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For refcode 1996ApJS..104...37M:
Retrieve 52 NED objects in this reference.
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1996ApJS..104...37M COMPARATIVE ANALYSIS OF THE HIGH- AND LOW-IONIZATION LINES IN THE BROAD- LINE REGION OF ACTIVE GALACTIC NUCLEI1 P. MARZIANI AND J. W. SULENTIC Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487 D. DULTZIN-HACYAN Instituto de Astronomla, UNAM, Apartado Postal 70-264, Mexico D. F. 04510, Mexico M. CALVANI Osservatorio Astronomico, Vicolo dell' Osservatorio 5,1-35122 Padova, Italy AND M. MOLES Instituto de Astrofisica de Andalucia, Apartado 3004, E- I 8080 Granada, Spain Received 1995 June 20; accepted 1995 October 2 ABSTRACT We present the first comparative study of high- and low-ionization lines in a large sample of active galactic nuclei (AGNs). We report measurements of C IV {lambda}1549, HeII {lambda}1640, and O III] {lambda}1663 paired to measurements of H{beta}, HeII {lambda}4686, and Fe II_opt_ in 52 low-redshift AGNs (z <~0.8). Ultraviolet archival spectra covering the region of C IV {lambda}1549 were obtained with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). Moderate- resolution optical spectra (~4-7 A) were obtained in most cases within two years of the HST observations. We present an atlas of matching C IV {lambda}1549 and H{beta}b broad-line profiles. Velocity centroids at different profile heights and other profile properties were measured after removal of narrow-line components and contaminating satellite lines of other elements. Our results add refinements to the "standard view" of nebular conditions in the broad-line region (BLR). (1) The average electron density is most probably weighted toward values higher than expected in standard BLR models. The weakness of O III] {lambda}1663 and N IV] {lambda}1486 relative to He II {lambda}1640 suggest that the semiforbidden lines are collisionally de-excited at n_e_ >~ 10^10.5^ cm^- 3^. (2) There is evidence, supporting earlier work, that photoionization via Ly{alpha} fluorescence plays a major role in the production of Fe II_UV_. We identify and discuss briefly the Fe II_UV_ multiplets in the range 1550-1750 A. (3) The observational distinction between the narrow- and broad-line regions is blurred by the contribution of a region of intermediate density (10^6^ cm^-3^ <~ n_e_ <~ 10^7^ cm^-3^). Best evidence for this emission comes from the [O III] {lambda}4363 and C IV {lambda}1549 profiles. It is most likely associated with the innermost part of the narrow-line region. Comparisons between the broad-line profile of C IV {lambda}1549, H{beta} and, whenever possible, HeII {lambda}1640 suggest (1) that radio- loud and radio-quiet AGNs are very different classes of objects that should be treated separately, and (2) that ionization structure varies within the velocity field. The extreme radial velocity emission is characterized by a high-ionization spectrum dominated by C IV {lambda} 1549 and HeII. Several basic results are: (i) C IV {lambda}1549 is almost always blueshifted with respect to H{beta}. (ii) There is a fundamental kinematic difference between radio loud and radio-quiet objects relative to the rest frame of the AGN. (iii) Radio-loud objects show predominantly redshifted and asymmetric H{beta} and unshifted symmetric C IV {lambda}1549. (iv) Radio-quiet objects show predominantly blueshifted and asymmetric C IV profiles with H{beta} usually symmetric and unshifted. Correlation analysis of the radio-quiet sample suggests that C IV {lambda}1549 EW, C IV {lambda}1549 shift/asymmetry, and the strength of Fe II_opt_ are related. C IV {lambda}1549 profiles with large blueshift/asymmetry show lower EW and stronger Fe II_opt_ emission. The results suggest that C IV {lambda}1549 and H{beta} arise in different velocity/geometry regimes. C IV {lambda}1549 may be predominantly emitted in an outflowing bicone of large aperture (~45^deg^), while Fe II_opt_ is most probably emitted in a strongly flattened geometry (possibly an accretion disk). Bulk H{beta} emission may come from a less flattened configuration of clouds. In this interpretation, the flux ratio Fe II_opt_/H{beta}_BC_ is an aspect indicator for radio-quiet objects. Radio-loud objects are more enigmatic, and the existence of a reliable optical aspect indicator remains uncertain. There is evidence that line profile properties of C IV {lambda}1549 and H{beta} are "coupled" in the radio-loud sample, suggesting that a common origin for the high- and low- ionization line emission is a possibility. If this is true, however, we do not have a reasonable explanation for the predominance of H{beta} redshifts and red asymmetries in that population. Subject headings: galaxies: active - galaxies: kinematics and dynamics - line: profiles - quasars: emission lines - ultraviolet: galaxies
Retrieve 52 NED objects in this reference.
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