• The obscuring starburst of NGC 6221 and implications for the hard x-ray background 

      Levenson, Nancy A.; Fernandes Junior, Roberto Cid; Weaver, Kim A.; Heckman, Timothy M.; Storchi-Bergmann, Thaisa (2001) [Artigo de periódico]
      We present NGC 6221 as a case study of "X-ray-loud composite galaxies", which appear similar to starbursts at optical wavelengths and resemble traditional active galactic nuclei in X-rays. The net optical spectrum of NGC ...