of the dynamical properties of each system. These simulations represent the largest collection of models of interacting galaxies to date, providing a valuable resource for the investigation of mergers. This paper present the simulation parameters generated by the project, available online. Though the best-fit model parameters are not an exact match to previously published models, the method for determining uncertainty measurements will aid future comparison between models. The dynamical clocks from the models agree with previous results of the time since the onset of SF from star burst models in interacting systems and suggests that tidally induced star formation is triggered very soon after closest approach.
1604.00652
Galaxy redshifts form discrete optimization of correlation functions
Lee, Budavári, Basu
Propose a new method of constraining the redshifts of individual extragalactic sources based on their celestial coordinates. Techniques from integer linear programming are utilized to optimize simultaneously for the angular 2-pt cross- and autocorrelation functions. The novel formalism introduced here not only transforms the otherwise hopelessly expensive, brute-force combinatorial search into a linear system with integer constraints but is also readily implementable in off-the-shelf solvers. Adopt Gurobi and use Python to dynamically build the cost function. The preliminary results on simulated data show great promise for future applications to sky surveys by complementing and enhancing photometric redshift estimators. The approach is the first use of linear programming in astronomy.
1604.00988
Galaxy populations in massive galaxy clusters to z=1.1: color distrubiton, concentration, halo occupation number and red sequence fraction
Hennig Mohr, et al
Study the galaxy populations in 74 SZE selected clusters from SPT survey that have been imaged in SV phase of DES. The sample extends up to z~1.1 with 4e14 Msun < M200 < 3e15 Msun. Using the band containing the 4000 A break and its reward neighbor, study the color-magnitude distributions of cluster galaxies to ~m*+2 fining: (1) the intrinsic rest frame g-4 color width of the red sequence (RS) population is ~0.03 out to z~0.85 with a preference for an increase to ~0.07 at z=1 and (2) the prominence of the RS declines beyond z~0.6. The spatial distribution of cluster galaxies is well described by the NFW profile out to 4R200 with a concentration of c_g=3.59±0.2, 5.37±0.27 and 1.38±0.2 for the full, the RS and the blue non-RS populations, respectively, but with ~40% to 55% cluster to cluster variation and no statistically significant redshift or mass trends. The number of galaxies within the viral region N200 exhibits a mass trend indicating that the number of galaxies per unit total mass is lower in the most massive clusters, and shows no significant redshift trend. The RS fraction within R200 is (68±3)% at z=0.46, varies from ~55% at z=1 to ~80% at z=0.1, and exhibits intrinsic variation among clusters of ~14%. Discuss a model that suggests the observed redshift trend in RS fraction favors a transformation timescale for infalling field galaxies to become RS galaxies of 2 to 3 Gyr.
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