TY - JOUR A1 - Plat, A. A1 - Charlot, S. A1 - Bruzual, G. A1 - Feltre, A. A1 - Vidal-Garcia, A. A1 - Morisset, C. A1 - Chevallard, Jacopo A1 - Todt, Helge Tobias T1 - Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies JF - Monthly notices of the Royal Astronomical Society N2 - We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionization-bounded and density-bounded H II regions, active-galactic-nucleus (AGN) narrow-line regions, and radiative shocks computed all using the same physically consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous exploration of more spectral diagnostics than typically available at once for individual subsamples. We confirm that current single- and binary-star population synthesis models do not produce hard-enough radiation to account for the high-ionization emission of the most metal-poor galaxies. Introducing either an AGN or radiative-shock component brings models into agreement with observations. A published model including X-ray binaries is an attractive alternative to reproduce the observed rise in He II lambda 4686/H beta ratio with decreasing oxygen abundance in metal-poor star-forming galaxies, but not the high observed He II lambda 4686/H beta ratios of galaxies with large EW(H beta). A source of harder ionizing radiation appears to be required in these extreme objects, such as an AGN or radiative-shock component, perhaps linked to an initial-mass-function bias towards massive stars at low metallicity. This would also account for the surprisingly high [O I]/[O III] ratios of confirmed LyC leakers relative to ionization-bounded models. We find no simple by-eye diagnostic of the nature of ionizing sources and the escape of LyC photon, which require proper simultaneous fits of several lines to be discriminated against. KW - galaxies: general KW - galaxies: high-redshift KW - galaxies: ISM Y1 - 2019 U6 - https://doi.org/10.1093/mnras/stz2616 SN - 0035-8711 SN - 1365-2966 VL - 490 IS - 1 SP - 978 EP - 1009 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Eichler, David A1 - Pohl, Martin T1 - Can ultrahigh-energy cosmic rays come from Gamma-ray bursts? - cosmic rays below the ankle and galactic gamma-ray bursts JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - The maximum cosmic-ray energy achievable by acceleration by a relativistic blast wave is derived. It is shown that forward shocks from long gamma-ray bursts (GRBs) in the interstellar medium accelerate protons to large enough energies, and have a sufficient energy budget, to produce the Galactic cosmic-ray component just below the ankle at 4 x 10(18) eV, as per an earlier suggestion. It is further argued that, were extragalactic long GRBs responsible for the component above the ankle as well, the occasional Galactic GRB within the solar circle would contribute more than the observational limits on the outward flux from the solar circle, unless an avoidance scenario, such as intermittency and/or beaming, allows the present-day local flux to be less than 10(-3) of the average. Difficulties with these avoidance scenarios are noted. KW - cosmic rays KW - galaxies: general KW - gamma-ray burst: general Y1 - 2011 U6 - https://doi.org/10.1088/2041-8205/738/2/L21 SN - 2041-8205 VL - 738 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER -