The polarization and ultraviolet spectrum of Markarian 231

Paul S. Smith, Gary D. Schmidt, Richard G. Allen, J Roger P Angel

Research output: Contribution to journalArticle

63 Citations (Scopus)

Abstract

Ultraviolet spectropolarimetry acquired with the Hubble Space Telescope of the peculiar Seyfert galaxy Mrk 231 is combined with new high-quality ground-based measurements to provide the first, nearly complete, record of its linear polarization from 1575 to 7900 Å. The accompanying ultraviolet spectrum portrays the heavily extinguished emission-line spectrum of the active nucleus plus the emergence of a blue continuum shortward of ∼2400 Å. In addition, absorption features due to He I λ3188, Mg I λ12853, Mg II λ12798, and especially several resonance multiplets of Fe n are identified with a well-known optical absorption system blueshifted ∼4600 km s-1 with respect to the emission lines. The continuum is attributed to ∼ 105 hot, young stars surrounding the nucleus. This component dilutes the polarized nuclear light, implying that the intrinsic polarization of the active galactic nucleus (AGN) spectrum approaches 20% at 2800 A. The rapid decline in degree of polarization toward longer wavelengths is best explained by the strongly frequency-dependent scattering cross section of dust grains coupled with modest starlight dilution. Peculiar S-shaped inflections in both the degree and position angle of polarization through Hα and other major emission lines are interpreted as effects of scattering from two regions offset in velocity by several hundred km s-1. A third source of (weakly) polarized flux is required to explain a nearly 40° rotation in position angle between 3200 and 1800 Å. The displaced absorption features, polarimetry, and optical/infrared properties of Mrk 231 all point to its classification as a low-ionization, or "Mg H" broad absorption line quasar, in which most, if not all, lines of sight to the active nucleus are heavily obscured by dust and low-ionization gas clouds.

Original languageEnglish (US)
Pages (from-to)146-156
Number of pages11
JournalAstrophysical Journal
Volume444
Issue number1
StatePublished - May 1 1995

Fingerprint

ultraviolet spectra
polarization
nuclei
dust
peculiar galaxies
continuums
gas ionization
ionization
Seyfert galaxies
scattering
polarimetry
linear polarization
Hubble Space Telescope
active galactic nuclei
scattering cross sections
quasars
line of sight
line spectra
dilution
ground-based measurement

Keywords

  • Galaxies: individual (Markarian 231)
  • Galaxies: nuclei
  • Galaxies: Seyfert
  • Galaxies: stellar content
  • Polarization
  • Ultraviolet: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Smith, P. S., Schmidt, G. D., Allen, R. G., & Angel, J. R. P. (1995). The polarization and ultraviolet spectrum of Markarian 231. Astrophysical Journal, 444(1), 146-156.

The polarization and ultraviolet spectrum of Markarian 231. / Smith, Paul S.; Schmidt, Gary D.; Allen, Richard G.; Angel, J Roger P.

In: Astrophysical Journal, Vol. 444, No. 1, 01.05.1995, p. 146-156.

Research output: Contribution to journalArticle

Smith, PS, Schmidt, GD, Allen, RG & Angel, JRP 1995, 'The polarization and ultraviolet spectrum of Markarian 231', Astrophysical Journal, vol. 444, no. 1, pp. 146-156.
Smith PS, Schmidt GD, Allen RG, Angel JRP. The polarization and ultraviolet spectrum of Markarian 231. Astrophysical Journal. 1995 May 1;444(1):146-156.
Smith, Paul S. ; Schmidt, Gary D. ; Allen, Richard G. ; Angel, J Roger P. / The polarization and ultraviolet spectrum of Markarian 231. In: Astrophysical Journal. 1995 ; Vol. 444, No. 1. pp. 146-156.
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abstract = "Ultraviolet spectropolarimetry acquired with the Hubble Space Telescope of the peculiar Seyfert galaxy Mrk 231 is combined with new high-quality ground-based measurements to provide the first, nearly complete, record of its linear polarization from 1575 to 7900 {\AA}. The accompanying ultraviolet spectrum portrays the heavily extinguished emission-line spectrum of the active nucleus plus the emergence of a blue continuum shortward of ∼2400 {\AA}. In addition, absorption features due to He I λ3188, Mg I λ12853, Mg II λ12798, and especially several resonance multiplets of Fe n are identified with a well-known optical absorption system blueshifted ∼4600 km s-1 with respect to the emission lines. The continuum is attributed to ∼ 105 hot, young stars surrounding the nucleus. This component dilutes the polarized nuclear light, implying that the intrinsic polarization of the active galactic nucleus (AGN) spectrum approaches 20{\%} at 2800 A. The rapid decline in degree of polarization toward longer wavelengths is best explained by the strongly frequency-dependent scattering cross section of dust grains coupled with modest starlight dilution. Peculiar S-shaped inflections in both the degree and position angle of polarization through Hα and other major emission lines are interpreted as effects of scattering from two regions offset in velocity by several hundred km s-1. A third source of (weakly) polarized flux is required to explain a nearly 40° rotation in position angle between 3200 and 1800 {\AA}. The displaced absorption features, polarimetry, and optical/infrared properties of Mrk 231 all point to its classification as a low-ionization, or {"}Mg H{"} broad absorption line quasar, in which most, if not all, lines of sight to the active nucleus are heavily obscured by dust and low-ionization gas clouds.",
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