3 Observations and data reduction

3.1 The observations

The NIR observations reported in this paper were acquired in the photometric nights of March 26th and 27th, 2000 with the 3.6 m, f/11 ESO-NTT telescope, and of December 18th and 19th, 1999 during the science verification period at the 3.6 m, f/11 TNG telescope. The ESO-NTT Nasmyth focus was equipped with the SOFI 1024² pixel array camera. With a pixel scale of 0.29 arcsec/pixel, SOFI has a field-of-view of ${\sim}5\times5~\rm arcmin$. The TNG Nasmyth focus was equipped with the NICMOS3 256² pixel array camera ARNICA (Lisi et al. 1993; Lisi et al. 1996; Hunt et al. 1996), which, with a pixel scale of 0.352 arcsec/pixel, gives a field-of-view of ${\sim}1.5\times1.5~\rm arcmin$.

The seeing at ESO-NTT was always sub-arcsecond, except for one observation taken at a very high airmass (2.14). The mean seeing was 0.77 arcsec (FWHM), with a minimum of 0.59 arcsec. At TNG we observed with a mean seeing of 1.5 arcsec.

The NIR sky is extremely bright ( ${\sim}13~\rm mag\,arcsec^{-2}$) compared with the targets ( ${\sim}22~\rm mag\,arcsec^{-2}$), with significant fluctuations (up to $10\div20\%$ of the mean value) on time-scales comparable with the duration of one observation. In order to observe in linear and background limited regime, observations must be split into several elementary exposures ("coadds'') which are averaged together. In order to monitor the sky fluctuations, on-target observations are alternated with off-target observations, following typical pointing sequences ("mosaics'').

Depending on the extension of the observed sources, we used two types of mosaic. If the apparent size of the source is similar to the available field of view, half of the observing time was spent on the target, half on the sky. The 8 on-target positions were chosen with slight offsets in order to allow for median rejection of bad pixels. These fields were alternated with 8 sky observations. This was the case of all TNG observations and of some NTT fields in which more than one galaxy could be accomodated into one frame (e.g. 4 Centaurus fields and the galaxy pair VCC1491-1499). Thanks to the large field of view of SOFI compared to the target objects, most of the NTT observations of objects were performed using a second type of mosaic in which the target is always in the field, but is moved around in 6 never overlapping positions, making independent, time costly sky measurements unnecessary. We always avoided to set the object in the north-eastern quadrant of SOFI affected by a lower optical quality.

Table 2 reports the log-book of the observations, including parameters relevant to NIR observations, as follows:
Column (1): VCC (Binggeli et al. 1985), CCC (Jerjen & Dressler 1997) or CGCG (Zwicky et al. 1961-68) denomination.
Column (2): NGC/IC names.
Columns (3), (4): adopted (B1950.0) celestial coordinates, taken from NED, with typically one arcsec uncertainty.
Column (5): the morphological type taken from Binggeli et al. (1985), Jerjen & Dressler (1997).
Column (6): the photographic magnitude from the VCC and CCC.
Column (7): the observing date.
Column (8): the telescope used.
Column (9): the number $N_{\rm cds}$ of coadded (averaged) exposures for each frame.
Column (10): the number $N_{\rm cmb}$ of frames combined to obtain the final image.
Column (11): the exposure time for each coadded exposure.
Column (12): the total integration time.
Column (13): the mean airmass during the observation.
Column (14): the adopted filter.
Column (15): the seeing (FWHM) in arcsecs.

Optical photometric observations in the B and V passbands for 24 objects in the sample were obtained with the San Pedro Martir (SPM) 2.1 m Telescope from April 20 to 24, 1998 (20 galaxies), and with the Observatoire de Haute Provence (OHP) 120 cm telescope from March 1 to 3, 1998 (4 galaxies, namely VCC608, 745, 1073 and 1254). Both telescopes were equipped with a TK1024 1024² pixel CCD camera. The pixel scale is $0.30~\rm arcsec\,pix^{-1}$at SPM, and $0.69~\rm arcsec~pix^{-1}$ at OHP. Exposure times were of 600 s for the V-band and of 900 s for the B-band observations.

3.2 Photometric calibration

Observations of standard stars, from Hunt et al. (1998), and Persson et al. (1998), listed in Table 3, were taken one per hour for calibration purposes.

The calibration stars were observed with a third pointing sequence which consists of five positions, starting with the star near the center of the array, followed by positioning the star in each of the four quadrants of the array. At TNG the telescope was defocussed to avoid saturation, since we observed the two brightest stars of the list. The typical photometric uncertainty is 0.05 mag, both for ESO-NTT and TNG observations.

   

Table 2: The logbook of the observations.

