Predicted UV properties of very metal-poor starburst galaxies

Abstract

Aims. We study the expected properties of starburst galaxies in order to provide the point of reference for interpretation of high-z galaxy surveys and of very metal-poor galaxies. We concentrate mainly on the UV characteristics such as the ionizing spectra, the UV continuum, the Lyα and He ii λ1640 line and two-photon continuum emission.Methods. We use evolutionary synthesis models covering metallicities from Pop III to solar and a wide range of IMFs. We also combine the synthetic SEDs with the CLOUDY photoionization code for more accurate predictions of nebular emission, and to study possible departures from case B assumed in the synthesis models.Results. The ionizing fluxes, UV continuum properties, and predicted Lyα and He ii λ1640 line strengths are presented for synthesis models covering a wider range of parameter space than our earlier calculations. Strong departures from case B predictions are obtained for Lyα and 2γ continuum at low metallicities. At low nebular densities both are shown to be enhanced proportionally to the mean energy carried by the Lyman continuum photons emitted by the ionizing source. Larger Lyα equivalent widths are therefore predicted at low metallicity. The He ii λ1640 line can be weaker than case B predicts (in terms of flux as well as the equivalent width) due to its ionization parameter dependence and to the enhanced underlying 2γ continuum. Conclusions. Our results have implications for the interpretation of star-forming metal-poor and/or high redshift galaxies, for galaxies among the Lyα emitters (LAE) and Lyman Break galaxy (LBG) populations, and for searches of Population III stars in the distant Universe.

The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

“…The ionizing emissivity and spectrum of the star particles are computed from stellar synthesis models for both Pop III (Raiter et al 2010) and Pop II (Leitherer et al 1999) stars, taking into account the age and metallicity of the stellar population. There is considerable uncertainty in the total number of ionizing photons produced by a Pop II stellar population between different stellar synthesis models, depending on the physics included.…”

The reionization of carbon

“…The emissivity is tabulated at 7 distinct metallicities between Z = 0-0.04, and each gas particle's actual emissivity is computed by interpolating to its Z. The Z = 0 emissivity comes from Schaerer (2002); the Z = 10 −5 and Z = 10 −7 emissivities come from Raiter et al (2010); and the Z = 0.001-0.040 emissivities come from Starburst 99 (Leitherer et al 1999), running with the Geneva tracks (high mass-loss version, without rotation) and Pauldrach/Hillier atmospheres. Each model is adjusted to a Kroupa IMF.…”

Intergalactic magnetogenesis at Cosmic Dawn by photoionization

“…For quasars, we take α ∼ −1.7, ν1 = 100ν0 and a total luminosity of 10 12 L which fixes L0 (e.g. Shang et al 2011 which uses the Schaerer (2002) and Raiter et al (2010) single stellar populations for population III stars, differing by their initial mass functions (IMF). We used the PopIII.1 model for Population III clusters, a zero-metallicity population with an extremely top-heavy IMF (50 − 500M , Salpeter slope), from which we obtained α ∼ −0.3, ν1 = 4ν0 and L0 = 10 20 erg s −1 Hz −1 .…”