NICS--TNG infrared spectroscopy of NGC1068:
the first extragalactic measurement of PII and a new tool to constrain
the origin of FeII line emission in galaxies.
E. Oliva, A. Marconi, R. Maiolino, L. Testi, et al.
We report 0.9-1.4um spectroscopic observations of
NGC1068 collected during the commissioning phase of the
near infrared camera spectrometer (NICS) of the Telescopio
Nazionale Galileo (TNG).
These yielded the first extragalactic measurement of PII (1.188um)
In the central 0.75"x2" the FeII/PII
line-intensity ratio is close to unity,
similar to that measured in the Orion bar and
a factor of <20 smaller than in supernova remnants.
This indicates that most of iron is locked
into grains and, therefore, argues against shock excitation being the
primary origin of FeII line emission in the central regions of NGC1068.
We propose the FeII/PII ratio as a simple and effective tool to
study and perhaps resolve the long debated questions related to the
origin of FeII line emission and, more generally,
to constrain the role of shock excitation in active galaxies.