When a modern painting tops $20 million at auction, a certain Rubicon of fame and prestige has been crossed. On February 8 at Christie’s in London, “Study for Portrait II” (1956) by the British painter Francis Bacon (1909–1992) is expected to sell for about $23 million, a record for the artist. One of a series of Bacon works depicting somber popes on thrones, “Study for Portrait II” — which according to the Daily Tele graph belongs to Sophia Loren — will handily top the record $15 million paid last November for a later work by Ba con, “Version No. 2 of Lying Figure with Hypodermic Syringe” (1968) at Sotheby’s in New York. How did Bacon, who according to biographers – including a longtime friend and confidant, Michael Peppiatt – began as a homeless adolescent hustler with an interest in interior design, develop into one of the most prized painters of the modern era? Mr. Peppiatt, who has already authored a life of the artist, “Francis Bacon: Anatomy of an Enigma” (1997), offers further explanations in “Francis Bacon in the 1950s” (Yale University Press, 224 pages, $50).