3.1 Observations

Thirty-one galaxies were observed with the 1.5 meter telescope (P60) of Palomar Observatory on the night of 1991 May 4 with the Wide Field Prime Focus Universal Extragalactic Instrument (Wide Field PFUEI). The wide field camera has a 306 mm f/4 aerial camera lens collimator and a Nikon 58 mm f/1.2 camera lens. The field of view is 16' x 16', and it is projected on an 800 x 800 Texas Instruments (TI) CCD in the Cassegrain focus, yielding a scale of 1.19 arcsec per pixel. The focal ratio of the system is f/1.65.

Normalized transmission curves of the g, r and i filters vs. wavelength (in nanometers)

Images were obtained in the g, r, and i bands of the Thuan-Gunn photometric system. The original, 4-band system (u, v, g, and r) was introduced by Thuan and Gunn in 1976. It was later extended by Wade et al. with the i band, and by Schneider et al. with the z band. Most CCDs are not efficient in the z band, but g, r, and i CCD surface photometry of galaxies have been extensively done in the past decade. These filters are centered at 500nm, 650nm and 820nm, respectively. The filters were placed in front of the camera optics to avoid problems with reflection. The system transmission functions are plotted on the right.

All exposures were 60 seconds. The 9 electron CCD readout noise was low enough to allow such a short exposure time and still ensure that the background was sky noise limited. The gain of the instrument is about 2 electrons/ADU (analog-to-digital units). The readout noise was negligible. Typical counts around the center of galaxies are 10,000-20,000 ADU. Keeping the exposure time short for all the observations made it possible to obtain more than 150 images (including flats and standard star observations) in one night. The centers of some of our brightest galaxies, however, are saturated. Saturation was limited to only a few pixels around the photometric center of these galaxies. We introduced a scheme to repair these regions and to calibrate these galaxies.

Eighty-two galaxies were observed with the 1.1 meter telescope of the Lowell Observatory on several nights between 1989 March 24 and April 4. A camera with a thinned, back-illuminated 320 x 512 pixel RCA CCD was in the Cassegrain focus. A 2:1 focal reducer gave an f/4 focal ratio, yielding a scale of 1.35 arcsec per pixel. The field of view was about 7' x 11'.

Normalized transmission curves of the J and R filters vs. wavelength (in nanometers)

We used the three-band J (sometimes designated as B_J), R and I photometric system, which was developed to take advantage of silicon CCDs. Only J and R images were obtained of each galaxy. These filters are centered at 450nm and 650nm. You will find a plot of the system transmission curves on the right. Typical exposure times were between 100 and 600 seconds, depending on the galaxy core brightness. Short test exposures were first obtained of each galaxy in each filter in order to avoid nuclear saturation. The readout noise of the CCD was 90 electron, and the gain of the instrument was 11 electron/ADU. Typical counts in central regions of the galaxies reach above 10,000 ADU.

 
3.2 Image processing

Debiasing and flat fielding the images of galaxies observed at Palomar were straightforward. We used the data in the extended horizontal register of the CCD to obtain the bias level, which was subtracted from the image. Twilight sky flats were obtained in all three passbands during the night of observations. These were used to create a median flat, which was used to flat field the images.

Besides subtracting the bias level, we had to use a more complicated flattening procedure for the images observed at Lowell. Because of the glass substrate of the RCA CCD, the night sky emission lines caused Fabry-Perot fringing in the R band (J is not affected since there are no strong atmospheric emission lines in this band). Because of fringing, we treated the R and the J images differently. Another problem was that observations took place in both bright and dark conditions, since the observing run was longer than a week. The color of the background sky is close to the color of the twilight flat in bright conditions, but is quite different when the Moon is down.

A few pixels around the photometric centers of some of the galaxies observed at Palomar were saturated. Compared to the total area of the fields, only a very small portion of the images were affected, accounting for only a negligible part of the total light of the galaxy. We modeled the light distribution around the photometric centers with a seven-parameter, two dimensional Gaussian distribution. First, to preserve integer representation of the images, we divided all pixel values by 2 in the entire image if the center was saturated; in no case did this compromise the sampling of the noise histogram. Next, we used the information in the image just around the saturated center to fit these parameters, and then replaced all saturated pixels with analytical values from our fit. Eleven of the 31 spiral galaxies observed at Palomar were saturated at the photometric center, eight of them in all bands, three of them only in two bands.

