@article{FurnissWorseckFumagallietal.2019,
  author    = {Furniss, Amy and Worseck, Gabor and Fumagalli, Michele and Johnson, Caitlin A. and Williams, David A. and Pontrelli, P. and Prochaska, J. Xavier},
  title     = {Spectroscopic Redshift of the Gamma-Ray Blazar B2 1215+30 from Ly alpha Emission},
  series = {The astronomical journal},
  volume    = {157},
  journal   = {The astronomical journal},
  number    = {2},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0004-6256},
  doi       = {10.3847/1538-3881/aaf28b},
  pages     = {4},
  year      = {2019},
  abstract  = {We report on Cosmic Origin Spectrograph observations of the gamma-ray bright blazar B2 1215+30, collected in 2015 November. These observations allow for the confirmation of the source redshift from the detection of a Lyα emission feature at λ ~ 1374 {\AA}. The emission feature places the source at a redshift of z = 0.1305 ± 0.003, confirming the source's ground-based spectral measurement. The gamma-ray emission of the source is discussed in the context of the source distance, required for the accurate reconstruction of the intrinsic gamma-ray emission taking the absorption by the extragalactic background light into account. The source distance is found to be low enough that the previously reported detection of an exceptional flaring event from B2 1215+30 in 2014 cannot be used to investigate opacity-specific spectral and variability characteristics introduced by possible ultra-high-energy cosmic-ray propagation.},
  language  = {en}
}
@article{BeckerPettiniRafelskietal.2019,
  author    = {Becker, George D. and Pettini, Max and Rafelski, Marc and Boera, Elisa and Christensen, Lise and Cupani, Guido and Ellison, Sara L. and Farina, Emanuele Paolo and Fumagalli, Michele and Lopez, Sebastian and Neeleman, Marcel and Ryan-Weber, Emma and Worseck, Gabor},
  title     = {The Evolution of OI over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  volume    = {883},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics},
  number    = {2},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0004-637X},
  doi       = {10.3847/1538-4357/ab3eb5},
  pages     = {37},
  year      = {2019},
  abstract  = {We present a survey for metal absorption systems traced by neutral oxygen over 3.2 < z < 6.5. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total, we detect 74 OI absorbers, of which 57 are separated from the background QSO by more than 5000 km s(-1). We use a maximum likelihood approach to fit the distribution of OI lambda 1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with W-1302 > 0.05 angstrom, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 < z < 5.7 is a factor of 1.7-4.1 lower (68\% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99\% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z similar to 6 than at lower redshifts. Absorption from highly ionized metals traced by CIV is also weaker in higher-redshift OI systems, supporting this picture. The evolution of OI absorbers implies that metal-enriched circumgalactic gas at z similar to 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.},
  language  = {en}
}