Ultraviolet imaging polarimetry of the Large Magellanic Cloud. I. Observations

Andrew A. Cole, Kenneth H. Nordsieck, Steven J. Gibson, Walter M Harris

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

We have used the rocketborne Wide-Field Imaging Survey Polarimeter (WISP) to image a 1°.5 × 4°.8 area of the western side of the Large Magellanic Cloud (LMC) at a wavelength of λ = 2150 Å and a resolution of 1′ × 1′.5. These are the first wide-field ultraviolet polarimetric images in astronomy. We find the UV background light of the LMC to be linearly polarized at levels ranging from our sensitivity limit of 4% to as high as ≈40%. In general, the polarization in a pixel increases as the flux decreases; the weighted mean value of polarization across the WISP field is 12.6% ± 2.3%. The LMC's diffuse UV background, in uncrowded areas, rises from a minimum of (5.6 ± 3.1) × 10-8 ergs s-1 cm-2 Å-1 sr-1 (23.6 ± 0.5 mag arcsec-2) to (9.3 ± 1.1) × 10-8 ergs s-1 cm-2 Å-1 sr-1 (23.1 ± 0.2 mag arcsec-2) in regions near the bright associations. We use our polarization maps to investigate the geometry of the interstellar medium in the LMC and to search for evidence of a significant contribution of scattered light from OB associations to the diffuse galactic light of the LMC. Through a statistical analysis of our polarization map, we identify nine regions of intense UV emission which may be giving rise to scattering halos in our image. We find that starlight from the N11 complex and the LH 15 association are the strongest contributors to the scattered light component of the LMC's diffuse galactic light. This region of the northwestern LMC can be thought of as a kiloparsec-scale reflection nebula in which OB stars illuminate distant dust grains that scatter the light into our sight line. In contrast, the polarization map does not support the scattering of light from the large B2 complex in the southern WISP field; this effect may be astrophysical, or it may be the result of bias in our analysis.

Original languageEnglish (US)
Pages (from-to)2280-2291
Number of pages12
JournalAstronomical Journal
Volume118
Issue number5
StatePublished - Nov 1999
Externally publishedYes

Fingerprint

polarimetry
Magellanic clouds
polarization
polarimeters
erg
field survey
reflection nebulae
scattering
visual perception
astronomy
statistical analysis
halos
astrophysics
dust
pixels
pixel
stars
wavelength
sensitivity
geometry

Keywords

  • ISM: structure
  • Magellanic Clouds
  • Physical data and processes
  • Stars: early-type
  • Ultraviolet emission

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Ultraviolet imaging polarimetry of the Large Magellanic Cloud. I. Observations. / Cole, Andrew A.; Nordsieck, Kenneth H.; Gibson, Steven J.; Harris, Walter M.

In: Astronomical Journal, Vol. 118, No. 5, 11.1999, p. 2280-2291.

Research output: Contribution to journalArticle

Cole, AA, Nordsieck, KH, Gibson, SJ & Harris, WM 1999, 'Ultraviolet imaging polarimetry of the Large Magellanic Cloud. I. Observations', Astronomical Journal, vol. 118, no. 5, pp. 2280-2291.
Cole, Andrew A. ; Nordsieck, Kenneth H. ; Gibson, Steven J. ; Harris, Walter M. / Ultraviolet imaging polarimetry of the Large Magellanic Cloud. I. Observations. In: Astronomical Journal. 1999 ; Vol. 118, No. 5. pp. 2280-2291.
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AB - We have used the rocketborne Wide-Field Imaging Survey Polarimeter (WISP) to image a 1°.5 × 4°.8 area of the western side of the Large Magellanic Cloud (LMC) at a wavelength of λ = 2150 Å and a resolution of 1′ × 1′.5. These are the first wide-field ultraviolet polarimetric images in astronomy. We find the UV background light of the LMC to be linearly polarized at levels ranging from our sensitivity limit of 4% to as high as ≈40%. In general, the polarization in a pixel increases as the flux decreases; the weighted mean value of polarization across the WISP field is 12.6% ± 2.3%. The LMC's diffuse UV background, in uncrowded areas, rises from a minimum of (5.6 ± 3.1) × 10-8 ergs s-1 cm-2 Å-1 sr-1 (23.6 ± 0.5 mag arcsec-2) to (9.3 ± 1.1) × 10-8 ergs s-1 cm-2 Å-1 sr-1 (23.1 ± 0.2 mag arcsec-2) in regions near the bright associations. We use our polarization maps to investigate the geometry of the interstellar medium in the LMC and to search for evidence of a significant contribution of scattered light from OB associations to the diffuse galactic light of the LMC. Through a statistical analysis of our polarization map, we identify nine regions of intense UV emission which may be giving rise to scattering halos in our image. We find that starlight from the N11 complex and the LH 15 association are the strongest contributors to the scattered light component of the LMC's diffuse galactic light. This region of the northwestern LMC can be thought of as a kiloparsec-scale reflection nebula in which OB stars illuminate distant dust grains that scatter the light into our sight line. In contrast, the polarization map does not support the scattering of light from the large B2 complex in the southern WISP field; this effect may be astrophysical, or it may be the result of bias in our analysis.

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