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Letter to the Editor
Observations of the host galaxies of the BL Lacertae objects H 0414+009 and OJ 287 with FORS1 at VLT-UT1 *
J. Heidt 1,
K. Nilsson 2,
I. Appenzeller 1,
K. Jäger 3,
W. Seifert 1,
T. Szeifert 1,4,
W. Gässler 5,
R. Häfner 5,
W. Hummel 5,
B. Muschielok 5,
H. Nicklas 3 and
O. Stahl 1
Received 11 August 1999 / Accepted 11 October 1999
We present imaging of the host galaxies of H 0414+009 and OJ 287 taken during the commissioning phases of FORS1 at the VLT-UT1. The host galaxy of H 0414+009 is well resolved in R and I, and marginally resolved in B. Based on our 2-dimensional modelling, it is a large and very luminous elliptical galaxy ( = -24.6, = 35 kpc) with colours commonly found in elliptical galaxies (B-R 1.45 and R-I 0.45). The results are consistent with previous findings.
The host galaxy of OJ 287 is marginally resolved. A de Vaucouleurs profile is slightly preferred over a disk-type profile. If true, the host galaxy is luminous ( = -23.4), compact ( = 4.4 kpc) and has a small offset to the south with respect to the active nucleus. This is consistent with the results obtained by Sillanpää et al. (1999), but different to the findings by Wurtz et al. (1996) and Yanny et al. (1997).
The analysis of the marginally resolved host galaxies was
complicated by a point spread function (PSF) varying across the field.
Consequently, better results were obtained when using a PSF which
varies with field position as compared to a constant PSF. This is
possible as long as a sufficient number of stars is present on the
images. Masking the central regions mostly affected by the PSF errors
may also improve the results. Based on our experience we describe
precaution which has to be taken for FORS1 observations and subsequent
analysis of marginally resolved targets such as AGN host galaxies or
planetary nebulae around young stellar objects.
Key words: methods: data analysis galaxies: active galaxies: BL Lacertae objects: individual: H 0414+009 galaxies: BL Lacertae objects: individual: OJ 287 galaxies: photometry
Send offprint requests to: J. Heidt (firstname.lastname@example.org)
Online publication: November 23, 1999