{ital Hubble} {ital Space} {ital Telescope} ultraviolet spectrum of ARP 102B, the prototypical double-peaked emission-line AGN
- Columbia Astrophysics Laboratory, Columbia University, 538 West 120th Street, New York, New York 10027 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218 (United States)
- Department of Astronomy, University of California, Berkeley, California 94720 (United States)
- Los Alamos National Laboratory, Theoretical Division, T-6, Los Alamos, New Mexico 87545 (United States)
UV spectra of the nucleus of the elliptical galaxy Arp 102B were obtained with the {ital HST}`s Faint Object Spectrograph in order to investigate the UV emission-line counterparts of its unusual double-peaked Balmer lines. Broad MgII {lambda}2798 is present with nearly the same profile as the Balmer lines (peaks separated by {approx_equal}12,000 kms{sup -1}), and a typical MgII/H{beta} ratio of 1. But there is little, if any CIII {lambda}1909 or CIV {lambda}1550 emission corresponding to the displaced Balmer-line peaks. Most important, there is no double-peaked component detected in Ly{alpha}; the Ly{alpha}/H{beta} ratio is less than 0.12 in the displaced peaks. However, there is an ``ordinary``, nondisplaced broad-line component with FWHM{approx_equal}3500 kms{sup -1} in {ital all} of the permitted lines, demonstrating the need to invoke different locations and different physical conditions for double-peaked and single-peaked line components in the same object. The striking absence of displaced peaks in Ly{alpha} probably cannot be explained solely by reddening. Rather, it indicates that high density and large optical depth in Ly{alpha} are required to destroy the line photons by collisional de-excitation and possibly by bound-free absorption out of the {ital n}=2 level of hydrogen. These results strongly support the application, at least to Arp 102B, of the accretion-disk model of Dumont & Collin-Souffrin, in which the disk produces only low-ionization lines and a Ly{alpha}/H{beta} ratio that agrees with our observed upper limit. Also present is an extraordinary system of absorption lines at the systemic redshift of Arp 102B, in which metastable levels of FeII up to 1.1 eV above the ground state participate in addition to the more common resonance transitions. Absorption from metastable levels of FeII have been seen previously only in two unusual, low-ionization broad absorption-line QSOs, Q0059-2735 and Mrk 231.
- OSTI ID:
- 288894
- Journal Information:
- Astrophysical Journal, Vol. 464, Issue 2; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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