The galaxies presented in this paper have been selected from the sample of elliptical
and lenticular galaxies whose ionized gas distribution has been studied
by Macchetto et al. (1996); the dust content of IC 5105, NGC 636 and NGC 1600
was studied by Ferrari et al. (1999). We selected those galaxies which were
compatible with the observation epoch. The selected galaxies are brighter
than
mag and their morphological types are from The Revised Shapley-Ames
Catalog of Bright Galaxies (Sandage & Tammann 1987). Table 1
presents morphological types, apparent
magnitudes, B extinction and distances (scaled to
H0=65 km s-1 Mpc-1) of the 12 selected objects.
The observations were made during 3 nights at the Las Campanas Observatory, Chile,
with the infrared camera C40IRC (NICMOS3 HgCdTe detector,
pixels)
attached to the 1 m Swope telescope. This instrumental arrange covers, on the sky, an
area of
arcmin2, with a scale of 0.6 arcsec/pixel. We used the
broadband filters J, H and
,
centered on 1.24, 1.65 and
2.16
m, with 0.22, 0.30 and 0.33
m passbands. The H filter is equivalent to
the H filter in the CIT/CTIO system; filters J and
are variations of standard
J and K filters. The J filter is less sensitive to variations in atmospheric
water vapor transmission, while
does not suffer from background thermal
radiation as much as the K filter. For the specific characteristics of these filters,
see Persson et al. (1998), who also give infrared photometric
data for several stars, allowing us to derive a transformation between
systems K and
;
from a least-square fit, we found
.
For all galaxies, we obtained a set of 32 exposures of 30, 30 and 25 s for J, Hand
respectively, except for NGC 720, NGC 7562 and NGC 7796, where we got
only 16 exposures. Images were dithered each 4 exposures. Seeing conditions were fair,
varying from 1.05
to 1.83
,
and all nights were photometric.
Standard stars from Persson et al. (1998) were also observed, taking 10 exposures
of 10 s, with the same dithering conditions used for the galaxies.
The IRAF reduction package was used to conduct all reduction steps. The images were dark-subtracted and flat-fielded. For each galaxy, the images were median-combined in order to produce its corresponding sky frame. Bad pixels were corrected using CCDMASK and FIXPIX tasks. The final image for each galaxy was obtained combining the sky-subtracted, bad-pixel corrected individual images.
A very pronounced effect in the H images is the formation of fringes.
The use of twilight sky as a flat-field,
with short exposures (6000 ADU), minimizes this effect
in flat-field frames; therefore this correction must be done only in object
frames. This correction is made as we calculate the median frame (sky)
in each pixel; as the fringing is fixed along the detector, the subtraction
of the median extracts this pattern from the science frames.
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The estimated calibration errors are 0.011 mag for J, 0.060 mag for H and
0.059 mag for .
While H and
errors are of the same order of those expected
from photoelectric photometry (Ducati et al. 2001), the J band shows lower values.
Copyright ESO 2002