Search

High velocity outflows from quasars are revealed by the absorption signatures they produce in the spectrum of the quasar. Clues on the nature and origin of these flows are important for our understanding of the dynamics of gas in the central regions of the Active Galactic Nucleus (AGNs) but also of the metal enrichment of the intergalactic space. Line radiation pressure has often been suggested to be an important process in driving these outflows, however no convincing evidence has been given so far. Here we report observation of a highly structured flow, toward Q~1511+091, where the velocity separations between distinct components are similar to O VI, N V and C IV doublet splittings with some of the profiles matching perfectly. This strongly favors the idea that the absorbing clumps originate at similar physical location and are driven by radiative acceleration due to resonance lines. The complex absorption can be understood if the flow is highly collimated so that the different optically thick clouds are aligned and cover the same region of the background source. One component shows saturated H I Lyman series lines together with absorptions from excited levels from C II and Si II but covers only 40% of the source of continuum. The fact that clouds cover only part of the small continuum source implies that the flow is located very close to it., Comment: 6 pages, 5 figures to appear in MNRAS

We present a search for spatial and redshift correlations in a 2 A resolution spectroscopic survey of the Lyman alpha forest at 2.15 < z < 3.37 toward ten QSOs concentrated within a 1-degree diameter field. We find a signal at 2.7 sigma significance for correlations of the Lyman alpha absorption line wavelengths between different lines of sight over the whole redshift range. The significance rises to 3.2 sigma if we restrict the redshift range to 2.60 < z < 3.37, and to 4.0 sigma if we further restrict the sample to lines with rest equivalent width 0.1 <= W0/(A) < 0.9. We conclude that a significant fraction of the Lyman alpha forest arises in structures whose correlation length extends at least over 30 arcmin (~26/h comoving Mpc at z=2.6 for H0 = 100h km/s/Mpc, Omega=1.0, Lambda=0). We have also calculated the three dimensional two point correlation function for Lyman alpha absorbers; we do not detect any significant signal in the data. However, we note that line blending prevents us from detecting the signal produced by a 100% overdensity of Lyman alpha absorbers in simulated data. We find that the Lyman alpha forest redshift distribution provides a more sensitive test for such clustering than the three dimensional two point correlation function., Comment: 33 pages, 11 figures, Latex, accepted for publication in ApJ, data to be published on ApJ CD-ROM, minor title correction, references updated, figures clarified

We present results from a survey of the Lyman alpha forest at 2.15

We present optical spectroscopic data for a complete sample of 161 S_5GHz >= 0.2 Jy, flat-spectrum radio sources. The sources were observed as part of a survey for high redshift, radio-loud quasars, and were selected for spectroscopic follow-up based on criteria of red optical colour and unresolved optical counterpart, as measured from APM scans of POSS-I plates. 13 objects from the spectroscopic sample were found to be radio-loud quasars with z > 3, of which two were previously known. We give positions, E (red) magnitudes, O-E colours, 5GHz radio fluxes, radio spectral indices, optical spectra and redshifts where possible for the spectroscopic sample. We also give finding charts for the z > 3 QSOs. The highest redshift object found is a QSO with z = 4.30 (GB1508+5714, the subject of an earlier Letter). The sample also contains a z = 3.05 QSO, GB1759+7539, which is optically very luminous (E=16.1). In addition, spectra are given for 18 S_5GHz >= 0.2 Jy, flat-spectrum radio sources that do not form part of the complete sample., Comment: 14 pages including tables and figures, except Figs. 3 and 4 (spectra) which are available from http://panisse.lbl.gov/public/isobelpage/ . To appear in MNRAS

