1812.09472
Big bang nucleosynthesis in a weakly non-ideal plasma
Jan, Kwan, Kwak, Cheoun
Propose a correction of standard BBN scenario to resolve the primordial Li problem by considering a possibility that the primordial plasma can deviate from the ideal state. In the standard BBN, the primordial plasma is assumed to be ideal, particles and photons satisfying the Maxwell-Boltzmann and Planck distribution, respectively. Suggest that this assumption of the primordial plasma being ideal might oversimplify the early universe and cause the Li problem. Find that deviation of photon distribution from the Planck distribution, which is parameterized with the help of Tsallis statistics, can resolve the primordial Li problem when the particle distributions of the primordial plasma still follow the Maxwell-Boltzmann distribution. Discuss how the primordial plasma can be weakly non-ideal in this specific fashion and its effects on the cosmic evolution.
1812.09473
Summing up Ultra-High-Energy Cosmic Rays from Radio Galaxies
Eichmann
Radio galaxies are intensively discussed as the sources of CRs observed above about 3 EeV, called UHECRs. The key issues from a recent investigation are summed up, where the individual characteristics of radio galaxies, as well as the impact by the extragalactic magnetic-field structures up to a distance of 120 Mpc has been taken into account. It is shown that the average contribution of radio galaxies taken over a very large volume cannot explain the observed features of UHECRs measured at Earth. However, obtain excellent agreement with the spectrum, composition, and arrival-direction distribution of UHECRs measured by the Pierre Auger Observatory, if assumed that most UHECRs observed arise from only two sources: the ultra-luminous radio galaxy Cygnus A, providing a mostly light composition of nuclear species dominating up to about 60 EeV, and the nearest radio galaxy Centaurus A, providing a heavy composition dominating above 60 EeV. Here, it is assumed that extra galactic magnetic fields out to 250 Mpc, which is not included in the sim, are able to isotropic the UHECR events at about 8 EeV arriving from Cygnus A.
1812.09673
Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies
Liu, Guo, Yuan
The origin of Galactic CRs (GCRs) remains a mystery after more than one century of their discovery. The diffusive propagation of charged particles in the turbulent Galactic magnetic field makes us unable to trace back to their acceleration sites. Nevertheless, nearby GCR source(s) may leave imprints on the locally measured energy spectra and the anisotropies of the arrival direction. In this work, propose a simple but natural description of the GCR production and propagation, within a two-zone disk-halo diffusion scenario together with a nearby source, to understand the up-to-date precise measurements of the energy spectra and anisotropies of GCRs. Find that a common energy scale of ~100 TeV appears in both energy spectra of protons and Helium nuclei measured recently by CREAM and large-scale anisotropies detected by various experiments. These results indicate that one or more local sources are very likely important contributors to GCRs below 100 TeV. This study provides a probe to identify source(s) of GCRs by means of joint efforts of spectral and anisotropy measurements.
1812.10480
Characterization of dust events on Earth and Mars: the ExoMars/DREAMS experiment and the field campaigns in the Sahara desert
Franzese
1812.10656
Radial trends in Galactic globular clusters and their possible origin
Kravtsov
The relaxation time at the half-mass radius of Galactic globular clusters (GGCs) is typically within a few Gyr. Hence, the majority of GGCs are expected to be well relaxed systems, given their age is around 12-13 yr. So any initial radial segregation between stars of the same initial mass on the main sequence (MS), in particular, the progenitors of the present day sub-giant and red-giant branch (SGB, RGB) stars should already have dissipated. However, a body of evidence contradicting to these expectations has been accumulated to date. The paradox could be solved by taking into account the effect of stellar collisions. They occur at particularly high rate in collapsing nuclei of GGCs and seem to be mainly responsible for unrelaxed central regions and the radial segregation observed. Draw attention that actually observed collisional blue stragglers should be less numerous than their lower-mass counterparts formed and accumulated at and below the present day MS turnoff. The effect of this is that MS/SGB/RGB stars on a given luminosity are not of the same mass but fall in a range of mass.
