Frederic H. Chaffee

BEAMING IN GAMMA-RAY BURSTS: EVIDENCE FOR A STANDARD ENERGY RESERVOIR

We present a comprehensive sample of all gamma-ray burst (GRB) afterglows with known distances, and we derive their conical opening angles based on observed broadband breaks in their light curves. Within the framework of this conical jet model, we correct for the geometry and we find that the gamma-ray energy release is narrowly clustered around 5 × 10^(50) ergs. We draw three conclusions. First, the central engines of GRBs release energies that are comparable to ordinary supernovae. Second, the broad distribution in fluence and luminosity for GRBs is largely the result of a wide variation of opening angles. Third, only a small fraction of GRBs are visible to a given observer, and the true GRB rate is several hundred times larger than the observed rate.

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 TEAM KECK TREASURY REDSHIFT SURVEY OF THE GOODS-NORTH FIELD

We report the results of an extensive imaging and spectroscopic survey in the Great Observatories Origins Deep Survey (GOODS)-North field completed using DEIMOS on the Keck II telescope. Observations of 2018 targets in a magnitude-limited sample of 2911 objects to RAB = 24.4 yield secure redshifts for a sample of 1440 galaxies and active galactic nuclei (AGNs) plus 96 stars. In addition to redshifts and associated quality assessments, our catalog also includes photometric and astrometric measurements for all targets detected in our R-band imaging survey of the GOODS-North region. We investigate various sources of incompleteness and find the redshift catalog to be 53% complete at its limiting magnitude. The median redshift of z = 0.65 is lower than in similar deep surveys because we did not select against low-redshift targets. Comparison with other redshift surveys in the same field, including a complementary Hawaii-led DEIMOS survey, establishes that our velocity uncertainties are as low as σ ≈ 40 km s-1 for red galaxies and that our redshift confidence assessments are accurate. The distributions of rest-frame magnitudes and colors among the sample agree well with model predictions out to and beyond z = 1. We will release all survey data, including extracted one-dimensional and sky-subtracted two-dimensional spectra, thus providing a sizable and homogeneous database for the GOODS-North field, which will enable studies of large-scale structure, spectral indices, internal galaxy kinematics, and the predictive capabilities of photometric redshifts.

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.

A Galaxy at z = 5.34*

We report the discovery of Lyα emission from a galaxy at z=5.34, the first object at z>5 with a spectroscopically confirmed redshift. The faint continuum emission [mAB(8000 A) ≈ 27], the relatively small rest-frame equivalent width of the emission line (WrestLyα ≈ 95 A), and the limits on the N V/Lyα ratio suggest that this is a star-forming galaxy and not an active galactic nucleus. The star formation rates implied by the UV continuum emission and the Lyα emission are (in the absence of dust extinction) fairly modest (~6 h−250 M☉ yr-1 for q0=0.5). The continuum luminosity is similar to that of sub-L*1500 star-forming galaxies at z~3, and the width of the Lyα line yields an upper limit to the mass of less than 2.6×1010 M☉. The strong emission line detected in this low-luminosity galaxy provides hope for the discovery of higher luminosity primeval galaxies at redshifts z>5.

SBS 0335–052, A Probable Nearby Young Dwarf Galaxy: Evidence Pro and Con*

The results of Multiple Mirror Telescope spectrophotometry of the extremely low-metallicity blue compact galaxy (BCG) SBS 0335-052 are presented. The oxygen abundance in central brightest part of the galaxy is found to be 12 + log(O/H) = 7.33+-0.01. The N/O, Ne/O, S/O and Ar/O abundance ratios are close to those derived in other BCGs, suggesting that heavy element enrichment in the HII region is due to massive star evolution. We detect auroral [OIII] 4363 emission in the inner part of HII region with a diameter of 3.6 kpc and find that the HII region inside this diameter is hot, T_e~20000K. The oxygen abundance in this region is nearly constant (12 + log(O/H) = 7.1 - 7.3), implying effective mixing of ionized gas on short time-scales. We also discuss the origin of blue underlying extended low-intensity emission detected in SBS 0335-052. The (V-I) and (R-I) color distributions suggest that a significant contribution to the extended envelope is due to ionized gas emission. However, the observed equivalent width of Hbeta emission in the extended envelope is 2-3 times lower than the value expected in the case of pure gaseous emission. These findings suggest that, along with the blue young (~10^7yr) stellar clusters, an older stellar population with age ~10^8yr may be present in the extended envelope of SBS 0335-052, having a total mass conclude that SBS 0335-052 is a young nearby dwarf galaxy with age ~10^8 yr.

A Survey of Organic Volatile Species in Comet C/1999 H1 (Lee) Using NIRSPEC at the Keck Observatory

The organic volatile composition of the long-period comet C/1999 H1 (Lee) was investigated using the —rst of a new generation of cross-dispersed cryogenic infrared spectrometers (NIRSPEC, at the Keck Observatory atop Mauna Kea, HI). On 1999 August 19¨21 the organics spectral region (2.9¨3.7 km) was completely sampled at both moderate and high dispersion, along with the CO fundamental region (near 4.67 km), revealing emission from water, carbon monoxide, methanol, methane, ethane, acetylene, and hydrogen cyanide. Many new multiplets from OH in the 1¨0 band were seen in prompt emission, and numerous new spectral lines were detected. Several spectral extracts are shown, and global production rates are presented for seven parent volatiles. Carbon monoxide is strongly depleted in comet Lee relative to comets Hyakutake and Hale-Bopp, demonstrating that chemical diversity occurred in the giant