THE He II POST-REIONIZATION EPOCH:<i>HST</i>/COS OBSERVATIONS OF THE QUASAR HS1700+6416

Syphers, David; Shull, J. M.

doi:10.1088/0004-637x/765/2/119

Cited by 35 publications

(93 citation statements)

References 65 publications

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“…They detect the proximity effect for at least one other foreground quasar which sets a lower lifetime limit of 17 Myr. Syphers & Shull (2014) claim a transverse proximity effect for another quasar 34 Mly away from the Q 0302−003 sightline, but this case is degenerate with the proximity effect of Q 0302−003 itself. In the limited sample of He ii spectra and foreground quasars Furlanetto & Lidz (2011) see indications against very long (t Q > 10 8 yr) and very short (t Q < 3 × 10 6 yr) quasar lifetimes, by simply counting He ii transmission spikes under the assumption that they are associated with foreground quasars.…”

Section: Introductionmentioning

confidence: 88%

“…Almost all spectra (20/22) have been taken with the HST /COS G140L grating (R = λ/∆λ ∼ 2000 at 1150Å, 0.24Å per Nyquist-binned pixel). Their signal-to-noise ratio per binned pixel at He ii Lyα of the background quasar varies between 2 and 15, mostly depending on whether the sightline was known before to be He ii-transparent (Shull et al 2010;Syphers & Shull 2013Zheng et al 2015), or had been discovered in recent HST /COS surveys Syphers et al 2012;Worseck et al 2016). The sightline to HS 1157+3143 was observed with the HST /STIS G140L grating (R ∼ 1000, 0.6Å pixel −1 ; Reimers et al 2005).…”

Section: He II Sightlinesmentioning

confidence: 99%

“…The sightline to HS 1157+3143 was observed with the HST /STIS G140L grating (R ∼ 1000, 0.6Å pixel −1 ; Reimers et al 2005). For the Q 0302−003 sightline we used the higher-quality HST /COS G130M data (R ≈ 18, 000, 0.03Å per Nyquist-binned pixel; Syphers & Shull 2014) instead of the HST /STIS data presented in Worseck et al (2016). We checked our reduction by comparing the measured He ii effective optical depths in the Q 0302−003 sightline to those presented by Syphers & Shull (2014), finding very good agreement.…”

Section: He II Sightlinesmentioning

confidence: 99%

“…Zheng et al 2015). By excluding the entire background quasar proximity zone we may have excluded the transverse proximity zones of foreground quasars at similar redshifts (Worseck & Wisotzki 2006;Syphers & Shull 2014), but as these cases are degenerate and therefore require detailed modeling we make sure that our sample is not affected by any background quasar proximity zone.…”

Section: He II Sightlinesmentioning

confidence: 99%

“…, the z > 2 He ii Lyα absorption is observable from space with far UV (FUV) spectrographs. Over the last two decades the Hubble Space Telescope (HST ) has obtained He ii Lyα spectra for a limited number of He ii-transparent quasars (Jakobsen et al 1994;Reimers et al 1997;Heap et al 2000;Shull et al 2010;Syphers & Shull 2013Zheng et al 2015;Worseck et al 2016). Many of these exhibit prominent line-of-sight proximity effects which itself sets a constraint on the quasar lifetime, similar to the hydrogen case (Khrykin et al 2016b).…”

Section: Introductionmentioning

confidence: 99%

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Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Schmidt

Worseck

Prochaska

et al. 2017

ApJ

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The He ii transverse proximity effect -enhanced He ii Lyα transmission in a background sightline caused by the ionizing radiation of a foreground quasar -offers a unique opportunity to probe the morphology of quasar-driven He ii reionization. We conduct a comprehensive spectroscopic survey to find z ∼ 3 quasars in the foreground of 22 background quasar sightlines with HST /COS He ii Lyα transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred He ii photoionization rates greater than the expected UV background at these redshifts (Γ HeII QSO > 5 × 10 −16 s −1 ) we perform the first statistical analysis of the He ii transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest Γ HeII QSO only one (previously known) quasar is associated with a significant He ii transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average He ii transmission near the foreground quasars at 3σ significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on Γ HeII QSO . Our detection places a purely geometrical lower limit on the quasar lifetime of t Q > 25 Myr. Improved modeling would additionally constrain quasar obscuration and the mean free path of He ii-ionizing photons.

