Eunchong Kim: Using Polarization to Uncover the Lyman Alpha Emission Mechanism in Lyman Alpha Nebulae

Thursday, 01 June 2023 2 p.m. — 3 p.m. MST

Gemini North Hilo Base Facility | 670 N A’ohoku Place Hilo, Hawaii, 96720, USA

Gemini North Talks
Eunchong Kim (KASI)

Ray Sharples

"Lya nebulae" are giant (~100 kpc), glowing gas clouds in the distant universe. Their extended Lya emission remains a mystery; it may be produced when the cloud is photoionized by UV emission from embedded/nearby sources or when Lya photons from an embedded source are resonantly scattered by the cloud. In the latter scenario, the observed Lya emission will be polarized, with the polarization fraction increasing with distance from the source. Mapping the polarization of Lya nebula thus provides important clues as to the contribution of scattering to the Lya glow. To date, imaging polarimetry of three Lya nebulae, SSA22-LAB1, B3 J2330+3927, and LABd05, reveals polarization that is hard to interpret given differences among the types and spatial configurations of the embedded sources. Here we more than double the size of the blob polarization sample, adding four nebulae known to host AGN. We detect the significant polarization in three blobs among the four nebulae we have observed in this survey. These detected polarization vectors are distributed at the extended Lya emitting gas. All targets that detected the polarization vectors show the increasing polarization gradient as the radiative transfer model expected in the scattering scenario. Through this survey result, including the previous three targets, scattering plays in whole Lya blobs of the universe in high possibilities. Although the detailed polarization properties are different as they have different physical properties and/or another mechanism also plays in the Lya nebulae, the Lya photons are scattered in extended HI gas and then escape that system. In this talk, I will introduce this polarization survey for Lya nebulae and my future work for relatively nearby galaxies using Gemini.

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