NGC 7679: an anomalous, composite Seyfert 1 galaxy whose X-ray luminous AGN vanishes at optical wavelengths

¹ INAF Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: buson@pd.astro.it
² Leiden Observatory, Postbus 9513, 2300 RA Leiden, The Netherlands
³ Dipartimento di Astronomia, Università di Padova, vicolo dell'Osservatorio 2, 35122 Padova, Italy
⁴ Scuola Galileiana di Studi Superiori, via VIII Febbraio 2, 35122 Padova, Italy
⁵ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 106, Taiwan

Received: 6 April 2005
Accepted: 24 September 2005

Abstract

Morphological disturbances and gas kinematics of the SB0 galaxy NGC 7679 = Arp 216 are investigated to understand the history of this highly composite object, where AGN and starburst signatures dominate in the X-ray and optical/IR regime, respectively. Perturbations of the ionized gas velocity field appear quite mild within (~5 kpc) of the center, so it can be straightforwardly modeled as a circularly rotating disk. Outside that radius, significant disturbances are seen. In particular, the eastern distorted arm as well as the huge neutral hydrogen bridge connecting NGC 7679 to the nearby Seyfert spiral NGC 7682 unambiguously represent the vestige of a close encounter of the two objects ~500 Myr ago. The relationship of such a past event with the much more recent, centrally located starburst (not older than 20 Myr) cannot be easily established. Together, the classification of NGC 7679 is less extreme than that proposed in the past, being simply a (disturbed) galaxy where starburst and AGN activity coexist with a starburst dominating the bolometric luminosity.