The Radio Signatures of the First Supernovae

Primordial stars are key to primeval structure formation as the first stellar components of primeval galaxies, the sources of cosmic chemical enrichment and likely cosmic reionization, and they possibly gave rise to the supermassive black holes residing at the centres of galaxies today. While the direct detection of individual Pop III stars will likely remain beyond reach for decades to come, we show their supernova remnants may soon be detectable in the radio. We calculate radio synchrotron signatures between 0.5 - 35 GHz from hydrodynamical computations of the supernova remnants of Pop III stars in minihaloes. We find that hypernovae yield the brightest systems, with observed radio fluxes as high as 1 - 10 muJy. Less energetic Type II supernovae yield remnants about a factor of 30 dimmer and pair-instability supernova remnants are dimmer by a factor of more than 10,000. Because of the high gas densities of the progenitor environments, synchrotron losses severely limit the maximum emission frequencies, producing a distinctive peaked radio spectrum distinguishable from normal galactic supernova remnant spectra. Hypernovae radio remnants should be detectable by existing radio facilities like eVLA and eMERLIN while Type II supernova remnants will require the Square Kilometre Array. The number counts of hypernova remnants at z > 20 with fluxes above 1 muJy are expected to be one per hundred square degree field, increasing to a few per square degree if they form down to z = 10. The detection of a z > 20 Type II supernova remnant brighter than 1 nJy would require a 100 - 200 square degree field, although only a 1 - 2 square degree field for those forming down to z = 10. Hypernova and Type II supernova remnants are easily separated from one another by their light curves, which will enable future surveys to use them to constrain the initial mass function of Pop III stars.Comment: 12 pages, 9 figures; major revision; to appear in MNRA

Low-mass star formation triggered by early supernova explosions

We study the formation of low-mass and extremely metal-poor stars in the early universe. Our study is motivated by the recent discovery of a low-mass (M < 0.8 Msun) and extremely metal-poor (Z <= 4.5 x 10^{-5} Zsun) star in the Galactic halo by Caffau et al. We propose a model that early supernova (SN) explosions trigger the formation of low-mass stars via shell fragmentation. We first perform one-dimensional hydrodynamic simulations of the evolution of an early SN remnant. We show that the shocked shell undergoes efficient radiative cooling and then becomes gravitationally unstable to fragment and collapse in about ten million years. We then follow the thermal evolution of the collapsing fragments using a one-zone code. Our one-zone calculation treats chemistry and radiative cooling self-consistently in low-metallicity gas. The collapsing gas cloud evolves roughly isothermally, until it cools rapidly by dust continuum emission at the density 10^{13}-10^{14} /cc. The cloud core then becomes thermally and gravitationally unstable and fragments. We argue that early SNe can trigger the formation of low-mass stars in the extremely metal-poor environment as Caffau et al. discovered recently.Comment: [v1] Submitted to ApJ Letters, 11 pages, 3 figures: [v2] matches version published in ApJ (main journal), 8 pages, 6 figures. Parameter regions we investigate (initial ambient gas density surrounding the progenitor star) are widene

The Nucleosynthetic Imprint of 15-40 Solar Mass Primordial Supernovae on Metal-Poor Stars

The inclusion of rotationally-induced mixing in stellar evolution can alter the structure and composition of presupernova stars. We survey the effects of progenitor rotation on nucleosynthetic yields in Population III and II supernovae using the new adaptive mesh refinement (AMR) code CASTRO. We examine spherical explosions in 15, 25 and 40 solar mass stars at Z = 0 and 10^-4 solar metallicity with three explosion energies and two rotation rates. Rotation in the Z = 0 models resulted in primary nitrogen production and a stronger hydrogen burning shell which led all models to die as red supergiants. On the other hand, the Z=10^-4 solar metallicity models that included rotation ended their lives as compact blue stars. Because of their extended structure, the hydrodynamics favors more mixing and less fallback in the metal free stars than the Z = 10^-4 models. As expected, higher energy explosions produce more enrichment and less fallback than do lower energy explosions, and less massive stars produce more enrichment and leave behind smaller remnants than do more massive stars. We compare our nucleosynthetic yields to the chemical abundances in the three most iron-poor stars yet found and reproduce the abundance pattern of one, HE 0557-4840, with a zero metallicity 15 solar mass, 2.4 x 10^51 erg supernova. A Salpeter IMF averaged integration of our yields for Z=0 models with explosion energies of 2.4x10^51 ergs or less is in good agreement with the abundances observed in larger samples of extremely metal-poor stars, provided 15 solar mass stars are included. Since the abundance patterns of extremely metal-poor stars likely arise from a representative sample of progenitors, our yields suggest that low-mass supernovae contributed the bulk of the metals to the early universe.Comment: 16 pages, 11 figures; submitted to Ap

