Narrow Absorption Line Systems Research Articles

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.

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.

Search for intrinsic NALs in BAL/mini-BAL quasar spectra

ABSTRACT Some fraction of narrow absorption lines (NALs) are physically associated to the quasar/host-galaxy materials (i.e. intrinsic NALs) like those of broad absorption lines (BALs) and mini-BALs. The relation between these three types of absorption lines has not been understood yet, however one interpretation is that these absorption features correspond to different inclination angles. In this study, we search for intrinsic NALs in 11 BAL/mini-BAL quasar spectra retrieved from VLT/UVES public archive, in order to test a possible relation of intrinsic NALs and BALs/mini-BALs in the geometry models. We use partial coverage analysis to separate intrinsic NALs from ones which are associated to cosmologically intervening materials like foreground galaxies and intergalactic medium (i.e. intervening NALs). We identify one reliable and two possible intrinsic NAL systems out of 36 NAL systems in 9 BAL/mini-BAL quasar spectra after removing two quasars without clear BAL features. In spite of a small sample size, we placed a lower limit on the fraction of BAL/mini-BAL quasars that have at least one intrinsic C iv NAL ($\sim 33^{+33}_{-18}{{\ \rm per\ cent}}$). This can be interpreted that intrinsic NAL absorbers exist everywhere regardless of inclination angle. We found that one of the intrinsic NAL systems detected in SDSS J121549.80−003432.1 is located at a large radial distance of R > 130 kpc, using a method of photoionization model with ground/excited-state lines. Considering the wide range of intrinsic NAL absorber distribution in inclination angles and radial distances, it suggests that origins and geometry of them are more complicated than we expected.

Probing the Line-locking Signatures within the C iv Broad Absorption Line in Quasar SDSS J092345+512710

Abstract Quasar SDSS J092345.19+512710.1 (hereafter J0923+5127) shows two broad absorption line (BAL) systems. The blue one at ∼14,000 km s−1, called BAL system A, has been reported to show a synchronized kinematic shift of its C iv and Si iv BALs. In this paper, we mainly concentrate on the red one at ∼4000 km s−1, called BAL system B, which can be resolved into multiple narrow absorption lines (NALs). We identify 11 NAL systems from BAL system B and find that these blended NALs show complex line-locking phenomena, which offers evidence for the idea that radiation pressure plays an important role in the dynamics of these clumpy outflow clouds.

Highly Structured Quasar Outflow in SDSS J010612.22+001920.1

Abstract Evidence for quasar outflows can be detected via blueshifted broad absorption lines (BALs) in rest-frame ultraviolet spectra of quasars. We have identified 18 narrow absorption line (NAL) systems in the BAL system of SDSS J010612.22+001920.1, indicating that this BAL outflow has achieved a high degree of clumpiness. Moreover, these NAL systems are highly structured in velocity space and separated from each other by the doublet spacings of multiple ionic species, including a sequence of 10 C iv doublets that form arithmetic progression with a common difference of ≈498 . Cases like J010612.22+001920.1 offer strong evidence for the dynamical process of radiative acceleration in quasar outflow, and open up a new way for the research of quasar outflow under the framework of the NAL complex.

An Increasing Radial Velocity of a Narrow Absorption-line System in Quasar SDSS J143530.49+142338.4

Abstract We report, for the first time, both the strengthening and radial velocity increases of a narrow absorption-line (NAL) system (C iv λλ1548, 1551 and N v λλ1239, 1243) from the two-epoch spectra of quasar SDSS J143530.49+142338.4. First, we speculate that the ionization changes of the outflow clouds are likely the cause of the strengthening in its equivalent width (EW) based on the obvious weakening of the ionization continuum, although other interpretations cannot be ruled out based on the current two-epoch spectra. According to the cloudy simulation, the asynchronized variations between the absorption-line EWs and the ionizing continuum indicate that the absorbers are at relatively high degrees of ionization, which is also consistent with the high ionization state revealed by the absence of Si iv NAL in the same system. Second, this NAL system exhibits a kinematic velocity shift of ∼138 within 445.2 days in the quasar rest frame (corresponding to an average acceleration of ∼0.36 ). We evaluate several possible causes for this kinematic shift. However, the current two-epoch spectra do not provide enough constraints to confirm the possible mechanisms, so future monitoring with high resolution will be helpful to achieve this goal.

Narrow-absorption Line Complex. IV. Line-driven Radiative Outflows in Broad-absorption Line Quasars

Abstract It has been reported that some broad-absorption lines (BALs) in quasar spectra can be decomposed into multiple narrow-absorption lines (NALs), which we define as “Type N BALs.” In this paper, using the spectra of 2005 BAL quasars from the Sloan Digital Sky Survey (SDSS), we have visually identified a total of 6764 C iv λλ1548 and 1551 NAL systems with 1.4186 ≤ z abs ≤ 3.8005, including 4174 C iv NAL systems within BAL troughs from 1349 quasars and 2590 outside BAL troughs from 1319 quasars. About two-thirds of the BAL quasars in the total sample contain Type N BALs, indicating the ubiquity of Type N BALs, which serve as a new perspective for studying outflows in the context of the NAL complex. Moreover, we find that, for both samples of C iv NAL systems within and outside BAL troughs, the distributions of velocity separation among distinct C iv NAL systems in the same quasar show significant excesses at the positions of C iv and Si iv doublet splittings, which offers statistical evidence for the idea that radiative forces play a significant role in driving both BAL and NAL outflows in BAL quasars.

