GREEN PEA GALAXIES REVEAL SECRETS OF Lyα ESCAPE

Yang, Huan; Malhotra, Sangeeta; Grönke, Max; Rhoads, James E.; Dijkstra, Mark; Jaskot, Anne; Zheng, Zhen-Ya; Wang, Junxian

doi:10.3847/0004-637x/820/2/130

Cited by 110 publications

(149 citation statements)

References 79 publications

(115 reference statements)

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“…They have strong Lyα emission lines (Jaskot et al 2014;Henry et al 2015;Yang et al 2016); and their Lyα EW distribution is similar to high-z LAEs (Yang et al 2016). Five Green Peas in our sample also show Lyman contin-uum emission (Izotov et al 2016).…”

Section: Introductionmentioning

confidence: 86%

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Lyα and UV Sizes of Green Pea Galaxies

Yang

Malhotra

Rhoads

et al. 2017

ApJ

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Green Peas are nearby analogs of high-redshift Lyα-emitting galaxies (LAEs). To probe their Lyα escape, we study the spatial profiles of Lyα and UV continuum emission of 24 Green Pea galaxies using the Cosmic Origins Spectrograph (COS) on Hubble Space Telescope (HST). We extract the spatial profiles of Lyα emission from their 2D COS spectra, and of UV continuum from both the 2D spectra and NUV images. The Lyα emission shows more extended spatial profiles than the UV continuum in most Green Peas. The deconvolved Full Width Half Maximum (FWHM) of the Lyα spatial profile is about 2 to 4 times that of the UV continuum in most cases. Since Green Peas are analogs of high-z LAEs, it suggests that most high-z LAEs likely have larger Lyα sizes than UV sizes. We also compare the spatial profiles of Lyα photons at blueshifted and redshifted velocities in eight Green Peas with sufficient data quality, and find the blue wing of the Lyα line has a larger spatial extent than the red wing in four Green Peas with comparatively weak blue Lyα line wings. We show that Green Peas and MUSE z = 3 − 6 LAEs have similar Lyα and UV continuum sizes, which probably suggests starbursts in both low-z and high-z LAEs drive similar gas outflows illuminated by Lyα light. Five Lyman continuum (LyC) leakers in this sample have similar Lyα to UV continuum size ratios (∼ 1.4 − 4.3) to the other Green Peas, indicating their LyC emission escape through ionized holes in the interstellar medium.

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Section: Introductionmentioning

confidence: 86%

“…Green Peas usually show double-peaked Lyα velocity profiles (Jaskot et al 2014;Henry et al 2015;Yang et al 2016). The Lyα photons with different velocities are scatterd differently by the HI gas.…”

Section: Comparing Spatial Profiles Of Lyα Photons At Different Velocmentioning

confidence: 99%

Lyα and UV Sizes of Green Pea Galaxies

Yang

Malhotra

Rhoads

et al. 2017

ApJ

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“…Also, the Ion2 extreme [O iii]λ5007/[O ii] ratio, the metallicity, and the ionization parameter are consistent with cloudy models with a non-zero Lyman continuum escape fraction (Nakajima & Ouchi 2014, Fig. 11) The identification of Lyman continuum leakage from green pea galaxies is a continuing line of research (e.g., Jaskot & Oey 2014;Nakajima & Ouchi 2014;Borthakur et al 2014;Yang et al 2015) and the green pea nature of Ion2 and its LyC leakage represent the first concrete attempt to link these two properties. Ion2 represents an extreme case of green pea galaxy; it is the highest redshift (z > 3), ultra-strong oxygen emitter (with EW([O iii]λλ4959, 5007) ∼ 1100 Å) currently known.…”

Section: Physical Properties Of the Interstellar Mediummentioning

confidence: 99%

“…By comparing SFR(UV) and SFR(Lyα), we derive a Lyman-α escape fraction f esc (Lyα) ≥ 0.78 ( f esc (Lyα) ≥ 0.28 by using SFR(Hβ) instead of SFR(UV)). This high Lyα escape fraction can be related to a blue β slope (e.g., Hayes et al 2014), but also to a low H i column density (N H i ≤ 10 18 cm −2 ; Yang et al 2015;Henry et al 2015). Fig.…”

