Polarimetry of the Lyα envelope of the radio-quiet quasar SDSS J124020.91+145535.6?

P. North, M. Hayes, M. Millon, A. Verhamme, M. Trebitsch, J. Blaizot, F. Courbin, D. Chelouche

Research output: Contribution to journalArticlepeer-review


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 3.8−5.500 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.

Original languageEnglish
Article numberA147
JournalAstronomy and Astrophysics
StatePublished - 1 Apr 2024

Bibliographical note

Publisher Copyright:
c The Authors 2024.


  • quasars: emission lines
  • quasars: individual: SDSS J124020.91 + 145535.6
  • uasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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