Day 1484

Wednesday.

1810.05649
Observable tests of self-interacting dark matter in galaxy clusters: cosmological simulations with SIDM and baryons
Robertson, et al

Present BAHAMAS-SIDM, the first large-volume, (400/h Mpc)^3, cosmological simulations including both self-interacting dark matter (SIDM) and baryonic physics.  These simulations are important for two primary reasons: 1) they include the effects of baryons on the DM distribution 2) the baryon particles can be used to make mock observables that can be compared directly with observations.  As is well known, SIDM haloes are systematically less dense in their centre, and rounder, than CDM haloes.  Here, find that these changes are not reflected in the distribution of gas or stars within galaxy clusters, or in their X-ray luminosities.  However, gravitational lensing observables can discriminate between DM models, and present a menu of tests that future surveys could use to measure the SIDM interaction strength.  Ray-trace the simulated galaxy clusters to produce strong lensing maps.  Including baryons boosts the lensing strength of clusters that produce no critical curves in SIDM-only simulations.  Comparing the Einstein radii of the simulated clusters with those observed in the CLASH survey, find that sigma/m<1cm^2/g at velocities around 1000 km/s.


1810.05765
A giant protocluster of galaxies at redshift 5.7
Jiang, et al

Galaxy clusters trace the large structures of the Universe and provide ideal laboratories for studying galaxy evolution and cosmology.  Clusters with extended X-ray emission have been discovered at redshifts up to z~2.5.  Meanwhile, there has been growing interest in hunting for protoclusters, the progenitors of clusters, at higher redshifts.  It is, however, very challenging to find the largest protoclusters at early times when they start to assemble.  Here, report a giant protoclusters of galaxy at z=5.7, when the Universe was only one billion years old.  This protocluster occupies a volume of about 35x35x35 cubic co-moving megaparsecs.  It is embedded in an even larger overdense region with at least 41 spectroscopically confirmed, luminous Lyman-alpha emitting galaxies (LAEs), including several previously reported LAEs.  Its LAE density is 6.6 times the average density at z~5.7.  It is the only one of its kind in an LAE survey in four square degrees on the sky.  Such a large structure is also rarely seen in current cosmological simulations.  This protocluster will collapse into a galaxy cluster with a mass of (3.6±0.9)e15 Msun, comparable to those of the most massive clusters or protoclusters known to date.


1810.05976
Relativistic electron scattering and bing bang nucleosynthesis
Sasankan et al

Big band nucleosynthesis (BBN) is a valuable tool to constrain the physics of the early universe and is the only probe of the radiation dominated epoch.  A fundamental assumption in BBN is that the nuclear velocity distributions obey Maxwell Boltzmann statistics as they do in stars  In this letter, however, point out that there is a fundamental difference between stellar reaction rates and BBN reaction rates.  Specifically, the BBN epoch is characterized by a dilute baryon plasma for which the velocity distribution of nuclei is mainly determined by the dominant Coulomb scattering with mildly relativistic electrons.  This modifies the nuclear velocity distributions and significantly alters the thermonuclear reaction rates, and hence, the light element abundances.  Show that this novel result alters all previous calculations of light element abundances from BBN, and indeed exacerbates the discrepancies between BBN and inferred primordial light-element abundances possibly suggesting the need for new physics in the early universe.