Donna S. Womble

The Lyα Forest at z ~ 4: Keck HIRES Observations of Q0000–26

We derive H I column density and Doppler width distributions for a sample of Lyα clouds with 3.4 14.5 may be present. The Doppler width distribution of the clouds is consistent with a Gaussian function with a mean of 23 km s–1 and a dispersion of 8 km s–1 but with a cutoff at 15 km s–1, i.e., no clouds with b < 15 km s–1 are required to describe the data. While the H I column density distribution found here is consistent with that derived from similar quality data at lower redshifts, both the mean Doppler width and the cutoff value are smaller than those found at lower redshift. There is a hint for clustering in the clouds line-of-sight distribution in the velocity interval 100 < Δv < 160 km s–1, but the evidence is only marginal. Analyses of the proximity effect indicate a value of JLLν ~ 2 × 10–22 ergs s–1 cm–2 Hz–1 sr–1 for the mean intensity of the megagalactic UV ionizing background at z ~ 4.1, which is consistent with that expected from high-redshift quasars.

1608+656 - A QUADRUPLE-LENS SYSTEM FOUND IN THE CLASS GRAVITATIONAL LENS SURVEY

The first phase of a large gravitational lens survey using the Very Large Array at a wavelength of 3.6 cm has been completed, yielding images for 3258 radio sources. The Cosmic Lens All-Sky Survey (CLASS) is designed to locate gravitational lens systems consisting of multiply imaged compact components with separations greater than 02. We report here the first discovery of a gravitational lens from the survey: 1608+656, a quadruply imaged object with a maximum separation of 21. Images from the Palomar 5 m and Keck 10 m telescopes show the lensed images and the lensing galaxy. An optical spectrum obtained with the Palomar 5 m telescope indicates a redshift of z=0.6304 for the lensing galaxy. No conclusive redshift for the lensed object has been determined, although a single strong emission line is found at 9240 A in the Keck low-resolution imaging spectrograph spectrum. The two most likely identifications for this line are Hβ (z=0.90) and Mg II (z=2.30). The preliminary lens model derived from the radio image reproduces the observed configuration and relative fluxes of the images, as well as the position, shape, and orientation of the lensing galaxy. Because a simple mass model is able to fit the observations, we argue that this lens system is promising for determining H0.

1608+656: A Gravitationally Lensed PostStarburst Radio Galaxy

The gravitational lens system 1608+656 displays four flat-spectrum, pointlike components that are the images of the unresolved core of a double-lobed radio source. The lensing mass is a galaxy at z = 0.630. New spectra of this system enable us to determine a conclusive redshift of 1.394 for the lensed object. The spectra show prominent high-order Balmer absorption lines and Mg II absorption. These lines, and the absence of [O II] emission, indicate that this is a poststarburst or E + A galaxy. It is unique among lensed objects in not being a quasar and among E + A galaxies in having the highest known redshift. Even allowing for lens magnification, the lensed object is a very luminous galaxy, with an absolute magnitude, M(r) = -22.8 mag. The deconvolved infrared image indicates that the galaxy may be slightly resolved. The radio luminosity density of the lobes is L_(1.4) = 5.78 × 10^(25) W Hz^(-1), which puts the source on the boundary between FR I and FR II radio galaxies. Together with the redshift for the lens and a satisfactory mass model, the determination of the lensed object redshift makes this system an excellent candidate for measuring H_0.

Temperature and Kinematics of C IV Absorption Systems

We use Keck HIRES spectra of three intermediate-redshift QSOs to study the physical state and kinematics of the individual components of C IV-selected heavy-element absorption systems. Fewer than 8% of all C IV lines with column densities greater than 1012.5 cm-2 have Doppler parameters b < 6 km s-1. A formal decomposition into thermal and nonthermal motion using the simultaneous presence of Si IV gives a mean thermal Doppler parameter btherm(C IV) = 7.2 km s-1, corresponding to a temperature of 3.8 × 104 K, although temperatures possibly in excess of 3 × 105 K occur occasionally. We also find tentative evidence for a mild increase of temperature with H I column density. Nonthermal motions within components are typically small (<10 km s-1) for most systems, indicative of a quiescent environment. The two-point correlation function (TPCF) of C IV systems on scales up to 500 km s-1 suggests that there is more than one source of velocity dispersion. The shape of the TPCF can be understood if the C IV systems are caused by ensembles of objects with the kinematics of dwarf galaxies on a small scale, while following the Hubble flow on a larger scale. Individual high-redshift C IV components may be the building blocks of future normal galaxies in a hierarchical structure formation scenario.

