A Possible New Population of Sources with Extreme X-Ray/Optical Ratios

  title={A Possible New Population of Sources with Extreme X-Ray/Optical Ratios},
  author={Anton M. Koekemoer and David M. Alexander and Franz Erik Bauer and Jacqueline Bergeron and W. N. Brandt and Eleni Chatzichristou and Stefano Cristiani and S. Michael Fall and Norman Grogin and Mario Livio and Vincenzo Mainieri and Leonidas A. Moustakas and Paolo Padovani and Piero Rosati and Ethan Joshua Schreier and C. Megan Urry},
  journal={The Astrophysical Journal},
We describe a possible new class of X-ray sources that have robust detections in ultradeep Chandra data yet have no detections at all in our deep multiband Great Observatories Origins Deep Survey Hubble Space Telescope Advanced Camera for Surveys (ACS) images, which represent the highest quality optical imaging obtained to date on these fields. These extreme X-ray/optical ratio sources (EXOs) have values of FX/Fopt at least an order of magnitude above those generally found for other active… 

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