Irish immigrants to New York City have played an enormous role in the cultural, social and political lives of this metropolis for centuries.

The community's strong presence is such an ingrained reality in neighborhoods like Bay Ridge and countless others across each of the other boroughs, that it's easy to take for granted.

But Ireland native John Crowley, the 46-year-old director of the new movie "Brooklyn," about a young Irish woman who immigrates to the borough in the 1950s, says the Irish-New York City connection is unparalleled anywhere else.

"What would pop," Crowley says of his first visit to America as a 22-year-old, "is the sort of endless ways in which the Irish community had woven itself into the place there, and the nature of how strong Irish-American identity is. Which is very different than the Irish people who've immigrated to Britain for instance."

The movie, adapted by Nick Hornby from the novel by Colm Tóibín, stars Saoirse Ronan as Ellis Lacey, who finds a home at a boarding house, a job at a department store and romance with a young Italian-American man.

The film, a strong Oscar contender opening Wednesday, is deeply connected to the mythology of the American Dream, as it took shape in mid-century Ireland, while subverting it by taking a hard look at the emotional and practical realities of immigration, Crowley observes.

Ronan, a 21-year-old Oscar nominee ("Atonement") and one of the most acclaimed actors of her generation, felt a strong personal connection to the story. Though raised in the Emerald Isle's countryside, she's a native of Woodlawn in the Bronx, the daughter of parents who spent 10 years living in New York City.

"Emotionally, this was the first time that, to begin with, I didn't feel like I was able to keep ahold over my emotions," says Ronan, who had become an immigrant herself around the time she took on the project by leaving home for London. "I wasn't able to put a lid on it at the end of the day and forget about it. I'd never worked that way before."

Crowley and company only had a couple days of filming in Brooklyn, capturing brownstones and Coney Island. The rest of the time, Montreal stands in for the borough. But don't worry, Brooklynites.

"The catchword was authenticity for me all the way," Crowley says.