HST Images of the Seyfert Galaxy NGC 5929 and Its Companion NGC 5930$^1$

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Session 4 -- AGNs
Display presentation, Monday, 9:20-6:30, Pauley Room

[4.06] HST Images of the Seyfert Galaxy NGC 5929 and Its Companion NGC 5930$^1$

G. A. Bower (STScI), A. S. Wilson, J. S. Mulchaey (STScI/U Md), G. K. Miley (Leiden Observatory), T. M. Heckman (STScI/JHU), J. H. Krolik (JHU)

Images of the Seyfert galaxy NGC 5929 and its interacting companion NGC 5930 have been obtained with HST's Planetary Camera. This interacting pair is also known as Arp 90. Each galaxy was imaged in the wavelength regions of [O III] $\lambda\lambda$ 4959, 5007, H$\alpha$+[N II] $\lambda\lambda$ 6548, 6583, and the green and red continua. The nuclei of both galaxies contain emission line gas, enhanced in the images by using the appropriate continuum image to remove the contribution of the continuum light in the on-band images.

Previous ground-based observations of the Seyfert galaxy NGC 5929 include [O III] and H$\alpha$+[N II] images, showing that its nucleus contains an elongated region of high-excitation emission line gas. In these HST images, this gas is clearly separated into two distinct regions separated by about $1.^{''}1$ (138 h$^{-1}$ pc). The nucleus, as defined by the peak in the continuum, lies halfway between these two distinct emission line regions. The correspondence of this distribution of emission line gas to the published VLA map is examined. The HST continuum images reveal a dust lane lying 0.3 arcsec SE of the nucleus with a length of $\sim$ 1 arcsec and N$_{\rm H}$ $\approx 4 \times 10^{21}$ cm$^{-2}$. The implications of these results in the context of ``unified models'' of Seyfert galaxies, the collimation of ionizing radiation, and the interaction between the radio sources and the ISM are examined.

The nuclear emission line gas in NGC 5930 is concentrated into a ring around the nucleus with a diameter of $\sim$ 250 h$^{-1}$ pc and L(H$\alpha$+[N II]) $\approx$ $1.6 \times 10^{39}$ h$^{-2}$ erg s$^{-1}$. These observations of Arp 90 present an opportunity to examine the details of the possible role of galaxy interactions in the triggering of an AGN.

$^1$ Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

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