Absorption Line Systems Research Articles

A Big Red Dot: Scattered light, host galaxy signatures and multi-phase gas flows in a luminous, heavily reddened quasar at cosmic noon

Abstract We present a deep X-Shooter rest-frame UV to optical spectral analysis of the heavily reddened quasar, ULASJ2315+0143 at z = 2.566, known to reside in a major-merger host galaxy. The rest-frame optical is best-fit by a dust-reddened quasar (E(B-V)QSO = 1.55) with black-hole mass $\rm log_{10}(H\beta , M\small {BH} [{\rm M}_{\odot }]) = 10.26 \pm 0.05$, bolometric luminosity $\rm L_{Bol}$ = $\rm 10^{48.16}\, erg\,\,s^{-1}$ and Eddington-scaled accretion rate log$_{10}(\rm \lambda _{Edd}) = -0.19$. We find remarkable similarities between ULASJ2315+0143 and the high-redshift Little Red Dots (LRDs). The rest-frame UV cannot be explained by a dusty quasar component alone and requires an additional blue component consistent with either a star-forming host galaxy or scattered AGN light. We detect broad high-ionisation emission lines in the rest-UV, supporting the scattered light interpretation for the UV excess. The scattering fraction represents just 0.05% of the total luminosity of ULASJ2315+0143 . Analysis of the mid infra-red SED suggests an absence of hot dust on torus-scales similar to what is observed for LRDs. The obscuring medium is therefore likely on galaxy scales. We detect narrow, blueshifted associated absorption line systems in 1 iv, 1 v, 1 iv and 1 iii. There is evidence for significant high-velocity (>1000 $\rm km\, s^{-1}$) outflows in both the broad and narrow line regions as traced by 1 iv and [1 iii] emission. The kinetic power of the [1 iii] wind is $\dot{\epsilon }_{k}^{ion} = 10^{44.61} \rm erg\, s^{-1} \sim 0.001\, L_{Bol}$. ULASJ2315+0143 is likely in an important transition phase where star formation, black-hole accretion and multi-phase gas flows are simultaneously occurring.

Detecting Novel Damped Lyα Absorbers in the Intergalactic Medium

Damped Lyα (DLA) absorbers are a class of quasar absorption line systems that can be used to trace hydrogen evolution and study gas, composition, kinematics, and stellar formation in galaxies or the intergalactic medium in the early universe. In this study, the number of DLA absorbers found with a deep learning algorithm is augmented using metal Mg ii absorbers as signposts. The artificial training data was generated by inserting synthetic absorption lines into spectra. Using previously identified DLAs as a test set, the model returned a 94.6% accuracy score and 1197 new DLA absorbers, which nearly doubles the previously known number of samples within the search catalog. Additionally, the column density and Doppler broadening are measured on the newly found DLA absorbers through Voigt profile fitting.

The outflowing ionised gas of I Zw 1 observed by HST COS

Aims. We present an analysis of the Hubble Space Telescope Cosmic Origins Spectrograph spectrum of I Zw 1 aiming to probe the absorbing medium associated with the active galactic nucleus (AGN). Methods. We fitted the emission spectrum and performed spectral analysis of the identified absorption features to derive the corresponding ionic column densities and covering fractions of the associated outflows. We employed photoionisation modelling to constrain the total column density and the ionisation parameter of four detected kinematic components. By investigating the implications of the results together with the observed kinematic properties of both emission and absorption features, we derived constraints on the structure and geometry of the absorbing medium in the AGN environment. Results. We find and characterise absorption line systems from outflowing ionised gas in four distinct kinematic components, located at −60, −280, −1950, and −2900 km s−1 with respect to the source rest frame. While the two slower outflows are consistent with a full covering of the underlying radiation source, the well-constrained doublet line ratios of the faster two, higher column density, outflows suggest partial covering, with a covering fraction of Cf ∼ 0.4. The faster outflows show also line-locking in the N V doublet, a signature of acceleration via line absorption. This makes I Zw 1 possibly the closest object that shows evidence for hosting line-driven winds. The observed −1950 km s−1 absorption is likely due to the same gas as an X-ray warm absorber. Furthermore, the behaviour in UV and X-ray bands implies that this outflow has a clumpy structure. We find that the highly asymmetric broad emission lines in I Zw 1, indicative of a collimated, outflowing broad line region, are covered by the absorbing gas. Finally, the strongest UV–X-ray absorber may be connected to some of the blueshifted line emission, indicative of a more spatially extended structure of this ionised medium.

