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Astron. Astrophys. 342, 363-377 (1999)

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4. The HDF data analysis

The data in the public domain on the Hubble Deep Field in the LW2 (6.7[FORMULA]) and LW3 (15[FORMULA]) ISOCAM-LW bands are analysed here with the method outlined above. Early results are given by Rowan-Robinson et al. (1997). The data were taken in three rasters for each wavelength centered on the optical centre of the Hubble Space Telescope WFPC quadrants number 2, 3 and 4. The 3 arcsecond lens was used for LW2 and the 6 arcsecond lens for LW3. The LW3 rasters are therefore largely overlapping. Adjacent raster positions are separated by resp. 5 and 9 arcseconds, roughly a pixel and a half apart. The resulting triple beam-switch method that we apply may miss a fraction of the flux (although we have tried to evaluate it in Sect. 3.2), in that particular case, especially if there are extended objects. Each raster is made of 8 by 8 positions aligned with the camera axes (see Fig. 1). Each LW2 (resp. LW3) raster position is made of resp. 9 to 10 (19 to 20) readouts of 72 (resp. 36) CAMTU (10 and 5 s resp.) integration times. Tables 1 and  2 and Tables 3, 4, & 5 give the details of potential sources with a quality different from 0 (either [FORMULA] or [FORMULA]) for each ISO raster (no significant source was found with LW2 in the third HDF quadrant). The source positions for each raster are corrected by an absolute astrometric offset. This offset was determined from the sources which are detected in several rasters, the optical identification for the primary astrometric corrector is a 19.5 magnitude object (with a redshift of 0.139, Cowie et al. 1998) situated at (J2000) RA= 12 36 48.33 and Dec= 62 14 26.4 at the upper part of the HDF, which is detected at both wavelengths. Note that we could not coadd LW2 rasters (they do not overlap much anyway) because of the lack of common sources or well identified sources. Figs. 6, 7 and 8 show the 3 independent LW3 rasters with intensity in greyscale and 3 [FORMULA] contours. One can notice at once the large consistency between the 3 independent datasets in the overlapping area. Fig. 9 shows an f814 HST image of the HDF (Williams et al. 1996) superposed by a 3 [FORMULA] contour of ISOCAM after shifting and optimally coadding the three individual LW3 rasters. Table 6 presents the final list of objects detected in the LW3 coadded map. Fig. 10 shows a K-band IRIM image of the HDF (Dickinson et al. 1997) superposed by a 3 [FORMULA] contour of the same ISOCAM LW3 total map. It is clear that the sources in the final catalog (Table 6) that are not in one or two of the raster tables (3, 4, & 5) are simply outside or at the edge of the corresponding observed area.


[TABLE]

Table 1. : HDF-2_LW2 list of significant sources at the [FORMULA] level found in the raster with TDT no 22401501, corrected by -1.90, -1.80 arcseconds



[TABLE]

Table 2. HDF-4_LW2 list of significant sources at the [FORMULA] level found in the raster with TDT no 22401305, corrected by 0, 0 arcseconds



[TABLE]

Table 3. : HDF-2_LW3 list of significant sources at the [FORMULA] level found in the raster with TDT no 22701702, corrected by -1.20, -4.10 arcseconds



[TABLE]

Table 4. : HDF-3_LW3 list of significant sources at the [FORMULA] level found in the raster with TDT no 22701604, corrected by -1.20, -7.10 arcseconds



[TABLE]

Table 5. HDF-4_LW3 list of significant sources at the [FORMULA] level found in the raster with TDT no 22202606, corrected by -1.20, -1.30 arcseconds



[TABLE]

Table 6. List of significant sources at the [FORMULA] level found in final combined LW3 map. Positions in J2000 system. Last column indicates likely associations with an LW2 source (Table 12), with the radio source catalog by Richards et al. (1998) and with a visible-IR source with redshift from the active catalogs by Cowie et al. (1998).


[FIGURE] Fig. 6. LW3 grey scale map of the HDF-2 raster. The contour is at about the 3 [FORMULA] level. Black corresponds to about 300[FORMULA] per beam, white to 0. Following maps are done on the same scale.

[FIGURE] Fig. 7. HDF LW3 grey scale map of the HDF-3 raster. Contour and greyscale are identical to the previous figure.

[FIGURE] Fig. 8. HDF LW3 grey scale map of the HDF-4 raster. Contour and greyscale are identical to the previous figure.

[FIGURE] Fig. 9. HDF optical f814 map (grey scale) overlaid with the LW3 contour of the 3 coadded rasters. The contour is at about the 3 [FORMULA] level. The outside contour (as defined by a minimum redundancy of 2) delimits the region where the source searching algorithm was applied.

[FIGURE] Fig. 10. HDF K band near IR map (grey scale) overlaid with the LW3 contour of the same 3 coadded rasters. The contour is at about the 3 [FORMULA] level.

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© European Southern Observatory (ESO) 1999

Online publication: February 22, 1999
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