Karl Forster

Emission Line Properties of the Large Bright Quasar Survey

We present measurements of the optical/UV emission lines for a large homogeneous sample of 993 quasars from the Large Bright Quasar Survey. Our largely automated technique accounts for continuum breaks and galactic reddening, and we perform multicomponent fits to emission line profiles, including the effects of blended iron emission, and of absorption lines both galactic and intrinsic. Here we describe the fitting algorithm and present the results of line fits to the LBQS sample, including upper limits to line equivalent widths when warranted. The distribution of measured line parameters, principally Wλ and FWHM, are detailed for a variety of lines, including upper limits. We thus initiate a large-scale investigation of correlations between the high-energy continuum and emission lines in quasars, to be extended to complementary samples using similar techniques. High-quality, reproducible measurements of emission lines for uniformly selected samples will advance our understanding of active galaxies, especially in a new era of large surveys selected by a variety of complementary methods.

Quasar Evolution and the Baldwin Effect in the Large Bright Quasar Survey

From a large homogeneous sample of optical/UV emission line measurements for 993 quasars from the Large Bright Quasar Survey (LBQS), we study correlations between emission-line equivalent width and both rest-frame ultraviolet luminosity (i.e., the Baldwin effect) and redshift. Our semiautomated spectral fitting accounts for absorption lines, fits blended iron emission, and provides upper limits to weak emission lines. Use of a single large, well-defined sample and consistent emission-line measurements allows us to sensitively detect many correlations, most of which have been previously noted. A new finding is a significant Baldwin effect in UV iron emission. Further analysis reveals that the primary correlation of iron emission strength is probably with redshift, implying an evolutionary rather than a luminosity effect. We show that for most emission lines with a significant Baldwin effect, and for some without, evolution dominates over luminosity effects. This may reflect evolution in abundances, in cloud covering factors, or overall cloud conditions such as density and ionization. We find that in our sample, a putative correlation between Baldwin effect slope and the ionization potential is not significant. Uniform measurements of other large quasar samples will extend the luminosity and redshift range of such spectral studies and provide even stronger tests of spectral evolution.

Extreme X-Ray Variability in the Narrow-Line QSO PHL 1092

A ROSAT observation of the narrow-line Fe II QSO PHL 1092 shows rapid variability that requires an efficiency of at least 0.13, exceeding the theoretical maximum for an accretion disk around a non-rotating black hole. Plausible explanations for this high efficiency incorporate anisotropic emission and/or accretion onto a rapidly rotating black hole, the latter recently suggested by Kwan et al. as a mechanism for generating PHL 1092s strong Fe II lines by mechanical heating in an accretion disk. The soft X-ray luminosity of PHL 1092 had also increased by a factor of 21 over the weak Einstein detection, to more than 5 x 10^46 ergs/s. Its photon spectral index of 4.2 is among the steepest of any AGN. These X-ray properties are characteristic of narrow-line Seyfert 1 galaxies, of which PHL 1092 is evidently a very luminous member. Narrow-line QSOs also extend a significant correlation between X-ray luminosity and X-ray spectral index which we have found among a large sample of optically-selected, narrow-line Seyfert 1 galaxies observed by ROSAT.

Evidence for Relativistic Outflows in Narrow-Line Seyfert 1 Galaxies

We report the observation of features near 1 keV in the ASCA spectra from three narrow-line Seyfert 1 (NLS1) galaxies. We interpret these as oxygen absorption in a highly relativistic outflow. If interpreted as absorption edges, the implied velocities are 0.2-0.3 c, near the limit predicted by line-locking radiative acceleration. If instead interpreted as broad absorption lines, the implied velocities are ~0.57 c, interestingly near the velocity of particles in the last stable orbit around a Kerr black hole, although a physical interpretation of this is not obvious. The features are reminiscent of the UV absorption lines seen in broad absorption line quasars (BALQSOs), but with larger velocities, and we note the remarkable similarities in the optical emission line and broadband properties of NLS1s and low-ionization BALQSOs.

