A Cluster of Low-Redshift Lyman-alpha Clouds toward PKS 2155-304. I. Limits on Metals and D/H

Abstract

We report observations from the Hubble Space Telescope (HST) and the VLA on the galactic environment, metallicity, and D/H in strong low-redshift Lya absorption systems toward the bright BL Lac object PKS 2155-304. GHRS/G160M spectra at 20 km/s resolution show 14 Lya absorbers, 6 clustered at cz = 16,100-18,500 km/s. ORFEUS claimed LyC absorption at z = 0.056 with N(HI) = (2-5)x10^16 cm^-2, while our Lya data suggest N(HI) = (3-10)x10^14 cm^-2. Higher columns are possible if the Lya line core at 17,000 +/- 50 km/s contains narrow HI components. We identify the Lya cluster with a group of five HI galaxies offset by 400-800 kpc from the sightline. The two strongest absorption features cover the same velocity range as the HI emission in the two galaxies closest to the line of sight. If the Lya is associated with these galaxies, they must have huge halos of highly turbulent, mostly ionized gas. The Lya absorption could also arise from an extended sheet of intragroup gas, or from smaller primordial clouds and halos of dwarf galaxies. We see no absorption from SiIII 1206, CIV 1548, or DI Lya. Photoionization models yield limits of (Si/H) < 0.003 solar, (C/H) < 0.005 solar, (D/H) < 2.8x10^-4 (4 sigma) if N(HI) = 2x10^16 cm^-2. The limits increase to 0.023 solar and D/H < 2.8x10^-3 if N(HI) = 2x10^15 cm^-2. The data suggest that the IGM in this group has not been enriched to the levels suggested by X-ray studies of intracluster gas and that these absorbers could be primordial gas clouds.

34 pages LATEX, 8 figures (.ps), accepted for Astron. J. Vol. 116, Nov. 1998

References in corpus (4)

• The Properties of Poor Groups of Galaxies: I. Spectroscopic Survey and Results
• The Properties of Poor Groups of Galaxies: II. X-ray and Optical Comparisons
• The Gaseous Extent of Galaxies and the Origin of \lya Absorption Systems. III. Hubble Space Telescope Imaging of \lya-Absorbing Galaxies at z < 1
• ORFEUS-II Far-Ultraviolet Observations of 3C273: 1. Interstellar and Intergalactic Absorption Lines

Cited by in corpus (38)

• The Nature of High-Redshift Galaxies
• The Baryon Census in a Multiphase Intergalactic Medium: 30% of the Baryons May Still Be Missing
• A High-Resolution Survey of Low-Redshift QSO Absorption Lines: Statistics and Physical Conditions of O VI Absorbers
• The Local Ly-alpha Forest IV: STIS G140M Spectra and Results on the Distribution and Baryon Content of HI Absorbers
• Chandra Detection of OVIII Ly-alpha Absorption from an Overdense Region in the Intergalactic Medium
• The Galaxy Environment of O VI Absorption Systems
• The Local Lya Forest. III. Relationship between Lya Absorbers and Galaxies, Voids and Superclusters
• The Local Lyman-alpha Forest. II: Distribution of HI Absorbers, Doppler Widths, and Baryon Content
• The Ionization and Metallicity of the Intervening O VI Absorber at z = 0.1212 in the Spectrum of H1821+643
• Confirmation of X-Ray Absorption by WHIM in the Sculptor Wall
• Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy: II. Methods and Models
• The Low-z Intergalactic Medium. II. LyB, OVI, and CIII Forest
• Absorption-Line Detections of $10^{5-6}$ K Gas in Spiral-Rich Groups of Galaxies
• The Local Lyman-alpha Forest. I: Observations with the GHRS/G160M on the Hubble Space Telescope
• The Multiphase Intergalactic Medium towards PKS 2155-304
• FUV and X-ray absorption in the Warm-Hot Intergalactic Medium
• High Metallicity, Photoionised Gas in Intergalactic Large-Scale Filaments
• Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304
• Quenched Cold Accretion of a Large Scale Metal-Poor Filament due to Virial Shocking in the Halo of a Massive z=0.7 Galaxy
• Missing baryons traced by the galaxy luminosity density in the large-scale WHIM filaments
• Chandra and Far Ultraviolet Spectroscopic Explorer Observations of z~0 Warm-Hot Gas Toward PKS 2155-304
• OVI, NV and CIV in the Galactic Halo: II. Velocity-Resolved Observations with Hubble and FUSE
• Chemical Abundance Constraints on White Dwarfs as Halo Dark Matter
• Detecting the warm-hot intergalactic medium through X-ray absorption lines
• The Local Lyman-Alpha Forest: Absorbers in Galaxy Voids
• The Impact of the Group Environment on the OVI Circumgalactic Medium
• Probing the Size of Low-Redshift Lyman-alpha Absorbers
• Evidence for Large Scale Structure in the Lyman alpha Forest at z>2.6
• A view of PKS 2155-304 with XMM-Newton Reflection Grating Spectrometers
• X-raying the Intergalactic OVI Absorbers
• Absorption Line Signatures of Gas in Mini Dark Matter Halos
• To be or not to be: hot WHIM absorption in the blazar PKS 2155-304 sight line?
• Probing Halos of Galaxies at Very Large Radii using Background QSOs
• Discovery of a Metal-Line Absorber Associated with a Local Dwarf Starburst Galaxy
• The evolution of chaos in active galaxy models with an oblate or a prolate dark halo component
• The Low-Redshift Intergalactic Medium
• The gaseous extent of galaxies and the origin of Lyman alpha absorption systems. IV: Lyman alpha absorbers arising in a galaxy group
• Chandra Detection of X-ray Absorption from Local Warm/Hot Gas