STIS Observations of He<scp>ii</scp>Gunn‐Peterson Absorption toward Q0302−003

Heap, Sara R.; Williger, G. M.; Smette, A.; Hubený, I.; Sahu, M. S.; Jenkins, Edward B.; Tripp, Todd M.; Winkler, Jonathan N.

doi:10.1086/308719

Cited by 144 publications

(274 citation statements)

References 42 publications

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“…The total energy output of QSOs can be obtained by integrating the emissivity over the history of the universe. If we define " B ðzÞ ¼ B " B ð B ; zÞ and B ¼ c=4400 Å , then we The rapid rise at z $ 3 for model A is qualitatively similar to that reported by Heap et al (2000). 15 In writing this paper, we explored another idea for separating the relative galaxy/AGN contribution to the background.…”

Section: Agn Characteristicssupporting

confidence: 76%

“…At z $ 2:5, the implied optical depth to He ii absorption is low enough that the background at these redshifts should be QSO dominated (Davidson, Kriss, & Wei 1996). However, at slightly higher redshifts, Heap et al (2000) appear to detect a GunnPeterson trough blueward of helium Ly in the spectra of Q0302À003. They conclude that the ratio of hydrogen to helium ionization rates rises abruptly at z % 3 to À H i =À He ii ' 800, suggesting that a soft stellar contribution is beginning to dominate the hard ionizing spectrum of AGNs at this epoch.…”

Section: Ionizing Sourcesmentioning

confidence: 92%

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Faint Active Galactic Nuclei and the Ionizing Background

Schirber

Bullock

2003

ApJ

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We determine the evolution of the faint, high-redshift, optical luminosity function (LF) of active galactic nuclei (AGNs) implied by several observationally motivated models of the ionizing background from 3 < z < 5. Our results depend crucially on whether we use the total ionizing rate measured by the proximity effect technique or the lower determination favored by the flux decrement distribution of Ly forest lines. Assuming a faint-end LF slope of 1.58 and the SDSS estimates of the bright-end slope and normalization, we find that the LF must break at M Ã B ¼ À24:2, À22.3, À20.8 at z ¼ 3, 4, 5 if we adopt the lower ionization rate and assume no stellar contribution to the background. The breaks must occur at M Ã B ¼ À20:6, À18.7, À18.7 for the proximity effect estimate. Since stars may also contribute to the background, these values are lower limits on the break luminosity, and they brighten by as much as $2 mag if the escape fraction of ionizing photons from high-z galaxies is consistent with recent estimates: f esc ¼ 0:16. By comparing our expectations to faint AGN searches in the Hubble Deep Field and high-z galaxy fields, we find that typically quoted proximity effect estimates of the background imply an overabundance of AGNs compared to the faint counts (even with f esc ¼ 1). Even adopting the lower bound on proximity effect measurements, the stellar escape fraction must be high: f esc e0:2. Conversely, the lower flux decrement-derived background requires a smaller number of ionizing sources, and faint AGN counts are consistent with this estimate only if there is a limited stellar contribution, f esc d0:05. Our derived LFs together with the locally estimated black hole density suggest that the efficiency of converting mass to light in optically unobscured AGNs is somewhat lower than expected, d0:05 (all models). Comparison with similar estimates based on X-ray counts suggests that more than half of all AGNs are obscured in the UV/optical. We also derive lower limits on typical AGN lifetimes and obtain e10 7 yr for favored cases.

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Section: Agn Characteristicssupporting

confidence: 76%

Section: Ionizing Sourcesmentioning

confidence: 92%

Faint Active Galactic Nuclei and the Ionizing Background

Schirber

Bullock

2003

ApJ

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“…Comparison of both H i and He ii absorption in QSO spectra can be used to constrain the relative contribution of massive stars and QSOs to the metagalactic flux. While in three out of four of the observed QSO spectra with an He ii Lya forest the interpretation is made difficult by the large fluctuations measured in the He ii scattering opacity-perhaps the signature of a delayed reionization at (see, He ii r He iii z տ 3 e.g., Reimers et al 1997 andHeap et al 2000)-the spectrum of HS 1700ϩ64 at somewhat lower redshifts ( ; 2.4 ! z !…”