OPTICAL AND X-RAY SPECTROSCOPY OF 1E 0449.4(1823: DEMISE OF THE ORIGINAL TYPE 2 QSO

New optical spectra of the original narrow-line quasar 1E 0449.4-1823 show that it now has broad emission lines of considerable strength, eliminating it as a type 2 QSO candidate. Although broad emission line components were probably weakly present in 1981 and 1984, they have certainly increased in strength and are accompanied by Balmer continuum emission that makes the spectrum bluer than it was previously. We suggest that the behavior of 1E 0449.4-1823 is the same as that of some Seyfert 1.8 and 1.9 galaxies, in which Goodrich attributed long-term variations of their broad Balmer lines to dynamical motions of obscuring material located in or around the broad-line region. The optical continuum and broad emission line regions of 1E 0449.4-1823 may still be partly covered in our line of sight, which would explain its large forbidden-line equivalent widths and flat αox relative to other low-redshift QSOs. Also present are apparent absorption features in the broad Balmer lines and in Mg II, which may be related to the past obscuration and current emergence of the broad-line region. However, it is difficult to distinguish absorption from broad emission line peaks that are displaced in velocity; we consider the latter a plausible competing interpretation of these peculiar line profiles. An ASCA X-ray spectrum of 1E 0449.4-1823 can be fitted with a power law of Γ=1.63 -->+ 0.12−0.09, intrinsic NH < 9 × 1020 cm-2, and no Fe Kα line emission. Its 2-10 keV luminosity is 6.7 × 1044 ergs s-1. Thus, there is no evidence for Seyfert 2 properties in the X-ray emission from 1E 0449.4-1823, which resembles that of an ordinary QSO. With regard to the still hypothetical type 2 QSOs, we argue that there is little evidence for the existence of any among X-ray-selected samples.

The X-Ray Spectra and Spectral Variability of Intermediate-Type Seyfert Galaxies: ASCA Observations of NGC 4388 and ESO 103-G35

The X-ray spectra of two intermediate-type Seyfert galaxies are investigated using ASCA observations separated by more than 1 yr. Both NGC 4388 and ESO 103-G35 exhibit strong, narrow Fe Kα line emission and absorption by cold neutral gas with a column density ~1023 cm-2, characteristic of the X-ray spectra of type 2 Seyfert galaxies. The power-law continuum flux has changed by a factor of 2 over a timescale of ~2 yr for both objects, declining in the case of NGC 4388 and rising in ESO 103-G35. No variation was observed in the equivalent width of the Fe Kα line in the spectra of NGC 4388, implying that the line flux declined with the continuum. We find that the strength of the line cannot be accounted for by fluorescence in line-of-sight material with the measured column density unless a leaky-absorber model of the type favored for IRAS 04575-7537 is employed. The equivalent width of the Fe Kα emission line is seen to decrease between the observations of ESO 103-G35 while the continuum flux increased. The 1996 observation of ESO 103-G35 can also be fitted with an absorption edge at 7.4 ± 0.2 keV due to partially ionized iron, and when an ionized absorber model is fitted to the data it is found that the equivalent column of neutral hydrogen rises to 3.5 × 1023 cm-2. The Fe Kα line flux can be accounted by fluorescence in this material alone, and this model is also a good representation of the 1988 and 1991 Ginga observations. There is then no requirement for a reflection component in the ASCA spectra of ESO 103-G35 or NGC 4388.

E 0336-248 : a new bl lac object found by an old Einstein

We obtained new ROSAT HRI and optical observations in the field of the Einstein X-ray source E 0336-248, which we use to identify it as a 19th magnitude BL Lacertae object at z=0.251 with an X-ray luminosity of 10^45 erg/s. It is also a 14 mJy radio source at 20 cm. An emission-line galaxy at z=0.043 that was previously considered a Seyfert identification for E 0336-248 is shown instead to be an unrelated, non-active H II region galaxy that lies 78 arcseconds from the X-ray source. The resolution of this historical case of mistaken identity illustrates that discoveries of non-AGN emission-line galaxies with high X-ray luminosity should be tested carefully. The properties of E 0336-248 are similar to those of other X-ray selected BL Lacs, including its location in an apparent group or cluster of galaxies. Somewhat unusual is the weak contribution of nonstellar optical light relative to the starlight in the spectrum of its host galaxy, which raises once again the possibility that even high-luminosity BL Lac objects may be difficult to identify in X-ray selected samples. We discuss a possible manifestation of this problem that appeared in the recent literature.