title: Down arrow symbol in matplotlib
body: <p>I would like to create a plot where some of the points have a downward pointing arrow (see image below). In Astronomy this illustrates that the true value is actually lower than what's measured.Note that only some of the points have this symbol. </p>
  
  <p>I would like to know how I can create such symbols in matplotlib. Are there downward arrow symbols that I can use? </p>
  
  <p>Thanks for your help in advance! </p>
  
  <p><img src="https://i.stack.imgur.com/aYBpc.jpg" alt="enter image description here"></p>