Unlocking the Full Potential of Extragalactic Lyα through Its Polarization Properties

Eide, Marius B.; Grönke, Max; Dijkstra, Mark; Hayes, Matthew

doi:10.3847/1538-4357/aab5b7

Cited by 29 publications

(42 citation statements)

References 102 publications

(164 reference statements)

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“…and winds flow or into which cloud gas falls (Lee & Ahn 1998;Dijkstra & Loeb 2008;Eide et al 2018). Dijkstra & Loeb (2008) investigate two simple scenarios: an expanding H I shell and an optically thick, spherically symmetric, collapsing gas cloud.…”

Section: Current Models For Lyα Nebulaementioning

confidence: 99%

“…Dijkstra & Loeb (2008) investigate two simple scenarios: an expanding H I shell and an optically thick, spherically symmetric, collapsing gas cloud. Eide et al (2018) further explore the polarization of Lyα emission for various geometries: static or expanding ellipsoids, biconical outflows, and the clumpy structure representative of a multiphase medium. All of these models predict that the observed Lyα polarization increases with projected radius in the nebula.…”

Section: Current Models For Lyα Nebulaementioning

confidence: 99%

“…If, on the other hand, the photoionization region is relatively small, i.e., within or very near a galaxy, some of the escaping Lyα photons will be scattered by the rest of the nebula and into our sightline. This Lyα emission will be polarized; the polarization strength will increase with projected distance from the source, and the polarization angles will be tangential to the direction of that gradient (Lee & Ahn 1998;Rybicki & Loeb 1999;Dijkstra & Loeb 2008;Trebitsch et al 2016;Eide et al 2018). These two scenarios represent the extremes; the reality might lie in between.…”

Section: Introductionmentioning

confidence: 99%

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What Makes Lyα Nebulae Glow? Mapping the Polarization of LABd05

Kim

Yang

Zabludoff

et al. 2020

ApJ

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Lyα nebulae" are giant (∼100 kpc), glowing gas clouds in the distant universe. The origin of their extended Lyα emission remains a mystery. Some models posit that Lyα emission is produced when the cloud is photoionized by UV emission from embedded or nearby sources, while others suggest that the Lyα photons originate from an embedded galaxy or active galactic nucleus (AGN) and are then resonantly scattered by the cloud. At least in the latter scenario, the observed Lyα emission will be polarized. To test these possibilities, we are conducting imaging polarimetric observations of seven Lyα nebulae. Here we present our results for LABd05, a cloud at z=2.656 with an obscured, embedded AGN to the northeast of the peak of Lyα emission. We detect significant polarization. The highest polarization fractions P are ∼10%-20% at ∼20-40 kpc southeast of the Lyα peak, away from the AGN. The lowest P, including upper limits, are ∼5% and lie between the Lyα peak and AGN. In other words, the polarization map is lopsided, with P increasing from the Lyα peak to the southeast. The measured polarization angles θ are oriented northeast, roughly perpendicular to the P gradient. This unique polarization pattern suggests that (1) the spatially offset AGN is photoionizing nearby gas and (2) escaping Lyα photons are scattered by the nebula at larger radii and into our sightline, producing tangentially oriented, radially increasing polarization away from the photoionized region. Finally we conclude that the interplay between the gas density and ionization profiles produces the observed central peak in the Lyα emission. This also implies that the structure of LABd05 is more complex than assumed by current theoretical spherical or cylindrical models.

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Section: Current Models For Lyα Nebulaementioning

confidence: 99%

Section: Current Models For Lyα Nebulaementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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What Makes Lyα Nebulae Glow? Mapping the Polarization of LABd05

Kim

Yang

Zabludoff

et al. 2020

ApJ

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“…Orlitová et al 2018). One caution is that Lyα photons trace preferably the low-NHI medium, and thus, the spectral information does not necessarily correspond to the line-of-sight physical conditions (Eide et al 2018;Kakiichi & Gronke 2019). We interpret these results in §7.4.…”

Section: Lyα Shell Modelsmentioning

confidence: 99%

Resolved Lyman-α properties of a luminous Lyman-break galaxy in a large ionized bubble at z = 6.53

