New Insights on Lyα and Lyman Continuum Radiative Transfer in the Greenest Peas*

Jaskot, Anne; Dowd, Tara; Oey, M. S.; Scarlata, Claudia; McKinney, Jed

doi:10.3847/1538-4357/ab3d3b

Cited by 128 publications

(161 citation statements)

References 121 publications

(226 reference statements)

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“…The most important difference between CR7 and the GPs is that the Lyα EWs of the GPs are significantly smaller (EW 0,red = 25±5Å; here we only consider the flux in the red part of the line for a fair comparison). Jaskot et al (2019) also report similarly low EW0 measurements in their sample of GPs with ∆v red ≈ +200 km s −1 . The EW difference could either be explained by a lower relative dust attenuation of Lyα photons compared to the UV continuum (i.e.…”

Section: On the High Ew For Cr7's Lyα Line Profilementioning

confidence: 60%

“…This is caused by a fainter Y band flux compared to the best-fitted continuum model ( §6.2). In princi- ple one explanation could be broad Lyα absorption on top of strong, narrow emission, as for example recently observed in lower-redshift analogues (Erb et al 2019;Jaskot et al 2019). However, such hypothetical absorption feature would need to be broader than in these known cases in order to extend far into the Y band.…”

Section: The Lyman-α Equivalent Widthmentioning

confidence: 91%

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The nature of CR7 revealed with MUSE: a young starburst powering extended Ly α emission at z = 6.6

Matthee

Pezzulli

Mackenzie

et al. 2020

Monthly Notices of the Royal Astronomical Society

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CR7 is among the most luminous Lyman-α emitters (LAEs) known at z = 6.6 and consists of at least three UV components that are surrounded by Lyman-α (Lyα) emission. Previous studies have suggested that it may host an extreme ionising source. Here, we present deep integral field spectroscopy of CR7 with VLT/MUSE. We measure extended emission with a similar halo scale length as typical LAEs at z ≈ 5. CR7’s Lyα halo is clearly elongated along the direction connecting the multiple components, likely tracing the underlying gas distribution. The Lyα emission originates almost exclusively from the brightest UV component, but we also identify a faint kinematically distinct Lyα emitting region nearby a fainter component. Combined with new near-infrared data, the MUSE data show that the rest-frame Lyα equivalent width (EW) is ≈100 Å. This is a factor four higher than the EW measured in low-redshift analogues with carefully matched Lyα profiles (and thus arguably HI column density), but this EW can plausibly be explained by star formation. Alternative scenarios requiring AGN powering are also disfavoured by the narrower and steeper Lyα spectrum and much smaller IR to UV ratio compared to obscured AGN in other Lyα blobs. CR7’s Lyα emission, while extremely luminous, resembles the emission in more common LAEs at lower redshifts very well and is likely powered by a young metal poor starburst.

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Section: On the High Ew For Cr7's Lyα Line Profilementioning

confidence: 60%

Section: The Lyman-α Equivalent Widthmentioning

confidence: 91%

The nature of CR7 revealed with MUSE: a young starburst powering extended Ly α emission at z = 6.6

Matthee

Pezzulli

Mackenzie

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…On the other hand, several models have been proposed to explain how the ionization state of gas in HII regions is connected to the Lyα optical depth. These include effects from intense radiation and/or enhanced stellar feedback (Clarke & Oey 2002;Jaskot & Oey 2013;Stark et al 2017) and density-bounded nebula and gas geometry (Nakajima & Ouchi 2014;Jaskot et al 2019). In both scenarios, Lyα photons escape through passageways with low HI column density and/or covering fraction.…”