Galaxy	NGC	RA	Dec	Type	$m_{\rm p}$	Obs Date	$T_{\rm el}$	$N_{\rm cds}$	$N_{\rm cmb}$	Exp T	Int. T	airm	Filt	seeing
		B1950.0			mag					sec	sec			arcsec
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)	(11)	(12)	(13)	(14)	(15)
VC0021	I3025	120749.80	+102800.0	dS0	14.75	2000-03-27	NTT	6	12	10	720	1.54	H	0.70
VC0033	I3032	120834.80	+143306.0	dE nuc	14.67	2000-03-28	NTT	10	12	6	720	1.38	H	0.75
VC0048	I3036	120942.10	+124559.0	Sm	14.30	2000-03-28	NTT	10	18	6	1080	1.37	H	0.93
VC0067	I3044	121015.50	+141515.0	dSc pec	13.98	2000-03-28	NTT	10	24	6	1440	1.41	H	0.73
VC0083	I3049	121100.60	+144530.0	Im	15.13	2000-03-27	NTT	6	18	10	1080	1.43	H	0.64
VC0162	I3074	121313.20	+105834.0	Sd	14.41	2000-03-28	NTT	10	24	6	1440	1.71	H	0.74
VC0170	I3077	121323.80	+144240.0	dS0	14.56	2000-03-27	NTT	10	12	6	720	1.73	H	0.71
VC0172	-	121327.60	+045542.0	BCD	14.50	2000-03-28	NTT	6	17	10	1020	1.80	H	0.77
VC0216	I3097	121428.20	+094112.0	dE pec	14.90	2000-03-27	NTT	10	15	6	900	1.86	H	0.90
VC0227	-	121441.40	+091312.0	dE nuc	14.90	2000-03-28	NTT	10	18	6	1080	1.37	H	0.99
VC0275	I3118	121538.40	+094642.0	dS0	14.54	2000-03-28	NTT	10	18	6	1080	2.13	H	0.87
VC0308	I3131	121618.00	+080818.0	dS0 nuc	14.30	2000-03-27	NTT	6	12	10	720	1.31	H	0.71
VC0437	-	121816.20	+174554.0	dE nuc	14.54	2000-03-28	NTT	10	18	6	1080	1.46	H	0.80
VC0620	I3239	122037.20	+120011.0	Sm	15.20	2000-03-27	NTT	10	18	6	1080	1.58	H	0.77
VC0688	N4353	122127.30	+080343.0	dSc	13.94	2000-03-28	NTT	6	12	10	720	1.42	H	0.87
VC0737	-	122206.60	+041636.0	dS/BCD	14.94	2000-03-27	NTT	6	18	10	1080	2.03	H	0.78
VC0750	-	122216.80	+070212.0	dE nuc	14.95	2000-03-27	NTT	6	18	10	1080	1.49	H	0.66
VC0856	I3328	122324.60	+101948.0	dE	14.25	2000-03-27	NTT	6	12	10	720	1.38	H	0.69
VC0951	I3358	122422.20	+115642.0	dE/dS0 pec	14.35	2000-03-27	NTT	10	6	6	360	1.52	H	0.80
VC0975	-	122438.30	+073223.0	Scd	13.58	2000-03-28	NTT	10	24	6	1440	1.67	H	0.90
VC1011	-	122456.50	+075514.0	S0E	14.85	2000-03-27	NTT	10	18	6	1080	1.37	H	0.73
VC1036	N4436	122510.20	+123530.0	dE/dS0 nuc	13.68	2000-03-27	NTT	10	6	6	360	1.42	H	0.73
VC1047	N4440	122521.50	+123411.0	Sa bar	12.48	2000-03-27	NTT	10	2	6	120	1.42	H	0.73
VC1183	I3413	122651.00	+114230.0	dS0 nuc	14.37	2000-03-27	NTT	6	12	10	720	1.44	H	0.67
VC1392	I3459	122922.80	+122660.0	dE/dS0 pec	14.86	2000-03-28	NTT	10	18	6	1080	1.48	H	0.59
VC1491	I3486	123042.40	+130800.0	dE nuc	15.24	2000-03-27	NTT	10	8	6	480	1.41	H	0.81
VC1499	I3492	123048.20	+130744.0	dE pec	14.94	2000-03-27	NTT	10	8	6	480	1.41	H	0.81
VC1514	-	123104.80	+080818.0	dE nuc	15.10	2000-03-27	NTT	6	18	10	1080	1.62	H	0.74
VC1528	I3501	123120.10	+133554.0	dE	14.51	2000-03-28	NTT	10	6	6	360	1.44	H	0.74
VC1549	I3510	123143.20	+112051.0	dE nuc	14.63	2000-03-27	NTT	6	12	10	720	1.31	H	0.64
VC1684	I3578	123407.80	+112242.0	dS0	14.87	2000-03-27	NTT	6	12	10	720	1.34	H	0.78
VC1695	I3586	123422.80	+124800.0	dS0	14.53	2000-03-27	NTT	6	12	10	720	1.34	H	0.61
VC1834	N4600	123749.40	+032338.0	S0 nuc	13.47	2000-03-28	NTT	10	12	6	720	2.09	H	0.87
VC1895	-	123920.40	+094030.0	dE	14.91	2000-03-28	NTT	10	12	6	720	2.10	H	0.87
VC1947	-	124023.30	+035701.0	dE nuc	14.56	2000-03-27	NTT	6	12	10	720	2.04	H	0.93
VC2042	-	124407.20	+093448.0	dE nuc	14.84	2000-03-27	NTT	6	18	10	1080	1.76	H	0.70
