EDP Sciences
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Volume 413, Number 1, January I 2004
Page(s) 97 - 105
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20031494

A&A 413, 97-105 (2004)
DOI: 10.1051/0004-6361:20031494

The nuclear region of low luminosity flat radio spectrum sources

II. Emission-line spectra
A. C. Gonçalves1, 2 and M. Serote Roos1

1  Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
    e-mail: adarbon@oal.ul.pt, serote@oal.ul.pt
2  LUTH, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France

(Received 8 January 2003 / Accepted 4 September 2003)

We report on the spectroscopic study of 19 low luminosity Flat Radio Spectrum (LL FRS) sources selected from Marchã's et al. (1996) 200 mJy sample. In the optical, these objects are mainly dominated by the host galaxy starlight. After correcting the data for this effect, we obtain a new set of spectra clearly displaying weak emission lines; such features carry valuable information concerning the excitation mechanisms at work in the nuclear regions of LL FRS sources. We have used a special routine to model the spectra and assess the intensities and velocities of the emission lines; we have analyzed the results in terms of diagnostic diagrams. Our analysis shows that 79% of the studied objects harbour a Low Ionization Nuclear Emission-line Region (or LINER) whose contribution was swamped by the host galaxy starlight. The remaining objects display a higher ionization spectrum, more typical of Seyferts; due to the poor quality of the spectra, it was not possible to identify any possible large Balmer components. The fact that we observe a LINER-type spectrum in LL FRS sources supports the idea that some of these objects could be undergoing an ADAF phase; in addition, such a low ionization emission-line spectrum is in agreement with the black hole mass values and sub-Eddington accretion rates published for some FRS sources.

Key words: galaxies: active -- galaxies: BL Lacertae objects: general -- galaxies: general

Offprint request: A. C. Gonçalves, anabela.goncalves@obspm.fr

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