1510.03426
Dynamics of stream-subhalo interactions
Sanders, Bovy, Erkal
Develop a formalism for modeling the impact of DM subhalos on cold thin streams. The formalism models the formation of a gap in a stream in angle-frequency space and is able to handle general stream and impact geometry. Analyse an N-body simulation of a cold stream formed from a progenitor on an eccentric orbit in an axisymmetric potential, which is perturbed by a direct impact from a 1e8 Msun sub halo, and produce a complete generative model of the perturbed stream that matches the simulation well at a range of times. Show how the results in angle-frequency space can be related to physical properties of the gaps and that previous results for more constrained simulations are recovered. Demonstrate how the results are dependent upon the mass of the sub halo and the location of the impact along the stream. Find that gaps formed far downstream grow more rapidly than those closer to the progenitor due to the more ordered nature of the stream members far from the progenitor. Additionally, show that the minimum gap density plateaus in time at a value that decreases with increasing sub halo mass.
1510.03431
Tetrahedral collapse: a rotational toy model of simultaneous dark-matter halo, filament and wall formation
Neyrinck
Discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest-possible fully 3-D halo collapse in the 'origami approximation,' in which voids are irrotational, and the DM sheet out of which DM structures form is allowed to fold in position-velocity phase space, but not stretch (i.e., it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only 3 other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighboring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.
1510.03486
Mapping the dark matter distribution of the "Toothbrush" cluster RX J0603.3+4214 with Hubble Space Telescope and Subaru Weak-lensing
Jee, Dawson, Stroe, Wittman,et al
The galaxy cluster at z=0.225 is one of the rarest clusters boasting an extremely large (~2Mpc) radio-relic. Because of the remarkable morphology of the relic, the cluster is nicknamed "Toothbrush Cluster". Although the cluster's underlying mass distribution is one of the critical pieces of information needed to reconstruct the merger scenario responsible for the puzzling radio-relic morphology, its proximity to the Galactic plane b~10 deg has imposed significant observational challenges. Present a high-resolution WL study of the cluster with Subaru/Suprime Cam and HST imaging data. The mass reconstruction reveals that the cluster is comprised of complicated DM substructures closely tracing the galaxy distribution, however in contrast with the relatively simple binary X-ray morphology. Nevertheless, find that the cluster mass is still dominated by the two most massive clumps aligned NS with a ~3:1 mass ratio (M200=6.29e14 Msun and 1.98e14 Msun for N/S clumps, respectively). The southern mass peak is ~2' offset toward the south with respect to the corresponding X-ray peak, which has a "bullet"-like morphology pointing south. Comparison of the current WL result with the X-ray, galaxy, and radio-relic suggests that perhaps the dominant mechanism responsible for the observed relic may be a high-speed collision of the two most massive subclusters, although the peculiarity of the morphology necessitates involvement of additional sub-clusters. Careful numerical simulations should follow in order to obtain more complete understanding of the merger scenario utilizing all existing observations.
1510.03489
The rotation of galaxy clusters
Tovmassian
Propose a method for detection of the galaxy cluster rotation based on the study of distribution of member galaxies with velocities higher and lower of the cluster mean velocity over the cluster image. The search for rotation is made for flat cluster with a/b>1.8and BMI type [?] clusters which are expected to be rotating. For comparison, studied also round clusters and clusters of NBMI type, the second by brightness galaxy in which does not differ significantly from the cluster cD galaxy. 17/65 clusters are found to be rotating. Found that the detection rate is sufficiently high for flat clusters, over 60%, and clusters of BMI type with dominant cD galaxy, ~35%. The obtained results show that clusters were formed from the huge primordial gas clouds and preserved the rotation of the primordial clouds, unless they did not have merging with other clusters and groups of galaxies, in the result of chic the rotation has been prevented.
1510.03554
Streaming velocities and the baryon-acoustic oscillation scale
Blazek, McEwen, Hirata
At the epoch of decoupling, cosmic baryons had supersonic velocities relative to the DM that were coherent on large scales. These velocities subsequently slow the growth of small-scale structures and, via feedback processes, can influence the formation of larger galaxies. Examine the effect of streaming velocities on the galaxy correlation function, including all leading-order contributions for the first time. Find that the impact on the BAO peak is dramatically enhanced (by a factor of ~5) over the results of previous investigations, with the primary new effect due to advection: if a galaxy retains memory of the primordial streaming velocity, it does so at its Lagrangian, rather than Eulerian, position. Since correlations in the streaming velocity change rapidly at the BAO scale, this advection term can cause a significant shift in the observed BAO position. If streaming velocities impact tracer density at the 1% level, compared to the linear bias, the recovered BAO scale is shifted by approximately 0.5%. This new effect greatly increases the importance of including streaming velocities in the analysis of upcoming BAO measurements and opens a new window to the astrophysics of galaxy formation.
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