The APM multicolor survey for bright z > 4 objects, covering 2500 deg^2 of sky to m(R)~19, resulted in the discovery of thirty-one quasars with z > 4. High signal-to-noise optical spectrophotometry at 5A resolution has been obtained for the twenty-eight quasars easily accessible from the northern hemisphere. These spectra have been surveyed to create new samples of high redshift Lyman-limit systems, damped Lyman-alpha absorbers, and metal absorption systems (e.g. CIV and MgII). In this paper we present the spectra, together with line lists of the detected absorption systems. The QSOs display a wide variety of emission and absorption line characteristics, with 5 exhibiting broad absorption lines and one with extremely strong emission lines (BR2248-1242). Eleven candidate damped Ly-alpha absorption systems have been identified covering the redshift range 2.83.5). An analysis of the measured redshifts of the high ionization emission lines with the low ionization lines shows them to be blueshifted by 430+/-60 km/s. In a previous paper (Storrie-Lombardi et. al. 1994) we discussed the redshift evolution of the Lyman limit systems catalogued here. In subsequent papers we will discuss the properties of the Ly-alpha forest absorbers and the redshift and column density evolution of the damped Ly-alpha absorbers., Comment: To appear in 1 September 1996, ApJS, 10 pages text, 22 pages of figures, 11 pages of tables

We have made a statistically complete, unbiased survey of C IV systems toward a region of high QSO density near the South Galactic Pole using 25 lines of sight spanning $1.5

We present results from 12 km/s resolution echelle spectroscopy of the bright $z=4.694$ QSO BR1202-0725. A preliminary analysis shows that high metallicity narrow line absorption clouds are present up to the redshift of the quasar. A damped Ly$\alpha$ system with an HI column density of $3.1 \times 10^{20}$ cm$^{-2}$ at $z=4.383$ has an [O/H] ratio that is about 0.01 solar, while another absorption system with an HI column density of $5.0 \times 10^{16}$ cm$^{-2}$ at $z=4.672$, may have an O/H ratio that is twice solar. An upper limit, or the possible detection of deuterium in this absorption cloud gives a D/H ratio of about 1.5\,10$^{-4}$. Because this cloud is metal rich at least some of the cloud gas has been processed after the beginning of the Universe., Comment: 23 pages, including 5 Postscript figures, in gzip-ed uuencoded postscript format. Accepted for publication in A&A

We have obtained high signal:to:noise optical spectroscopy at 5\AA\ resolution of 27 quasars from the APM z$>$4 quasar survey. The spectra have been analyzed to create new samples of high redshift Lyman-limit and damped Lyman-$\alpha$ absorbers. These data have been combined with published data sets in a study of the redshift evolution and the column density distribution function for absorbers with $\log$N(HI)$\ge17.5$, over the redshift range 0.01 $<$ z $<$ 5. The main results are: \begin{itemize} \item Lyman limit systems: The data are well fit by a power law $N(z) = N_0(1 + z)^{\gamma}$ for the number density per unit redshift. For the first time intrinsic evolution is detected in the product of the absorption cross-section and comoving spatial number density for an $\Omega = 1$ Universe. We find $\gamma = 1.55$ ($\gamma = 0.5$ for no evolution) and $N_0 = 0.27$ with $>$99.7\% confidence limits for $\gamma$ of 0.82 \& 2.37. \item Damped \lya systems: The APM QSOs provide a substantial increase in the redshift path available for damped surveys for $z>3$. Eleven candidate and three confirmed damped Ly$\alpha$ absorption systems, have been identified in the APM QSO spectra covering the redshift range $2.8\le z \le 4.4$ (11 with $z>3.5$). Combining the APM survey confirmed and candidate damped \lya absorbers with previous surveys, we find evidence for a turnover at z$\sim$3 or a flattening at z$\sim$2 in the cosmological mass density of neutral gas, $\Omega_g$. \end{itemize} The Lyman limit survey results are published in Storrie-Lombardi, et~al., 1994, ApJ, 427, L13. Here we describe the results for the DLA population of absorbers., Comment: latex, 5 pages + 4 postscript figures

We report the discovery of a radio loud quasar with a redshift of 4.30. This object, which is the first radio selected quasar with a redshift greater than four, was discovered during an observational investigation into the evolution of the luminosity function of radio loud quasars. Here we describe results based on a sample of ~300, flat spectrum radio sources with S(5GHz) > 200mJy. In this study, rather than carry out an indiscriminate redshift campaign on all the radio sources, we have used the APM POSS catalogue to preselect a subset of stellar-like optical counterparts with red optical colours. Such a subsample is expected to contain a high fraction of high redshift quasars. 10 of the ~300 sources were selected for follow-up optical spectroscopy and three of these are identified as quasars with redshifts greater than 3.0. One of the radio sources, GB1508+5714, is a quasar with z=4.30 and m(R)~19., Comment: 5 pages, one uuencoded compressed postscipt file (created with uufiles) including figures. MNRAS Letter, in press.

The discovery of an unresolved radio-quiet object with a redshift of 3.409 and visual magnitude of 24.3 +/-0.5 is reported. The object was identified during an imaging search for Ly-alpha emission near the redshift of a z(abs) = 3.390-damped Ly-alpha absorption-line system which appears in the spectrum of the z(em) = 4.11 QSO 0000-2619. It is determined that the bulk of the object's Ly-alpha and continuum emission comes from an unresolved region less than 9 kpc, and its absolute magnitude in the rest-frame UV near Ly-alpha is about -21.2. A long-slit CCD spectrum at 500 km/s resolution shows that it has kinematically unresolved Ly-alpha emission with a rest equivalent width in the range of about 10-20 A. The object is observed to be about 135 kpc in projection from the sight line to the WSO. No emission at the redshift of the damped Ly-alpha absorber is detected.

The scanning of a direct plate with the automatic plate measuring machine which results in the automated selection and description of images is described. The selection of QSO candidates based on color-color diagrams constructed from the APM image data and the analysis of APM raster data for QSOs selected visually from objective prism plates are also discussed.

Results are reported for digicon spectrophotometric observations of the radio source 0938+119, which was originally classified as a faint red galaxy. A prism spectrum of the source is presented along with the corresponding sky measurement, and several features of the spectrum are described. It is shown that this source is a QSO with a magnitude of 20.1, a redshift z = 3.19, and a spectrum similar to that of OH 471 or 4C 05.34. The question of whether other faint high-redshift QSOs have been misclassified as galaxies is considered.

The paper presents spectrophotometric observations of 76 optical objects identified with radio sources from the MC2 and MC3 catalogs. Line intensities, equivalent widths, line widths, and optical spectral indices are presented for 44 objects confirmed as quasi-stellar objects. The statistical and physical properties of the Molonglo sample are briefly discussed.

Spectra obtained for 92 QSO candidates selected mostly on the basis of their proximity to radio-source positions are presented. Thirty-two were classified as QSOs on the basis of broad emission lines and stellar appearance, whereas redshifts were determined in 14 instances.

The question is investigated whether QSO redshifts are cosmological in origin, taking into account the possibility that QSOs may be more local objects. A search is made for situations in which more than one blue stellar object (BSO) lay close to a radio position selected from the 4C catalog. It is found that in all four examples studied the radio emission arises in the QSO and not the galaxies or cluster of galaxies.

It is reported that 1548+115a is also a QSO. Spectral information is provided for 1548+115b and 1548+115a, giving attention to the very different redshifts of the objects. The observations reported are believed to add support to noncosmological theories of redshifts. Such theories will receive additional support if an interaction between the two components of a close pair can be shown.

The absorption-rich optical and near-infrared spectrum of the quasi-stellar object 1331 + 170 is analyzed. The emission-line redshift is about 2.08, and at least three absorption systems are shown to be present; the absorption redshifts are 1.7755, 1.7851, and 1.9637. We conclude that the absorbing material giving rise to the three systems is intrinsic to the QSO despite the high velocity difference between emission and absorption systems and the low velocity dispersion within each absorption system.