A&A 405, 959-967 (2003)
DOI: 10.1051/0004-6361:20030678
I Zw 1 : Decomposition of the nearby QSO host
J. Scharwächter1, A. Eckart1, S. Pfalzner1, J. Moultaka1, C. Straubmeier1 and J. G. Staguhn21 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
2 NASA/Goddard Space Flight Center, Building 21, Code 685, Greenbelt, MD 20771, USA
(Received 28 January 2003 / Accepted 28 April 2003 )
Abstract
The paper presents an analysis of the nearby QSO host
I Zw 1
based on new
J-band
imaging data, obtained
with ISAAC at the Very Large Telescope (VLT) of the European
Southern Observatory (ESO).
As one of the best-studied QSOs with
exceptional properties lying between those of QSOs, narrow-line
Seyfert 1s, and ultraluminous infrared galaxies,
I Zw 1
is a
prime candidate for a detailed case study of a QSO host.
With its high angular resolution and sensitivity, the new
J-band image
provides strong evidence for an interaction between
I Zw 1
and
the western companion galaxy.
We present a procedure for subtracting the QSO nucleus from the
I Zw 1
image to obtain an undisturbed view on the underlying host
galaxy. Based on the derived surface brightness profile and the gas
rotation curve, the host is classified as a
high-surface-brightness Freeman type I galaxy with a central disk surface
brightness significantly larger than that of normal spirals.
The surface-brightness profile
is decomposed into a Plummer bulge and a Kuzmin disk with similar luminosities
and a bulge-to-disk scale length ratio of 0.29, comparable to that of
nearby spiral hosts with active galactic
nuclei (AGN). Different models for the
decomposition of the gas rotation curve are discussed. The
resulting
J-band mass-to-light ratio
(
M/L) of
for the disk component
suggests a mean solar-type stellar population with a tendency towards young
stars.
The bulge exhibits a lower
M/L of
,
which
supports previous findings of enhanced starburst
activity
in the nuclear and circumnuclear region.
Key words: galaxies: individual: I Zw 1 -- galaxies: active -- galaxies: photometry -- galaxies: structure -- methods: observational
Offprint request: J. Scharwächter, scharw@ph1.uni-koeln.de
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