TikZ 绘制高度和子浮点垂直对齐

Question

我正在使用此代码将两个 TikZ 图形放在一行上：

\documentclass{book}

\usepackage{tikz}
\usepackage{pgfplots} 

\usepackage{float}
\usepackage{subcaption}

\pgfplotsset{compat=1.16}
\tikzset{declare function={gauss(\x,\y,\z)=
1/(\z*sqrt(2*pi))*exp(-((\x-\y)^2)/(2*\z^2));}}

\usetikzlibrary{positioning}
\usetikzlibrary{shapes}
\usetikzlibrary{arrows}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{decorations.pathmorphing}

\begin{document}

\begin{figure}[ht]
 \centering
  \begin{subfigure}{0.45\textwidth}
   \centering
   \include{./figures/HypothesisTestingTwoTailed}
   \caption{two-tailed test}
   \label{fig:OneAndTwoTailedTests-Two}
  \end{subfigure}
  \quad
  \begin{subfigure}{0.45\textwidth}
   \centering
   \include{./figures/HypothesisTestingOneTailed}
   \caption{one-tailed test}
   \label{fig:OneAndTwoTailedTests-One}
  \end{subfigure}\\
  \caption{One- and two-tailed tests}
  \label{fig:OneAndTwoTailedTests}
\end{figure}

\end{document}

结果如下：

这是其中一张图片：

\begin{tikzpicture}
 \begin{axis}[%
   no markers,
   domain=-3:3,
   height=4cm, width=7cm,
   samples=61, smooth,
   axis x line=bottom,
   axis y line=none,
   xtick=\empty, ytick=\empty,
   clip=false,
   enlargelimits=upper
  ]

  \node [coordinate] at (axis cs:0,0) (origin) {};
  \node [coordinate] at (axis cs:-2.5,0) (alphaleft) {};
  \node [coordinate] at (axis cs:2.5,0) (alpharight) {};

  \node[coordinate] (zleft)  at (axis cs:-2,{gauss(-2,0,1)}) {};
  \draw (axis cs:-2,0) -- (zleft);

  \node[coordinate] (zright) at (axis cs:2,{gauss(2,0,1)}) {};
  \draw (axis cs:2,0) -- (zright);

  \addplot [thick] {gauss(x,0,1)};

  \node[coordinate] (top) at (axis cs:0,{gauss(0,0,1)}) {};
  \draw [dashed] (axis cs:0,0) -- (top);

  \node [below = 1mm of origin] {$\mu$};
  \node [below = 1mm of alphaleft, anchor=north] {$\alpha/2$};
  \node [below = 1mm of alpharight, anchor=north] {$\alpha/2$};
 \end{axis}
\end{tikzpicture}

唯一的区别应该是左图中的“a/2”，由于“/”的原因，它比“a”高。

我想让两个水平轴对齐。我更愿意处理图片大小，而不是使用子浮点的对齐选项。我正在寻找一种方法来设置绘图周围（具体来说，是下方）的填充，以便两张图片的填充相同，这将使它们正确对齐。我要添加第三张图片，并在其中两张图片下方添加一些内容，所以我认为设置填充是获得正确对齐的最佳方法。这可能吗？

谢谢你！