Abstract We present the implementation and the first results of cosmic ray (CR) feedback in the Feedback In Realistic Environments (FIRE) simulations. We investigate CR feedback in non-cosmological simulations of dwarf, sub-L⋆ starburst, and L⋆ galaxies with different propagation models, including advection, isotropic and anisotropic diffusion, and streaming along field lines with different transport coefficients. We simulate CR diffusion and streaming simultaneously in galaxies with high resolution, using a two moment method. We forward-model and compare to observations of γ-ray emission from nearby and starburst galaxies. We reproduce the γ-ray observations of dwarf and L⋆ galaxies with constant isotropic diffusion coefficient κ ∼ 3 × 1029 cm2 s−1. Advection-only and streaming-only models produce order-of-magnitude too large γ-ray luminosities in dwarf and L⋆ galaxies. We show that in models that match the γ-ray observations, most CRs escape low-gas-density galaxies (e.g. dwarfs) before significant collisional losses, while starburst galaxies are CR proton calorimeters. While adiabatic losses can be significant, they occur only after CRs escape galaxies, so they are only of secondary importance for γ-ray emissivities. Models where CRs are “trapped” in the star-forming disk have lower star formation efficiency, but these models are ruled out by γ-ray observations. For models with constant κ that match the γ-ray observations, CRs form extended halos with scale heights of several kpc to several tens of kpc.
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Low-luminosity gamma-ray bursts as the sources of ultrahigh-energy cosmic ray nuclei
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Two carbonate units from Southwest Florida, the Caloosahatchee and Fort Thompson Formations, were studied using X-ray instruments to understand more about their origins. The Caloosahatchee Fm. is late Pliocene to early Pleistocene in age while the Fort Thompson Fm. is late Pleistocene in age. Powdered X-ray diffraction (PXRD) was used to obtain the mineral composition of these formations. PXRD revealed the Caloosahatchee Fm. consists predominantly of calcite with lesser quartz and aragonite. PXRD of the carbonate rocks from the Fort Thompson Fm. are also predominantly calcite with lesser quartz and aragonite. Fossils were picked by hand from poorly cemented Caloosahatchee Fm. samples and analyzed on the PXRD. These fossils were predominantly aragonite with minor calcite. Carbonates from the Caloosahatchee and Fort Thompson Fms. were also analyzed for their major and trace element geochemistry using a portable X-Ray fluorescence (pXRF). The Caloosahatchee Fm. has a Mg/Ca ratio which ranges from 0.07 to 0.10, Sr which ranges from 368 to 1650 ppm, and Al which ranges from 0.08 to 0.35 wt.%. No As was detected in the Caloosahatchee Fm. The Fort Thompson Fm. was divided into lower and upper units for pXRF analysis. The lower Fort Thompson Fm. has a Mg/Ca ratio which ranges from 0.08 to 0.10, Sr which ranges from 197 to 1097 ppm, and Al which ranges from 0.05 to 0.38 wt.%. The upper Fort Thompson Fm. has a Mg/Ca ratio which ranges from 0.07 to 0.10, Sr which ranges from 92 to 1015 ppm, and Al which ranges from 0.21 to 1.33 wt.%. The lower Fort Thompson Fm. has no As detected in it, but the upper Fort Thompson had 5 ppm As. The low (< 0.8) Mg/Ca ratio and calcite being the predominant mineral in both formations indicate they are limestone. The presence of quartz, and the Al values suggest both formations have terrestrial contributions and are not pure marine limestone. The higher Al of the upper Fort Thompsons suggest it might have the largest terrestrial contribution. The Sr values for the Caloosahatchee Fm. are higher than the Fort Thompson Fms. This could be due to a higher marine influence in the Caloosahatchee Fm. The PXRD suggests the aragonite is originating from the shells within the formations. The lack of significant As in all rocks suggests leaching of this metal into the environment is not a concern.more » « less
