HII regions in the CALIFA survey: I. Catalog presentation
  We present a new catalog of HII regions based on the integral field
spectroscopy (IFS) data of the extended CALIFA and PISCO samples. The selection
of HII regions was based on two assumptions: a clumpy structure with high
contrast of H$\alpha$ emission and an underlying stellar population comprising
young stars. The catalog provides the spectroscopic information of 26,408
individual regions corresponding to 924 galaxies, including the flux
intensities and equivalent widths of 51 emission lines covering the wavelength
range between 3745-7200A. To our knowledge, this is the largest catalog of
spectroscopic properties of HII regions. We explore a new approach to
decontaminate the emission lines from diffuse ionized gas contribution. This
diffuse gas correction was estimated to correct every emission line within the
considered spectral range. With the catalog of HII regions corrected, new
demarcation lines are proposed for the classical diagnostic diagrams. Finally,
we study the properties of the underlying stellar populations of the HII
regions. It was found that there is a direct relationship between the
ionization conditions on the nebulae and the properties of stellar populations
besides the physicals condition on the ionized regions.
