The nearby QSO host I Zw 1: The stellar disk and adjacent objects

TL;DR

This study investigates the relationship between tidal interactions, star formation, and AGN activity in the nearby QSO host galaxy I Zw 1, revealing signs of merger-induced star formation and tidal interaction with a companion galaxy.

Contribution

It provides high-resolution NIR imaging and spectral analysis of I Zw 1, demonstrating evidence of tidal interaction and merger-related star formation in this prototypical NLS1 galaxy.

Findings

Evidence of tidal interaction between I Zw 1 and a small companion galaxy.

Blue color concentration indicating merger-induced star formation.

Confirmation of the companion's old stellar population and identification of a new separate source.

Abstract

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.