Nested mappings and searches - does the nesting have to be in one document

[cord_thomas]

I come from an RDBMS background; please forgive.

I have the following two data structures, pubs and authors:

pubs:

{
    "_id": "WP138",
    "title": "Practical Insights for School Leaders",
    ...
    "authors": ["/pubs/authors/s/stecher_brian_m",
                        "/pubs/authors/h/hamilton_laura_s",
                       "/pubs/authors/g/gonzalez_gabriella_c"],
     ...
}

authors:

{
    "_id":"/pubs/authors/s/stecher_brian_m",
    "fname": "Brian",
     "lname": "Stecher",
    ...
}

I'd like to be able to query the publications authored by Brian and vis-versa, the authors that have published on topics of "School Leaders".

In reading about nested and parent-child relations, i believe nested is the preferred way to go as parent-child is only for one-to-many rather than many-to-many unless I read that wrong.

Question - is it possible to do nesting across indices? I can script something that would inject the authors structure into the pubs just fine and then define the nested mapping. I ask because I ultimately will be "joining" up another 1/2 dozen different data sources to ask a series of compound questions and would rather not create one massive document that is totally denormalized.

My ultimate goal is to make a simple Kibana interface people can use to query rather than a custom application. I say this because i understand another approach is to create the subqueries in code.

What are my best options?