Section: A Closer Look At the Lyα Versus [O Iii]λ5007 Relationmentioning

confidence: 99%

Searching for z > 6.5 Analogs Near the Peak of Cosmic Star Formation

Shapley

Tang

et al. 2020

ApJ

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Strong [O III]λλ4959,5007+Hβ emission appears to be typical in star-forming galaxies at z>6.5. As likely contributors to cosmic reionization, these galaxies and the physical conditions within them are of great interest. At z>6.5, where Lyα is greatly attenuated by the intergalactic medium, rest-UV metal emission lines provide an alternative measure of redshift and constraints on the physical properties of star-forming regions and massive stars. We present the first statistical sample of rest-UV line measurements in z∼2 galaxies selected as analogs of those in the reionization era based on [O III]λλ4959,5007 equivalent width (EW) or rest-frame U − B color. Our sample is drawn from the 3D-HST Survey and spans the redshift range   z 1.36 2.49. We find that the median Lyα and CIII]λλ1907,1909 EWs of our sample are significantly greater than those of z∼2 UV-continuum-selected starforming galaxies. Measurements from both individual and composite spectra indicate a monotonic, positive correlation between CIII] and [O III], while a lack of trend is observed between Lyα and [O III] at EW [O III] 1000 Å. At higher EW [O III] , extreme Lyα emission starts to emerge. Using stacked spectra, we find that Lyα and CIII] are significantly enhanced in galaxies with lower metallicity. Two objects in our sample appear comparable to z>6.5 galaxies with exceptionally strong rest-UV metal line emission. These objects have significant CIVλλ1548,1550, HeIIλ1640, and OIII]λλ1661,1665 emission in addition to intense Lyα or CIII]. Detailed characterization of these lower-redshift analogs provides unique insights into the physical conditions in z>6.5 star-forming regions, motivating future observations of reionization-era analogs at lower redshifts. Unified Astronomy Thesaurus concepts: High-redshift galaxies (734); H II regions (694); Emission line galaxies (459)

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“…There exist galaxies with comparable O32 ratios and Lyman-α features that do not have detectable LyC fluxes, which are thought to be line-of-sight variations (e.g. Jaskot et al 2019;Malkan & Malkan 2019;Nakajima et al 2019;Izotov et al 2020). Moreover, moderate fesc ∼ 0.1-0.2 have been reported recently for considerably large spectroscopic samples of galaxies at z ∼ 3 after a careful examination of foreground contamination (e.g.…”

mentioning

confidence: 93%

No missing photons for reionization: moderate ionizing photon escape fractions from the FIRE-2 simulations

Quataert

Wetzel

et al. 2020

Monthly Notices of the Royal Astronomical Society

126

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We present the escape fraction of hydrogen ionizing photons (fesc) from a sample of 34 high-resolution cosmological zoom-in simulations of galaxies at z ≥ 5 in the Feedback in Realistic Environments project, post-processed with a Monte Carlo radiative transfer code for ionizing radiation. Our sample consists of 8500 halos in Mvir ∼ 108–1012 M⊙ (M* ∼ 104–1010 M⊙) at z = 5–12. We find the sample average 〈fesc〉 increases with halo mass for Mvir ∼ 108–109.5 M⊙, becomes nearly constant for 109.5–1011 M⊙, and decreases at ≳ 1011 M⊙. Equivalently, 〈fesc〉 increases with stellar mass up to M* ∼ 108 M⊙ and decreases at higher masses. Even applying single-star stellar population synthesis models, we find a moderate 〈fesc〉 ∼ 0.2 for galaxies at M* ∼ 108 M⊙. Nearly half of the escaped ionizing photons come from stars 1–3 Myr old and the rest from stars 3–10 Myr old. Binaries only have a modest effect, boosting 〈fesc〉 by ∼25–35% and the number of escaped photons by 60–80%. Most leaked ionizing photons are from vigorously star-forming regions that usually contain a feedback-driven kpc-scale superbubble surrounded by a dense shell. The shell is forming stars while accelerated, so new stars formed earlier in the shell are already inside the shell. Young stars in the bubble and near the edge of the shell can fully ionize some low-column-density paths pre-cleared by feedback, allowing a large fraction of their ionizing photons to escape. The decrease of 〈fesc〉 at the high-mass end is due to dust attenuation, while at the low-mass end, 〈fesc〉 decreases owing to inefficient star formation and hence feedback. At fixed mass, 〈fesc〉 tends to increase with redshift. Although the absolute 〈fesc〉 does not fully converge with resolution in our simulations, the mass- and redshift-dependence of 〈fesc〉 is likely robust. Our simulations produce sufficient ionizing photons for cosmic reionization.

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New Insights on Lyα and Lyman Continuum Radiative Transfer in the Greenest Peas*

Cited by 128 publications

References 121 publications

The nature of CR7 revealed with MUSE: a young starburst powering extended Ly α emission at z = 6.6

The nature of CR7 revealed with MUSE: a young starburst powering extended Ly α emission at z = 6.6

Searching for z > 6.5 Analogs Near the Peak of Cosmic Star Formation

No missing photons for reionization: moderate ionizing photon escape fractions from the FIRE-2 simulations

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