A Uniform Analysis of the Ly-alpha Forest at z=0 - 5: V. The extragalactic ionizing background at low redshift

Abstract

In Paper III of our series "A Uniform Analysis of the Ly-alpha forest at z=0 - 5", we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph on the Hubble Space Telescope. A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J(ν_0), the mean intensity of the hydrogen-ionizing background radiation field, at low redshift. Using a maximum likelihood technique and the best estimates possible for each QSO's Lyman limit flux and systemic redshift, we find J(ν_0)= 7.6^+9.4_-3.0 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1 at at 0.03 < z < 1.67. This is in good agreement with the mean intensity expected from models of the background which incorporate only the known quasar population. When the sample is divided into two subsamples, consisting of lines with z < 1 and z > 1, the values of J(ν_0) found are 6.5^+38._-1.6 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1, and 1.0^+3.8_-0.2 x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1, respectively, indicating that the mean intensity of the background is evolving over the redshift range of this data set. Relaxing the assumption that the spectral shapes of the sample spectra and the background are identical, the best fit HI photoionization rates are found to be 6.7 x 10^-13 s^-1 for all redshifts, and 1.9 x 10^-13 s^-1 and 1.3 x 10^-12 s^-1 for z < 1 and z > 1, respectively. This work confirms that the evolution of the number density of Ly-alpha lines is driven by a decrease in the ionizing background from z ~ 2 to z ~ 0 as well as by the formation of structure in the intergalactic medium. (Abridged)

71 LaTeX pages, 20 encapsulated Postscript figures, Accepted for publication in ApJ, Figure 4 available at http://lithops.as.arizona.edu/~jill/QuasarSpectra/ or http://hea-www.harvard.edu/QEDT/QuasarSpectra/

References in corpus (9)

• The Rest-Frame Extreme Ultraviolet Spectral Properties of QSOs
• The Lyman-Alpha Forest at 1.5 < z < 4
• The Statistical and Physical Properties of the Low Redshift Lyman Alpha Forest Observed with HST/STIS
• A uniform analysis of the Lyman alpha forest at z = 0-5: III. HST FOS Spectral Atlas
• The contribution of galaxies to the UV ionising background and the evolution of the Lyman forest
• The proximity effect in a close group of QSOs
• A New Observational Upper Limit to the Low Redshift Ionizing Background Radiation
• Discovery of the Galaxy Proximity Effect and Implications for Measurements of the Ionizing Background Radiation at Low Redshifts
• A uniform analysis of the Lyman alpha forest at z = 0-5: IV. The clustering and evolution of clouds at z < 1.7

Cited by in corpus (55)

• Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ~ 6 Quasars II: A Sample of 19 Quasars
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Star formation thresholds and galaxy edges: why and where
• The galaxy stellar mass-star formation rate relation: Evidence for an evolving stellar initial mass function?
• New Constraints on the Lyman Continuum Escape Fraction at z~1.3
• Detection of dark galaxies and circum-galactic filaments fluorescently illuminated by a quasar at z=2.4
• Abundance Profiles and Kinematics of Damped Lyman-alpha Absorbing Galaxies at z < 0.65
• The intergalactic medium over the last 10 billion years I: Lyman alpha absorption and physical conditions
• The Photon Underproduction Crisis
• An unbiased measurement of the UV background and its evolution via the proximity effect in quasar spectra
• Cosmological parameters sigma_8, the baryon density, and the UV background intensity from a calibrated measurement of H I Lyman-alpha absorption at z = 1.9
• Imprint of Intergalactic Shocks on the Radio Sky
• The faint end of the QSO luminosity function at z=3
• Molecular Hydrogen in the Damped Ly alpha Absorber of Q1331+170
• The Baryon Content of Dark Matter Halos: Empirical Constraints from MgII Absorbers
• Escape fraction of ionizing photons from galaxies at z=0--6
• High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function
• A STIS Survey for OVI Absorption Systems at 0.12 < z < 0.5 II.: Physical Conditions of the Ionised Gas
• The Heavy Element Enrichment of Lyman alpha Clouds in the Virgo Supercluster
• The transverse proximity effect in the z ~ 2 Lyman-alpha forest suggests QSO episodic lifetimes of ~1 Myr
• On the importance of local sources of radiation for quasar absorption line systems
• On Star Formation and the Non-Existence of Dark Galaxies
• Highly Ionized Gas in the Galactic Halo and the High Velocity Clouds Toward PG 1116+215
• Hubble Space Telescope Observations of Sub-Damped Lyman-alpha Absorbers at z < 0.5, and Implications for Galaxy Chemical Evolution
• The Gas-Galaxy Connection at z = 0.35: OVI and HI Absorption Towards J0943+0531
• Continuous statistics of the Lyman-alpha forest at 0 < z < 1.6: the mean flux, flux distribution, and autocorrelation from HST FOS spectra
• HIDEEP - An extragalactic blind survey for very low column-density neutral hydrogen
• The Mysterious Absence of Neutral Hydrogen within One Mpc of a Luminous Quasar at Redshift 2.168
• The density structure around quasars from optical depth statistics
• Are Compact High-Velocity Clouds Extragalactic Objects?
• On the Nature of the Heat Source for Damped Lya Systems
• Molecular hydrogen in damped Ly-alpha systems: clues to interstellar physics at high-redshift
• Amount of intergalactic dust: constraints from distant supernovae and thermal history of intergalactic medium
• The Impact of Temperature Fluctuations on the Lyman-alpha Forest Power Spectrum
• The Kinematic Properties of the Extended Disks of Spiral Galaxies: A Sample of Edge-On Galaxies
• Searching for Intergalactic Shocks with the SKA
• The effect of stellar and AGN feedback on the low redshift Lyman-$\alpha$ forest in the Sherwood simulation suite
• The effects of an ionizing background on the HI column density distribution in the local Universe
• Galaxies at Redshift ~0.5 Around Three Closely Spaced Quasar Sightlines
• Molecular Hydrogen in Damped Ly-alpha Systems: Spatial Distribution
• Spectral shape of the UV ionizing background and OVI absorbers at z ~ 1.5 towards HS0747+4259
• A uniform analysis of the Lyman alpha forest at z = 0-5: IV. The clustering and evolution of clouds at z < 1.7
• A cold metal-poor cloud traced by a weak MgII absorption at z~0.45. First detection of SiI, CaI and FeI in a QSO absorber
• The relationship between gas and galaxies at z<1 using the Q0107 quasar triplet
• Statistical characteristics of observed Ly-$\alpha$ forest and the shape of initial power spectrum
• An HST/COS Observation of Broad Ly$\alpha$ Emission and Associated Absorption Lines of the BL Lacertae Object H 2356-309
• Statistical characteristics of observed Ly-$\alpha$ forest and the shape of linear power spectrum
• Cosmological radiative transfer for the line-of-sight proximity effect
• The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. I. Spectroscopy of QSO Pairs with Arcminute Separations and Similar Redshifts
• Fate of clumps in damped Ly$\alpha$ systems
• Thermodynamic evolution of the cosmological baryonic gas : II. Galaxy formation
• Galaxies as Fluctuations in the Ionizing Background Radiation at Low Redshift
• Evidence for overdensity around z_em > 4 quasars from the proximity effect
• Where has all the neutral hydrogen gone?
• The HI Detection of Low Column Density Clouds and Galaxies