All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{9500fig1.ps} \end{figure}$ Figure 1: Effective radial beam profile of LABoCa, combining all the bolometers that were usable during the observing run. The error bars are derived from the standard deviation of the pixels in the map. The profile is well described either by a single Gaussian of ${\it HPBW} =20.4\pm 0.5$ $^{\prime \prime }$ (thick line), or by a Gaussian main beam of ${\it HPBW} =19.1\pm 0.6$ $^{\prime \prime }$ (dashed line) and a Gaussian error beam of ${\it HPBW} =54\pm 5$ $^{\prime \prime }$ (dotted line), once deconvolved from the median Mars diameter at the time of observation. The peak ratio between the error and the main beam is 2.1%.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9500fig2.ps}\end{figure}$ Figure 2: Noise map around the z=2.38 galaxy protocluster J2143-4423. Contours are at pixel rms 1.9, 2.9, 4.4, 6.6, 9.9, 15.0 mJy/beam in exponential progression, the thick white contour corresponds to the region of interest with pixel rms below 5 mJy/beam (see text). The axes denote the offsets in arc minutes from the map center ( $\alpha = 21^{\rm h}42^{\rm m}43\hbox{$.\!\!^{\rm s}$ }7$ , $\delta = -44\degr25\hbox{$^\prime$ }30\hbox{$.\!\!^{\prime\prime}$ }0$ (J2000)).
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In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{9500fig3_cmyk.ps} \end{figure}$ Figure 3: The 870 ${\mu {\rm m}}$ LABoCa Gaussian-matched-filtered detection threshold map around the z=2.38 galaxy protocluster J2143-4423. The map pixels are about $6\hbox {$^{\prime \prime }$ }\times 6\hbox {$^{\prime \prime }$ }$ . detection threshold greater than 1.2 (1.0) are circled (boxed). This detection threshold corresponds roughly to a signal-to-noise ratio of 4.3 (3.4). The thick white contour corresponds to the region of interest (see text). The LABoCa HPBW beam shape is represented in the lower left corner. Ly $\alpha$ Blobs present in the field are represented by open stars (Palunas et al. 2004). Triangles are QSOs detected by Francis et al. (2004).
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In the text

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{9500fig4.ps} \end{figure}$ Figure 4: Histograms in Log-Normal coordinates of the pixel signal-to-noise values of the Gaussian-machted maps. a) in the signal map, where a clear excess (shaded area) on the positive-side is present compared to the jackknife histogram fit (solid line) or the astrometry-corrupted fit (dashed-line). b) in the mean jackknife and c) astrometry-corrupted map (see text) which can both be very well fitted by a Gaussian distribution (solid line in b) and dashed line in c).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9500fig5.eps}\end{figure}$ Figure 5: Expected average spurious detection rate in our map as a function of the Gaussian matched-filtered signal-to-noise ratio. The solid line is an exponential fit to the data. Error bars are 1 $\sigma$ standard deviations of the jackknifed maps. The upper axis presents roughly the corresponding signal-to-noise ratio for point sources.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{9500fig6.ps}\end{figure}$ Figure 6: Results of Monte-Carlo simulations with a Gaussian-matched-filtered detection threshold ratio of 1.0 (diamond) and 1.2 (triangle), to test for completeness, flux boosting and position uncertainties as a function of the input flux. Error bars are the 1 $\sigma$ standard deviation of the jackknifed maps. a) Completeness function, i.e. the fraction of recovered sources. b) Flux boosting, i.e. the ratio between the extracted and input flux. c) Positional uncertainties, i.e. difference between the input and recovered source positions. The solid line represent fits to the data, using an error function for a), as $f(S_{\rm in}) = (1+{\rm Erf}((S_{\rm in}-a)/b))/2$ with a = 3.8 (4.7) and b = 1.8 (2.0) for a detection threshold of 1.0 (1.2) and an exponential function of the form $f(S_{\rm in}) = a\exp(-b~ {S_{\rm in}})+1$ with a=6.3 b=0.7 for b) and $f(S_{\rm in}) = a\exp(-b~ {S_{\rm in}})+c$ with a=8.7 b=0.2 and c=0.8 for c). Results for b) and c) are similar for the two detection thresholds and only one is presented for clarity.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9500fig7.ps}\end{figure}$ Figure 7: Cumulative number counts at 870 ${\mu {\rm m}}$ (full square) based on the sources detected in this paper. The errors bars are the 1 $\sigma$ two-sided Poissonian confidence level. The thick plain line is a power law fit to the data (see text). Also shown are the 850 ${\mu {\rm m}}$ cumulative number counts and fit of the SHADES survey with triangles and thin line, respectively (Coppin et al. 2006). The 850 ${\mu {\rm m}}$ number counts have been rescaled to 870 ${\mu {\rm m}}$ with a spectral index of $\nu ^2$ . Furthermore, the number counts in a 5 $^\prime$ diameter circle around the source L06 are presented in open squares and a dashed line that has been fitted to them is also shown. Shaded area represent the 1 $\sigma$ uncertainties of the fit.
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In the text

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{9500fig8} \end{figure}$ Figure 8: Spitzer images of the sources detected at 870 ${\mu {\rm m}}$ with $\Delta F/F>1.2$ plus L24 and L31. From left to right, IRAC 3.6 ${\mu {\rm m}}$ and MIPS 24 ${\mu {\rm m}}$ . Contours show the 870 ${\mu {\rm m}}$ detection threshold $F/\Delta F$ at 0.8, 1.0, 1.2, ..., 5.0 in exponential progression. The axes denote the offsets in arc seconds from the 870 ${\mu {\rm m}}$ source position. Sources are labeled in the top left corner (see text and Tables 1 and 2). Squares show sources identified in Table 2 with P<0.05 whereas triangles show identifications with P>0.05.
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In the text

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{9500fig9.ps}\end{figure}$ Figure 9: $S_{24~\mu {\rm m}}/S_{8~\mu {\rm m}}$ versus $S_{8~\mu {\rm m}}/S_{4.5~\mu {\rm m}}$ color-color diagram for the SMGs of Table 2 with P<0.05 as full square, and open square for those with P>0.05. The lines are color-color tracks with redshift starting from 0.5 to 4, dots denote redshift 1 to 4, from top to bottom for the starburst-like SEDs (plain lines), Seyfert Galaxies (dotted lines) and QSOs (dashed lines). The rectangle defines the region where we expect most of the starbursts, whereas the ellipse shows the region of QSOs. Stars are the submillimeter galaxies of Pope et al. (2006) with secure Mid-IR counterparts, triangles are the radio galaxies of Seymour et al. (2007).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{9500fig5.eps}\end{figure}$	Figure 5: Expected average spurious detection rate in our map as a function of the Gaussian matched-filtered signal-to-noise ratio. The solid line is an exponential fit to the data. Error bars are 1 $\sigma$ standard deviations of the jackknifed maps. The upper axis presents roughly the corresponding signal-to-noise ratio for point sources.
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