1812.10714
On the absence of dark matter in dwarf galaxies surrounding the Milky Way
Hammer, et al
It is widely accepted that MW dwarfs are the most DM dominated galaxies. Their DM content is estimated through its projected density along the LoS. Here, demonstrate that this quantity correlates with their distance to the MW, falsifying the calculations of DM in dwarfs. Moreover, show that the acceleration deduced from the LoS velocity dispersion is entirely due to MW tidal shocks. This regime is expected in the astronomical context for which MW dwarfs are descendants of inflating gas rich galaxies. It implies that they have no DM, or alternatively that DM could not play a role in them, questioning, e.g., their use as targets for DM searches.
1812.10750
Ultra High Energy Cosmic Rays: Origin, composition and spectrum
Aloisio
The physics of UHECRs will be reviewed, discussing the latest experimental results and theoretical models aiming at explaining the observations in terms of spectra, mass composition and possible sources. It will be also discussed the emission of secondary particles such as neutrinos and gamma rays produced by the interaction of UHECRs with astrophysical photon backgrounds.
1812.11210
Galaxy assembly bias of central galaxies in the Illustris simulations
Xu, Zheng
Galaxy assembly bias, the correlation between galaxy properties and halo properties at fixed halo mass, could be an important ingredient in halo-based modeling of galaxy clustering. Investigate the central galaxy assembly bias by studying the relation between various galaxy and halo properties in the Illustris hydro galaxy formation sim. Galaxy stellar mass M* is found to have a tighter correlation with peak maximum halo circular velocity V_peak than with halo mass M_h. Once the correlation with V_peak is accounted for, M* has nearly no dependence on any other halo assembly variables. The correlations between galaxy properties related to SFH and halo assembly properties also show a cleaner form as a function of V_peak than as a function of M_h, with the main correlation being with halo formation time and to a less extent halo concentration. Based on the galaxy-halo relation, present a simple model to relate the bias factors of a central galaxy sample and the corresponding halo sample, both selected based on assembly-related properties. It is found that they are connected by the correlation coefficient of the galaxy and halo properties used to define the two samples, which provides a reasonable description for the samples in the simulation and suggests a simple prescription to incorporate galaxy assembly bias into the halo model. By applying the model to the local galaxy clustering measurements in Lin+2016, infer that the correlation between SFH or sSFR and halo formation time is consistent with being weak.
1812.11717
Chemically defining the building blocks of the Earth
Yoshizaki, et al
Chondrites are undifferentiated sediments of material left over from the earliest solar system and are widely considered as representatives of the unprocessed building blocks of the terrestrial planets. The chondrites, along with processed igneous meteorites, have been divided into two broad categories based upon their isotopic signatures; these have been termed the CC and NC groups and have been interpreted as reflecting their distinctive birth places within the SS. The isotopic distinctiveness of NC and CC meteorites document limited radial-mixing in the accretionary disk. The enstatite and ordinary chondrites are NC-type and likely represent samples from inner solar system (likely <4 AU). Coupling isotopic observations with oxidation-reduction indices and their Fe/Al values constrain models for the Earth's composition. Measurement and modeling of ratios of refractory lithophile elements (RLE) in enstatite chondrites establish these meteorites as the closest starting materials for the bulk of the silicate Earth and the core. Comparing chondritic and terrestrial RLE ratios demonstrate that the Bulk Silicate Earth, not the core, host the Earth's inventory of Ti, Zr, Nb, and Ta, but not the full complement of V.
1901.00376
Contribution of cosmic rays from sources with a mono energetic proton spectrum to the extragalactic diffuse gamma-ray emission
Uryson
The extragalactic sources of ultra-high-energy (E>4e19 eV) cosmic rays that make a small contribution to the flux of particles recorded by ground-based arrays are discussed. Show that CRs from such sources can produce a noticeable diffuse gamma-ray flux in intergalactic space compared to the data obtained with Fermi LAT (onboard the Fermi space observatory). A possible type of AGNs in which CR protons can be accelerated to energies 1e21 eV is considered as an illustration of such sources. Conclude that UHECRs from the AGNs being discussed can contribute significantly to the extragalactic diffuse gamma-ray emission. In addition, a constraint on the fraction of the AGNs under consideration relative to the BL Lac objects and radio galaxies has been obtained from a comparison with the Fermi LAT data.
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