Do readers consider the passive voice as more authoritative?
Short answer
I haven't found scientific literature on it. Non-scientific sources generally do seem to acknowledge that the passive voice radiates authority.  

Background
To answer the question if there's scientific research on this topic - I wasn't able to find anything of value on an, admittedly, quite cursory Google Scholar search. 

In fact, given the high element of subjectivity in 'finding a text sounding authoritative', I think this question may be more suitable for Writing.SE. However, since the question is heavily upvoted, and since it does indeed touch on the Psychological Sciences, I'll give my two-cents worth based on two non-scientific, non-peer-reviewed book quotes and a regular website entry.

Online Writing Training says:


  One of the main reasons why the passive voice gets such a bad name is that many [] writers overuse it to make their writing seem more formal and authoritative. The result is often turgid, difficult-to-read prose. Take this example


Lebrun Jean-luc says in his book Scientific Writing 2.0: A Reader And Writer's Guide


  [The] passive voice [] give[s] the paper a more authoritative disembodies voice,...


As a last example, William M. Vatavuk states in his book Marketing Yourself with Technical Writing: A Guide for Today's Professionals:


  Maybe technical writers feel that  that the passive voice is more formal, more professional sounding, and that it gives their writing a more authoritative ring...


I think that last quote is important: people feel that way, but it's entirely a subjective thing; some may find the passive voice boring, others may regard it as authoritative.