Combination of the Imaging Data Sets of the NTT Deep Field

Field

The source detection and extraction is done using the astronomical software SEx-

tractor (Sources Extractor; Bertin & Arnouts, 1996) of a noise-scaled co-addition of the

BVRIzJK images. SExtractor provides a wide variety of parameters for optimizing de-

tection of astronomical sources in images (e.g., number of contiguous pixels, detection threshold, seeing, zero-point). In Fig. 2.3, the setup applied for the source extraction is presented. The quality of the catalog, i.e. its robustness and completeness is tested man- ually by varying the important source extraction parameters like DETECT MINAREA, DETECT TRESH, DEBLEND NTHRESH and by a visual inspection of the source cata- log output, especially the surrounding of the MAMBO 1.2 mm sources. Fig. 2.4 illustrates

the source extraction performed bySExtractorbased on our setup presented in Fig. 2.3. A major part of the visual inspection of our source detections — checking for completeness — is achieved by blinking these two panels. In addition, source counts in different bands and for different source populations e.g., extremely red objects or optical red galaxies, were compared with the literature and agreed within expected uncertainties. We aimed

# Default configuration file for SExtractor V1.2b14 − > 2.0 # EB 23/07/98

# (*) indicates parameters which can be omitted from this config file. #−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Catalog −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− CATALOG_NAME NTTDF_K_mc.cat # name of the output catalog

CATALOG_TYPE ascii # "NONE","ASCII_HEAD","ASCII","FITS_1.0" # or "FITS_LDAC"

PARAMETERS_NAME default.param # name of the file containing catalog contents #−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Extraction −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− DETECT_TYPE CCD # "CCD" or "PHOTO" (*)

FLAG_IMAGE flag.fits # filename for an input FLAG−image DETECT_MINAREA 10 # minimum number of pixels above threshold DETECT_THRESH 1.0 # <sigmas> or <threshold>,<ZP> in mag.arcsec−2 ANALYSIS_THRESH 1.0 # <sigmas> or <threshold>,<ZP> in mag.arcsec−2 FILTER Y # apply filter for detection ("Y" or "N")? FILTER_NAME gauss_3.0_5x5.conv # name of the file containing the filter DEBLEND_NTHRESH 32 # Number of deblending sub−thresholds DEBLEND_MINCONT 0 # Minimum contrast parameter for deblending CLEAN Y # Clean spurious detections? (Y or N)? CLEAN_PARAM 1.0 # Cleaning efficiency

MASK_TYPE NONE # type of detection MASKing: can be one of # "NONE", "BLANK" or "CORRECT"

#−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Photometry −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− PHOT_APERTURES 9 # MAG_APER aperture diameter(s) in pixels PHOT_AUTOPARAMS 2.5, 3.5 # MAG_AUTO parameters: <Kron_fact>,<min_radius> SATUR_LEVEL 50000.0 # level (in ADUs) at which arises saturation MAG_ZEROPOINT 22.17 # magnitude zero−point

MAG_GAMMA 4.0 # gamma of emulsion (for photographic scans) GAIN 0.0 # detector gain in e−/ADU.

PIXEL_SCALE 0 # size of pixel in arcsec (0=use FITS WCS info). #−−−−−−−−−−−−−−−−−−−−−−−−− Star/Galaxy Separation −−−−−−−−−−−−−−−−−−−−−−−−−−−− SEEING_FWHM 0.98 # stellar FWHM in arcsec

STARNNW_NAME /opt/sextractor2.1.6/config/default.nnw # Neural−Network_Weight table filename #−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Background −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

BACK_SIZE 64 # Background mesh: <size> or <width>,<height> BACK_FILTERSIZE 3 # Background filter: <size> or <width>,<height> BACKPHOTO_TYPE LOCAL # can be "GLOBAL" or "LOCAL" (*)

BACKPHOTO_THICK 24 # thickness of the background LOCAL annulus (*) #−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Check Image −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− CHECKIMAGE_TYPE APERTURES # can be one of "NONE", "BACKGROUND",

# "MINIBACKGROUND", "−BACKGROUND", "OBJECTS", # "−OBJECTS", "SEGMENTATION", "APERTURES", # or "FILTERED" (*)

CHECKIMAGE_NAME check_Kalign_mc.fits # Filename for the check−image (*) #−−−−−−−−−−−−−−−−−−−−− Memory (change with caution!) −−−−−−−−−−−−−−−−−−−−−−−−− MEMORY_OBJSTACK 2000 # number of objects in stack

