Hidden Activity in High-redshift Spheroidal Galaxies

Rodighiero, Gruppioni, Civano, Comastri, Franceschini, Mignoli, Fritz, Vignali

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We exploit very deep mid-IR and X-ray observations by Spitzer and Chandra in the HDFN to identify signs of hidden activity in spheroidal galaxies between z~0.3 to 1. The nature of the mid-IR emission in these sources is analyzed through their SEDs based on the available multi-wavelength photometry and optical spectroscopy. We conclude that 20% of the original sample of spheroidal galaxies in HDFN are detected during phases of prominent activity, of both stellar and quasar origin.