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The HST Spectrum of I Zw 1: Implications of the C III* λ1176 Emission Line

Published online by Cambridge University Press:  12 April 2016

Ari Laor ,
Buell T. Jannuzi ,
Richard F. Green  and
Todd A. Boroson
Ari Laor
Affiliation:
Physics Department, Technion, Haifa 32000, Israel
Buell T. Jannuzi
Affiliation:
National Optical Astronomy Observatories, Tucson, AZ 85719, USA
Richard F. Green
Affiliation:
National Optical Astronomy Observatories, Tucson, AZ 85719, USA
Todd A. Boroson
Affiliation:
National Optical Astronomy Observatories, Tucson, AZ 85719, USA

Abstract

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I Zw 1 is a well-known narrow-line quasar with very strong Fe II emission. High S/N spectra obtained with the HST FOS show a remarkably rich emission-line spectrum. The C III*λ1176 line is clearly detected in emission for the first time in AGNs. This line arises from radiative decay to the 2s2p3Pº0,1,2 metastable levels of C III. The observed flux is ~ 50 times larger than expected from collisional excitation or dielectronic recombination in photoionized gas. The most plausible mechanism for the large enhancement in the C III* λ1176 flux is resonance scattering of continuum photons by C III* ions. This mechanism requires large velocity gradients (~ 1000 km s−1) within each emitting cloud in the BLR. Such large velocity gradients can be induced by forces external to the gas in the BLR clouds, such as tidal disruption, or radiation pressure.

Type
II. Broad Emission Lines
Information
International Astronomical Union Colloquium , Volume 159: Emission Lines in Active Galaxies: New Methods and Techniques , 1997 , pp. 116 - 117
Copyright
Copyright © Astronomical Society of the Pacific 1997

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