Style of axes in TikZ

Question

I have the following two TikZ pictures (see code at bottom). How can I achieve that the style of the axes in the second picture (the function plot) is the same as in the first picture?

\documentclass{amsart}

\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{pgffor}

\begin{document}

\begin{tikzpicture}[scale=1] 
\draw[->] (-0.3,0) -- (7,0);
\draw (8,0) node[below] {$\gamma$};
\draw[->] (0,-0.3) -- (0,5) node[left] {$b_{1+\gamma}$};
\draw (2,.1) -- (2,-.1) node[below] {$p(\rho)-1$};
\draw[dashed] (2,0) -- (2,1.8);
\draw[dashed] (0,2) -- (2,2);
\draw (-.1,2) -- (.1,2) node[left] {$b_\#(\rho)\;$};
\draw (6,.1) -- (6,-.1) node[below] {$1$};
\draw (-0.1,1) -- (0.1,1) node[left] {$b_2\;$};
\draw (0,3.5) .. controls (2,1.8) and (3,1.2) .. (6,1);
\draw[dashed] (0,1) -- (6,1);
\fill[color=white] (0,3.5) circle (3pt);
\draw[color=black] (0,3.5) circle (3pt);
\fill[color=black] (0,4.3) circle (3pt) node[left] {$b_\ast$};
\end{tikzpicture}

\medskip

\begin{tikzpicture}
  \begin{axis}[domain = 0:1, samples = 100]
    \addplot[color = black]  {pi/(((pi/2)+atan(x/sqrt(1-x^2))*pi/180)};
  \end{axis}
\end{tikzpicture}

\end{document}

Answer 1

Add axis lines=center to the axis options. You can also add axis line style={shorten >=-10pt, shorten <=-10pt} to make the axes go a bit further (by 10pt), so the plot doesn't touch the arrow tips.

In order to change the arrow tips, you can load arrows.meta and then add -{>} for a simple arrow tip.

Output

Code

\documentclass{amsart}
\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{pgffor}

\usetikzlibrary{arrows.meta}

\begin{document}
\begin{tikzpicture}
  \begin{axis}[domain=0:1,samples = 100, axis lines=center, axis line style={shorten >=-10pt, shorten <=-10pt,-{>}}, ymin=0.6,ytick={0.8,1,...,2}]
    \addplot[color = black]  {pi/(((pi/2)+atan(x/sqrt(1-x^2))*pi/180)};
  \end{axis}
\end{tikzpicture}
\end{document}