We used an empirical two dimensional point-spread-function (PSF) to fit and remove the foreground stars from the images. The program we developed for this purpose first identifies stars off the galaxy to be used for constructing the PSF. Second, it finds those objects that are likely to be foreground stars (versus HII regions, bright stars belonging to the galaxy, etc.) and removes them by using a PSF fit. Third, the residuals left in the image are repaired cosmetically. Although the program does not perform all necessary steps automatically, it was very useful for the purpose of cleaning these images. Details of this procedure are to be found in Frei: "Semi-automatic removal of foreground stars from images of galaxies," in the Publications of the Astronomical Society of the Pacific, vol. 108, p. 624, 1996.

On several occasions the area occupied by the galaxy was much smaller than the total area of the original image, so we chose to extract square regions out of the original images that contained the galaxy, thereby saving a considerable amount of storage space. The CCD chip used at Lowell was not square, making it necessary to crop to obtain square images. We decided to construct the catalog using only square images of a few standard sizes. Offsets (the coordinates of the lower left corner of the trimmed image in the original image) and the coordinates of the photometric center of the galaxies in the final clipped images were recorded in the FITS file headers.

We also calibrated all the galaxies photometrically, but not without difficulty. Conditions during several nights of observations at Lowell, and part of the observing night at Palomar, were non-photometric. Moreover, observations of standard stars were not available for all nights at Lowell. In Frei and Gunn: "Generating colors and k-corrections from existing catalog data," in the Astronomical Journal, vol. 108, p. 1476, 1994, we derived transformation relations for colors of galaxies among five different photometric systems. These were used to calculate magnitudes in the given filter systems from data available in the Third Reference Catalog of Bright Galaxies (RC3). For those data from Palomar, both the calculated magnitudes and the magnitudes obtained from standard-star-calibrations are given in the FITS file headers (seven standard stars were observed during the night of observations). The Lowell data contain only magnitudes calculated via color transformations of the RC3 data.

 
3.3 Properties of galaxies in the catalog

All of the galaxies in our catalog are listed in RC3. We list the most important parameters in the table below. The first column is the New Galaxy Catalog (NGC) number of the galaxy in our catalog. The second column identifies the source of the image (Palomar Observatory or Lowell Observatory). The revised morphological type (T) on the "Handbuch der Physik" system is listed next. T=-5 for elliptical galaxies, T=-3 for lenticular galaxies and T is between 0 and 9 for spirals. T=10 and above describes irregular and peculiar galaxies. Columns 4 and 5 are right ascensions and declinations as recorded in the file headers at the time of observations. Columns 6 to 10 are the total B_T magnitudes, heliocentric mean radial velocities (v), major axis isophotal diameters (D), inclination angles, and position angles, respectively.

 NGC   Obs.     T  alpha        delta        B_T    v      D    I   p.a.
 ___   ____     _  _____        _____       _____  ___     _    _   ___