Confined Population III Enrichment and the Prospects for Prompt Second-Generation Star Formation

It is widely recognized that nucleosynthetic output of the first, Population III supernovae was a catalyst defining the character of subsequent stellar generations. Most of the work on the earliest enrichment was carried out assuming that the first stars were extremely massive and that the associated supernovae were unusually energetic, enough to completely unbind the baryons in the host cosmic minihalo and disperse the synthesized metals into the intergalactic medium. Recent work, however, suggests that the first stars may in fact have been somewhat less massive, with a characteristic mass scale of a few tens of solar masses. We present a cosmological simulation following the transport of the metals synthesized in a Population III supernova assuming that it had an energy of 1e51 ergs, compatible with standard Type II supernovae. A young supernova remnant is inserted in the first star's relic HII region in the free expansion phase and is followed for 40 Myr employing adaptive mesh refinement and Lagrangian tracer particle techniques. The supernova remnant remains partially trapped within the minihalo and the thin snowplow shell develops pronounced instability and fingering. Roughly half of the ejecta turn around and fall back toward the center of the halo, with 1% of the ejecta reaching the center in 30 kyr and 10% in 10 Myr. The average metallicity of the combined returning ejecta and the pristine filaments feeding into the halo center from the cosmic web is 0.001 - 0.01 Z_sun, but the two remain unmixed until accreting onto the central hydrostatic core that is unresolved at the end of the simulation. We conclude that if Population III stars had less extreme masses, they promptly enriched the host minihalos with metals and triggered Population II star formation.Comment: 13 pages, 8 figure

Reduction of the temperature sensitivity of minerotrophic fen methane emissions by simulated glacial atmospheric carbon dioxide starvation

Variations to the global wetland CH4 source strength in response to changes in orbital insolation patterns and atmospheric CO2 concentration ([CO2]a) are hypothesized to play an important role in determining glacial-interglacial variations in atmospheric CH4 concentration ([CH4]a). Here the interactive effects of temperature, a major controlling variable determining wetland CH4 flux, and the low [CO2]a of glacial intervals are investigated for the first time. We measured the temperature dependence of CH4 emissions from replicated mesocosms (n = 8 per CO2 treatment) collected from a minerotrophic fen and an ombrotrophic bog incubated in either ambient (c. 400 ppm) or glacial (c. 200 ppm) [CO2]a located in the United Kingdom. CH4 fluxes were measured at 5°C, 10°C, 15°C, 20°C, and 25°C and then in reverse order over a 20 day period under each [CO2]a treatment. Results showed that the Q10 temperature response of CH4 emissions from the Carex/Juncus-dominated fen declined significantly by approximately 39% under glacial [CO2]a (ambient [CO2]a = 2.60, glacial [CO2]a = 1.60; P 4 emissions from the Sphagnum-dominated bog remained unaltered (ambient [CO2]a = 3.67, glacial [CO2]a = 3.67; P > 0.05). This contrasting response may be linked to differences in plant species assemblage and the varying impact of CO2 starvation on plant productivity and carbon availability in the rhizosphere. Furthermore, our results provide empirical evidence to support recent model-based indications that glacial-interglacial variations in [CH4]a may be explained by changes in wetland CH4 source strength in response to orbitally forced changes in climate and [CO2]a

Environmental and vegetation controls on the spatial variability of CH4 emission from wet-sedge and tussock tundra ecosystems in the Arctic

Aims Despite multiple studies investigating the environmental controls on CH4 fluxes from arctic tundra ecosystems, the high spatial variability of CH4 emissions is not fully understood. This makes the upscaling of CH4 fluxes from plot to regional scale, particularly challenging. The goal of this study is to refine our knowledge of the spatial variability and controls on CH4 emission from tundra ecosystems. Methods CH4 fluxes were measured in four sites across a variety of wet-sedge and tussock tundra ecosystems in Alaska using chambers and a Los Gatos CO2 and CH4 gas analyser. Results All sites were found to be sources of CH4, with northern sites (in Barrow) showing similar CH4 emission rates to the southernmost site (ca. 300 km south, Ivotuk). Gross primary productivity (GPP), water level and soil temperature were the most important environmental controls on CH4 emission. Greater vascular plant cover was linked with higher CH4 emission, but this increased emission with increased vascular plant cover was much higher (86 %) in the drier sites, than the wettest sites (30 %), suggesting that transport and/or substrate availability were crucial limiting factors for CH4 emission in these tundra ecosystems. Conclusions Overall, this study provides an increased understanding of the fine scale spatial controls on CH4 flux, in particular the key role that plant cover and GPP play in enhancing CH4 emissions from tundra soils

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT≥20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≤pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≤{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration