Craig B. Foltz

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.

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 FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later

We have used the Very Large Array (VLA) FIRST survey and the Automated Plate Measuring Facility (APM) catalog of the Palomar Observatory Sky Survey I (POSS-I) plates as the basis for constructing a new radio-selected sample of optically bright quasars. This is the first radio-selected sample that is competitive in size with current optically selected quasar surveys. Using only two basic criteria, radio-optical positional coincidence and optical morphology, quasars and BL Lac objects can be identified with 60% selection efficiency; the efficiency increases to 70% for objects fainter than 17 mag. We show that a more sophisticated selection scheme can predict with better than 85% reliability which candidates will turn out to be quasars. This paper presents the second installment of the FIRST Bright Quasar Survey (FBQS), with a catalog of 636 quasars distributed over 2682 deg2. The quasar sample is characterized and all spectra are displayed. The FBQS detects both radio-loud and radio-quiet quasars out to redshift z > 3. We find a large population of objects of intermediate radio loudness; there is no evidence in our sample for a bimodal distribution of radio characteristics. The sample includes ~29 broad absorption line quasars, both high and low ionization, and a number of new objects with remarkable optical spectra.

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

SN 1991T : further evidence of the heterogeneous nature of type Ia supernovae

Optical spectra of SN 1991T obtained approximately one week before B maximum showed no evidence of the Si, Ca, and S absorption lines which normally dominate the spectra of type Ia supernovae at early phases. Nevertheless, within two weeks after maximum, the spectrum of SN 1991T had evolved to resemble closely that of other type Ia events. These observations suggest that the abundances of Si, Ca, and S in the outer ejecta of SN 1991T were unusually low. The B and V light curves of SN 1991T resembled those of other type Ia supernovae, but the slope of the initial decline following maximum was less steep than normal in both colors

The Frequency and Radio Properties of Broad Absorption Line Quasars

A sample of 67 broad absorption line quasars (BALQSOs) from the Large Bright Quasar Survey (LBQS) is used to estimate the observed and intrinsic fraction of BAL quasars in optically selected samples at intermediate (BJ 18.5) magnitudes. The observed BALQSO fraction in the redshift range 1.5 ≤ z ≤ 3.0 is 15% ± 3%. A well-determined empirical k-correction, to allow for the differences in the spectral energy distributions of non-BALQSOs and BALQSOs shortward of 2100 A in the rest frame, is applied to the sample. The result is an estimate of the intrinsic fraction of BALQSOs of 22% ± 4% for the redshift range 1.5 ≤ z ≤ 3.0. This value is twice that commonly cited for the occurrence of BALQSOs in optically selected samples, and the figure is in reasonable agreement with that from a preliminary analysis of the SDSS Early Data Release. The fraction of BALQSOs predicted to be present in an optical survey with flux limits equivalent to that of the FIRST Bright Quasar Survey (FBQS) is shown to be 20%. The BALQSO fractions derived from the FBQS and the LBQS suggest that optically bright BALQSOs are half as likely as non-BALQSOs to be detectable as S1.4 GHz 1 mJy radio sources.

Helium Abundance in the Most Metal-deficient Blue Compact Galaxies: I Zw 18 and SBS 0335–052*

We present high-quality spectroscopic observations of the two most metal-deficient blue compact galaxies known, I Zw 18 and SBS 0335-052. We use the data to determine the heavy-element and helium abundances. The oxygen abundances in the northwest and the southeast components of I Zw 18 are found to be the same within the errors, 7.17 ± 0.03 and 7.18 ± 0.03, respectively, although marginally statistically significant spatial variations of oxygen abundance might be present. In contrast, we find a statistically significant gradient of oxygen abundance in SBS 0335-052. The largest oxygen abundance, 12 + log O/H = 7.338 ± 0.012, is found in the region 06 to the northeast of the brightest part of the galaxy, and it decreases toward the southwest to values of ~7.2, comparable to that in I Zw 18. The underlying stellar absorption strongly influences the observed intensities of He I emission lines in the brightest northwest component of I Zw 18, and hence this component should not be used for primordial He abundance determination. The effect of underlying stellar absorption, though present, is much smaller in the southeast component. Assuming all systematic uncertainties are negligible, the He mass fraction Y = 0.243 ± 0.007 derived in this component is in excellent agreement with recent measurements by Izotov & Thuan, suggesting the robustness of the technique applied in measurements of the helium abundance in low-metallicity blue compact galaxies. The high signal-to-noise ratio spectrum (≥100 in the continuum) of SBS 0335-052 allows us to measure the helium mass fraction with a precision better than 2%-5% in nine different regions along the slit. We show that, while underlying stellar absorption in SBS 0335-052 is important only for the He I 4471 A emission line, other mechanisms such as collisional and fluorescent enhancements are influencing the intensities of all He I emission lines and should be properly taken into account. When the electron number density derived from [S II] emission lines is used in SBS 0335-052, the correction of He I emission lines for collisional enhancement leads to systematically different He mass fractions for different He I emission lines. This unphysical result implies that the use of the electron number density derived from [S II] emission lines, being characteristic of the S+ zone but not of the He+ zone, will lead to an incorrect inferred value of Y. In the case of SBS 0335-052 it leads to a significant underestimate of the He mass fraction. In contrast, the self-consistent method using the five strongest He I emission lines in the optical spectrum for correction for collisional and fluorescent enhancements shows excellent agreement of the He mass fraction derived from the He I 5876 A and He I 6678 A emission lines in all nine regions of SBS 0335-052 used for the He abundance determination. Assuming all systematic uncertainties are negligible, the weighted mean He mass fraction in SBS 0335-052 is Y = 0.2437 ± 0.0014 when the three He I 4471, 5876 and 6678 A emission lines are used, and it is 0.2463 ± 0.0015 when the He I 4471 A emission line is excluded. These values are in very good agreement with recent measurements of the He mass fraction in SBS 0335-052 by Izotov and coworkers. The weighted mean helium mass fraction in the two most metal-deficient blue compact galaxies, I Zw 18 and SBS 0335-052, Y = 0.2462 ± 0.0015, after correction for the stellar He production results in a primordial He mass fraction Yp = 0.2452 ± 0.0015. The derived Yp leads to a baryon-to-photon ratio of 4.7 × 10-10 and to a baryon mass fraction in the universe Ωbh = 0.068, consistent with the values derived from the primordial D and 7Li abundances, and supporting the standard big bang nucleosynthesis theory. For the most consistent set of primordial D, 4He, and 7Li abundances we derive an equivalent number of light neutrino species Nν = 3.0 ± 0.3 (2 σ).

An objective classification scheme for QSO spectra

A new approach to the classification of QSO rest-frame optical and ultraviolet spectra is presented. The statistical technique of principal component analysis (PCA) is applied directly to a sample of QSO ultraviolet spectra, rest-frame wavelengths λλ1150-2000, taken from the Large, Bright QSO Survey. A detailed discussion of the application of the PCA technique to QSO spectra is given. The PCA approach provides new insights into the relation between the continuum, emission-line, and broad-absorption-line properties of QSOs

Continuum and Emission-Line Strength Relations for a Large Active Galactic Nuclei Sample

We report on the analysis of a large sample of 744 type 1 active galactic nuclei, including quasars and Seyfert 1 galaxies across the redshift from 0 z 5 and spanning nearly 6 orders of magnitude in continuum luminosity. We discuss correlations of continuum and emission-line properties in the rest-frame ultraviolet and optical spectral ranges. The well-established Baldwin effect is detected for almost all emission lines from O VI ?1034 to [O III] ?5007. Their equivalent widths are significantly anticorrelated with the continuum strength, while they are nearly independent of redshift. This is the well-known Baldwin effect. Its slope ?, measured as log W? ? log ?L?(1450 ?), shows a tendency to become steeper toward higher luminosity. The slope of the Baldwin effect also increases with the ionization energy needed to create the individual lines. In contrast to this general trend, the N V ?1240 equivalent width is nearly independent of continuum luminosity and remains nearly constant. The overall line behaviors are consistent with softer UV continuum shapes and perhaps increasing gas metallicity in more luminous active galactic nuclei.

Extinction in low-ionization broad absorption line quasi-stellar objects

Recently, Weymann et al. (1991, ApJ, 373) presented composite spectra of broad absorption line (BAL) QSOs as divided into two classes, those with spectra containing absorption from both high and low-ionization ionic species, and those showing only high-ionization absorption troughs. They showed that the spectral properties of the former class differed from those of the latter (and non-broad absorption line QSOs) in that their spectra contain stronger emission from Fe II and possibly Fe III, their continua are substantially redder, and Lyman α and N V emission lines are weaker. Here, it is shown that correction for the extinction of a modest amount of dust can bring the spectra into coincidence