The Fluctuating Intergalactic Radiation Field at Redshifts z = 2.3-2.9 from He II and H I Absorption towards HE 2347-4342

We provide an in-depth analysis of the He II and H I absorption in the intergalactic medium (IGM) at redshifts z = 2.3-2.9 toward HE 2347-4342, using spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Ultraviolet-Visual Echelle Spectrograph (UVES) on the VLT telescope. Following up on our earlier study (Kriss et al. 2001, Science, 293, 1112), we focus here on two major topics: (1) small-scale variability (Delta z = 10^-3) in the ratio eta = N(He II)/N(H I); and (2) an observed correlation of high-eta absorbers (soft radiation fields) with voids in the (H I) Ly-alpha distribution. These effects may reflect fluctuations in the ionizing sources on scales of 1 Mpc, together with radiative transfer through a filamentary IGM whose opacity variations control the penetration of 1-5 ryd radiation over 30-40 Mpc distances. Owing to photon statistics and backgrounds, we can measure optical depths over the ranges 0.1 < tau(HeII) < 2.3 and 0.02 < tau(HI) < 3.9, and reliably determine values of eta = 4 tau(HeII)/tau(HI) over the range 0.1 to 460. Values of eta = 20-200 are consistent with models of photoionization by quasars with observed spectral indices alpha_s = 0-3. Values of eta > 200 may require additional contributions from starburst galaxies, heavily filtered quasar radiation, or density variations. Regions with eta < 30 may indicate the presence of local hard sources. We find that eta is higher in "void" regions, where H I is weak or undetected and 80% of the path length has eta > 100. These voids may be ionized by soft sources (dwarf starbursts) or by QSO radiation softened by escape from the AGN cores or transfer through the "cosmic web". The apparent differences in ionizing spectra may help to explain the 1.45 Gyr lag between the reionization epochs, z(HI) = 6.2 +/-0.2 and z(HeII) = 2.8 +/-0.2.Comment: 27 pages, 7 figures, to appear in Ap

STUDIES ON ANEMIA IN F1 HYBRID MICE INJECTED WITH PARENTAL STRAIN LYMPHOID CELLS

The survival of 51Cr-labeled erythrocytes has been studied in F1 hybrid mice in which wasting disease was produced by injection of parental lymphoid cells taken either from lymph nodes and thymus or from the spleen. Coincident with the development of the disease syndrome, there occurred a severe anemia accompanied by a sudden loss of circulating labeled erythrocytes, whether host or parental. This finding suggests that the anemia is not due solely to specific immunologic reaction of donor tissue against host erythrocytes

On the Significance of Absorption Features in HST/COS Data

We present empirical scaling relations for the significance of absorption features detected in medium resolution, far-UV spectra obtained with the Cosmic Origins Spectrograph (COS). These relations properly account for both the extended wings of the COS line spread function and the non-Poissonian noise properties of the data, which we characterize for the first time, and predict limiting equivalent widths that deviate from the empirical behavior by \leq 5% when the wavelength and Doppler parameter are in the ranges \lambda = 1150-1750 A and b > 10 km/s. We have tested a number of coaddition algorithms and find the noise properties of individual exposures to be closer to the Poissonian ideal than coadded data in all cases. For unresolved absorption lines, limiting equivalent widths for coadded data are 6% larger than limiting equivalent widths derived from individual exposures with the same signal-to-noise. This ratio scales with b-value for resolved absorption lines, with coadded data having a limiting equivalent width that is 25% larger than individual exposures when b \approx 150 km/s.Comment: 25 pages, 3 tables, 7 figures, accepted for publication in PAS

Associated Absorption Lines in the Radio-Loud Quasar 3C 351: Far-Ultraviolet Echelle Spectroscopy from the Hubble Space Telescope

