All Figures

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[angle=0]{8292fig1.eps}}\end{figure}$ Figure 1: Numerical distribution of the positionally coincident NVSS/XMM sources as a function of their angular separation. The coincidences were selected adopting an offset between NVSS/XMM positions of $R\leq (\epsilon _{\rm XMM}$ + $\epsilon _{\rm NVSS}$ ), where $\epsilon _{\rm XMM}$ and $\epsilon _{\rm NVSS}$ are the absolute (RA, Dec) errors in the position of the XMM and NVSS sources, respectively. Of a total 86 sources in the histogram (shadowed area), 41 (dashed line) refer to sources with a radio flux lower than 15 mJy. The dotted line refer to the expected XMM-NVSS sources cross-identified by chance.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{8292fig2.eps}\end{figure}$ Figure 2: Ratios of source counts in different spectral bands. Soft (S_x: 0.5-2.0 keV), Medium (M_x: 2.0-4.5 keV), and Hard (H_x: 4.5-12.0 keV). (S-M)/(S+M) on X-axis and (H-M)/(H+M) on Y-axis. The $1 \sigma$ error bars are shown for all the sources. Filled (black) points correspond to unidentified objects in our sample while those shown as open (yellow) points correspond to already known sources. Well-known microquasars are also indicated as (red) diamonds.
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In the text

$\begin{figure} \par\resizebox{18cm}{!}{\includegraphics[angle=0]{8292fig3.eps}}\end{figure}$ Figure 3: Color-color diagram (J-H/H-K) of the positional correlated sources. The intrinsic colors of the main sequence (Siess et al. 2000), the CTTS locus (Meyer et al. 1997), and giant stars are shown, as well as the slope and magnitude of the interstellar reddening vector ( $A_{\rm V}=15$ mag). Well-known MQs (in red) and HMXB systems (white open triangles) are also shown. The most promising MQ candidates (indicated as black points) lie inside the region shaded in grey.
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In the text