How to place text and image above the exact subfigure?

You need something like this,

\begin{figure}
  \centering
  \begin{tabular}[t]{cccc}
    &\multicolumn{3}{c}{
      \begin{tikzpicture}
        \draw (0,0) rectangle (10.0,0.8);
      \end{tikzpicture}
    }\\
  &{\bfseries Something}&\multicolumn{2}{c}{\bfseries Something}\\
  \subfloat[Iteration Domain for a Tile]{
....
  }&
  \subfloat[Convex Bounding Boxes]{
....
  }&
  \subfloat[Disjoint Bounding Boxes]{
....    
}&
  \subfloat[Disjoint Bounding Boxes]{
....    
}
\end{tabular}
  \caption{Bounding boxes for disjoint union of data regions}
\end{figure}

My result was this,

To control the inter-column spacing, use \setlength{\tabcolsep}{some value} and other inter-row space control techniques to control vertical placements.