  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. This study investigates possible signs
of a relation between merger process, star formation activity, and AGN
properties in the case of I Zw 1. The morphology of I Zw 1 and nearby sources
is investigated via high-resolution 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. 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.
