NEW YORK (AP) â¿¿ Investment firm Cowen Group Inc. said Friday it is buying Dahlman Rose & Co., a privately held investment bank. Cowen is buying Dahlman Rose with stock but the two firms did not disclose further financial details. Dahlman Rose specializes in the energy, metals and mining, transportation, chemicals, and agriculture sectors. The boards of both companies have approved the deal, which is expected to close during the first quarter. Cowen Group shares rose 3 cents to $2.69 Friday and were unchanged in aftermarket trading.