EDP Sciences
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Volume 369, Number 1, April I 2001
Page(s) L5 - L8
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20010214

A&A 369, L5-L8 (2001)
DOI: 10.1051/0004-6361:20010214

NICS-TNG infrared spectroscopy of NGC 1068: The first extragalactic measurement of [ PII] and a new tool to constrain the origin of [ FeII] line emission in galaxies

E. Oliva1, 2, A. Marconi1, R. Maiolino1, L. Testi1, F. Mannucci3, F. Ghinassi2, J. Licandro2, L. Origlia4, C. Baffa1, A. Checcucci1, G. Comoretto1, V. Gavryussev3, S. Gennari1, E. Giani1, L. K. Hunt3, F. Lisi1, D. Lorenzetti5, G. Marcucci6, L. Miglietta1, M. Sozzi3, P. Stefanini1 and F. Vitali5

1  Osservatorio di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
2  Centro Galileo Galilei & Telescopio Nazionale Galileo, PO Box 565, 38700 S. Cruz de La Palma, Spain
3  CAISMI-CNR, Largo E. Fermi 5, 50125 Firenze, Italy
4  Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
5  Osservatorio Astronomico di Roma, Via Frascati 33, 00044 Rome, Italy
6  Università degli studi di Firenze, dipartimento di Astronomia, Largo E. Fermi 5, 50125 Firenze, Italy

( Received 26 January 2001 / Accepted 7 February 2001 )

We report 0.9-1.4 $\mu$m spectroscopic observations of NGC 1068 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] (1.188 $\mu$m) line emission. In the central $0.75\arcsec\times2\arcsec$ the [ FeII] /[ PII] line-intensity ratio is close to unity, similar to that measured in the Orion bar and a factor of $\la$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 NGC 1068. 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.

Key words: line: formation -- line: identification -- galaxies: active -- galaxies: individual: NGC 1068 -- galaxies: seyfert -- infrared: galaxies

Offprint request: E. Oliva, oliva@tng.iac.es

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