Neutral Gas Properties and Lyα Escape in Extreme Green Pea Galaxies<sup>∗</sup>

McKinney, Jed; Jaskot, Anne; Oey, M. S.; Yun, Min S.; Dowd, Tara; Lowenthal, James D.

doi:10.3847/1538-4357/ab08eb

Cited by 46 publications

(88 citation statements)

References 76 publications

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“…Given the current scant knowledge of the spectral properties of LyC emitters, the fact that Ion1 shows Lyα in absorption is, empirically speaking, interesting. The coexistence of LyC emission and Lyα absorption could be explained by the partial covering fraction of neutral gas (McKinney et al 2019). The fact that the metal absorption lines don't reach zero flux is consistent with this picture.…”

Section: Spectrumsupporting

confidence: 53%

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

Giavalisco

Vanzella³

et al. 2020

ApJ

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We report on the HST detection of the Lyman-continuum (LyC) radiation emitted by a galaxy at redshift z = 3.794, dubbed Ion1 (Vanzella et al. 2012). The LyC from Ion1 is detected at restframe wavelength λλ 820∼890Å with HST WFC3/UVIS in the F410M band (m 410 = 27.60 ± 0.36 m AB , peak SNR = 4.17 in a circular aperture with radius r = 0.12") and at λλ 700∼830Å with the VLT/VIMOS in the U-band (m U = 27.84 ± 0.19 m AB , peak SNR = 6.7 with a r = 0.6" aperture). A 20-hr VLT/VIMOS spectrum shows low-and high-ionization interstellar metal absorption lines, the P-Cygni profile of C IV and Lyα in absorption. The latter spectral feature differs from what observed in known LyC emitters, which show strong Lyα emission. An HST far-UV color map reveals that the LyC emission escapes from a region of the galaxy that is bluer than the rest, presumably because of lower dust obscuration. The F410M image shows that the centroid of the LyC emission is offset from the centroid of the non-ionizing UV emission by 0.12"±0.03", corresponding to 0.85±0.21 kpc (physical), and that its morphology is likely moderately resolved. These morphological characteristics favor a scenario where the LyC photons produced by massive stars escape from low H I columndensity "cavities" in the ISM, possibly carved by stellar wind and/or supernova. We also collect the VIMOS U-band images of a sample of 107 Lyman-break galaxies with spectroscopic redshifts at 3.40 < z < 3.95, i.e. sampling the LyC, and stack them with inverse-variance weights. No LyC emission is detected in the stacked image, resulting in a 32.5 m AB flux limit (1σ) and an upper limit of absolute LyC escape fraction f abs esc ≤ 0.63%. LyC emitters like Ion1 are very likely at the bright-end of the LyC luminosity function.

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Section: Spectrumsupporting

confidence: 53%

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

Giavalisco

Vanzella³

et al. 2020

ApJ

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“…Dijkstra et al 2016) and feedback effects (e.g. McKinney et al 2019). The low S/N of our data and the likely presence of geocoronal Lyα contamination at lower velocities preclude a detailed analysis of these issues, but higher S/N follow-up observations and mapping of the global Lyα emission from UGC 5282 could provide valuable insights on these topics.…”

Section: Lyα Emission From Ugc 5282mentioning

confidence: 84%

Absorption-line Abundances in the SMC-like Galaxy UGC 5282: Evidence of ISM Dilution from Inflows on Kiloparsec Scales*

Bowen

Tripp

Jenkins

et al. 2020

ApJ

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We present an HST Cosmic Origins Spectrograph (COS) spectrum of the QSO SDSS J095109.12+330745.8 (z em = 0.645) whose sightline passes through the SMC-like dwarf galaxy UGC 5282 (M B = −16.0, cz = 1577 km s −1 ), 1.2 kpc in projection from the central H II region of the galaxy. Damped Lyα (DLA) absorption is detected at the redshift of UGC 5282 with log [N(H I) cm −2 ] = 20.89 +0.12 −0.21 . Analysis of the accompanying S II, P II and O I metal lines yields a neutral gas metallicity, Z H I , of [S/H] [P/H] = −0.80 ± 0.24. The metallicity of ionized gas from the central H II region, Z H II , measured from its emission lines is [O/H]= −0.37 ± 0.10, a difference of +0.43 ± 0.26 from Z H I . This difference δ is consistent with that seen towards H II regions in other star-forming galaxies and supports the idea that ionized gas near star forming regions shows systematically higher metallicities than exist in the rest of a galaxy's neutral interstellar medium (ISM). The positive values of δ found in UGC 5282 (and the other star forming galaxies) is likely due to infalling low metallicity gas from the intergalactic medium that mixes with the galaxy's ISM on kpc scales. This model is also consistent with broad Lyα emission detected at the bottom of the DLA absorption, offset by ∼ 125 km s −1 from the absorption velocity. Models of galaxy evolution that attempt to replicate population characteristics, such as the mass-metallicity relation, may need to start with a galaxy metallicity represented by Z H I rather than that measured traditionally from Z H II .