MEMORY_PIXSTACK 100000 # number of pixels in stack MEMORY_BUFSIZE 1024 # number of lines in buffer

#−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Miscellaneous −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− VERBOSE_TYPE NORMAL # can be "QUIET", "NORMAL" or "FULL" (*) #−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− New Stuff −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

Figure 2.3 Example of the setup applied for the extraction of objects with SExtractor in the Ks band.

to detect sources with a minimum number of pixels (10 pixels in our case, at least as large

as the seeing disk with each pixel 1σ above the local background) down to a detection

limit of 3σ. The individual parameters were adjusted until this goal was achieved. The

magnitude is determined in a 200 wide aperture (MAG APER). Due to the seeing of the

2.2. OPTICAL/NEAR-INFRARED IMAGING 23

The source position is determined from the multi-color image. Wavelength-dependent morphology can lead to small offsets of the peaks in certain bands from these average positions. Thus, we measure the magnitude or upper limit for each source in the in- dividual bands on the previously determined position. Finally, the individual catalogs are combined into one. We excluded sources from this catalog classified to be stars by

SExtractor (CLASS STAR). This catalog contains more than 14000 sources and is used for all following data analysis. In Tab. 2.1, an overview of our multi-wavelength data set described in the subsections before is given.

The estimate of the astrometric uncertainty is crucial given the high density of faint

potential counterparts to mm sources. Both the PdBI and VLA positions are ob-

tained in the radio reference frame. The positions of the PdBI and VLA detections for

Figure 2.4 Left Panel: Part of the NTT Deep Field in the K band. Right Panel: Objects

and its local background extracted by SExtractorin the part of the NDF displayed in the left panel using the setup presented in Fig. 2.3.

Table 2.1. Summary of the multi-wavelength follow-up observations of the NDF

Band Field Size det. Limit Seeing Instrument Comment

(1) (2) (3) (4) (5) (6) mB 340×330 27.4 mag 1.1800 WFI mV 340×330 26.6 mag 1.3200 WFI mR 340×330 26.2 mag 1.0600 WFI mI 340×330 25.5 mag 0.9200 WFI mz 13.30×13.00 26.4†mag 0.5000 FORS2

mJ 13.30×13.00 24.0 mag 0.8000 SOFI central field public data (ESO)

mKs 13.30×13.00 21.9 mag 0.9800 SOFI central field public data (ESO)

mKs 3 fields a 2.50×2.50 22.7∗mag 0.30–0.4000 ISAAC pointing on PdBI detections

S1.2mm ∼125 sq. arcmin 1.5–3.0 mJy MAMBO

S1.26mm 4 fields a 2500×2500 1.5–3.6 mJy PdBI four PdBI observations

S1.4GHz ∼ 320 39µJy VLA

Note. — Col. (1) — Band in which flux is measured. Col. (2) — Field size.

Col. (3) — Optical/near-IR magnitudes were measured except for the ISAAC imaging in a 200 diameter aper- ture, and are except for the z band on the ‘Vega’ system. † _{: For the z band, we performed the photometric}

measurements in the BD+17 4708 system. ∗: For the ISAAC imaging, we used a 1.500 diameter aperture. Both optical/near-IR and radio/mm limits are 3σ.

Col. (4) — Seeing.

Col. (5) — Name of instrument. Col. (6) — Comments.

MM J120546–0741.5, MM J120539–0745.4 and MM J154127+6615 (Table 2.2 and Bertoldi et al. (2000)) are consistent within their errors which are 0.400–0.500 for PdBI,

and ∼ 100 for the large-beam VLA data of these faint sources. The systematic errors

contribute significantly to the PdBI uncertainty in the cases of MM J120517–0743.1 and J154127+6615 (e.g., Downes et al., 1999), whereas random errors are the most important source of uncertainty in the 1.4 GHz positions. The mean offset between the near-infrared and the VLA frame is 000._19±000_{.07 in RA and 0}00_.23±000_{.05 in DEC (see § 2.2.2 for more}

detail). Optical/near-infrared positions used below have been corrected for the small sys- tematic offset, i.e. they should be in the radio coordinate system to a good approximation.