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Section: Introductionmentioning

confidence: 88%

Section: He II Sightlinesmentioning

confidence: 99%

Section: He II Sightlinesmentioning

confidence: 99%

Section: He II Sightlinesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Schmidt

Worseck

Prochaska

et al. 2017

ApJ

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Measurement of the primordial helium abundance from the intergalactic medium

Cooke

Fumagalli

2018

Nat Astron

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Almost every helium atom in the Universe was created just a few minutes after the Big Bang through a process commonly referred to as Big Bang Nucleosynthesis 1, 2 .The amount of helium that was made during Big Bang Nucleosynthesis is determined by the combination of particle physics and cosmology 3 . The current leading measures of the primordial helium abundance (Y P ) are based on the relative strengths of H I and He I emission lines emanating from star-forming regions in local metal-poor galaxies 4-7 . As the statistical errors on these measurements improve, it is essential to test for systematics by developing independent techniques. Here we report the first determination of the primordial helium abundance based on a near-pristine intergalactic gas cloud that is seen in absorption against the light of a background quasar. This gas cloud, observed when the Universe was just one-third of its present age (z abs = 1.724), has a metal content ∼ 100 times less than the Sun, and 30% less metals than the most metal-poor H II region currently known where a determination of the primordial helium abundance is afforded. We conclude that the helium abundance of this intergalactic gas cloud is Y = 0.250 +0.033 −0.025 , which agrees with the Standard Model primordial value 8-10 , Y P = 0.24672 ± 0.00017. Our determination 1 arXiv:1810.06561v1 [astro-ph.CO]

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On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613

Tramper

Gräfener

Hartoog

et al. 2013

A&A

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Context. Oxygen sequence Wolf-Rayet (WO) stars are thought to represent the final evolutionary stage of the most massive stars. The characteristic strong O  emission possibly originates from an enhanced oxygen abundance in the stellar wind. Alternatively, the O  emission can be caused by the high temperature of these stars, in which case the WO stars are the high-temperature extension of the more common carbon sequence Wolf-Rayet (WC) stars. Aims. By constraining the physical properties and evolutionary status of DR1, a WO star in the low-metallicity Local Group dwarf galaxy IC 1613 and one of only two objects of its class known in a SMC-like metallicity environment, we aim to investigate the nature of WO stars and their evolutionary connection with WC stars. Methods. We use the non-local thermodynamic equilibrium atmosphere code  to model the observed spectrum of DR1 and to derive its stellar and wind parameters. We compare our values with other studies of WC and WO stars, as well as with the predictions of evolutionary models. We also model the surrounding nebula using the photo-ionization code . Results. The oxygen and carbon abundances that we obtain are comparable to values found for WC stars. The temperature and luminosity are, however, higher than those of WC stars. DR1 is embedded in the hottest known H  region in the Local Group. The nebular properties can be consistently reproduced by  models adopting DR1 as central ionizing source. Conclusions. Comparison of the abundances and temperature of DR1 with core helium-burning models show that DR1 is currently well into the second half of helium burning. If the properties of DR1 are representative for the WO class, it would imply that WO stars are the high-temperature and high-luminosity extension of the WC stars, and do not necessarily represent a later evolutionary stage.

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THE He II POST-REIONIZATION EPOCH:HST/COS OBSERVATIONS OF THE QUASAR HS1700+6416

Cited by 35 publications

References 65 publications

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Statistical Detection of the He ii Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

Measurement of the primordial helium abundance from the intergalactic medium

On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613

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