The CaII triplet in Quasars: from the accretion disk to the star formation

Active  galactic  nuclei  (AGN)  show  a  great  diversity  of  optical  and  UV  emission  line properties. Dynamical  and  physical  models should  be built  accordingly. The  presence of strong FeII emission suggested the existence of a region  shielded  from high energy photons,  where the  low ionization lines  are  emitted. However, due to  the complexity  of the  FeII  emission  features,  the  physical  conditions  and  the  location  of  this  shielded region have remained an open issue for a long time. In the near-infrared region two low ionization  lines  the  CaII  triplet  8498,  8542,  8662  and  the  OI  8446  remains  almost unexplored  in  intermediate/high  z  quasars.  We  carried  out  a spectroscopic  survey  of luminous  (-26>Mv>-29)  and  intermediate  redshift  (0.60<z<1.85)  quasars,  covering  the CaII  triplet  and  OI  8446  region  using  the  Infrared  Spectrometer  and  Array  Camera (ISAAC)  at  the  ESO  Very  Large  Telescope  (VLT).  We  found that  CaII  profiles  are narrower  than  the  ones  of  Hbeta,  suggesting  that  CaII  is  emitted  in  an  outer  region, further  from  the  continuum  source  than  the  Hydrogen  lines.  We  built  photoionization models  which  indicate  that  CaII  and  FeII  emission  is  favored  in  similar  physical conditions  while  hydrogen  line  emission  is  possible  under  a  broader  range  of  physical condition. We conclude that the low ionization lines may be preferentially  emitted in the outer  zone  of  the  accretion  disk,  while  the  hydrogen  lines  can  be  also  emitted  by  less dense,  less   optically-thick  clouds/filaments   within  the  broad   line  region  (BLR).  In addition, we found that the CaII/FeII is systematically higher relative to a low-z sample. If the ratio CaII/FeII is considered as a chemical clock, this result may imply a significant enrichment  of  the  BLR  gas  by  a  recent  burst  of  circumnuclear  star  formation  in  the luminous quasars of our sample.

17/11/2016 - 12:30
Mary Loli Martínez Aldama