Our observations were made throughout the period between December 1998 and October 1999,
using a total of about 150 hours of telescope time. We obtained our observations
in total power (position-switching) mode using consecutive pairs
of two-minute on- and two-minute off-source integrations. Off-source integrations
were taken at approximately E of the target position.
The autocorrelator was divided into two pairs
of cross-polarized receiver banks, each with 512 channels and a 6.4 MHz
bandpass. This yielded a channel spacing of 2.64 kms-1 and an effective
velocity resolution of
3.3 kms-1, which was smoothed
to a channel separation of 13.2 and a velocity resolution of 15.8 kms-1 during the data reduction, in order to search for faint features. The centre
frequencies of the two banks were set to the known redshifted H I
frequency of the target.
We reduced our H I spectra using the standard Nançay spectral line reduction
packages available at the Nançay site. With this software
we subtracted baselines (generally third order polynomials), averaged
the two receiver polarizations, and applied a declination-dependent
conversion factor to convert from units of
to flux density
in mJy. The
-to-mJy conversion factor is determined via a standard
calibration relation established by the Nançay staff
through regular monitoring of strong continuum sources. This
procedure yields a calibration accuracy of
15%.
In addition, we applied a flux scaling factor of 1.26 to our spectra
based on statistical comparisons (see Matthews et al. 1998;
Matthews & van Driel 2000) of Nançay data of samples of late-type spirals
with past observations of these galaxies made at Nançay and elsewhere.
Copyright The European Southern Observatory (ESO)