Comparing the VANDELS Sample to a Zoom-in Radiative Hydrodynamical Simulation: Using the Si ii and C ii Line Spectra as Tracers of Galaxy Evolution and Lyman Continuum Leakage

Abstract

We compare mock ultraviolet C ii and Si ii absorption and emission line features generated using a ∼10 ^9 M _⊙ virtual galaxy with observations of 131 z ∼ 3 galaxies from the vandels survey. We find that the mock spectra reproduce reasonably well a large majority (83%) of the vandels spectra ( χ ^2 < 2), but do not resemble the most massive objects (⪆10 ^10 M _⊙ ), which exhibit broad absorption features. Interestingly, the best-matching mock spectra originate from periods of intense star formation in the virtual galaxy, where its luminosity is 4 times higher than in periods of relative quiescence. Furthermore, for each galaxy, we predict the Lyman continuum (LyC) escape fractions ( ${f}_{\mathrm{esc}\ (\mathrm{pred})}^{\mathrm{LyC}}$ ) using the environment of the virtual galaxy. We derive an average ${f}_{\mathrm{esc}\ (\mathrm{pred})}^{\mathrm{LyC}}$ of 0.01 ± 0.02, consistent with other estimates from the literature. The ${f}_{\mathrm{esc}\ (\mathrm{pred})}^{\mathrm{LyC}}$ are tightly correlated with the Ly α escape fractions and highly consistent with observed empirical trends. Additionally, galaxies with larger ${f}_{\mathrm{esc}\ (\mathrm{pred})}^{\mathrm{LyC}}$ exhibit bluer β slopes, more Ly α flux, and weaker low-ionization absorption lines. Building upon the good agreement between ${f}_{\mathrm{esc}\ (\mathrm{pred})}^{\mathrm{LyC}}$ and observationally established LyC diagnostics, we examine the LyC leakage mechanisms in the simulation. We find that LyC photon leakage is enhanced in directions where the observed flux dominantly emerges from compact regions depleted of neutral gas and dust, mirroring the scenario inferred from observational data. In general, this study further highlights the potential of high-resolution radiation hydrodynamics simulations in analyzing UV absorption and emission line features and providing valuable insights into the LyC leakage of star-forming galaxies.

Keywords

• Ultraviolet astronomy
• Interstellar medium
• Starburst galaxies
• Galaxy evolution