As one of the most luminous radio-loud quasars showing intrinsic ultraviolet (UV) and X-ray absorption, 3C 351 provides a laboratory for studying the kinematics and physical conditions of such ionized absorbers. We present an analysis of the intrinsic absorption lines in the high-resolution ($\sim$ 7 km/s) far-UV spectrum which was obtained from observations with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). The spectrum spans wavelengths from 1150 \AA to 1710 \AA, and shows strong emission lines from O VI and Ly$\alpha$. Associated absorption lines are present on the blue wings of the high-ionization emission doublets O VI $\lambda\lambda$ 1032,1038 and N V $\lambda\lambda$ 1238,1242, as well as the Lyman lines through Ly$\epsilon$. These intrinsic absorption features are resolved into several distinct kinematic components, covering rest-frame velocities from -40 to -2800 km/s, with respect to the systemic redshift of $z_{em}=0.3721$. For the majority of these absorption line regions, strong evidence of partial covering of both the background continuum source and the BELR is found, which supports the intrinsic absorption origin and rules out the possibility that the absorption arises in some associated cluster of galaxies. The relationship between the far-UV absorbers and X-ray `warm' absorbers are studied with the assistance of photoionization models. Most of the UV associated absorption components have low values of the ionization parameter and total hydrogen column densities, which is inconsistent with previous claims that the UV and X-ray absorption arises in the same material. Analysis of these components supports a picture with a wide range of ionization parameters, temperatures, and column densities in AGN outflows.Comment: 27 pages with 5 figures, accepted by Ap

HUT observations of carbon monoxide in the coma of Comet Levy (1990c)

Observations of comet Levy (1990c) were made with the Hopkins Ultraviolet Telescope during the Astro-1 Space Shuttle mission on 10 Dec. 1990. The spectrum, covering the wavelength range 415 to 1850 A at a spectral emission of 3 A (in first order), shows the presence of carbon monoxide and atomic hydrogen, carbon, and sulfur in the coma. Aside from H I Lyman-beta, no cometary features are detected below 1200 A, although cometary O I and O II would be masked by the same emissions present in the day airglow spectrum. The 9.4 x 116 arcsec aperture corresponds to 12,000 x 148,000 km at the comet. The derived production rate of CO relative to water, 0.13 + or - 0.02, compared with the same ratio derived from IUE observations (made in Sep. 1990) which sample a much smaller region of the coma, 0.04 + or - 0.01, suggests the presence of an extended source of CO, as was found in comet Halley. Upper limits on Ne and Ar abundance are within an order of magnitude or solar abundances

A Composite HST Spectrum of Quasars

We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z > 0.33. The spectrum covers the wavelengths between 350 and 3000 A in the rest frame. There is a significant steepening of the continuum slope around 1050 A. The continuum between 1050 and 2200 A can be modeled as a power law with alpha = -0.99. For the full sample the power-law index in the extreme ultraviolet (EUV) between 350 and 1050 A is alpha = -1.96. The continuum flux in the wavelengths near the Lyman limit shows a depression of about 10 percent. The break in the power-law index and the slight depression of the continuum near the Lyman limit are features expected in Comptonized accretion-disk spectra.Comment: 10 figures To appear in the February 1, 1997, issue of the Ap.

Multiwavelength campaign on Mrk 509 XII. Broad band spectral analysis

(Abridged) The simultaneous UV to X-rays/gamma rays data obtained during the multi-wavelength XMM/INTEGRAL campaign on the Seyfert 1 Mrk 509 are used in this paper and tested against physically motivated broad band models. Each observation has been fitted with a realistic thermal comptonisation model for the continuum emission. Prompted by the correlation between the UV and soft X-ray flux, we use a thermal comptonisation component for the soft X-ray excess. The UV to X-rays/gamma-rays emission of Mrk 509 can be well fitted by these components. The presence of a relatively hard high-energy spectrum points to the existence of a hot (kT~100 keV), optically-thin (tau~0.5) corona producing the primary continuum. On the contrary, the soft X-ray component requires a warm (kT~1 keV), optically-thick (tau~15) plasma. Estimates of the amplification ratio for this warm plasma support a configuration close to the "theoretical" configuration of a slab corona above a passive disk. An interesting consequence is the weak luminosity-dependence of its emission, a possible explanation of the roughly constant spectral shape of the soft X-ray excess seen in AGNs. The temperature (~ 3 eV) and flux of the soft-photon field entering and cooling the warm plasma suggests that it covers the accretion disk down to a transition radius $R_{tr}$ of 10-20 $R_g$. This plasma could be the warm upper layer of the accretion disk. On the contrary the hot corona has a more photon-starved geometry. The high temperature ($\sim$ 100 eV) of the soft-photon field entering and cooling it favors a localization of the hot corona in the inner flow. This soft-photon field could be part of the comptonised emission produced by the warm plasma. In this framework, the change in the geometry (i.e. $R_{tr}$) could explain most of the observed flux and spectral variability.Comment: 19 pages, 14 figures. Accepted for publication in A&