VC2050	I3779	124449.80	+122624.0	dE nuc	15.20	2000-03-27	NTT	6	12	10	720	1.34	H	0.67
2MASX	-	120848.10	+143120.0	Im/S	17.24	2000-03-28	NTT	10	4	6	240	1.38	H	0.68
CCC045	-	124537.20	-405103.2	E	14.93	2000-03-27	NTT	10	16	6	960	2.20	H	0.84
CCC059	-	124553.20	-405046.0	dE nuc	18.60	2000-03-27	NTT	10	16	6	960	2.20	H	0.84
CCC094	-	124639.50	-410926.0	dS0 nuc	16.67	2000-03-27	NTT	10	16	6	960	1.61	H	0.84
CCC095	-	124640.20	-411303.0	S0	14.56	2000-03-27	NTT	10	16	6	960	1.61	H	0.84
CCC096	-	124640.70	-411127.4	S0	14.70	2000-03-27	NTT	10	16	6	960	1.61	H	0.84
CCC104	-	124649.80	-410916.0	dE nuc	18.25	2000-03-27	NTT	10	16	6	960	1.61	H	0.84
CCC113	-	124656.00	-405725.0	E	17.33	2000-03-26	NTT	6	16	10	960	2.14	H	1.10
CCC119	-	124705.60	-405714.1	E	14.64	2000-03-26	NTT	6	16	10	960	2.14	H	1.10
CCC122	N4706	124708.10	-410026.3	S0a	14.18	2000-03-26	NTT	6	16	10	960	2.14	H	1.10
CCC125	-	124710.40	-405917.0	dE nuc	17.14	2000-03-26	NTT	6	16	10	960	2.14	H	1.10
CCC136	-	124725.70	-410138.4	E	16.25	2000-03-28	NTT	10	8	6	480	1.71	H	0.84
CCC142	-	124731.30	-410156.0	Sm	18.40	2000-03-28	NTT	10	8	6	480	1.71	H	0.84
CCC150	-	124738.00	-410130.0	dE nuc	18.23	2000-03-28	NTT	10	8	6	480	1.71	H	0.84
CCC153	-	124741.60	-410210.0	dE nuc	18.24	2000-03-28	NTT	10	8	6	480	1.71	H	0.84
CCC157	-	124747.30	-410351.0	Sm	18.23	2000-03-28	NTT	10	8	6	480	1.71	H	0.84
CCC205	-	124901.60	-404321.0	S0	15.95	2000-03-28	NTT	6	6	10	360	1.90	H	0.78
CCC216	-	124915.80	-410454.0	dE nuc	18.22	2000-03-27	NTT	10	16	6	960	1.70	H	0.78
CCC222	-	124926.20	-410402.9	dSc	14.74	2000-03-27	NTT	10	16	6	960	1.70	H	0.78
CCC226	N4743	124929.30	-410708.6	S0a	14.08	2000-03-27	NTT	10	16	6	960	1.70	H	0.78
CEG050	-	124828.10	-410903.0	dE	?	2000-03-27	NTT	10	16	6	960	2.20	H	0.84
VC0010	I3017	120651.70	+135110.0	BCD	14.75	1999-12-19	TNG	6	8	10	480	1.78	H	1.50
VC0608	N4322	122029.70	+161058.0	dE nuc	14.94	1999-12-20	TNG	6	8	10	480	1.90	H	1.30
VC0745	N4366	122214.40	+073748.0	dE nuc	14.67	1999-12-20	TNG	4	5	10	200	1.22	H	1.09
VC0786	I3305	122243.80	+120754.0	dE nuc	15.11	1999-12-20	TNG	6	9	10	540	1.25	H	1.21
VC0965	I3363	122431.20	+125006.0	dE nuc	15.40	1999-12-20	TNG	6	8	10	480	1.77	H	1.27
VC1073	I794	122536.50	+122211.0	dE nuc	14.23	1999-12-20	TNG	6	8	10	480	1.08	H	0.90
VC1078	-	122539.00	+100224.0	dE ?	15.30	1999-12-19	TNG	6	12	10	720	1.20	H	1.06
VC1122	I3393	122609.60	+131130.0	dE nuc	14.60	1999-12-19	TNG	4	8	10	320	1.76	H	1.90
VC1173	-	122643.00	+131516.0	dE nuc	16.06	1999-12-20	TNG	6	8	10	480	1.58	H	1.76
VC1254	-	122732.80	+082103.0	dE nuc	15.51	1999-12-20	TNG	6	8	10	480	1.15	H	0.88
VC1308	I3437	122814.40	+113700.0	dE nuc	15.64	1999-12-20	TNG	4	8	10	320	1.46	H	1.17
VC1348	I3443	122843.90	+123628.0	dE pec	15.87	1999-12-20	TNG	4	8	10	320	1.36	H	1.12
VC1386	I3457	122919.20	+125600.0	dE nuc	14.32	1999-12-19	TNG	4	10	10	400	1.51	H	1.13
VC1453	I3478	123012.80	+142819.0	dE nuc	14.34	1999-12-19	TNG	4	8	10	320	1.63	H	1.48
VC1491	I3486	123042.40	+130800.0	dE nuc	15.24	1999-12-19	TNG	6	8	10	480	1.36	H	1.10
97073	-	114020.75	+201438.1	pec	15.60	1999-12-19	TNG	6	8	10	480	1.67	H	1.27
97087	-	114113.19	+201449.1	pec	14.30	1999-12-20	TNG	3	11	10	330	1.62	H	1.31
1ZW018	-	093030.10	+552747.0	BCD	16.08	1999-12-20	TNG	6	8	10	480	1.28	H	1.10

