Ray J. Weymann

Comparisons of the emission-line and continuum properties of broad absorption line and normal quasi-stellar objects

The emission-line and continuum properties of a set of 25 broad absorption line QSOs (BALs) and 29 normal QSOs (i.e., non-BALs) are compared. This sample is augmented by an additional 17 BALs. A balnicity index is defined in order to separate the non-BALs from the BALs as objectively as possible, as well as to provide a measure of the strength of the broad absorption line features. It is found that the emission-line properties and the continua of non-BALs and BALs are remarkably similar.

0957 + 561 A, B: twin quasistellar objects or gravitational lens?

0957 + 561 A, B are two QSOs of mag 17 with 5.7 arc s separation at redshift 1.405. Their spectra leave little doubt that they are associated. Difficulties arise in describing them as two distinct objects and the possibility that they are two images of the same object formed by a gravitational lens is discussed.

A high signal-to-noise ratio composite quasar spectrum

A very high signal-to-noise ratio (S/N of about 400) composite spectrum of the rest-frame ultraviolet and optical region of high luminosity quasars is presented. The spectrum is derived from 718 individual spectra obtained as part of the Large Bright Quasar Survey. The moderate resolution, 4A or less, and high signal-to-noise ratio allow numerous weak emission features to be identified. Of particular note is the large equivalent-width of the Fe II emission in the rest-frame ultraviolet and the blue continuum slope of the composite. The primary aim of this paper is to provide a reference spectrum for use in line identifications, and a series of large-scale representations of the composite spectrum are shown. A measure of the standard deviation of the individual quasar spectra from the composite spectrum is also presented. 12 refs.

The radio properties of the broad-absorption-line QSOs

A VLA radio detection survey has been conducted for a large sample of broad-absorption-line (BAL) QSOs. Together with results from a similar, previous survey and a few observations from two other surveys, 68 BALQSOs have now been well observed with no strong radio sources detected. The absence of luminous radio sources among 68 known BALQSOs reported here, together with a complementary spectroscopic study which finds no BALQSOs among a large sample of radio-loud quasars, establishes a strong anticorrelation between luminous radio sources and the BALQSO phenomenon

The Hubble Space Telescope quasar absorption line key project. I. First observational results, including Lyman-alpha and Lyman-limit systems

Spectra are presented for 37 quasars with small and moderate redshifts; the quasars were observed with the Faint Object Spectrograph of the HST. New higher resolution measurements of the absorption lines in the UV spectra of 11 quasars with emission-line redshifts that lie between 0.3 and 1.0 are reported. Calibrated spectra and continuum fits are shown for each object. A total of 104 extragalactic Ly-alpha systems are identified, nine of which are found at the same redshifts as metal-line systems. The local number density of Ly-alpha systems with rest equivalent widths larger than 0.32 A and without detected metal lines is about 15.1 +/- 4.3 Ly-alpha systems per unit redshift with gamma = 0.30 +/- 0.62 and W* = 0.22 +/- 0.02 A. A total of 10 Lyman-limit systems with an optical depth greater than 0.4 are identified. The paucity of damped Ly-alpha lines at small and moderate redshifts shows that the number density of damped absorption systems decreases with decreasing redshift.

Multiwavelength Observations of Short-Timescale Variability in NGC 4151. IV. Analysis of Multiwavelength Continuum Variability

For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)

The Hα Luminosity Function and Global Star Formation Rate from Redshifts of 1-2

We present a luminosity function for Hα emission from galaxies at redshifts between 0.7 and 1.9 based on slitless spectroscopy with the near-infrared camera and multiobject spectrometer on the Hubble Space Telescope. The luminosity function is well fit by a Schechter function over the range 6 × 1041 < L (Hα) < 2 × 1043 ergs s-1 with L* = 7 × 1042 ergs s-1 and φ* = 1.7 × 10-3 Mpc-3 for H0 = 50 km s-1 Mpc-1 and q0 = 0.5. We derive a volume-averaged star formation rate at z = 1.3 ± 0.5 of 0.13 M⊙ yr-1 Mpc-3 without correction for extinction. The star formation rate that we derive at ∼6500 A is a factor of 3 higher than that deduced from 2800 A continua. If this difference is caused entirely by reddening, the extinction correction at 2800 A is quite significant. The precise magnitude of the total extinction correction at rest-frame UV wavelengths (e.g., 2800 and 1500 A) is sensitive to the relative spatial distribution of the stars, gas, and dust, as well as to the extinction law. In the extreme case of a homogeneous foreground dust screen and a Milky Way or LMC extinction law, we derive a total extinction at 2800 A of 2.1 mag, or a factor of 7 correction to the UV luminosity density. If we use the Calzetti reddening curve, which was derived for the model in which stars, gas, and dust are well mixed and nebular gas suffers more extinction than stars, our estimate of A2800 is increased by more than 1 mag.

