J/A+A/424/519 Naked active galactic nuclei (Hawkins+, 2004)
Naked active galactic nuclei.
Hawkins M.R.S.
<Astron. Astrophys., 424, 519-529 (2004)>
=2004A&A...424..519H 2004A&A...424..519H
ADC_Keywords: QSOs ; Active gal. nuclei ; Spectroscopy
Keywords: galaxies: quasars: general - galaxies: active
Abstract:
In this paper we report the discovery of a new class of active
galactic nucleus in which although the nucleus is viewed directly, no
broad emission lines are present. The results are based on a survey
for AGN in which a sample of about 800 quasars and emission line
galaxies were monitored yearly for 25 years. Among the emission line
galaxies was the expected population of Seyfert 2 galaxies with only
narrow forbidden lines in emission, and no broad lines. However, from
the long term monitoring programme it was clear that some 10% of these
were strongly variable with strong continuum emission. It is argued
that these objects can only be Seyfert 1 galaxies in which the nucleus
is viewed directly, but in which broad emission lines are completely
absent. We compare these observations with other cases from the
literature where the broad line region is reported to be weak or
variable, and investigate the possibility that the absence of the
broad line component is due to reddening. We conclude that this does
not account for the observations, and that in these AGN the broad line
region is absent. We also tentatively identify more luminous quasars
from our sample where the broad emission lines also appear to be
absent. The consequences of this for AGN models are discussed, and a
case is made that we are seeing AGN in a transition stage between the
fuel supply from a surrounding star cluster being cut off, and the
nucleus becoming dormant.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 70 67 Seyfert galaxy line widths
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (B1950)
4- 5 I2 min RAm Right ascension (B1950)
7- 11 F5.2 s RAs Right ascension (B1950)
13 A1 --- DE- Declination sign (B1950)
14- 15 I2 deg DEd Declination (B1950)
17- 18 I2 arcmin DEm Declination (B1950)
20- 23 F4.1 arcsec DEs Declination (B1950)
25- 29 F5.3 --- z Redshift
31- 34 F4.2 mag AmpB Amplitude in the Bj band measured over the
period from 1975 to 2002
36- 39 I4 km/s FWHM[OII] FWHM line width of the [O II]3727 line
41- 44 I4 km/s FWHM[NeIII] FWHM line width of the [Ne III]3869 line
46- 49 I4 km/s FWHMHβ FWHM line width of the Hβ4861 line
51- 54 I4 km/s FWHM[OIII]4 FWHM line width of the [OIII]4959 line
56- 59 I4 km/s FWHM[OIII]5 FWHM line width of the [OIII]5007 line
61- 64 I4 km/s FWHMHα FWHM line width of the Hα6563 line
66- 70 F5.2 --- O/H Line strength ratio [OIII]5007/Hβ
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 27-Jul-2005