The Local Lyman-alpha Forest. I: Observations with the GHRS/G160M on the Hubble Space Telescope

Abstract

We present the target selection, observations, and data reduction and analysis process for a program aimed at discovering numerous, weak (equivalent width < 100 mA) Lya absorption lines in the local Universe (0.003 < z < 0.069). The purpose of this program is to study the physical conditions of the local intergalactic medium, including absorber distributions in Doppler width and H I column density, absorber number density and evolution with redshift, line-of-sight two-point correlation function, and the baryonic content and metallicity. By making use of large-angle, nearby galaxy redshift surveys, we will investigate the relationship (if any) between these Lya absorbers and galaxies, superclusters and voids. In Paper I, we present high resolution (~19 km/s) spectroscopic observations of 15 very bright (V < 14.5) AGN targets made with the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST). We find 81 definite (> 4 sigma) and 30 possible (3-4 sigma) Lya absorption lines in these spectra, which probe a total pathlength of 116,000 km/s (delta z ~ 0.4) at very low redshift (z < 0.069) and column density (12.5< Log[Nh] < 14.5). We found numerous metal lines arising in the Milky Way halo, including absorption from 14 distinct high velocity clouds and numerous absorptions intrinsic to the target AGN. Here, we describe the details of the target selection, HST observations, and spectral reduction and analysis. We present reduced spectra and absorption line lists and ``pie diagrams'' showing the known galaxy distributions in the direction of each target. In Papers II and III, we use the data presented here to determine the basic physical characteristics of the low-z Lya forest and to investigate the relationship of the absorbers to the local galaxy distribution.

98 pages, 10 tables, 35 figures, To Appear in ApJS (Sep 2000) The continuum fits near Ly-alpha emission features are greatly improved, resulting in changes to the line lists and tables

References in corpus (5)

• The Metagalactic Ionizing Radiation Field at Low Redshift
• The Local Lyman-alpha Forest. II: Distribution of HI Absorbers, Doppler Widths, and Baryon Content
• Metal Abundances in the Magellanic Stream
• FUSE Observations of the Galactic and Intergalactic Medium Towards H1821+643
• FUSE Observations of Intrinsic Absorption in the Seyfert 1 Galaxy Mrk 509

Cited by in corpus (50)

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• Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy
• Intervening O VI Quasar Absorption Systems at Low Redshift: A Significant Baryon Reservoir
• The Low-z Intergalactic Medium. III. HI and Metal Absorbers at z<0.4
• Chandra Discovery of a Tree in the X-ray Forest towards PKS 2155-304: the Local Filament?
• An HST/COS Survey of the Low-Redshift IGM. I. Survey, Methodology, & Overall Results
• The Local Ly-alpha Forest IV: STIS G140M Spectra and Results on the Distribution and Baryon Content of HI Absorbers
• An OVI Baryon Census of the Low-z Warm-Hot Intergalactic Medium
• Chandra Detection of the First X-ray Forest along the Line of Sight To Mkn 421
• Highly Ionized Gas Surrounding High Velocity Cloud Complex C
• The Galaxy Environment of O VI Absorption Systems
• The Local Lya Forest. III. Relationship between Lya Absorbers and Galaxies, Voids and Superclusters
• The Relationship Between Intergalactic HI/OVI and Nearby (z<0.017) Galaxies
• Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption Toward 3C 273
• Probing the Local Group Medium Toward Mkn 421 with Chandra and FUSE
• High-Velocity Cloud Complex C: Galactic Fuel or galactic Waste?
• The Low-z Intergalactic Medium. II. LyB, OVI, and CIII Forest
• The Heavy Element Enrichment of Lyman alpha Clouds in the Virgo Supercluster
• A Uniform Analysis of the Ly-alpha Forest at z=0 - 5: V. The extragalactic ionizing background at low redshift
• Does the Milky Way Produce a Nuclear Galactic Wind?
• Enrichment of the Intergalactic Medium by Radiation Pressure Driven Dust Efflux
• Continuous statistics of the Lyman-alpha forest at 0 < z < 1.6: the mean flux, flux distribution, and autocorrelation from HST FOS spectra
• Warm Gas in the Virgo Cluster: I. Distribution of Lya Absorbers
• HST/COS Spectra of Three QSOs That Probe The Circumgalactic Medium of a Single Spiral Galaxy: Evidence for Gas Recycling and Outflow
• Discovery of a Dwarf Post-Starburst Galaxy Near a High Column Density Ly-alpha Absorber
• Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304
• Intrinsic Absorption in the Spectrum of Mrk 279: Simultaneous Chandra, FUSE, and STIS Observations
• OVI, NV and CIV in the Galactic Halo: II. Velocity-Resolved Observations with Hubble and FUSE
• Multiwavelength campaign on Mrk 509. VI. HST/COS observations of the far-ultraviolet spectrum
• The Local Lyman-Alpha Forest: Absorbers in Galaxy Voids
• An Intrinsic Absorption Complex Toward RXJ1230.8+0115: Geometry and Photoionization Conditions
• Probing the Size of Low-Redshift Lyman-alpha Absorbers
• The Influence of Environment on the Circumgalactic Medium
• The Metallicity of Intergalactic Gas in Cosmic Voids
• The association between gas and galaxies I: CFHT spectroscopy and pair analysis
• Broad Ly alpha Emission from Three Nearby BL Lacertae Objects
• Warm Gas in and Around Simulated Galaxy Clusters as Probed by Absorption Lines
• Ultraviolet and X-ray Variability of the Seyfert 1.5 Galaxy Markarian 817
• Predicted Sizes of Pressure-Supported HI Clouds in the Outskirts of the Virgo Cluster
• The low redshift Lyman-$\alpha$ Forest as a constraint for models of AGN feedback
• The Search for Intergalactic Hydrogen Clouds in Voids
• Searching for the Intra-Group Medium in Loose Groups of Galaxies
• Chandra and XMM-Newton view of the Warm Absorbing Gas in Mrk 290
• ELUCID VII: Using Constrained Hydro Simulations to Explore the Gas Component of the Cosmic Web
• Comparing Simulations and Observations of the Lyman-Alpha Forest I. Methodology
• Measured Cosmological Mass Density in the WHIM: the Solution to the 'Missing Baryons' Problem
• Modeling the Void H I Column Density Spectrum
• The Nature and Origin of the Non-Void Lyman alpha Cloud Population