1999/08/31 by Peter W. Gorham, P. W. Gorham, Liese van Zee +4 · 13 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Elliptical galaxy #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hubble space telescope #Photometry (optics) #Physics #Solar mass #Spectral line #Spectroscopy #Spiral galaxy #Stars #Stellar, planetary, and galactic studies #Velocity dispersion #astro-ph
paper · pdf · doi:10.1086/301289
published in The Astronomical Journal 119(4), 1677-1686 (Institute of Physics) · LaTeX (aaspp4 style), 28 pages, 8 figures, to appear in AJ. Revised text from ref. comments; new & modified figures; new photometry included; minor corrections of typos. Color version of Fig. 1 to appear in Feb. 2000 Sky & Telescope
arxiv created 2000/01/05 · openalex publication_date 2000/04/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present Hubble Space Telescope (HST) imagery and photometry of the active galaxy Markarian 421 and its companion galaxy 14 arcsec to the ENE. The HST images indicate that the companion is a morphological spiral rather than elliptical as previous ground--based imaging has concluded. The companion has a bright, compact nucleus, appearing unresolved in the HST images. This is suggestive of Seyfert activity, or possibly a highly luminous compact star cluster. We also report the results of high dynamic range long-slit spectroscopy with the slit placed to extend across both galaxies and nuclei. We detect no emission lines in the companion nucleus, though there is evidence for recent star formation. Velocities derived from a number of absorption lines visible in both galaxies indicate that the two systems are probably tidally bound and thus in close physical proximity. Using the measured relative velocities, we derive a lower limit on the MKN 421 mass within the companion orbit (R ∼ 10 kpc) of 5.9 × 1011 solar masses, and a mass-to-light ratio of >= 17. Our spectroscopy also shows for the first time the presence of Hα and [NII] emission lines from the nucleus of MKN 421, providing another example of the appearance of new emission features in the previously featureless spectrum of a classical BL Lac object. We see both broad and narrow line emission, with a velocity dispersion of several thousand km s-1 evident in the broad lines.