Influence of physical galaxy properties on Lyαescape in star-forming galaxies

Abstract

Context. Among the different observational techniques used to select high-redshift galaxies, the hydrogen recombination line Lymanalpha (Lyα) is of particular interest because it gives access to the measurement of cosmological quantities such as the star formation rate (SFR) of distant galaxy populations. However, interpreting this line and calibrating such observables are still subject to serious uncertainties. Aims. In this context, it important to understand the mechanisms responsible for the attenuation of Lyα emission, and under what conditions the Lyα emission line can be used as a reliable star formation diagnostic tool. Methods. We used a sample of 24 Lyα emitters at z ∼ 0.3 with an optical spectroscopic follow-up to calculate the Lyα escape fraction and its dependence upon different physical properties. We also examined the reliability of Lyα as a SFR indicator. We combined these observations with a compilation of Lyα emitters selected at z = 0−0.3 from the literature to assemble a larger sample. Results. We confirm that the Lyα escape fraction clearly depends on the dust extinction following the relation f esc (Lyα) = C Lyα × 10 −0.4 E(B−V) k Lyα where k Lyα ∼ 6.67 and C Lyα = 0.22. However, the correlation does not follow the expected curve for a simple dust attenuation. A higher attenuation can be attributed to a scattering process, while f esc (Lyα) values that are clearly above the continuum extinction curve can be the result of various mechanisms that can lead to an enhancement of the Lyα output. We also observe that the strength of Lyα and the escape fraction appear unrelated to the galaxy metallicity. Regarding the reliability of Lyα as a SFR indicator, we show that the deviation of SFR(Lyα) from the true SFR (as traced by the UV continuum) is a function of the observed SFR(UV), which can be seen as the decrease in f esc (Lyα) with increasing UV luminosity. Moreover, we observe redshift dependence of this relationship, revealing the underlying evolution of f esc (Lyα) with redshift.

The Lyα Reference Sample. VIII. Characterizing Lyα Scattering in Nearby Galaxies

“…This behavior suggests that Lyα photons do not scatter as far in galaxies with higher dust content. This is consistent with studies that show that the Lyα escape fraction decreases with dust content (Hayes et al 2013;Atek et al 2014).…”

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

“…Blanc et al (2011) report a correlation between the Ly α equivalent width and reddening in high-z LAEs. Similarly, Atek et al (2014) observe a clear dependence of the Ly α escape fraction on the dust extinction in nearby galaxies.…”

Lyα Profile, Dust, and Prediction of Lyα Escape Fraction in Green Pea Galaxies

“…dust extinction, stellar mass, and metallicity These Green Peas are very well studied galaxies and provide a great opportunity to explore the dependence of Lyα escape on other galactic properties. Previous studies have found that f the relation between f Lyα esc and metallicity are unclear Atek et al 2014;Hayes et al 2014; Paper I). Our sample covers the full ranges of dust extinction and metallicity of Green Peas.…”