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Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He-II reionisation at z~6 (2012)
Journal Article
S. Bolton, J., D. Becker, G., Raskutti, S., Stuart B. Wyithe, J., G. Haehnelt, M., & L. W. Sargent, W. (2012). Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He-II reionisation at z~6. Monthly Notices of the Royal Astronomical Society, 419(4), 2880–2892. https://doi.org/10.1111/j.1365-2966.2011.19929.x

We present measurements of the intergalactic medium (IGM) temperature within ~5 proper Mpc of seven luminous quasars at z~6. The constraints are obtained from the Doppler widths of Lyman-alpha absorption lines in the quasar near-zones and build upon... Read More about Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He-II reionisation at z~6.

How neutral is the intergalactic medium surrounding the redshift z=7.085 quasar ULAS J1120+0641? (2011)
Journal Article
S. Bolton, J., G. Haehnelt, M., J. Warren, S., C. Hewett, P., J. Mortlock, D., P. Venemans, B., …Simpson, C. (2011). How neutral is the intergalactic medium surrounding the redshift z=7.085 quasar ULAS J1120+0641?. Monthly Notices of the Royal Astronomical Society: Letters, 416(1), L70–L74. https://doi.org/10.1111/j.1745-3933.2011.01100.x

The quasar ULAS J1120+0641 at redshift z=7.085 has a highly ionised near zone which is smaller than those around quasars of similar luminosity at z~6. The spectrum also exhibits evidence for a damping wing extending redward of the systemic Lya redshi... Read More about How neutral is the intergalactic medium surrounding the redshift z=7.085 quasar ULAS J1120+0641?.

The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon (2011)
Journal Article
S. Bolton, J., & Viel, M. (2011). The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon. Monthly Notices of the Royal Astronomical Society, 414(1), 241–252. https://doi.org/10.1111/j.1365-2966.2011.18384.x

Spatial inhomogeneities in the spectral shape of the ultra-violet background (UVB) at the tail-end of HeII reionisation are thought to be the primary cause of the large fluctuations observed in the HeII to HI Ly-a forest optical depth ratio, tau_HeII... Read More about The impact of spatial fluctuations in the ultra-violet background on intergalactic carbon and silicon.

Resolving the high redshift Lyman-alpha forest in smoothed particle hydrodynamics simulations (2009)
Journal Article
S. Bolton, J., & D. Becker, G. (2009). Resolving the high redshift Lyman-alpha forest in smoothed particle hydrodynamics simulations. Monthly Notices of the Royal Astronomical Society: Letters, 398(1), L26–L30. https://doi.org/10.1111/j.1745-3933.2009.00700.x

We use a large set of cosmological smoothed particle hydrodynamics (SPH) simulations to examine the effect of mass resolution and box size on synthetic Lya forest spectra at 2 \leq z \leq 5. The mass resolution requirements for the convergence of the... Read More about Resolving the high redshift Lyman-alpha forest in smoothed particle hydrodynamics simulations.

The evolution of the Lyman-alpha forest effective optical depth following HeII reionisation (2009)
Journal Article
S. Bolton, J., Peng Oh, S., & R. Furlanetto, S. (2009). The evolution of the Lyman-alpha forest effective optical depth following HeII reionisation. Monthly Notices of the Royal Astronomical Society, 396(4), 2405–2418. https://doi.org/10.1111/j.1365-2966.2009.14914.x

Three independent observational studies have now detected a narrow (\Delta z ~ 0.5) dip centred at z=3.2 in the otherwise smooth redshift evolution of the Lya forest effective optical depth. This feature has previously been interpreted as an indirect... Read More about The evolution of the Lyman-alpha forest effective optical depth following HeII reionisation.

Photo-heating and the fate of hard photons during the reionisation of HeII by quasars (2009)
Journal Article
S. Bolton, J., Peng Oh, S., & R. Furlanetto, S. (2009). Photo-heating and the fate of hard photons during the reionisation of HeII by quasars. Monthly Notices of the Royal Astronomical Society, 395(2), 736–752. https://doi.org/10.1111/j.1365-2966.2009.14597.x

We use a combination of analytic and numerical arguments to consider the impact of quasar photo-heating during HeII reionisation on the thermal evolution of the intergalactic medium (IGM). We demonstrate that rapid (\Delta z< 0.1-0.2), strong (\Delta... Read More about Photo-heating and the fate of hard photons during the reionisation of HeII by quasars.