Deep Learning Voigt Profiles. I. Single-Cloud Doublets

Voigt profile (VP) decomposition of quasar absorption lines is key to studying intergalactic gas and the baryon cycle governing the formation and evolution of galaxies. The VP velocities, column densities, and Doppler b parameters inform us of the kinematic, chemical, and ionization conditions of these astrophysical environments. A drawback of traditional VP fitting is that it can be human-time intensive. With the coming next generation of large all-sky survey telescopes with multiobject high-resolution spectrographs, the time demands will significantly outstrip our resources. Deep learning pipelines hold the promise to keep pace and deliver science-digestible data products. We explore the application of deep learning convolutional neural networks (CNNs) for predicting VP-fitted parameters directly from the normalized pixel flux values in quasar absorption line profiles. A CNN was applied to 56 single-component Mg ii λ λ2796, 2803 doublet absorption line systems observed with HIRES and UVES (R = 45,000). The CNN predictions were statistically indistinct from those of a traditional VP fitter. The advantage is that, once trained, the CNN processes systems ∼105 times faster than a human expert fitting VP profiles by hand. Our pilot study shows that CNNs hold promise to perform bulk analysis of quasar absorption line systems in the future.

Cold molecules in H I 21 cm absorbers across redshifts ∼0.1–4

Absorption lines at high-redshift in front of quasars are quite rare in the millimeter (mm) domain. Only five associated and five intervening systems have been reported in the literature. Nevertheless, these discoveries provide very useful information that is complementary to emission lines, allowing, for instance, to distinguish between inflows and outflows. These lines are also good candidates for studying the variations of the fundamental constants of physics. Here we report the findings of our search for CO and other molecules in emission and absorption in front of a sample of 30 targets, comprising 16 associated and 14 intervening H I 21 cm absorbers. The observations were made with the IRAM-30 m telescope simultaneously at 3 mm and 2 mm, exploring several lines of the CO ladder and HCO+, depending on the redshift. We detected eight targets in emission, of which five are new. The derived molecular gas masses range from 109 to 7 × 1011 M⊙ and the highest redshift detection (z = 3.387) corresponds to a relatively average-metallicity damped Lyman-α absorber for this redshift. We also report four new detections in absorption. Two of the associated CO absorption line detections at high-redshift (z = 1.211 and 1.275) result from high-spatial-resolution follow-up observations with NOEMA. The disparity between the mm molecular and H I 21 cm absorption lines for these and another intervening system detected in HNC at z = 1.275 is attributable to radio and mm sight lines tracing different media. We compare the atomic and molecular column densities of 14 known high-redshift (z > 0.1) molecular absorption line systems. The associated H I absorption lines are broad and exhibit multiple components, and the molecular absorption generally corresponds to the broader and weaker 21 cm absorption component. This indicates two distinct phases: one near galaxy centers with a larger CO-to-H I abundance ratio, and another with lower molecular abundance in the outer regions of the galaxy. In comparison, intervening absorption profiles correspond primarily to H I-dominated gas structure in galaxy outskirts, except for gas at low impact parameters in gravitationally lensed systems. The comparison of interferometric and single-dish observations presented here shows that the detection of absorption requires sufficient spatial resolution to overcome the dilution by emission and will be an important criterion for mm follow-up of 21 cm absorbers from ongoing large-scale surveys.

Metal enrichment and evolution in four z > 6.5 quasar sightlines observed with JWST/NIRSpec