 2403  Palomar  6  07:32:02.7   +65:42:43    8.93   129  1312  55.8  127   
 2541  Palomar  6  08:11:01.9   +49:13:00   12.26   556   378  59.9  165   
 2683  Lowell   3  08:51:54.2   +33:27:34   10.64   402   559  76.4   44   
 2715  Lowell   5  09:06:01.0   +78:06:17   11.79  1317   293  70.2   22   
 2768  Lowell  -5  09:07:45.2   +60:14:40   10.84  1334   487  58.3   95   
 2775  Lowell   2  09:09:46.1   +07:05:06   11.03  1350   255  39.1  155   
 2903  Palomar  4  09:29:19.9   +21:43:11    9.68   556   755  61.4   17   
 2976  Lowell   5  09:45:58.5   +67:57:18   10.82     1   353  62.8  143   
 2985  Lowell   2  09:45:52.6   +72:30:45   11.18  1317   274  37.4    0   
 3031  Palomar  2  09:51:29.9   +69:18:19    7.89   -37  1614  58.3  157   
 3077  Lowell  12  10:02:09.1   +68:43:11   10.61    11   322  33.7   45   
 3079  Lowell   5  09:58:35.4   +55:55:11   11.54  1124   476  79.5  165   
 3147  Lowell   4  10:15:23.4   +73:27:23   11.43  2810   233  27.0  155   
 3166  Lowell   0  10:11:09.3   +03:40:25   11.32  1344   287  60.7   87   
 3184  Lowell   6  10:17:38.7   +41:28:29   10.36   589   444  21.1  135   
 3198  Palomar  5  10:16:53.0   +45:47:59   10.87   663   510  67.1   35   
 3319  Palomar  6  10:36:14.1   +41:56:46   11.48   745   369  56.7   37   
 3344  Lowell   4  10:42:48.5   +24:58:46   10.45   584   424  24.2    0   
 3351  Lowell   3  10:43:15.6   +11:45:15   10.53   777   444  47.5   13   
 3368  Lowell   2  10:44:06.9   +12:05:05   10.11   898   455  46.2    5   
 3377  Lowell  -5  10:47:09.1   +14:02:35   11.24   691   314  54.9   35   
 3379  Lowell  -5  10:47:12.6   +12:38:22   10.24   888   322  27.0    0   
 3486  Lowell   5  10:59:44.8   +29:02:10   11.05   680   424  42.2   80   
 3556  Lowell   6  11:10:40.1   +55:43:56   10.69   693   522  75.1   80   
 3596  Lowell   5  11:12:27.9   +15:03:38   11.95  1191   238  17.3    0   
 3623  Lowell   1  11:18:19.5   +13:09:31   10.25   806   586  72.8  174   
 3631  Lowell   5  11:18:13.3   +53:26:43   11.01  1157   300  17.3    0   
 3672  Lowell   5  11:24:31.1   -09:44:33   12.09  1862   250  62.1   12   
 3675  Lowell   3  11:25:33.3   +43:38:45   11.00   765   353  58.3  178   
 3726  Lowell   5  11:32:39.1   +47:05:49   10.91   848   369  46.2   10   
 3810  Lowell   5  11:38:23.5   +11:44:55   11.35   993   255  44.9   15   
 3877  Lowell   5  11:43:29.4   +47:46:18   11.79   902   329  76.4   35   
 3893  Lowell   5  11:46:01.1   +48:59:20   11.16   971   268  51.9  165   
 3938  Lowell   5  11:50:13.6   +44:24:07   10.90   807   322  24.2    0   
 3953  Lowell   4  11:53:02.2   +52:22:19   10.84  1053   415  59.9   13   
 4013  Lowell   3  11:57:51.8   +44:01:12   12.19   836   314  78.8   66   
 4030  Lowell   4  11:59:45.8   -01:02:30   11.42  1460   250  43.6   27   
 4088  Lowell   4  12:04:54.3   +50:35:47   11.15   758   345  67.1   43   
 4123  Lowell   5  12:07:30.9   +02:57:17   11.98  1328   261  42.2  135   
 4125  Lowell  -5  12:07:25.1   +65:13:41   10.65  1354   345  56.7   95   
 4136  Lowell   5  12:06:45.7   +30:12:18   11.69   607   238  21.1    0   
 4144  Lowell   6  12:07:28.3   +46:44:07   12.05   267   361  77.4  104   
 4157  Lowell   5  12:10:26.7   +50:33:20   12.66  2294   134  39.1  115   
 4178  Palomar  8  12:10:13.8   +11:08:48   11.90   376   307  69.2   30   
 4189  Palomar  6  12:11:13.9   +13:42:11   12.51  2112   143  43.6   85   
 4192  Palomar  2  12:11:15.9   +15:10:49   10.95  -142   586  73.6  155   
 4216  Palomar  3  12:13:20.9   +13:25:22   10.99   129   487  77.4   19   
 4242  Lowell   8  12:16:57.5   +45:40:37   11.37   517   300  40.7   25   
 4254  Palomar  5  12:16:18.0   +14:41:42   10.44  2407   322  29.4    0   
 4258  Palomar  4  12:16:29.0   +47:35:00    9.10   450  1117  67.1  150   
 4303  Palomar  4  12:19:22.0   +04:45:04   10.18  1569   387  27.0    0   
 4321  Palomar  4  12:20:22.9   +16:06:01   10.05  1585   444  31.7   30   
 4340  Lowell  -1  12:23:04.9   +16:46:54   12.10   915   212  37.4  102   
 4365  Lowell  -5  12:23:56.0   +07:22:41   10.52  1227   415  43.6   40   
 4374  Lowell  -5  12:24:30.1   +12:56:41   10.09   956   387  29.4  135   
 4394  Palomar  3  12:23:24.9   +18:29:23   11.73   920   217  27.0    0   
 4406  Lowell  -5  12:23:39.7   +13:13:25    9.83  -248   534  49.8  130   
