Low-ionization iron-rich Broad Absorption-Line Quasar SDSS J1652+2650: Physical conditions in the ejected gas from excited FeII and metastable HeI

We present high-resolution VLT/UVES spectroscopy and a detailed analysis of the unique Broad Absorption-Line system towards the quasar SDSS J165252.67+265001.96. This system exhibits low-ionization metal absorption lines from the ground states and excited energy levels of Fe II and Mn II, and the meta-stable 2^3S excited state of He I. The extended kinematics of the absorber encompasses three main clumps with velocity offsets of -5680, -4550, and -1770 km s$^{-1}$ from the quasar emission redshift, $z=0.3509\pm0.0003$, derived from [O II] emission. Each clump shows moderate partial covering of the background continuum source, $C_f \approx [0.53; 0.24; 0.81]$. We discuss the excitation mechanisms at play in the gas, which we use to constrain the distance of the clouds from the Active Galactic Nucleus (AGN) as well as the density, temperature, and typical sizes of the clouds. The number density is found to be $n_{\rm H} \sim 10^4\rm cm^{-3}$ and the temperature $T_e \sim 10^4\rm\,K$, with longitudinal cloudlet sizes of $\gtrsim0.01$ pc. Cloudy photo-ionization modelling of He I$^{*}$, which is also produced at the interface between the neutral and ionized phases, assuming the number densities derived from Fe II, constrains the ionization parameter to be $\log U \sim -3$. This corresponds to distances of a few 100 pc from the AGN. We discuss these results in the more general context of associated absorption-line systems and propose a connection between FeLoBALs and the recently-identified molecular-rich intrinsic absorbers. Studies of significant samples of FeLoBALs, even though rare per se, will soon be possible thanks to large dedicated surveys paired with high-resolution spectroscopic follow-ups.Comment: Accepted for publication in MNRAS, 27 pages, 21 Figure

C II*/C II ratio in high-redshift DLAs: ISM phase separation drives the observed bimodality of [C II] cooling rates

International audienceWe discuss observations of C II*/C II ratios and cooling rates due to [C II] 158μm emission in high-redshift intervening damped Lyman-α (DLA) systems towards quasars. We show that the observed bimodality in the C II cooling rates actually reflects a bimodality in the C II*/C II-metallicity plane that can be naturally explained by phase segregation of the neutral medium, without invoking differences in star-formation scenarios. Assuming realistic distributions of the physical parameters to calculate the phase diagrams, we also reproduce qualitatively the metallicity dependence of this bimodality. We emphasize that high-z DLAs mostly probe low-metallicity gas ($Z\lesssim 0.1 \, \mathrm{Z}_{\odot }$), where heating is dominated by cosmic rays (and/or turbulence), and not by photoelectric heating. Therefore, even if the gas of DLA is predominantly cold (where the cooling is dominated by [C II]), the excitation of C II can be used to derive the cosmic ray ionization rate (and/or turbulent heating), but not the UV field, as was previously considered. Alternatively, if the gas in DLA is predominantly warm, C II*/C II can be used to constrain its number density. Finally, we also discuss the importance of the ionized medium, which, if also present along the line of sight, can significantly increase the average C II*/C II ratio

Extremely strong DLAs at high redshift: gas cooling and H<SUB>2</SUB> formation

International audienceWe present a spectroscopic investigation with the Very Large Telescope/X-shooter of seven candidate extremely strong damped Lyman-α absorption systems [ESDLAs, N(H I) ≥ 5 × 1021 cm-2] observed along quasar sightlines. We confirm the extremely high column densities, albeit slightly (0.1 dex) lower than the original ESDLA definition for four systems. We measured low-ionization metal abundances and dust extinction for all systems. For two systems, we also found strong associated H$\rm _2$ absorption \log N(\rm{H\rm _2})\,\text{(cm^{-2})}=18.16\pm 0.03 and 19.28 ± 0.06 at z = 3.26 and 2.25 towards J2205+1021 and J2359+1354, respectively, while for the remaining five we measured conservative upper limits on the H$\rm _2$ column densities of typically \log N(\rm{H\rm _2})\,\text{(cm^{-2})}\,\, 17.3. The increased H2 detection rate (10-55 per cent at 68 per cent confidence level) at high H I column density compared with the overall damped Lyman-α population (~5-10 per cent) confirms previous works. We find that these seven ESDLAs have similar observed properties as those previously studied towards quasars and γ-ray burst afterglows, suggesting they probe inner regions of galaxies. We use the abundance of ionized carbon at the excited fine-structure level to calculate the cooling rates through the C II λ158 μm emission, and compare them with the cooling rates from damped Lyman-α systems in the literature. We find that the cooling rate distribution of ESDLAs also presents the same bimodality as previously observed for the general (mostly lower H I column density) damped Lyman-α population