Photometric and Spectroscopic Observations of SN 1990E in NGC 1035: Observational Constraints for Models of Type II Supernovae

We present 126 photometric and 30 spectral observations of SN 1990E spanning from 12 days before B maximum to 600 days past discovery. These observations show that SN 1990E was of type II-P, displaying hydrogen in its spectrum, and the characteristic plateau in its light curve. SN 1990E is one of the few SNe II which has been well observed before maximum light, and we present evidence that this SN was discovered very soon after its explosion. In the earliest spectra we identify, for the first time, several N II lines. We present a new technique for measuring extinction to SNe II based on the evolution of absorption lines, and use this method to estimate the extinction to SN 1990E, A(V) = 1.5 +/- 0.3 mag. From our photometric data we have constructed a bolometric light curve for SN 1990E and show that, even at the earliest times, the bolometric luminosity was failing rapidly. We use the late-time bolometric light curve to show that SN 1990E trapped a majority of the gamma rays produced by the radioactive decay of Co-56, and estimate that SN 1990E ejected an amount of Ni-56 virtually identical to that of SN 1987A.

A new radio double lens from CLASS: B1127‡385

We present the discovery of a new gravitational lens system with two compact radio images separated by 0.701 +/- 0.001 arcsec, The lens system was discovered in the Cosmic Lens All Sky Survey (CLASS) as a flat-spectrum radio source. Both radio components show structure in a Very Long Baseline Array (VLBA) 8.4-GHz radio image. No further extended structure is seen in Very Large Array (VLA), Multi-Element Radio Linked Interferometer Network (MERLIN) or VLBA images, Hubble Space Telescope (HST) WFPC2 images in F555W and F814W show two extended objects close to the radio components, which we identify as two lens galaxies, Their colours and mass-to-light ratios seem to favour two late-type spiral galaxies at relatively high redshifts (z(d) greater than or similar to 0.5). Faint emission is also detected at positions corresponding to the radio images, A two-lens mass model can explain the observed VLBA structure. The best-fitting model has a reduced chi(2) of 1.1. The relative positions of the VLBA subcomponents are reproduced within 0.08 mas, and the flux density ratios within 20 per cent. We also reproduce the position angle and separation of the two VLBA subcomponents in A and B within the observational errors, which we consider strong evidence for the validity of the lens model. Moreover, we find a surface density axis ratio of 0.74(-0.12)(+0.10) for the primary lens (G1), consistent with the surface brightness axis ratio of 0.69 +/- 0.15. Also, the surface density position angle of (4.9(-22.4)(+28.2))degrees of G1 compares well with the (-6 +/- 13)degrees position angle of the surface brightness distribution. The errors indicate the 99 per cent confidence interval.

Properties of a High-Redshift Galaxy at z = 4.4

We discuss the absorption properties of a high-redshift galaxy at z = 4.3829 identified as a damped Ly? system in the Keck spectrum of the quasar BRI 1202-0725 (zem = 4.7). This is at present the highest redshift damped Ly? system known, observed when the age of the universe was only 1 Gyr (q0 = 0.5, H0 = 50). Both the high redshift and low metallicity ([Fe/H] = -2.2) of the system indicate that it is an extremely young galaxy in an early stage of evolution. The relative elemental abundance patterns are consistent with extreme Population II metallicities, providing evidence for enrichment by Type II supernovae only. Kinematic evidence suggests that the absorbing galaxy may be a massive spiral. We discuss the implications of this result on theories of galaxy formation. The Si IV and C IV absorption in the system appears unusually weak. Several plausible explanations are provided. We estimate T < 19.6 K for the cosmic microwave background radiation at z = 4.3829, which is consistent with the predicted temperature of 14.7 K from the big bang cosmology.

Diffuse Soft X-Ray Emission from Several Nearby Spiral Galaxies

We observed several nearby face-on spiral galaxies with the ROSAT PSPC to study their 0.1-2.0 keV diffuse emission. After the exclusion of resolved discrete sources, there is unresolved X-ray emission in all the galaxies observed. Since this emission is a combination of diffuse emission and a contribution from unresolved point sources, it represents an upper limit to the truly diffuse soft X-ray emission. The derived upper limits on the diffuse emission can be interpreted in terms of upper limits to the average intensity of a putative hot halo. They can also be used to derived limits to the total energy radiated by hot gas in the observed galaxies as a function of its temperature for various assumed absorbing geometries. Beyond the equivalent solar radius (the radius at which the Sun would be in the observed galaxies), the temperature of hot gas radiating more than 30% of the total supernova power in the galaxies must be less than

Limits to the 14 keV Extragalactic X-Ray Background

10^{6.1} K

Ca II and Na I absorption in the QSO S4 0248 + 430 due to an intervening galaxy

if it is located within the disk with an assumed absorbing overburden of