We present JWST/NIRSpec R ≃ 2700 spectra of four high-redshift quasars: VDES J0020–3653 (z = 6.860), DELS J0411–0907 (z = 6.825), UHS J0439+1634 (z = 6.519), and ULAS J1342+0928 (z = 7.535). The exquisite data quality, signal-to-noise ratio of 50–200, and large 0.86 μm ≤ λ ≤ 5.5 μm spectral coverage allowed us to identify between 13 and 17 intervening and proximate metal absorption line systems in each quasar spectrum, with a total number of 61 absorption-line systems detected at 2.42 < z < 7.48 including the highest redshift intervening O Iλ1302 and Mg II systems at z = 7.37 and z = 7.44. We investigated the evolution of the metal enrichment in the epoch of re-ionisation (EoR) at z > 6 and found the following: i) a continued increase in the low-ionisation O I, C II, and Si II incidence, ii) decreasing high-ionisation C IV and Si IV incidence with a transition from predominantly high- to low-ionisation at z ≈ 6.0, and iii) a constant Mg II incidence across all redshifts. The observations support a change in the ionisation state of the intergalactic medium in the EoR rather than a change in metallicity. The abundance ratio of [Si/O] in five z > 6 absorption systems show enrichment signatures produced by low-mass Pop III pair instability supernovae, and possibly Pop III hypernovae. In the Gunn-Peterson troughs, we detected transmission spikes where Lyα photons can escape. From 22 intervening absorption line systems at z > 5.7, only a single low-ionisation system out of 13 lies within 2000 km s−1 from a spike, while four high-ionisation systems out of nine lie within ∼2000 km s−1 from a spike. Most spikes do not have associated metal absorbers close by. This confirms that star-forming galaxies responsible for producing the heavy elements that are transported to the circumgalactic medium via galaxy winds do so in predominantly high-density, neutral environments, while lower density environments are ionised without being polluted by metals at z ≈ 6 − 7.

Outlier Detection in the DESI Bright Galaxy Survey

We present an unsupervised search for outliers in the Bright Galaxy Survey (BGS) data set from the DESI Early Data Release. This analysis utilizes an autoencoder to compress galaxy spectra into a compact, redshift-invariant latent space, and a normalizing flow to identify low-probability objects. The most prominent outliers show distinctive spectral features, such as irregular or double-peaked emission lines or originate from galaxy mergers, blended sources, and rare quasar types, including one previously unknown broad absorption line system. A significant portion of the BGS outliers are stars spectroscopically misclassified as galaxies. By building our own star model trained on spectra from the DESI Milky Way Survey, we have determined that the misclassification likely stems from the principle component analysis of stars in the DESI pipeline. To aid follow-up studies, we make the full probability catalog of all BGS objects and our pretrained models publicly available.

Low-ionization iron-rich broad absorption-line quasar SDSS J 1652+2650: physical conditions in the ejected gas from excited Fe ii and metastable He i

ABSTRACT We present high-resolution VLT/UVES spectroscopy and a detailed analysis of the unique broad absorption-line system towards the quasar SDSS J 165252.67+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 ± 0.0003, derived from [O ii] emission. Each clump shows moderate partial covering of the background continuum source, Cf ≈ [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 nH ∼ 104 cm−3 and the temperature Te ∼ 104 K, with longitudinal cloudlet sizes of ≳0.01 pc. cloudy photoionization 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 ∼ −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 due to large dedicated surveys paired with high-resolution spectroscopic follow-ups.

EIGER. I. A Large Sample of [O iii]-emitting Galaxies at 5.3 < z < 6.9 and Direct Evidence for Local Reionization by Galaxies

We present a first sample of 117 [O iii] λλ4960, 5008–selected star-forming galaxies at 5.33 < z < 6.93 detected in JWST/NIRCam 3.5 μm slitless spectroscopy of a field centered on the hyperluminous quasar SDSS J0100+2802, obtained as part of the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) survey. Three prominent galaxy overdensities are observed, one of them at the redshift of the quasar. Galaxies are found within 200 pkpc and 105 km s−1 of four known metal absorption-line systems. We focus on the role of the galaxies in ionizing the intergalactic medium (IGM) during the later stages of cosmic reionization and construct the mean Lyα and Lyβ transmission as a function of distance from the galaxies. At the lowest redshifts in our study, 5.3 < z < 5.7, the IGM transmission rises monotonically with distance from the galaxies, as seen previously at lower redshifts. In contrast, at 5.7 < z < 6.14, the transmission of both Lyα and Lyβ first increases with distance but then peaks at a distance of 5 cMpc before declining. Finally, in the region 6.15 < z < 6.26, where the additional ionizing radiation from the quasar dominates, the monotonic increase in transmission with distance is reestablished. This result is interpreted to represent evidence that the transmission of the IGM at z ∼ 5.9 toward J0100+2802 results from the “local” ionizing radiation of galaxies that dominates over the much-reduced cosmic background.

Compact [C II] emitters around a C IV absorption complex at redshift 5.7.

