Statistical detection of the heII transverse proximity effect: evidence for sustained quasar activity for $>$25 million years
The HeII transverse proximity effect -- enhanced HeII Ly$\alpha$~transmission in a background sightline caused by the ionizing radiation of a foreground quasar -- offers a unique opportunity to probe the morphology of quasar-driven HeII reionization. We conduct a comprehensive spectroscopic survey t...
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| Main Author: | |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
February 1, 2017
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| In: |
The astrophysical journal
Year: 2017, Volume: 847, Issue: 1 |
| ISSN: | 1538-4357 |
| DOI: | 10.3847/1538-4357/aa83ac |
| Online Access: | Verlag, kostenfrei, Volltext: http://dx.doi.org/10.3847/1538-4357/aa83ac Verlag, kostenfrei, Volltext: http://arxiv.org/abs/1701.08769 
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| Author Notes: | Tobias M. Schmidt, Gabor Worseck, Joseph F. Hennawi, J. Xavier Prochaska, Neil H.M. Crighton |
| Summary: | The HeII transverse proximity effect -- enhanced HeII Ly$\alpha$~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 HeII reionization. We conduct a comprehensive spectroscopic survey to find $z\sim3$ quasars in the foreground of 22 background quasar sightlines with HST/COS HeII Ly$\alpha$~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 HeII photoionization rates greater than the expected UV background at these redshifts ($\Gamma_\mathrm{QSO}^\mathrm{HeII} > 5 \times 10^{-16}\,\mathrm{s}^{-1}$) we perform the first statistical analysis of the HeII transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest $\Gamma_\mathrm{QSO}^\mathrm{HeII}$ only one (previously known) quasar is associated with a significant HeII transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average HeII transmission near the foreground quasars at $3\sigma$ significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on $\Gamma_\mathrm{QSO}^\mathrm{HeII}$. Our detection places a purely geometrical lower limit on the quasar lifetime of $t_\mathrm{Q} > 25\,\mathrm{Myr}$. Improved modeling would additionally constrain quasar obscuration and the mean free path of HeII-ionizing photons. |
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| Item Description: | Gesehen am 04.06.2018 |
| Physical Description: | Online Resource |
| ISSN: | 1538-4357 |
| DOI: | 10.3847/1538-4357/aa83ac |