\documentclass[twocolumn]{article}
\usepackage{tikz}

% Main Document
\begin{document}

% Title
\title{\bf x}
\author{\it x}
\maketitle

\begin{figure}
 \includegraphics{figures_design-ancestor-query-legend.pdf}
 \includegraphics{figures_design-backfill-query.pdf}
\end{figure}
%

\end{document}