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“…The superposition of strong Lyα emission and absorption is not uncommon in extreme, highly ionized galaxies. In a sample of 17 Green Pea galaxies with [O III]λ5007/[O II]λ3727 ≥ 6.6 (but somewhat higher metallicities than SL2S J0217), McKinney et al (2019) find six with both strong, double-peaked Lyα emission and Lyα absorption, and determine column densities in the range 19.5 < log(N HI /cm −2 ) < 21.4 by fitting Voigt profiles to the wings of the absorption. Particularly notable is the extreme galaxy J1608, with [O III]/[O II] = 35 (Jaskot et al 2017); this object shows both absorption with log(N HI /cm −2 ) = 21.4 and very strong emission with narrow peak separation ∆ peak = 214 km s −1 .…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Low mass, low metallicity, highly ionized galaxies in the local universe now account for most of the objects with individual detections of LyC radiation (Leitet et al 2013;Leitherer et al 2016;Izotov et al 2016aIzotov et al ,b, 2018a, and an understanding of the neutral gas properties of such objects is therefore paramount. In the absence of direct measurements of H I, which are prohibitively difficult outside of the very nearby universe and even then may result in upper limits (Puschnig et al 2017;McKinney et al 2019), perhaps the best way to constrain the properties of neutral hydrogen is through the observation of the resonantly scattered Lyα emission line.…”

Section: Introductionmentioning

confidence: 99%

“…shows a potential very broad absorption feature underlying the emission line. Broad Lyα absorption is seen in other low metallicity, highly ionized galaxies:McKinney et al (2019) have recently presented examples of Lyα emission with underlying absorption in extreme Green Pea galaxies, and in Figure The Keck LRIS spectrum of SL2S J0217 (black) compared with the HST COS spectrum of the local low metallicity galaxy SBS 0335−052 (red). Both spectra are normalized, and the grey dashed lines in both panels show the SL2S J0217 1σ error spectrum.…”

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confidence: 99%

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Subkiloparsec Imaging of Lyα Emission in a Low-mass, Highly Ionized, Gravitationally Lensed Galaxy at z = 1.84^∗

Erb

Berg

Auger

et al. 2019

ApJ

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Low mass, low metallicity galaxies at low to moderate (z 3) redshifts offer the best opportunity for detailed examination of the interplay between massive stars, ionizing radiation and gas in sources similar to those that likely reionized the universe. We present new narrowband Hubble Space Telescope observations of Lyα emission and the adjacent ultraviolet (UV) continuum in the low mass (M = 2 × 10 8 M ), low metallicity (Z ∼ 1/20 Z ) and highly ionized gravitationally lensed galaxy SL2S J02176−0513 at z = 1.844. The galaxy has strong Lyα emission with photometric equivalent width W phot Lyα = 218 ± 12 Å, at odds with the Lyα escape fraction of 10%. However, the spectroscopic Lyα profile suggests the presence of broad absorption underlying the emission, and the total equivalent width is consistent with the escape fraction once this underlying absorption is included. The Lyα emission is more spatially extended than the UV continuum, and the 0. 14 spatial resolution of HST coupled with the magnification of gravitational lensing enables us to examine the distribution of Lyα and the UV continuum on sub-kiloparsec scales. We find that the peaks of the Lyα emission and the UV continuum are offset by 650 pc, and there is no Lyα emission arising from the region with the strongest UV light. Our combined spectroscopic and imaging data imply a significant range in neutral hydrogen column density across the object. These observations offer indirect support for a model in which ionizing radiation escapes from galaxies through channels with low column density of neutral gas.

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Neutral Gas Properties and Lyα Escape in Extreme Green Pea Galaxies^∗

Cited by 46 publications

References 76 publications

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

Absorption-line Abundances in the SMC-like Galaxy UGC 5282: Evidence of ISM Dilution from Inflows on Kiloparsec Scales*

Subkiloparsec Imaging of Lyα Emission in a Low-mass, Highly Ionized, Gravitationally Lensed Galaxy at z = 1.84^∗

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Neutral Gas Properties and Lyα Escape in Extreme Green Pea Galaxies∗

Cited by 46 publications

References 76 publications

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

Absorption-line Abundances in the SMC-like Galaxy UGC 5282: Evidence of ISM Dilution from Inflows on Kiloparsec Scales*

Subkiloparsec Imaging of Lyα Emission in a Low-mass, Highly Ionized, Gravitationally Lensed Galaxy at z = 1.84∗

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Product

Resources

About

Neutral Gas Properties and Lyα Escape in Extreme Green Pea Galaxies^∗

Subkiloparsec Imaging of Lyα Emission in a Low-mass, Highly Ionized, Gravitationally Lensed Galaxy at z = 1.84^∗