Intervening metal absorption lines in the spectra of z ≳ 6 quasars are fundamental probes of the ionization state and chemical composition of circumgalactic and intergalactic gas near the end of the reionization epoch. Large absorber samples are required to robustly measure typical absorber properties and to refine models of the synthesis, transport, and ionization of metals in the early Universe. The Ultimate XSHOOTER legacy survey of quasars at z ∼ 5.8–6.6 (XQR-30) has obtained high signal-to-noise spectra of 30 luminous quasars, nearly quadrupling the existing sample of 12 high quality z ∼ 6 quasar spectra. We use this unprecedented sample to construct a catalogue of 778 systems showing absorption in one or more of Mg ii (360 systems), Fe ii (184), C ii (46), C iv (479), Si iv (127), and N v (13) which span 2 ≲ z ≲ 6.5. This catalogue significantly expands on existing samples of z ≳ 5 absorbers, especially for C iv and Si iv which are important probes of the ionizing photon background at high redshift. The sample is 50 per cent (90 per cent) complete for rest-frame equivalent widths W ≳ 0.03 Å (0.09 Å). We publicly release the absorber catalogue along with completeness statistics and a python script to compute the absorption search path for different ions and redshift ranges. This data set is a key legacy resource for studies of enriched gas from the era of galaxy assembly to cosmic noon, and paves the way for even higher redshift studies with JWST and 30 m-class telescopes.
We assemble the largest C iv absorption line catalogue to date, leveraging machine learning, specifically Gaussian processes, to remove the need for visual inspection for detecting C iv absorbers. The catalogue contains probabilities classifying the reliability of the absorption system within a quasar spectrum. Our training set was a sub-sample of DR7 spectra that had no detectable C iv absorption in a large visually inspected catalogue. We used Bayesian model selection to decide between our continuum model and our absorption-line models. Using a random hold-out sample of 1301 spectra from all of the 26 030 investigated spectra in DR7 C iv catalogue, we validated our pipeline and obtained an 87 per cent classification performance score. We found good purity and completeness values, both $\sim 80{{\ \rm per\ cent}}$, when a probability of $\sim 95{{\ \rm per\ cent}}$ is used as the threshold. Our pipeline obtained similar C iv redshifts and rest equivalent widths to our training set. Applying our algorithm to 185 425 selected quasar spectra from SDSS DR12, we produce a catalogue of 113 775 C iv doublets with at least 95 per cent confidence. Our catalogue provides maximum a posteriori values and credible intervals for C iv redshift, column density, and Doppler velocity dispersion. We detect C iv absorption systems with a redshift range of 1.37–5.1, including 33 systems with a redshift larger than 5 and 549 absorbers systems with a rest equivalent width greater than 2 Å at more than 95 per cent confidence. Our catalogue can be used to investigate the physical properties of the circumgalactic and intergalactic media.
more » « less- Award ID(s):
- 2215705
- NSF-PAR ID:
- 10469899
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 526
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 4557-4574
- Size(s):
- p. 4557-4574
- Sponsoring Org:
- National Science Foundation
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