The nearby QSO host I Zw 1: the stellar disk and adjacent objects*
1
European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: jscharwa@eso.org
2
I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
Received:
7
September
2006
Accepted:
9
May
2007
Context.The relation between tidal interactions, starbursts, and the onset and/or fueling of active galactic nuclei (AGN) is a matter of debate. I Zw 1 is considered as the prototypical narrow-line Seyfert 1 galaxy (NLS1) and as one of the closest quasi-stellar objects (QSOs). With a clear spiral host and a small companion galaxy to the west, I Zw 1 is a possible example of minor-merger-related nuclear activity.
Aims.This study investigates possible signs of a relation between merger process, star formation activity, and AGN properties in the case of I Zw 1.
Methods.The morphology of I Zw 1 and nearby sources is investigated via high-resolution near-infrared (NIR) images. Color trends in the host galaxy of I Zw 1 are discussed by means of optical-to-NIR color composites. Long-slit spectra of the QSO nucleus of I Zw 1 and of the two nearby sources to the north and the west of the I Zw 1 disk are analyzed.
Results.The data support the scenario of a tidal interaction between I Zw 1 and the small companion galaxy to the west. A concentration of blue color in the western part of the I Zw 1 host galaxy might be the manifestation of merger-induced star formation activity. Previous findings that the likely companion has an old evolved stellar population are substantiated by the new data. An extension to the west of the putative companion emerges as a separate source. The source to the north of the I Zw 1 disk is reconfirmed as a late-type foreground star. Lines in the nuclear K-band spectrum of I Zw 1 are discussed in comparison to data prior to this article and line fluxes are reported.
Key words: galaxies: quasars: individual: I Zw 1 / galaxies: Seyfert / galaxies: interactions / methods: observational
Based on observations collected at the Very Large Telescope (UT1) of the European Southern Observatory, Paranal (Chile), under service mode project 67.B-0009. Complementary data are based on observations made with the 3.6 m telescope of the European Southern Observatory, La Silla (Chile), and with the NASA/ESA Hubble Space Telescope, obtained from the ESO/ST-ECF Science Archive Facility (joint collaboration of the European Southern Observatory and the Space Telescope – European Coordinating Facility).
© ESO, 2007