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Polarimetry of the Lyα envelope of the radio-quiet quasar SDSS J124020.91+145535.6?
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The radio quiet quasar SDSS J1240+1455 lies at a redshift of z = 3.11, is surrounded by a Lyα blob (LAB), and is absorbed by a proximate damped Lyα system. In order to better define the morphology of the blob and determine its emission mechanism, we gathered deep narrow-band images isolating the Lyα line of this object in linearly polarized light. We provide a deep intensity image of the blob, showing a filamentary structure extending up to 1600 (or 122 physical kpc) in diameter. No significant polarization signal could be extracted from the data, but 95% probability upper limits were defined through simulations. They vary between ∼3% in the central 0.7500 disk (after subtraction of the unpolarized quasar continuum) and ∼10% in the 3.8−5.5 00 annulus. The low polarization suggests that the Lyα photons are emitted mostly in situ, by recombination and de-excitation in a gas largely ionized by the quasar ultraviolet light, rather than by a central source and scattered subsequently by neutral hydrogen gas. This blob shows no detectable polarization signal, contrary to LAB1, a brighter and more extended blob that is not related to the nearby active galactic nucleus (AGN) in any obvious way, and where a significant polarization signal of about 18% was detected.
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NORTH, P., HAYES, M., MILLON, M., VERHAMME, A., TREBITSCH, M., BLAIZOT, J., COURBIN, Frédéric, CHELOUCHE, D.. Polarimetry of the Lyα envelope of the radio-quiet quasar SDSS J124020.91+145535.6?. _Astronomy & Astrophysics_. 2024. Vol. 684, núm. A147, pàgs. 1-15. [consulta: 21 de gener de 2026]. ISSN: 0004-6361. [Disponible a: https://hdl.handle.net/2445/218855]