The physical conditions of the circumgalactic medium are investigated by means of intervening absorption-line systems in the spectrum of background quasi-stellar objects (QSOs) out to the epoch of cosmic reionization1-4. A correlation between the ionization state of the absorbing gas and the nature of the nearby galaxies has been suggested by the sources detected in either Lyα or [C II] 158 μm near to, respectively, highly ionized and neutral absorbers5,6. This is also probably linked to the global changes in the incidence of absorption systems of different types and the process of cosmic reionization7-12. Here we report the detection of two [C II]-emitting galaxies at redshift z ≈ 5.7 that are associated with a complex, high-ionization C IV absorption system. These objects are part of an overdensity of galaxies and have compact sizes (<2.4 kpc) and narrow linewidths (full width at half maximum (FWHM) ≈ 62-64 km s-1). Hydrodynamic simulations predict that similar narrow [C II] emission may arise from the heating of small (≲3 kpc) clumps of cold neutral medium or a compact photodissociation region13,14. The lack of counterparts in the rest-frame ultraviolet (UV) indicates severe obscuration of the sources that are exciting the [C II] emission. These results may suggest a connection between the properties of the [C II] emission, the rare overdensity of galaxies and the unusual high ionization state of the gas in this region.

On the Fine-tuning and Physical Origin of Line-locked Absorption Systems in Active Galaxies

Line locking (LL) of absorption-line systems is a clear signature of the dynamical importance of radiation-pressure force in driving astrophysical flows, with recent findings suggesting that it may be common in quasars exhibiting multiple intrinsic narrow absorption-line (NAL) systems. In this work, we probe the phase space conducive to LL and follow the detailed kinematics of those systems that may lock at the velocity separation of the C iv λ λ1548.19, 1550.77 doublet. We find that a small volume of the phase-phase admits LL, suggesting a high degree of fine-tuning between the physical properties of locked systems. The stability of LL against quasar luminosity variations is quantified with implications for the long-term variability amplitude of quasars and the velocity-separation statistic between multiple NAL systems. The high occurrence of LL by the C iv doublet implies that the hidden extreme-UV emission from quasars is unlikely to be significantly underestimated by current models. Further, the ratio of the LL velocity to the outflow velocity may serve as a powerful constraint on the composition of the accelerating medium. We conclude that LL poses significant challenges to current theories for the formation of nonintervening NAL systems, and speculate that it may be a manifestation of expanding circumstellar shells around asymptotic giant branch stars in the quasar-host bulge.

The WISSH quasars project

We report on the variability of a multi-component broad absorption line (BAL) system observed in the hyper-luminous quasar J1538+0855 at z = 3.6. Observations from the Sloan Digital Sky Survey (SDSS), Very Large Telescope (VLT), Large Binocular Telescope (LBT), and Subaru telescope taken at five different epochs, spanning 17 yr in the observed frame, are presented. We detect three (A, B, and C) CIV variable troughs exhibiting extreme velocities (∼40 000–54 000 km s−1) similar to the ultra-fast outflows (UFOs) typically observed in the X-ray spectra. The A component of the BAL UFO (vufo ∼ 0.17c) shows strength variations, while B (vufo ∼ 0.15c) and C (vufo ∼ 0.13c) components show changes both in shape and strength, appearing and disappearing at different epochs. In addition, during the last observation on June 2021, the entire BAL system disappeared. The variability trends observed during the first two epochs (1.30 yr rest frame) in the CIV, SiIV, OVI, and NV absorption spectral regions are the same for B and C troughs, while the A component of the BAL varies independently. This suggests a change in the ionization state of the absorbing gas for B and C components and tangential motion for the A component, as the cause of this temporal behaviour. Accordingly, it is possible to provide an upper limit for distance of the gas responsible for the A component of RoutA ≤ 58 pc and, in turn, a kinetic power of ĖK,ufo ≤ 1.37 × 1045 erg s−1. We also obtain RoutB,C ≤ 1.9 kpc for B and C components, which implies an upper limit estimation of ĖK,ufo ≤ 1.94 × 1046 erg s−1 and ĖK,ufo ≤ 1.33 × 1046 erg s−1, respectively. Future spectral monitoring with high-resolution instruments is mandatory to accurately constrain physical properties of the BAL UFO discovered in the UV spectrum of J1538+0855 and investigate its role as a promising mechanism for the origin of the extended (∼75 kpc) CIV nebula surrounding this hyper-luminous quasar.