Section: The Uv Escape Fraction Of Galaxies and The Redshift Evolutiomentioning

confidence: 98%

An Ionizing Ultraviolet Background Dominated by Massive Stars

Haehnelt

Madau

Kudritzki

et al. 2001

The Astrophysical Journal

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We discuss the implications of a stellar-dominated UV background at high redshifts for the star formation history of Lyman break galaxies (LBGs) and the thermal and ionization state of the intergalactic medium (IGM). The composite spectrum of 29 LBGs evaluated by Steidel et al. at can be well fitted by a stellar AzS p 3.4 population with ongoing star formation, a Salpeter initial mass function, modest or negligible dust reddening, and no intrinsic H i photoelectric absorption. Fading starbursts in which star formation has ceased for 10 7 yr or more cannot reproduce the observed flux shortward of 1 ryd. The small H i optical depth in LBGs suggests that the neutral gas from which stars form is most likely contained in compact clouds of neutral gas with small covering factor. The escape fraction of H-ionizing photons must be close to 100% for the observed sample of LBGs. The spectrum of ionizing photons produced by a stellar population with ongoing star formation is similar to that of QSOs between 1 and 3 ryd but becomes softer between 3 and 4 ryd and drops sharply shortward of 4 ryd. A galaxy-dominated UV background appears inconsistent with the observed He ii/H i opacity ratio at but might be able to explain the Si iv/C iv abundances measured at in QSO absorption spectra. z p 2.4 z 1 3 A scenario may be emerging where star-forming galaxies reionize intergalactic hydrogen at and dominate z 1 6 the 1 ryd metagalactic flux at , with quasi-stellar sources taking over at lower redshifts. If the large amplitude z 1 3 of the H-ionizing flux estimated by Steidel et al. is correct, hydrodynamical simulations of structure formation in the IGM within the cold dark matter paradigm require a baryon density (to explain the observed opacity of the Lya forest in QSO absorption spectra) that is similar to or larger than that favored by recent cosmic microwave background experiments and is inconsistent with standard nucleosynthesis values.

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“…There are different ways to produce a void in the forest: a large fluctuation in the gas density of absorbers, enhanced UV ionizing radiation from nearby faint QSOs or star-forming galaxies, feedback processes (including shock heating) from galaxy formation (Dobrzycki & Bechtold 1991;Heap et al 2000;Theuns et al 2000a). We recall here that the void B in the spectrum of HE 2217-2818 corresponds to a region of above-average Doppler parameter (Sect.…”

Section: Voidsmentioning

confidence: 99%

The Lyαforest at $\mathsf{1.5 < {\vec z} < 4}$

Kim¹,

Cristiani

D’Odorico³

2001

A&A

119

191

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Abstract. Using high resolution (R ∼ 45 000), high S/N (∼20-50) VLT/UVES data, we have analyzed the Lyα forest of 3 QSOs in the neutral hydrogen (H i) column density range NH i = 10 12.5−16 cm −2 at 1.5 < z < 2.4. We combined our results with similar high-resolution, high S/N data in the literature at z > 2.4 to study the redshift evolution of the Lyα forest at 1.5 < z < 4. We have applied two types of analysis: the traditional Voigt profile fitting and statistics on the transmitted flux. The results from both analyses are in good agreement: 1. The differential column density distribution function, f (NH i), of the Lyα forest shows little evolution in the column density range NH i = 10 12.5−14 cm −2 , f (NH i) ∝ N −β H i , with β ∼ 1.4-1.5 at 1.5 < z < 4 and with a possible increase of β to β ∼ 1.7 at z < 1.8. A flattening of the power law slope at lower column densities at higher z can be attributed to more severe line blending. A deficiency of lines with NH i > 10 14 cm −2 is more noticeable at lower z than at higher z. The one-point function and the two-point function of the flux confirm that strong lines do evolve faster than weak lines; 2. The line number density per unit redshift, dn/dz, at NH i = 10 13.64−16 cm −2 is well fitted by a single power law, dn/dz ∝ (1 + z) 2.19±0.27 , at 1.5 < z < 4. In combination with the HST results from the HST QSO absorption line key project, the present data indicate that a flattening in the number density evolution occurs at z ∼ 1.2. The line counts as a function of the filling factor at the transmitted flux F in the range 0 < F < 0.9 are constant in the interval 1.5 < z < 4. This suggests that the Hubble expansion is the main drive governing the forest evolution at z > 1.5 and that the metagalactic UV background changes more slowly than a QSO-dominated background at z < 2; 3. The observed cutoff Doppler parameter at the fixed column density NH i = 10 13.5 cm −2 , bc,13.5, shows a weak increase with decreasing z, with a possible local bc,13.5 maximum at z ∼ 2.9; 4. The two-point velocity correlation function and the step optical depth correlation function show that the clustering strength increases as z decreases; 5. The evolution of the mean H i opacity, τ H i, is well approximated by an empirical power law, τ H i ∝ (1+z) 3.34±0.17 , at 1.5 < z < 4; 6. The baryon density, Ω b , derived both from the mean H i opacity and from the one-point function of the flux is consistent with the hypothesis that most baryons (over 90%) reside in the forest at 1.5 < z < 4, with little change in the contribution to the density, Ω, as a function of z.

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STIS Observations of HeiiGunn‐Peterson Absorption toward Q0302−003

Cited by 144 publications

References 42 publications

Faint Active Galactic Nuclei and the Ionizing Background

Faint Active Galactic Nuclei and the Ionizing Background

An Ionizing Ultraviolet Background Dominated by Massive Stars

The Lyαforest at $\mathsf{1.5 < {\vec z} < 4}$

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