Section: Physical Properties Derived From the Photometrymentioning

confidence: 99%

An extreme [O III] emitter atz= 3.2: a low metallicity Lyman continuum source

Barros

Vanzella

Amorín

et al. 2015

A&A

183

158

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Aims. Cosmic reionization is an important process occurring in the early epochs of the Universe. However, because of observational limitations due to the opacity of the intergalactic medium to Lyman continuum photons, the nature of ionizing sources is still not well constrained. While high-redshift star-forming galaxies are thought to be the main contributors to the ionizing background at z > 6, it is impossible to directly detect their ionizing emission. Therefore, looking at intermediate redshift analogues (z ∼ 2−4) can provide useful hints about cosmic reionization. Methods. We investigate the physical properties of one of the best Lyman continuum emitter candidate at z = 3.212 found in the GOODS-S/CANDELS field with photometric coverage from the U to the MIPS 24 μm band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. These observations allow us to derive physical properties such as stellar mass, star formation rate, age of the stellar population, dust attenuation, metallicity, and ionization parameter, and to determine how these parameters are related to the Lyman continuum emission. Results. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with S /N > 5.Non-zero Lyα flux at the systemic redshift and high Lyman-α escape fraction ( f esc (Lyα) ≥ 0.78) suggest a low H i column density.The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The subsolar abundances are consistent with a young and extreme starburst. The [O iii]λλ4959, 5007+Hβ equivalent width (EW) is one of the largest reported for a galaxy at z > 3 (EW([O iii]λλ4959, 5007 + Hβ) 1600 Å, rest-frame; 6700 Å observed-frame) and the near-infrared spectrum shows that this is mainly due to an extremely strong [O (>10) and high ionization parameter are consistent with prediction from photoionization models in the case of a density-bounded nebula scenario. Furthermore, the EW([O iii]λλ4959, 5007+Hβ) is comparable to recent measurements reported at z ∼ 7−9, in the reionization epoch. We also investigate the possibility of an AGN contribution to explain the ionizing emission but most of the AGN identification diagnostics suggest that stellar emission dominates instead. Conclusions. This source is currently the first high-z example of a Lyman continuum emitter exhibiting indirect and direct evidences of a Lyman continuum leakage and having physical properties consistent with theoretical expectation from Lyman continuum emission from a density-bounded nebula. A low H i column density, low covering fraction, compact star formation activity, and a possible interaction/merging of two systems may contribute to the Lyman continuum photon leakage.

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“…However, low-z LAEs are rare and many nearby Lyα emission line galaxies are older and more evolved galaxies than typical high-z LAEs and may be a different population of Lyα emitters. Perhaps the most relevant nearby analogs of high-z LAEs are Green Pea galaxies (Jaskot & Oey 2014;Henry et al 2015;Yang et al 2016a, hereafter Paper I).…”

Section: Introductionmentioning

confidence: 99%

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

Yang

Malhotra

Grönke

et al. 2017

ApJ

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We studied Lyman-α (Lyα) escape in a statistical sample of 43 Green Peas with HST/COS Lyα spectra. Green Peas are nearby star-forming galaxies with strong [OIII]λ5007 emission lines. Our sample is four times larger than the previous sample and covers a much more complete range of Green Pea properties. We found that about 2/3 of Green Peas are strong Lyα line emitters with rest-frame Lyα equivalent width > 20Å. The Lyα profiles of Green Peas are diverse. The Lyα escape fraction, defined as the ratio of observed Lyα flux to intrinsic Lyα flux, shows anti-correlations with a few Lyα kinematic features -both the blue peak and red peak velocities, the peak separations, and FWHM of the red portion of the Lyα profile. Using properties measured from SDSS optical spectra, we found many correlations -Lyα escape fraction generally increases at lower dust reddening, lower metallicity, lower stellar mass, and higher [OIII]/[OII] ratio. We fit their Lyα profiles with the HI shell radiative transfer model and found Lyα escape fraction anti-correlates with the best-fit N HI . Finally, we fit an empirical linear relation to predict f Lyα esc from the dust extinction and Lyα red peak velocity. The standard deviation of this relation is about 0.3 dex. This relation can be used to isolate the effect of IGM scatterings from Lyα escape and to probe the IGM optical depth along the line of sight of each z > 7 Lyα emission line galaxy in the JWST era.

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GREEN PEA GALAXIES REVEAL SECRETS OF Lyα ESCAPE

Cited by 110 publications

References 79 publications

Lyα and UV Sizes of Green Pea Galaxies

Lyα and UV Sizes of Green Pea Galaxies

An extreme [O III] emitter atz= 3.2: a low metallicity Lyman continuum source

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

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