The Hubble Space Telescope Quasar Absorption Line Key Project. XIV. The Evolution of Lyα Absorption Lines in the Redshift Interval z = 0-1.5*

We present the results of an analysis of the rate of evolution of the Lyα absorption lines in the redshift interval 0.0 to ~1.5 based upon a sample of 987 Lyα absorption lines identified in the spectra of 63 QSOs obtained with the Faint Object Spectrograph (FOS) of the Hubble Space Telescope (HST). These spectra were obtained as part of the QSO Absorption Line Survey, an HST Key Project during the first four years of observations with the telescope. Fits to the evolution of the number of absorbers per unit redshift (dN/dz) of the form dN/dz = A × (1 + z)γ continue to yield values of γ in the range 0.1-0.3, decidedly flatter than results from ground-based data pertaining to the redshift range z > 1.7. These results are consistent with our previous results based on a much smaller sample of lines, but the uncertainties in the fit have been greatly reduced. The combination of the HST and ground-based data suggest a marked transition in the rate of evolution of the Lyα lines at a redshift of about 1.7. The 19 Lyα lines from an additional higher redshift QSO from our sample for which tentative line identifications are available (UM 18; zem = 1.89) support the suggestion of a rapid increase at around this redshift. We derive the cumulative distribution of the full sample of Lyα lines and show that the distribution in redshift can indeed be well represented by a power law of the form (1 + z)γ. For this same sample, the distribution of equivalent widths of the Lyα absorbers above a rest equivalent width of 0.1 A is fit quite well by an exponential. Comparing samples of Lyα lines, one set of which has redshifts the same as, or very near to, the redshifts of ions from heavy elements and another set in which no ions from heavy elements have been identified, we find that the Lyα systems with heavy element detections have a much steeper slope than the high rest equivalent width portion of the Lyman-only sample. We argue that this result is not likely to be due to either line misidentification or incomplete spectral coverage. Considering the insensitivity of the equivalent width to large changes in the column density for saturated lines, we suggest that this result is probably attributable to rapid evolution of the very highest column density systems, rather than real differences in metallicity. We find evidence that the rate of evolution increases with increasing equivalent width. We compare our results for the variation of line density with redshift to recent numerical simulations of Lyα absorbers, in particular, to those of Riediger, Petitjean, & Mucket, which extend to zero redshift. We find fairly good agreement between these simulations and our results, though the rapid evolution we find in the Lyα systems containing heavy element ions is not predicted in their models. We speculate that these heavy element-containing Lyα systems involve those clouds closely associated with galaxies, whose column densities are too high and whose sizes are too small to be included in the Riediger et al. simulations. Our results for Lyα lines at the high end of our equivalent width distribution are compatible with the recent analysis of the absorber-galaxy correlation by Chen et al. For the weaker lines, however, our results suggest that whatever association exists between absorbers and galaxies is different from that for the stronger lines. We conclude with some suggestions for further observations.

The Hubble Space Telescope Quasar Absorption Line Key Project. XIII. A Census of Absorption-Line Systems at Low Redshift*

We present a catalog of absorption lines obtained from the analysis of the ultraviolet spectra of 66 quasars. The data were acquired with the Faint Object Spectrograph of the Hubble Space Telescope (HST) as part of the Quasar Absorption Line Survey, a Key Project for the first four cycles of HST observations. This is the third of a series of catalogs of absorption lines produced from the survey and increases the number of quasars whose higher resolution (R = 1300) spectra we have published from 17 to 83. The general properties and execution of the survey are reviewed, including descriptions of the final sample of observed objects and the algorithmic processes used to construct the catalog. This database is suitable for a wide variety of studies of gaseous systems in the nearby universe. This third catalog includes 2594 absorption lines and brings the total number of absorption lines in the combined catalog to 3238. The third catalog has 878 identified Lyα lines, 27 extensive metal line systems (detected absorption lines from four or more metal ions), 88 C IV systems, and 34 O VI systems. The combined catalog contains the following numbers of extragalactic absorption lines: 1129 Lyα lines, 107 C IV systems, 41 O VI systems, 16 Lyman limit systems, and one damped Lyα system (in the spectrum of PG 0935+416). In addition, there are 25 pairs of identified Lyα lines that are candidate C IV doublets. Of the 122 identified C IV and candidate C IV systems in the completely identified sample of absorption lines, 24 ± 5 are expected to be chance coincidences of other lines (based upon Monte Carlo simulations). The detection of a single damped Lyα system in a path length of Δz = 49 yields an observed number of damped systems per unit redshift of (dN/dz)damp(z = 0.58) = 0.020 with 95% confidence boundaries of 0.001-0.096 systems per unit redshift. We include notes on our analysis of each of the observed quasars and the absorption systems detected in each spectrum. Some especially interesting systems include low-redshift Lyα absorbers suitable for extensive follow-up observations (e.g., in the spectra of TON 28 and PG 1216+069), possibly physically associated pairs of extensive metal line absorption systems (e.g., in the spectrum of PG 0117+213), and systems known to be associated with galaxies (e.g., in the spectrum of 3C 232). The spectra of five broad absorption line (BAL) quasars (UM 425, PG 1254+047, PG 1411+442, PG 1700+518, and PG 2112+059) can be found in this third catalog, bringing the total number of BAL quasars in the combined catalog to six (including PG 0043+039).

The Hubble Space Telescope Quasar Absorption Line Key Project. VII. Absorption Systems at Z abs <= 1.3

We present evidence that clumps of \lya lines are physically associated with about half of the extensive metal-line systems (absorption systems with four or more observed metal-line species) found in this paper, demonstrate that all four \lylimit systems discussed here correspond to extensive metal-line absorption systems, and present an extraordinary pair of extensive metal-line absorption systems within 2000~km/s of each other at