VLT/UVES observation of the outflow in quasar SDSS J1439-0106

ABSTRACT We analyse the VLT/UVES spectrum of the quasar SDSS J143907.5-010616.7, retrieved from the UVES Spectral Quasar Absorption Database. We identify two outflow systems in the spectrum: a mini broad absorption line (mini-BAL) system and a narrow absorption line (NAL) system. We measure the ionic column densities of the mini-BAL ($v$ = −1550 km s−1) outflow, which has excited state absorption troughs of ${\rm Fe\, \rm {\small {ii}}}$. We determine that the electron number density $\log {n_e}=3.4^{+0.1}_{-0.1}$, based on the ratios between the excited and ground state abundances of ${\rm Fe\, \rm {\small {ii}}}$, and find the kinetic luminosity of the outflow to be ${\lesssim}0.1\,\hbox{per cent}$ of the quasar’s Eddington luminosity, making it insufficient to contribute to AGN feedback.

The scaling relation between galaxy luminosity and WHIM density from EAGLE simulations with application to SDSS data

ABSTRACT This paper presents an updated scaling relation between the optical luminosity density (LD) of galaxies in the r band and the density of the warm–hot intergalactic medium (WHIM) in cosmic filaments, using the high-resolution EAGLE simulations. We find a strong degree of correlation between the WHIM density and the galaxy luminosity density, resulting in a scaling relation between the two quantities that permits us to predict the WHIM density of filaments with a scatter of less than $\frac {1}{2}$ dex in a broad range of smoothed filament luminosity densities. In order to estimate the performance of the simulation-based calibration of the LD–WHIM density relation, we applied it to a sample of low-redshift filaments detected with the Bisous method in the Legacy Survey SDSS DR12 data. In the volume covered by the SDSS data, our relation predicts a WHIM density amounting to 31 ± 7 ± 12 per cent (statistical errors followed by systematic) of cosmic baryon density. This agrees, albeit within the large uncertainties, with the current estimates of the cosmological missing baryon fraction, implying that our LD–WHIM density relation may be a useful tool in the search for the missing baryons. This method of analysis provides a new promising avenue to study the physical properties of the missing baryons, using an observable that is available for large volumes of the sky, complementary and independent from WHIM searches with absorption-line systems in the FUV or X-rays.

Microwave background temperature at a redshift of 6.34 from H2O absorption

Distortions of the observed cosmic microwave background provide a direct measurement of the microwave background temperature at redshifts from 0 to 1 (refs. 1,2). Some additional background temperature estimates exist at redshifts from 1.8 to 3.3 based on molecular and atomic line-excitation temperatures in quasar absorption-line systems, but are model dependent3. No deviations from the expected (1 + z) scaling behaviour of the microwave background temperature have been seen4, but the measurements have not extended deeply into the matter-dominated era of the Universe at redshifts z > 3.3. Here we report observations of submillimetre line absorption from the water molecule against the cosmic microwave background at z = 6.34 in a massive starburst galaxy, corresponding to a lookback time of 12.8 billion years (ref. 5). Radiative pumping of the upper level of the ground-state ortho-H2O(110–101) line due to starburst activity in the dusty galaxy HFLS3 results in a cooling to below the redshifted microwave background temperature, after the transition is initially excited by the microwave background. This implies a microwave background temperature of 16.4–30.2 K (1σ range) at z = 6.34, which is consistent with a background temperature increase with redshift as expected from the standard ΛCDM cosmology4.

Feeding the Accretion Disk from the Dusty Torus in a Reddened Quasar

Abstract We present here a detailed analysis of an unusual absorption line system in the quasar SDSS J122826.79+100532.2. The absorption lines in the system have a common redshifted velocity structure starting from v ∼ 0 and extending to ∼1000 km s−1, and are clearly detected in the hydrogen Balmer series up to Hι, in the metastable neutral helium triplet, and in optical lines of excited states of single ionized iron. We estimated that the absorber has a density n H ≈ 108.4 cm−3 and an ionization parameter U ≈ 10−1.2, thereupon we located it at r abs ≈ 1.5 pc from the central supermassive black hole. The inferred distance is remarkably similar to the evaporation radius for dust grains r evap ≈ 1 pc in the quasar. Thus the absorber may be a probe of an inflow starting from the dusty torus and feeding the accretion disk. Both the featureless continuum and the broad emission lines are heavily reddened with E(B − V) ≈ 0.66, in contrast to the narrow emission lines whose reddening is negligible. The dusty medium could be located in between the broad and narrow emission line regions, and possibly be associated with a “cold” narrow absorption line system detected in Ca ii and Na i doublets nearly unshifted from the quasar systemic velocity. SDSS J122826.79+100532.2 might represent such a rare case that both the inflow and the torus could be tracked by absorption lines.

