@article{PerrottaHamannCristianietal.2018,
  author    = {Perrotta, S. and Hamann, F. and Cristiani, S. and Prochaska, J. X. and Ellison, Sara L. and Lopez, S. and Cupani, G. and Becker, G. and Berg, T. A. M. and Christensen, Lise and Denney, K. D. and Worseck, G{\´a}bor},
  title     = {Hunting for metals using XQ-100 Legacy Survey composite spectra},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {481},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {1},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/sty2205},
  pages     = {105 -- 121},
  year      = {2018},
  abstract  = {We investigate the NV absorption signal along the line of sight of background quasars, in order to test the robustness of the use of this ion as the criterion to select intrinsic (i.e. physically related to the quasar host galaxy) narrow absorption lines (NALs). We build composite spectra from a sample of similar to 1000 CIV absorbers, covering the redshift range 2.55 < z < 4.73, identified in 100 individual sight lines from the XQ-100 Legacy Survey. We detect a statistically significant NV absorption signal only within 5000 km s(-1) of the systemic redshift, z(em). This absorption trough is similar to 15 sigma when only CIV systems with N(CIV) > 10(14) cm(-2) are included in the composite spectrum. This result confirms that NV offers an excellent statistical tool to identify intrinsic systems. We exploit stacks of 11 different ions to show that the gas in proximity to a quasar exhibits a considerably different ionization state with respect to gas in the transverse direction and intervening gas at large velocity separations from the continuum source. Indeed, we find a dearth of cool gas, as traced by low-ionization species and in particular by MgII, in the proximity of the quasar. We compare our findings with the predictions given by a range of CLOUDY ionization models and find that they can be naturally explained by ionization effects of the quasar.},
  language  = {en}
}
@article{BergEllisonSanchezRamirezetal.2019,
  author    = {Berg, Trystyn A. M. and Ellison, Sara L. and Sanchez-Ramirez, Ruben and Lopez, Sebastian and Becker, George D. and Christensen, Lise and Cupani, Guido and Denney, Kelly D. and Worseck, Gabor},
  title     = {Sub-damped Lyman alpha systems in the XQ-100 survey - I. Identification and contribution to the cosmological H I budget},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {488},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {3},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stz2012},
  pages     = {4356 -- 4369},
  year      = {2019},
  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}
}