 4414  Palomar  5  12:23:56.9   +31:29:55   10.96   718   217  55.8  155   
 4429  Lowell  -1  12:24:54.2   +11:23:05   11.02  1137   337  62.8   99   
 4442  Lowell  -2  12:27:32.3   +09:50:48   11.38   530   274  67.1   87   
 4449  Lowell  10  12:27:36.0   +44:09:15    9.99   201   369  44.9   45   
 4450  Lowell   2  12:27:58.3   +17:08:37   10.90  1957   314  42.2  175   
 4472  Lowell  -5  12:29:13.8   +08:03:42    9.37   915   613  35.6  155   
 4477  Lowell  -3  12:29:29.4   +13:41:46   11.38  1348   228  24.2   15   
 4486  Lowell  -4  12:30:17.4   +12:27:00    9.59  1282   499  37.4    0   
 4487  Lowell   6  12:28:29.5   -07:46:41   11.63  1037   250  47.5   75   
 4498  Palomar  7  12:29:07.9   +17:07:49   12.79  1505   177  57.5  133   
 4501  Palomar  3  12:29:27.9   +14:41:43   10.36  2278   415  57.5  140   
 4526  Lowell  -2  12:33:34.0   +07:45:58   10.66   463   434  70.7  113   
 4527  Palomar  4  12:31:35.0   +02:55:42   11.38  1734   369  70.2   67   
 4535  Palomar  5  12:31:47.9   +08:28:35   10.59  1957   424  44.9    0   
 4548  Palomar  3  12:32:55.1   +14:46:22   10.96   485   322  37.4  150   
 4559  Palomar  6  12:33:29.0   +28:14:07   10.46   814   642  66.0  150   
 4564  Lowell  -5  12:35:51.2   +11:30:17   12.05  1119   212  65.4   47   
 4569  Palomar  2  12:34:17.9   +13:26:25   10.26  -237   572  62.8   23   
 4571  Palomar  7  12:34:25.0   +14:29:34   11.82   341   217  27.0   55   
 4579  Palomar  3  12:35:12.0   +12:05:34   10.48  1521   353  37.4   95   
 4593  Lowell   3  12:39:01.4   -05:16:29   11.67  2497   233  42.2    0   
 4594  Lowell   1  12:39:29.9   -11:33:57    8.98  1090   522  66.0   90   
 4621  Lowell  -5  12:41:26.2   +11:42:53   10.57   431   322  46.2  165   
 4636  Lowell  -5  12:42:12.8   +02:44:48   10.43  1018   361  39.1  150   
 4651  Palomar  5  12:41:13.0   +16:40:05   11.39   805   238  48.6   80   
 4654  Palomar  6  12:41:25.9   +13:23:59   11.10  1035   293  54.9  128   
 4689  Palomar  4  12:45:14.9   +14:02:04   11.60  1617   255  35.6    0   
 4710  Lowell  -1  12:49:08.5   +15:13:27   11.91  1119   293  76.1   27   
 4725  Palomar  2  12:47:59.9   +25:46:30   10.11  1206   642  44.9   35   
 4731  Lowell   6  12:50:30.9   -06:19:11   11.90  1495   396  60.7   95   
 4754  Lowell  -3  12:51:49.8   +11:22:12   11.52  1396   274  57.5   23   
 4826  Lowell   2  12:56:08.7   +21:43:50    9.36   412   600  57.5  115   
 4861  Lowell   9  12:56:40.3   +35:07:56   12.90   843   238  68.2   15   
 4866  Lowell  -1  12:56:57.9   +14:26:25   12.14  1987   378  77.7   87   
 5005  Lowell   4  13:10:25.8   +37:06:53   10.61   948   345  61.4   65   
 5033  Palomar  5  13:11:07.9   +36:51:46   10.75   877   642  62.1  170   
 5055  Palomar  4  13:13:34.8   +42:17:48    9.31   504   755  54.9  105   
 5204  Lowell   9  13:29:08.1   +58:27:20   11.73   202   300  52.9    5   
 5248  Lowell   4  13:35:32.4   +09:08:23   10.97  1153   369  43.6  110   
 5322  Lowell  -5  13:48:36.0   +60:14:50   11.14  1915   353  48.6   95   
 5334  Lowell   5  13:50:20.3   -00:52:05   11.99  1382   250  43.6   15   
 5364  Lowell   4  13:53:41.1   +05:15:33   11.17  1240   405  49.8   30   
 5371  Lowell   4  13:55:04.4   +40:30:53   11.32  2554   261  37.4    8   
 5377  Lowell   1  13:55:46.3   +47:17:24   12.24  1793   222  55.8   20   
 5585  Lowell   7  14:19:26.8   +56:46:43   11.20   305   345  49.8   30   
 5669  Lowell   6  14:32:13.8   +09:57:12   12.03  1374   238  44.9   50   
 5701  Lowell   0  14:36:41.5   +05:34:50   11.76  1506   255  17.3    0   
 5746  Lowell   3  14:44:22.4   +01:59:59   11.29  1724   444  79.8  170   
 5792  Lowell   3  14:57:51.5   -01:02:29   12.08  1929   415  75.5   84   
 5813  Lowell  -5  15:00:40.2   +01:45:39   11.45  1926   250  43.6  145   
 5850  Lowell   3  15:06:39.4   +01:36:13   11.54  2553   255  29.4  140   
 5985  Lowell   3  15:39:24.1   +59:22:00   11.87  2519   329  57.5   13   
 6015  Lowell   6  15:50:51.5   +62:20:17   11.69   824   322  66.5   28   
 6118  Lowell   6  16:19:12.6   -02:09:57   12.42  1572   280  64.7   58   
 6384  Lowell   4  17:29:59.0   +07:05:43   11.14  1667   369  48.6   30   
 6503  Lowell   6  17:48:53.7   +70:09:00   10.91    42   424  70.2  123   

