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An HST Snapshot Survey of Markarian Galaxies

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* In order to conduct a statistically meaningful study of the small-scale peri-nuclear structure of Seyfert and Starburst galaxies, We have obtained Hubble Space Telescope images of a sample of 52 Markarian Seyfert galaxies and a comparison sample of 48 non-Seyfert Markarian galaxies. This sample comprises essentially all Markarian Seyferts known as of 1983 with recession velocities between 3000 and 13000 km/s, M_{pg} less than -19mag (assuming, H_0=75 km/s/Mpc) m_pg less than 16.5mag, and declinations between -20 and +60 degrees. Also 7 NGC galaxies with apparent magnitudes brighter than the limit of the Markarian survey were added. This is as close to a complete sample of luminous Seyfert galaxies as can be constructed while maintaining a sufficiently large number of galaxies to properly represent this diverse population. To date our data and its analysis have been presented in three papers. The abstracts of these papers appear below: *

I. Markarian 315: A Test-Bed for the AGN-Merger Hypothesis?

  • John W. MacKenty, Space Telescope Science Institute
  • Susan M. Simkin, Michigan State University
  • Richard E. Griffiths, Johns Hopkins University
  • James S. Ulvestad, Jet Propulsion Lab
  • Andrew S. Wilson, Space Telescope Science Institute

    • ABSTRACT

    Using the HST WF/PC, we have detected a diffuse, continuum knot in the inner regions of the Seyfert galaxy Markarian 315. This knot may be a remnant nucleus. It is associated with a complex, ring-like structure in both the continuum and ionized gas emission. We have measured the kinematics of the ionized gas in two position angles and find velocities which are consistent with a non-axisymmetric gravitational disturbance. The galaxy is associated with an extended ionized filament, or tidal tail, and our measurements show that the ionized gas in this feature is redshifted by up to 500 $km\,s^{-1}$ in the line of sight relative to the Seyfert nucleus. This combination of morphological and kinematic features suggests that Markarian 315 has suffered a disruptive, tidal interaction whose influence extends well into the inner one-kiloparsec region.

    Published in: Ap.J. 466, 713, 1996.

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    II. Seyfert Galaxies IV. Nuclear Profiles of Markarian Seyfert Galaxies from HST Images

  • Charles H. Nelson, Space Telescope Science Institute
  • John W. MacKenty, Space Telescope Science Institute
  • Susan M. Simkin, Michigan State University, Dept. of Physics and Astronomy,
  • Richard E. Griffiths, Johns Hopkins University, Physics and Astronomy,

    • ABSTRACT

    We have examined the nuclear profiles of the Seyfert and non-Seyfert Markarian galaxies in our near infrared HST WF/PC-1 snapshot survey. We find that nuclei of type 1 -- 1.5 Seyfert galaxies are dominated by strong point sources, while those of Seyfert 2 and non-Seyfert Markarian galaxies tend to be resolved, less distinguished, and similar in shape to normal galaxy luminosity profiles. Two possible interpretations of this result for type 2 Seyfert galaxies are that the nuclear continuum sources are undetected in our bandpass, contributing less than 10\% of the nuclear light in all cases or that their nuclear components are resolved and blend in smoothly with the brightness profile of the host galaxy's bulge. Since spectroscopic studies support typical nuclear continuum fractions distinctly greater than 10\%, the latter conclusion is clearly preferable and supports the unified model for active galactic nuclei (AGN) which predicts extended nuclear sources in type 2 Seyferts. However, the similarity of the profiles of non-Seyfert Markarian and type 2 Seyfert nuclei suggests that circumnuclear star formation may also be an important component in the nuclear profiles of the latter.

    Published in: Ap.J. 435, 71, 1996.

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    III. Seyfert Galaxies. V. HST Observations of Sub-Kiloparsec Scale Nuclear Structures in Markarian Seyfert Galaxies

  • John W. MacKenty Space Telescope Science Institute
  • Charles H. Nelson Space Telescope Science Institute
  • Susan M. Simkin Michigan State University, Dept. of Physics and Astronomy,
  • Richard E. Griffiths Johns Hopkins University, Physics and Astronomy,
  • Gina Jones Space Telescope Science Institute

    • ABSTRACT

    We present {\it Hubble Space Telescope WF/PC-1 images of the inner regions of 5 Seyfert galaxies with interesting small-scale morphologies. These galaxies are selected from those in our Cycle 2 snapshot program of 102 Seyfert and non-Seyfert Markarian galaxies to illustrate morphologies which theory suggests may be identified with the mechanisms responsible for ``feeding'' the active nucleus at scales within 1 kpc. These continuum light structures include misaligned small bars, double nuclei, and more complex multi-component structures. Assuming that a morphological disturbance is an essential ingredient in the formation of an AGN, the frequency of these structures in our sample allows us to estimate the lifetime of an AGN based on dynamical considerations. Our results suggest a typical lifetime of $10^8$ years for an active nucleus consistent with canonical values.

    Submited for publication in: Ap.J. Oct, 1996.

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    Susan Simkin (Simkin@grus.pa.msu.edu) last updated: 03 Nov '96