Lyα EMISSION FROM GREEN PEAS: THE ROLE OF CIRCUMGALACTIC GAS DENSITY, COVERING, AND KINEMATICS

By A. Henry, Claudia Scarlata, Crystal L. Martin, D. Erb. 2015

137 citations recorded by the source corpus.

We report Hubble Space Telescope/Cosmic Origins Spectrograph observations of the Lyα emission and interstellar absorption lines in a sample of 10 star-forming galaxies at z ∼ 0.2. Selected on the basis of high equivalent width optical emission lines, the sample, dubbed “Green Peas,” make some of the best analogs for young galaxies in an early universe. We detect Lyα emission in all ten galaxies, and 9/10 show double-peaked line profiles suggestive of low H i column density. We measure Lyα/Hα flux ratios of 0.5–5.6, implying that 5%–60% of Lyα photons escape the galaxies. These data confirm previous findings that low-ionization metal absorption (LIS) lines are weaker when Lyα escape fraction and equivalent width are higher. However, contrary to previously favored interpretations of this trend, increased Lyα output cannot be the result of a varying H i covering: the Lyman absorption lines (Lyβ and higher) show a covering fraction near unity for gas with NH i ≳ 1016 cm−2. Moreover, we detect no correlation between Lyα escape and the outflow velocity of the LIS lines, suggesting that kinematic effects do not explain the range of Lyα/Hα flux ratios in these galaxies. In contrast, we detect a strong anticorrelation between the Lyα escape fraction and the velocity separation of the Lyα emission peaks, driven primarily by the velocity of the blue peak. As this velocity separation is sensitive to H i column density, we conclude that Lyα escape in these Green Peas is likely regulated by the H i column density rather than outflow velocity or H i covering fraction.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a031440ee4ad8b18535c4e088629d2eb3150f25a

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Citations in the corpus

An extreme [O III] emitter at z = 3.2: a low metallicity Lyman continuum source (2015, background): “Their strong Lyα emission has been recently observed (Henry et al. 2015).”
Lyman-α spectral properties of five newly discovered Lyman continuum emitters (2016, methodology): “In practice we have been able to compile measurements for 12 GPs (Jaskot & Oey 2014; Henry et al. 2015; Yang et al. 2016), and 8 LBAs (Heckman et al. 2011).”
The Circumgalactic Medium (2017, background): “…as Ca ii, Na i, Mg ii, and Fe ii (Martin 2005; Kornei et al. 2012; Bordoloi et al. 2011; Rubin et al. 2014) to study outflows from galaxies out to z ∼ 1, in UV lines for low-redshift star-forming galaxies (Henry et al. 2015; Heckman et al. 2015), or even to examine accretion (Rubin et al. 2012).”
J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons (2017, background): “…Lyα profile in J1154+2443 is similar to that observed in known LyC leakers (Verhamme et al. 2017) and in some other GP galaxies (Jaskot & Oey 2014; Henry et al. 2015; Yang et al. 2017), the separation between the blue and red peaks of 199 km s−1 is the lowest among all low-redshift LyC leakers…”
The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “Observations of z < 4 galaxies confirm high Nhi correlates with high Lyα velocity offset (Yang et al. 2016; Hashimoto et al. 2015; Henry et al. 2015), and more Lyα extended halos (Hayes et al. 2013; Guaita et al. 2017).”
Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios (2018, result): “This shape is similar to that observed in known LyC leakers (Verhamme et al. 2017) and in some other galaxies (Jaskot & Oey 2014; Henry et al. 2015; Yang et al. 2017).”
Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies (2016, result): “Their profiles show two peaks with a small separation between the blue and red peaks, similar to profiles observed in some other GP galaxies (Jaskot & Oey 2013; Henry et al. 2015; Izotov et al. 2016; Yang et al. 2016).”