We recorded useful information in the header keys in the FITS files of the images. There are several keys among those we used that are standard FITS keys: SIMPLE BITPIX, NAXIS, NAXIS1, NAXIS2, BSCALE, BZERO, BUNIT, OBJECT, DATE, DATE-OBS, INSTRUME, TELESCOP, OBSERVER, HISTORY, CRVALn, CRPIXn, CDELTn, CTYPEn, DATAMAX, DATAMIN, and EQUINOX. There are several keys that we added to describe the data as best as we could. These are listed in the table below.

The first column contains the name of the header key, the second column has the type of the variable, and the last column gives a short description. The first six keys (EXPOSURE to TIME) were recorded during the observations. We obtained PSF_FWHM from the data at the time of foreground star removal, and SKY and SKYSIG at the time of calibration. The photometric zero-points DNAT0_ST and DNAT0_BV are calculated from observations of standard stars (not available for the Lowell data) and by using data from RC3, respectively. We recorded the photometric center of the galaxy in the trimmed, square image (G_CENT_X and G_CENT_Y). The parameter SATURATE is used to tell whether the galaxy center was saturated and repaired. The last seven header keys (B_RC3 to VELO_RC3) are populated with data from RC3. These are well described in RC3 and in the previous section. We gave the location (column and line) of the actual data entry in the RC3 table.

 Name       Type       Description
 ____       ____       ___________  


 EXPOSURE   float      Length of exposure in seconds.

 FILTER1    character  Photometric passband used for the observation.

 RA         character  Right ascension of the pointing center during the 
                       observation.

 DEC        character  Declination of the pointing center during the 
                       observation.

 AIRMASS    float      Airmass at the beginning of the exposure. 

 TIME       character  Universal time (UT) at the beginning of the exposure.

 SKY        float      The background sky level (in ADU). 

 SKYSIG     float      RMS noise per pixel of the sky (in ADU). 

 DNAT0_ST   float      Counts (in ADU) representing 0 magnitude in the 
                       image, calibrated using observations of standard 
                       stars. 

 DNAT0_BV   float      Counts (in ADU) representing 0 magnitude in the 
                       image, calibrated using B and B-V from RC3. 

 G_CENT_X   integer    Horizontal (x) coordinate of the photometric center 
                       of the galaxy in the trimmed image, in pixels. 

 G_CENT_Y   integer    Vertical (y) coordinate of the photometric center
                       of the galaxy in the trimmed image, in pixels. 

 SATURAT    integer    Equals 1 if the galaxy center was not saturated, 
                       2 if it was saturated (and divided by 2). 

 PSF_FWHM   float      Width (in arcsec) of the point spread function, 
                       obtained from stars before foreground star removal. 

 B_RC3      float      Total (asymptotic) Johnson B magnitude from RC3, 
                       column 6, line 1.

 B-V_RC3    float      Total (asymptotic) Johnson B-V color from RC3, 
                       column 7, line 1. 

 PA_RC3     float      Major axis position angle, (measured from north 
                       through east, between 0 deg. and 180 deg.) from 
                       RC3, column 5, line 1. 

 BOA_RC3    float      Decimal logarithm of the ratio of the major axis 
                       isophotal diameter to the minor isophotal diameter, 
                       both reduced to mu_B=25 mag / arcsec**2, 
                       from RC3, column 4, line 2. 

 SIZE_RC3   float      Decimal logarithm of the apparent major axis 
                       isophotal  diameter reduced to mu_B=25 mag / 
                       arcsec**2, from RC3, column 4, line 1. 

 TYPE_RC3   character  Numerical morphological type T from RC3, 
                       column 3, line 1. 

 VELO_RC3   float      Weighted mean heliocentric radial velocity, 
                       calculated from RC3, column 10, line 4.