 

 

Table 3: Standard calibration stars.

Star	$H_{\rm mag}$
AS 08_0	$8.723\pm0.014$
AS 18_0	$12.402\pm0.004$
AS 21_0	$9.043\pm0.015$
AS 27_1	$12.677\pm0.024$
AS 29_1	$13.566\pm0.019$
AS 31_1	$12.131\pm0.011$
P550_C	$12.121\pm0.005$

3.3 Image reduction procedures

The multiplicative system response, or flat-field (FF), was derived for the ESO-NTT observations from a set of dome exposures which allow to remove both the dependence of the dark current level from the illumination of the array and the additive contributions. For the TNG observations, since dome exposures could not be taken, the FF was obtained averaging, and normalizing to their median counts, a large number ( 30) of sky frames taken throughout the night, with mean levels differing by less than 5%.

The image reduction procedure was as follows. For each target frame the sky contribution was determined and subtracted. This was done by combining, with a median sigma clipping algorithm, as many as possible contiguous sky exposures, unless their count level differed by more than 10% from the target frame. In the case of mosaics with the source always in the field, all frames were treated as sky frames. The median sigma clipping algorithm is necessary to remove unwanted star and galaxy images in the resulting sky frames. The sky frame was first normalized to its median, then multiplied by the median counts of the individual target frames. Finally, the rescaled frame was subtracted from the target observation. Such a procedure accounts for temporal variations in the sky level, but introduces an additive offset which is subsequently removed (see below). The sky-subtracted target frames were then divided by the FF frame. Each of the corrected frames was analyzed for low-spatial-frequency gradients, and if necessary, fitted with a two-dimensional 3 degree polynomial which was then subtracted. If this process was not effective in removing the spatial gradients, the corresponding frames were rejected from further analysis. The corrected frames were then aligned using field stars and combined with a median filter with sigma clipping, which allows bad pixel removal.

Finally the residual sky background in the combined frame was determined as the mean number of counts measured in regions of "empty'' sky, and it was subtracted from the frame.

All image reduction and analysis was performed in the IRAF environment and relied on the STSDAS package, and on GALPHOT (developed for IRAF-STSDAS mainly by W. Freudling, J. Salzer, and M. P. Haynes and adapted by us to handle NIR data).

The final images, with superposed isophotes, are shown in Figs. 1-2.

Figure 1: ESO-NTT images. North is up, East to the left. Contours are drawn from 21.5 mag arcsec-2, in steps of 1 mag arcsec-2.

Figure 1: continued.

Figure 1: continued.

Figure 1: continued.

Figure 2: TNG images. North is up, East to the left. Contours are drawn from 21.0 mag arcsec-2, in steps of 1 mag arcsec-2 (except for IZw018 whose fainter isophote is 21.5 mag arcsec-2).

Figure 2: continued.

Figure 3: The surface brightness profiles (dots). The solid line is the fitted profile; the dashed and the dotted lines represent the bulge and disk component respectively. The vertical dashed line represents the seeing disk.

Figure 3: continued.

Figure 3: continued.

Figure 4: Radial light and color profiles of 24 galaxies having at least 2 band measurements. The vertical dashed line represents the seeing disk of the optical observations.

Figure 4: continued.