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▪ Abstract  Broad emission lines hold fundamental clues about the kinematics and structure of the central regions in AGN. In this article we review the most robust line profile properties and correlations emerging from the best data available. We identify fundamental differences between the profiles of radio-quiet and radio-loud sources as well as differences between the high- and low-ionization lines, especially in the radio-quiet majority of AGN. An Eigenvector 1 correlation space involving FWHM Hβ, W(FeIIopt)/W(Hβ), and the soft X-ray spectral index provides optimal discrimination between all principal AGN types (from narrow-line Seyfert 1 to radio galaxies). Both optical and radio continuum luminosities appear to be uncorrelated with the E1 parameters. We identify two populations of radio-quiet AGN: Population A sources (with FWHM(Hβ) [Formula: see text] 4000 km s−1, generally strong FeII emission and a soft X-ray excess) show almost no parameter space overlap with radio-loud sources. Population B shows optical properties largely indistinguishable from radio-loud sources, including usually weak FeII emission, FWHM(Hβ) [Formula: see text] 4000 km s−1 and lack of a soft X-ray excess. There is growing evidence that a fundamental parameter underlying Eigenvector 1 may be the luminosity-to-mass ratio of the active nucleus (L/M), with source orientation playing a concomitant role.

We identify a correlation space involving optical and UV emission-line parameters as well as the soft X-ray spectral index that provides optimal discrimination between all principal classes of active galactic nuclei (AGNs). Most of the sources in our three high-quality data samples show a strong intercorrelation with narrow-line Seyfert 1 (NLSy1) galaxies and steep-spectrum radio galaxies occupying opposite extrema in the space. NLSy1 sources show a clear continuity with broader line sources, indicating that they are not a disjoint class of AGN as is sometimes suggested. We interpret the principal intercorrelation in the parameter space as being driven by the AGN luminosity-to-black hole mass ratio (L&solm0;M is proportional to the Eddington ratio). Source orientation no doubt also plays an important role, but it is not yet clear whether FWHM Hbeta or C iv lambda1549 line shift is the better indicator. We tentatively identify two radio-quiet populations: an almost pure radio-quiet population A, with FWHM

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We recently discussed an Eigenvector 1 (E1) parameter space that provides optimal discrimination between the principal classes of broad-line active galactic nuclei (AGNs). In this paper we begin a search for the most important physical parameters that are likely to govern correlations and data point distribution in E1 space. We focus on the principal optical parameter plane involving the width of the Hb broad component and the equivalent width ratio between the Fe II blend at 4570We show that the observed correlation for radio-quiet sources can be accounted for if it is Hb BC . primarily driven by the ratio of AGN luminosity to black hole mass (L /M P Eddington ratio) convolved with source orientation. L /M apparently drives the radio-quiet correlation only for FWHM(Hb) [ 4000 km s~1, which includes narrow-line Seyfert 1 galaxies and can be said to deÐne an AGN "" main sequence.ÏÏ Source orientation plays an increasingly important role as increases. We also FWHM(Hb BC ) argue that AGNs lying outside the radio-quiet main sequence, and speciÐcally those with optical Fe II much stronger than expected for a given may all be broad absorption line QSOs.

[LaTeX removed] Recent work has shown that it is possible to systematize quasar spectral diversity in a parameter space called ``Eigenvector 1'' (E1). We present median AGN spectra for fixed regions of the E1 (optical) parameter space (FWHM(H-beta) vs. equivalent width ratio RFE=W(FeII4570)/W(H-beta). Comparison of the median spectra for different regions show considerable differences. We suggest that an E1-driven approach to median/average spectra emphasizes significant differences between AGN, and offers more insights into AGN physics and dynamics than a single population median/average derived from a large and heterogeneous sample of sources. We find that the H-beta broad component line profile changes in shape along the E1 sequence both in average centroid shift and asymmetry. While objects with FWHM(H-beta)< 4000 km/s are well fitted by a Lorentz function, AGN with FWHM(H-beta)> 4000 km/s are well fitted if two broad line components are used: a broad (the "classical" broad line component) and a very broad/redshifted component.Comment: 1 table + 3 figures, accepted for publication in ApJ

Stephan's Quintet (SQ) is a compact group that we find in an atypical moment when a high velocity intruder is passing through it. The intrusion is particularly interesting because a previous intruder had stripped most of the gas from the group members. This debris field was shocked in the ongoing collision with the new intruder. This evolutionary history agrees well with observations and explains how a strongly interacting system can show low levels of star formation. We present new multiwavelength data including previously unpublished ROSAT X-ray, Hα interference filter/Fabry-Perot, ISO MIR/FIR and radio line and continuum images. These observations and previously published data provide new insights as well as support for some previous hypotheses. 1) Fabry-Perot and HI velocities allow us to unambiguously distinguish between gas associated with SQ and the new intruder. 2) Most detected emission regions are found in the remnant ISM of the NI which allows us to infer its size and present physical state.3) The few emission regions associated with the stripped ISM of SQ include the best candidate tidal dwarf galaxy. 4) Multiwavelength data suggest that strong MIR/FIR emission from the Seyfert 2 nucleus of NGC7319 comes from dust heated directly by a power-law continuum rather than a starburst. 5) The correspondance between extended X-ray/radio continuum/forbidden optical emission confirms the existence of a -2large scale shock in SQ. 6) We confirm the presence of two stripped spiral members in the process of transformation into E/S0 morphology. Finally, 7) Observations are consistent with the idea that the collision in SQ is ongoing with possible detection of HII region ablation and Rayleigh-Taylor instabilities.

We investigate the radial velocity difference between the [OIII]λλ4959,5007 and Hβ lines for a sample of ≈ 200 low redshift AGN. We identify seven objects showing an [OIII]λ5007 blueshift relative to Hβ with amplitude larger than 250 km s −1 (blue "outliers"). These line shifts are found in sources where the broad high ionization lines (e.g. CIVλ1549) also show a large systematic blueshift. Such blueshifts occur only in the population A region of the Eigenvector 1 parameter domain (that also contains NLSy1 sources). We suggest that [OIII]λλ4959,5007 blueshifts are also associated with the high ionization outflow originating in these sources. This is a direct kinematic linkage between narrow and broad line emitting gas.