Possible evidence for an inverted temperature-density relation in the intergalactic medium from the flux distribution of the Lyman-alpha forest (2008)
Journal Article
S. Bolton, J., Viel, M., -S. Kim, T., G. Haehnelt, M., & F. Carswell, R. (2008). Possible evidence for an inverted temperature-density relation in the intergalactic medium from the flux distribution of the Lyman-alpha forest. Monthly Notices of the Royal Astronomical Society, 386(2), 1131-1144. https://doi.org/10.1111/j.1365-2966.2008.13114.x

An improved measurement of the flux distribution of the Ly-alpha forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties (2007)
Journal Article
-S. Kim, T., S. Bolton, J., Viel, M., G. Haehnelt, M., & F. Carswell, R. (2007). An improved measurement of the flux distribution of the Ly-alpha forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties. Monthly Notices of the Royal Astronomical Society, 382(4), 1657–1674. https://doi.org/10.1111/j.1365-2966.2007.12406.x

We have performed an extensive Voigt profile analysis of the neutral hydrogen (HI) and metal absorption present in a sample of 18 high resolution, high signal-to-noise QSO spectra observed with VLT/UVES. We use this analysis to separate the metal con... Read More about An improved measurement of the flux distribution of the Ly-alpha forest in QSO absorption spectra: the effect of continuum fitting, metal contamination and noise properties.

A closer look at using quasar near-zones as a probe of neutral hydrogen in the intergalactic medium (2007)
Journal Article
S. Bolton, J., & G. Haehnelt, M. (2007). A closer look at using quasar near-zones as a probe of neutral hydrogen in the intergalactic medium. Monthly Notices of the Royal Astronomical Society: Letters, 381(1), L35-L39. https://doi.org/10.1111/j.1745-3933.2007.00361.x

We examine a large set of synthetic quasar spectra to realistically assess the potential of using the relative sizes of highly ionized near-zones in the Lya and Lyb forest as a probe of the neutral hydrogen content of the intergalactic medium (IGM) a... Read More about A closer look at using quasar near-zones as a probe of neutral hydrogen in the intergalactic medium.

The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization (2007)
Journal Article
S. Bolton, J., & G. Haehnelt, M. (2007). The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization. Monthly Notices of the Royal Astronomical Society, 382(1), 325–341. https://doi.org/10.1111/j.1365-2966.2007.12372.x

We use a large set of hydrodynamical simulations, combined with measurements of the Lyman alpha opacity of the IGM taken from the literature, to obtain robust estimates for the photoionization rate per hydrogen atom at z=5 and 6. We find the photoion... Read More about The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization.

The nature and evolution of the highly ionized near-zones in the absorption spectra of z~6 quasars (2006)
Journal Article
S. Bolton, J., & G. Haehnelt, M. (2007). The nature and evolution of the highly ionized near-zones in the absorption spectra of z~6 quasars. Monthly Notices of the Royal Astronomical Society, 374(2), 493–514. https://doi.org/10.1111/j.1365-2966.2006.11176.x

We use state-of-the-art hydrodynamical simulations combined with a 1D radiative transfer code to assess the extent to which the highly ionized regions observed close to z~6 quasars, which we refer to as near-zones, can constrain the ionization state... Read More about The nature and evolution of the highly ionized near-zones in the absorption spectra of z~6 quasars.

Spatial fluctuations in the spectral shape of the UV background at 2 (2006)
Journal Article
S. Bolton, J., G. Haehnelt, M., Viel, M., & F. Carswell, R. (2006). Spatial fluctuations in the spectral shape of the UV background at 2. Monthly Notices of the Royal Astronomical Society, 366(4), 1378-1390. https://doi.org/10.1111/j.1365-2966.2006.09927.x

The low density hydrogen and helium in the IGM probed by QSO absorption lines is sensitive to the amplitude and spectral shape of the metagalactic UV background. We use realistic HI and HeII Ly-alpha forest spectra, constructed from state-of-the-art... Read More about Spatial fluctuations in the spectral shape of the UV background at 2.