Matthee

Sobral

Grönke

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The observed properties of the Lyman-α (Lyα) emission line are a powerful probe of neutral gas in and around galaxies. We present spatially resolved Lyα spectroscopy with VLT/MUSE targeting VR7, a UV-luminous galaxy at z = 6.532 with moderate Lyα equivalent width (EW 0 = 38Å). These data are combined with deep resolved [CII] 158µm spectroscopy obtained with ALMA and UV imaging from HST. Lyα emission is clearly detected with S/N ≈ 40 and FWHM of 370 km s −1 . We also detect UV continuum with MUSE. Lyα and [CII] are similarly extended beyond the UV, with effective radius r eff = 2.1±0.2 kpc for a single component or r eff,Lyα,halo = 3.45 +1.08 −0.87 kpc when measured jointly with the UV continuum. The Lyα profile is broader and redshifted with respect to the [CII] line (by 220 km s −1 ), but there are spatial variations that are qualitatively similar in both lines and coincide with resolved UV components. This suggests that the emission originates from two components, while spatially varying HI column densities are also present. We place VR7 in the context of other galaxies at similar and lower redshift. The Lyα halo scale length is similar at different redshifts and velocity shifts with respect to the systemic are typically smaller. Overall, we find little indications of a more neutral vicinity at higher redshift. This means that the local (∼ 10 kpc) neutral gas conditions that determine the observed Lyα properties in VR7 resemble the conditions in post-re-ionisation galaxies.

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“…The exact value of the degree of polarization depends strongly on the physical properties of the scattering medium (i.e., its bulk and turbulent velocity, as well as its Hi density). The Lyα polarization pattern (i.e., the angle of polarization) around the sources depends strongly on the isotropy and homogeneity of the emission and gas distribution (Lee & Ahn 1998;Ahn et al 2002;Chang et al 2016;Eide et al 2018). These dependences make the polarization signal very sensitive to the specific conditions of the medium, and, as we will show, this boosts the amount of information on galaxies and their environment retrievable from polarization, compared to that from emission alone.…”

Section: Introductionmentioning

confidence: 76%

Lyman-αpolarization intensity mapping

Mas-Ribas¹,

Chang

2020

Phys. Rev. D

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We present a formalism that incorporates hydrogen Lyman-alpha (Lyα) polarization arising from the scattering of radiation in galaxy halos into the intensity mapping approach. Using the halo model, and Lyα emission profiles based on simulations and observations, we calcualte auto and cross power spectra at redshifts 3 ≤ z ≤ 13 for the Lyα total intensity, I, polarized intensity, P, degree of polarization, Π = P/I, and two new quantities, the astrophysical E and B modes of Lyα polarization. The one-halo terms of the Π power spectra show a turnover that signals the average extent of the polarization signal, and thus the extent of the scattering medium. The position of this feature depends on redshift, as well as on the specific emission profile shape and extent, in our formalism. Therefore, the comparison of various Lyα polarization quantities and redshifts can break degeneracies between competing effects, and it can reveal the true shape of the emission profiles, which, in turn, are associated to the physical properties of the cool gas in galaxy halos. Furthermore, measurements of Lyα E and B modes may be used as probes of galaxy evolution, because they are related to the average degree of anisotropy in the emission and in the halo gas distribution across redshifts. The detection of the polarization signal at z ∼ 3 − 5 requires improvements in the sensitivity of current ground-based experiments by a factor of ∼ 10, and of ∼ 100 for space-based instruments targeting the redshifts z ∼ 9 − 10, the exact values depending on the specific redshift and experiment. Interloper contamination in polarization is expected to be small, because the interlopers need to also be polarized. Overall, Lyα polarization boosts the amount of physical information retrievable on galaxies and their surroundings, most of it not achievable with total emission alone.

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Unlocking the Full Potential of Extragalactic Lyα through Its Polarization Properties

Cited by 29 publications

References 102 publications

What Makes Lyα Nebulae Glow? Mapping the Polarization of LABd05

What Makes Lyα Nebulae Glow? Mapping the Polarization of LABd05

Resolved Lyman-α properties of a luminous Lyman-break galaxy in a large ionized bubble at z = 6.53

Lyman-αpolarization intensity mapping

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