Characterizing the accuracy of ALMA linear-polarization mosaics - Archive ouverte HAL
Article Dans Une Revue Publ.Astron.Soc.Pac. Année : 2020

Characterizing the accuracy of ALMA linear-polarization mosaics

Charles L.H. Hull
  • Fonction : Auteur
Paulo C. Cortes
  • Fonction : Auteur
Josep M. Girart
  • Fonction : Auteur
Hiroshi Nagai
  • Fonction : Auteur
Kouichiro Nakanishi
  • Fonction : Auteur
Seiji Kameno
  • Fonction : Auteur
Edward B. Fomalont
  • Fonction : Auteur
Crystal L. Brogan
  • Fonction : Auteur
George A. Moellenbrock
  • Fonction : Auteur
Rosita Paladino
  • Fonction : Auteur
Eric Villard
  • Fonction : Auteur

Résumé

We characterize the accuracy of linear-polarization mosaics made using the Atacama Large Millimeter/submillimeter Array (ALMA). First, we observed the bright, highly linearly polarized blazar 3C 279 at Bands 3, 5, 6, and 7 (3 mm, 1.6 mm, 1.3 mm, and 0.87 mm, respectively). At each band, we measured the blazar’s polarization on an 11 × 11 grid of evenly spaced offset pointings covering the full-width at half-maximum (FWHM) area of the primary beam. After applying calibration solutions derived from the on-axis pointing of 3C 279 to all of the on- and off-axis data, we find that the residual polarization errors across the primary beam are similar at all frequencies: the residual errors in linear polarization fraction P frac and polarization position angle χ are ≲0.001 (≲0.1% of Stokes I) and ≲ 1° near the center of the primary beam; the errors increase to ∼0.003–0.005 (∼0.3%–0.5% of Stokes I) and ∼1°–5° near the FWHM as a result of the asymmetric beam patterns in the (linearly polarized) Q and U maps. We see the expected double-lobed “beam squint” pattern in the circular polarization (Stokes V) maps. Second, to test the polarization accuracy in a typical ALMA project, we performed observations of continuum linear polarization toward the Kleinmann–Low nebula in Orion (Orion-KL) using several mosaic patterns at Bands 3 and 6. We show that after mosaicking, the residual off-axis errors decrease as a result of overlapping multiple pointings. Finally, we compare the ALMA mosaics with an archival 1.3 mm Combined Array for Research in Millimeter-wave Astronomy polarization mosaic of Orion-KL and find good consistency in the polarization patterns.

Dates et versions

hal-02922214 , version 1 (25-08-2020)

Identifiants

Citer

Charles L.H. Hull, Paulo C. Cortes, Valentin J.M. Le Gouellec, Josep M. Girart, Hiroshi Nagai, et al.. Characterizing the accuracy of ALMA linear-polarization mosaics. Publ.Astron.Soc.Pac., 2020, 132 (1015), pp.094501. ⟨10.1088/1538-3873/ab99cd⟩. ⟨hal-02922214⟩
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