Star of the Show? The Art Dealer Andy Warhol Foundation for the Visual Arts, via Artists Rights Society (ARS), New York Warhol's 1973 portrait of the gallery owner and collector Ileana Sonnabend, acrylic and silk-screen on canvas, at the Museum of Modern Art. Trace the history of the finest pieces of postwar art, and many of them lead back to Ileana Sonnabend, the gallery owner and collector, who died in 2007. Andy Warhol's "Liz #1 (Early Colored Liz)," which sold at Sotheby's for $18 million last month? Sonnabend. Robert Rauschenberg's 20th-century mixed-media collage "Canyon," which the Museum of Modern Art won over the Metropolitan Museum last year? In honor of that gift from the Sonnabend family, the Modern is presenting an exhibition devoted to Sonnabend's career, which spanned half a century. She is widely credited with introducing postwar American art to Europe in the 1960s and Italian Arte Povera to the United States. She also supported the Conceptual, new-media and performance-based art of the 1970s. The show, "Ileana Sonnabend: Ambassador for the New," explores her eye through works that she presented in her galleries in Paris and New York. Among the 40 artists included are Jasper Johns, Vito Acconci, John Baldessari and Jeff Koons. Through April 21, 212-708-9400, moma.org.