Optical detection of the hidden nuclear engine in NGC 4258

Belinda J. Wilkes, Gary D. Schmidt, Paul S. Smith, Smita Mathur, Kim K. McLeod

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

Abstract

The subparsec masing disk recently found to be orbiting a central mass of ~3.6 X 107 Mʘ in the Seyfert/LINER galaxy NGC 4258 (Miyoshi and coworkers) provides the most compelling evidence to date for the existence of a massive black hole in the nucleus of a galaxy. The disk is oriented nearly edge-on, and the X-ray spectrum is heavily absorbed. Therefore, in this galaxy, the optical emission-line spectrum generally exhibited by an active galactic nucleus is perhaps best sought using polarized light: probing for light scattered off material surrounding the central source. New polarimetry of NGC 4258 has uncovered a compact polarized nucleus whose spectrum consists of a faint blue continuum similar to those of unobscured quasars (Fv Ɓ v-1.1), plus broadened (~1000 km s-1) emission lines. The lines are strongly linearly polarized (5%-10%) at a position angle (85° ± 2°) coincident with the plane of the maser disk. This result provides substantiating evidence for a weakly active central engine in NGC 4258 and for the existence of obscuring, orbiting tori, which impart many of the perceived distinctions between various types of active galaxies.

Original languageEnglish (US)
Pages (from-to)L13-L16
JournalAstrophysical Journal
Volume455
Issue number1
DOIs
StatePublished - Dec 10 1995
Externally publishedYes

Keywords

  • Galaxies: Active
  • Galaxies: Individual (NGC 4258)
  • Galaxies: Nuclei
  • Polarization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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