Toward an understanding of the seyfert galaxy NGC 5252: A spectroscopic study

José A. Acosta-Pulido, Baltasar Vila-Vilaró, Ismael Pérez-Fournon, Andrew S. Wilson, Zlatan Tsvetanov, Vilspa Isophot Idt

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Abstract

We present long-slit spectra of the Seyfert 2 galaxy NGC 5252, covering the nucleus and part of the extranuclear emission-line region. All the regions sampled by our spectra have emission-line ratios characteristic of photoionization by an active galactic nucleus-like (AGN-like) continuum source. The spectrum of the nucleus differs from those measured in extranuclear regions, showing higher values of the line ratios [O I] λ6300/Hα, [S II] λλ6716, 6731/Hα, and [N II] λ6584/Hα, and a lower value of He II λ4686/Hα. These differences can be understood in terms of either a larger fraction of matter-bounded (optically thin) clouds in the extended gas than at the nucleus, or an additional excitation mechanism in the nucleus, such as interaction with the radio-emitting plasma. The excitation of the gas in the extended emission-line region, as measured by the line ratios [O III] λ5007/Hα, [O III] λ5007/[O II] λ3727, and [O III] λ5007/[N II] λ6584, is correlated with the emissionline brightness. This result is another piece of evidence favoring an important contribution from matter-bound clouds in the extranuclear gas. The electron temperatures in the extended emission-line regions are in the range 20,000-24,000 K, higher than predicted by the simplest photoionization models but similar to the temperatures found in other extended emission-line regions associated with active galactic nuclei. The higher spectral resolution observations are used to study the kinematics of the line-emitting gas. Very close to the nucleus, two different kinematical components are found: one extending toward the northwest of the nucleus and blueshifted with respect to the adopted systemic velocity and the other extending toward the southeast and redshifted. Such kinematical components may be associated with the nuclear jet-like radio structure or with bright, compact knots recently detected in Hubble Space Telescope images. Outside the nucleus, the velocity field of the gas is complex, suggesting that radial motions, perhaps driven by the active nucleus, in addition to rotation, are present. A broad Hα component (FWHM ∼2500 km s-1) is detected in the nucleus, but no similar one is found for Hβ. The luminosity derived for the nucleus using recombination lines is relatively high for a Seyfert 2 nucleus. Both results are consistent with the hypothesis that NGC 5252 contains a partially hidden broad-line region and a more luminous nucleus than is directly observed.

Original languageEnglish
Pages (from-to)177-197
Number of pages21
JournalAstrophysical Journal
Volume464
Issue number1 PART I
Publication statusPublished - 1996
Externally publishedYes

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Keywords

  • Galaxies: Individual (ngc 5252)
  • Galaxies: Nuclei
  • Galaxies: Seyfert

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Space and Planetary Science

Cite this

Acosta-Pulido, J. A., Vila-Vilaró, B., Pérez-Fournon, I., Wilson, A. S., Tsvetanov, Z., & Isophot Idt, V. (1996). Toward an understanding of the seyfert galaxy NGC 5252: A spectroscopic study. Astrophysical Journal, 464(1 PART I), 177-197.