Abstract
Aims. We aim to study several key physical properties of quasar absorption-line systems that are subtly encoded in their absorption profiles and have not yet been thoroughly investigated or constrained. Methods. We analysed a high-resolution (R = 140 000) spectrum of the bright quasar HE 0001−2340 (zem = 2.26) obtained with ESPRESSO, which was recently installed at the Very Large Telescope. We analysed three systems at z = 0.45, z = 1.65, and z = 2.19 using multiple-component Voigt-profile fitting. We also compared our spectrum with those obtained with VLT/UVES, covering a total period of 17 years. Results. We disentangle turbulent and thermal broadening in many components spread over about 400 km s−1 in the z ≈ 2.19 sub-damped Lyman-α system. We derive an average temperature of 16 000 ± 1300 K, which is about twice the canonical value of the warm neutral medium in the Galactic interstellar medium (ISM). A comparison with other high-z, low-metallicity absorbers reveals an anti-correlation between gas temperature and total H I column density. Although requiring confirmation, this could be the first observational evidence of a thermal decrease with galactocentric distance; in other words, we may be witnessing a thermal transition between the circumgalactic medium and the cooler ISM. We revisit the Mg isotopic ratios at z = 0.45 and z = 1.65 and constrain them to be ξ = (26Mg + 25Mg)/24Mg < 0.6 and < 1.4 in these two systems, respectively. These values are consistent with the standard solar ratio; that is, we do not confirm strong enhancement of heavy isotopes previously inferred from UVES data. Finally, we confirm the partial coverage of the quasar emission-line region by a Fe I-bearing cloud in the z = 0.45 system and present evidence for velocity substructure of the gas that has Doppler parameters of the order of only ∼0.3 km s−1. This agrees well with the low kinetic temperature of T ∼ 100 K inferred from modelling of the gas physical conditions. Conslusions. This work demonstrates the unique insight provided by high-fidelity, high-resolution optical spectrographs on large telescopes when used to investigate the thermal state of the gas in and around galaxies as well as its spatial and velocity structure on small scales, and to constrain the associated stellar nucleosynthetic history.
Highlights
This work demonstrates the unique insight provided by high-fidelity, high-resolution optical spectrographs on large telescopes when used to investigate the thermal state of the gas in and around galaxies as well as its spatial and velocity structure on small scales, and to constrain the associated stellar nucleosynthetic history
The advent of high-resolution spectrographs on 8–10 m class telescopes, in particular the High Resolution Echelle Spectrometer (HIRES, Vogt et al 1994) on the Keck telescope followed by the Ultraviolet and Visual Echelle Spectrograph (UVES, Dekker et al 2000) on the Very Large Telescope (VLT), has played a crucial role in the exploration of the distant Universe in absorption towards quasars and Gamma-ray burst afterglows
We present an analysis of a very high-resolution spectrum (R 130 000) of the quasar HE 0001−2340 obtained using the new VLT/ESPRESSO spectrograph
Summary
The advent of high-resolution spectrographs on 8–10 m class telescopes, in particular the High Resolution Echelle Spectrometer (HIRES, Vogt et al 1994) on the Keck telescope followed by the Ultraviolet and Visual Echelle Spectrograph (UVES, Dekker et al 2000) on the Very Large Telescope (VLT), has played a crucial role in the exploration of the distant Universe in absorption towards quasars and Gamma-ray burst afterglows These spectrographs have enormously increased the number and variety of absorption-line systems observed at high spectral resolution and the amount of information that can be extracted from them. 2021 and references therein), constraints on the sizes of the background source emission-line regions (Balashev et al 2011; Bergeron & Boissé 2017), measurements of the cosmic microwave background temperature at high-z (Noterdaeme et al 2011), measurements of the primordial abundance of deuterium (e.g., Cooke et al 2014), and so on.
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