What are the rules for the plural suffix ～ら


I came across the following in a newspaper article:

> 藤沢健太教授（宇宙物理学）らの研究グループ

The first part (藤沢健太教授) is the name of a professor (Professor Kenta Fujisawa).
The parentheses say "Astrophysics", and the last part (の研究グループ) indicates his
research group. It's the `～ら` that confuses me.

I had only ever heard `～ら` after `かれ` or `お前`, so I did some searching, and I
found these sites.

  * [This source](http://japanese.about.com/od/Grammar/a/Personal-Pronouns.htm) says it is used for `かれ`, but doesn't elaborate.
  * [This source](http://thejapanesepage.com/w/index.php?title=Plurals) says that it is an informal version of `～たち`, which doesn't seem to fit in the context of a newspaper (unless I'm wrong about that), or the very technical topic. 
  * And [this source](http://en.wikibooks.org/wiki/Japanese/Grammar/Nouns) simply says that it's another version of `～たち`.

I'm still unclear as to when one should use ら if it's informal, yet also in
the paper. Does anyone know the nuance of it?




It is rather the other way around of what the second link says, and the reason
for that description is that it is probably confusing politeness and
formality.

  * ら: non-polite, formal
  * たち: slightly polite, informal
  * がた: polite

As for 俺ら, 俺 is highly informal, and the whole combination is informal because
of that even if ら is formal.

And besides that, some personal pronouns only go with either of them as noted
in the first link.




It is rather the other way around of what the second link says, and the reason
for that description is that it is probably confusing politeness and
formality.

  * ら: non-polite, formal
  * たち: slightly polite, informal
  * がた: polite

As for 俺ら, 俺 is highly informal, and the whole combination is informal because
of that even if ら is formal.

And besides that, some personal pronouns only go with either of them as noted
in the first link.