Discovery of a Fast Iron Low-ionization Outflow in the Early Evolution of the Nearby Tidal Disruption Event AT 2019qiz

Abstract We report the results of ultraviolet (UV) and optical photometric and spectroscopic analysis of the tidal disruption event (TDE) AT 2019qiz. Our follow-up observations started &lt;10 days after the source began to brighten in the optical and lasted for a period of six months. Our late-time host-dominated spectrum indicates that the host galaxy likely harbors a weak active galactic nucleus. The initial Hubble Space Telescope (HST) spectrum of AT 2019qiz exhibits an iron and low-ionization broad absorption line (FeLoBAL) system that is seen for the first time in a TDE. This spectrum also bears a striking resemblance to that of Gaia16apd, a superluminous supernova. Our observations provide insights into the outflow properties in TDEs and show evidence for a connection between TDEs and engine-powered supernovae at early phases, as originally suggested by Metzger &amp; Stone. In a time frame of 50 days, the UV spectra of AT 2019qiz started to resemble those of previous TDEs with only high-ionization broad absorption lines. The change in UV spectral signatures is accompanied by a decrease in the outflow velocity, which began at 15,000 km s−1 and decelerated to ∼10,000 km s−1. A similar evolution in the Hα emission-line width further supports the speculation that the broad Balmer emission lines are formed in TDE outflows. In addition, we detect narrow absorption features on top of the FeLoBAL signatures in the early HST UV spectrum of AT 2019qiz. The measured H i column density corresponds to a Lyman-limit system, whereas the metal absorption lines (such as N v, C iv, Fe ii, and Mg ii) are likely probing the circumnuclear gas and interstellar medium in the host galaxy.

Ultradense Gas Tracked by Unshifted Broad Absorption Lines in a Quasar

Abstract We present a detailed analysis of the broad absorption line system in the quasar SDSS J122017.06+454941.1, which are clearly detected in hydrogen Lyman series and metal lines, such as C iv, Si iv, Si iii, Al iii, and C ii, with a similar velocity as that of the broad emission lines. We reliably measured the column densities of H i, Al iii, and C ii, and obtained a low limit to Si iv and Si iii. With the help of the photoionization simulations, we found that the absorption gas has a hydrogen number density n H ≈ 1011.03 cm−3 and a hydrogen column density N H ≈ 1021.0 cm−2, and is exposed to the radiation with an ionization parameter U ≈ 10−1.25, and thus located the absorber at ∼0.3 pc from the central supermassive black hole, remarkably similar to the radius of the broad-line region (BLR; 0.17–0.84 pc as estimated by the luminosity–radius relation) of the quasar. It is likely that our line of sight may happen to intercept the low-column part of the BLR with a high density similar to that of the inferred value of the absorber. We suggest that detection of Al iii absorption line doublet in moderate quality quasar spectra could be a good indicator of dense gases, provided that the neutral hydrogen column density of the absorber is .

Sharpening quasar absorption lines with ESPRESSO. Temperature of warm gas at z ~ 2, constraints on the Mg isotopic ratio, and structure of cold gas at z ~ 0.5

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 &lt; 0.6 and &lt; 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.

The Mg ii absorption line systems in quasar spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope

Making use of quasar spectra from LAMOST, in the spectral data around the Mg ii emission lines, research described in this paper has detected 217 Mg ii narrow absorption lines (NALs) with and in a redshift range of 0.4554 ≤ z abs ≤ 2.1110. For quasars observed by both LAMOST and SDSS, we find that 135 Mg ii NALs were obviously observed in the LAMOST spectra, 347 Mg ii NALs were were apparent in the SDSS spectra, and 132 Mg ii NALs were clearly present in both the SDSS and LAMOST spectra. The missed Mg ii NALs are likely ascribed to low signal-to-noise ratios of corresponding spectra. Among the Mg ii NALs obviously observed in SDSS or LAMOST spectra, eight Mg ii NALs were significantly changed with in time intervals of Δ MJD/(1 + z em) = 359 – 2819 d.