Probing quasar winds using intrinsic narrow absorption lines

ABSTRACT We use the spectra of 73 quasars (1.5 ≲ z ≲ 5) from the VLT UVES archive to catalogue and study narrow absorption lines (NALs) that are physically associated with (intrinsic to) the quasars. We identify 410 NAL systems containing C iv, N v, and/or Si iv doublets. Based on the assumption that only systems intrinsic to the quasar can exhibit partial coverage of the background source(s), we identify 34 reliably intrinsic NAL systems and 11 systems that are potentially intrinsic, as well as 4 mini-broad absorption lines (BALs) and 1 BAL. The minimum fraction of quasars with at least one intrinsic system is shown to be 38 per cent. We identify intrinsic NALs with a wide range of properties, including apparent ejection velocity, coverage fraction, and ionization level. There is a continuous distribution of properties, rather than discrete families, ranging from partially covered C iv systems with black Ly α and with a separate low-ionization gas phase to partially covered N v systems with partially covered Ly α and without detected low-ionization gas. Even more highly ionized associated and intrinsic absorption systems (O vi, Ne viii, and Mg x doublets) have been presented in separate studies; these may represent an extension of the above sequence. We also use the properties of the NALs in conjunction with recent models of accretion disc winds that predict the origins of the absorbing gas in order to determine the model that best characterizes our sample. Additionally, we construct a model describing the spatial distributions, geometries, and varied ionization structures of intrinsic NALs.

Narrow C iv Absorption Lines with Multi-epoch Observations

Abstract Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for C IV λλ1548,1551 narrow absorption doublets in spectral data from the blue wing υ r = 30,000 km s−1 until the red wing of C IV λ1549 emission lines. We have obtained 21,239 C IV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from ΔMJD = 0.24 to 1842.38 days at rest-frame. Both samples of the C IV NAL systems with multi-epoch observations and the variable C IV NAL systems are the largest ones to date. The offset velocity distribution of the variable C IV NALs from quasars has a peak at υ r ≈ 2000 km s−1 and gently extends to a larger offset velocity. There are 110 variable C IV NALs with υ r > 12,000 km s−1. In addition, about 10% intrinsic C IV NALs show time variability on a timescale of <2000 days. We find that the variations of C IV NALs are positively or negatively correlated with the alternations of quasar continua. The two kinds of correlations suggest that the variable C IV NALs included in our absorber catalog can be classified into at least two populations: (1) highly ionized systems that are dominated by highly ionized absorbing gas and negatively respond to the fluctuations of quasar emissions; and (2) lowly ionized systems that are dominated by lowly ionized absorbing gas and positively respond to fluctuations of quasar emissions. We also find that the absolute fractional changes in the absorption strengths of C IV NALs are inversely correlated with absorption strengths.

Narrow Absorption Lines Complex. II. Probing the Line-locking Signatures within the Trough-like Broad Absorption Line

Abstract In this paper, we report the line-locking phenomenon of the blended narrow absorption lines (NALs) within trough-like broad absorption lines (BALs) in quasar SDSS J021740.96–085447.9 (hereafter J0217–0854). Utilizing the two-epoch spectroscopic observations of J0217–0854 from the Sloan Digital Sky Survey, we find that each of its C iv, Si iv, N v, and Lyα BAL troughs actually contain at least seven NAL systems. By splitting these BAL troughs into multiple NAL systems, we find that the velocity separations between the NAL systems are similar to their doublet splittings, with some of them matching perfectly. Cases like J0217–0854, showing line-locking signatures of NALs within BAL troughs, offer direct observational evidence for the idea that radiative forces play a significant role in driving BAL (at least for Type N BAL) outflows.

Saturation Effect on Photoionization-driven Broad Absorption Line Variability

Abstract We study the saturation effect on broad absorption line (BAL) variability through a variation phenomenon, which shows significant variation in Si iv BAL but no, or only small, change in C iv BAL (hereafter Phenomenon I). First, we explore a typical case showing Phenomenon I, quasar SDSS J153715.74+582933.9 (hereafter J1537+5829). We identify four narrow absorption line (NAL) systems within its Si iv BAL and two additional NAL systems within its C iv BAL, and confirm their coordinated weakening. Combining with the obvious strengthening of the ionizing continuum, we attribute the BAL variability in J1537+5829 to the ionization changes caused by the continuum variations. Second, a statistical study based on multiobserved quasars from SDSS-I/II/III are presented. We confirm that (1) the moderate anticorrelation between the fractional variations of Si iv BALs and the continuum in 74 quasars show Phenomenon I and (2) the sample showing BAL variations tends to have larger ionizing continuum variations. These results reveal the ubiquitous effect of the continuum variability on Phenomenon I and BAL variation. We attribute the relative lack of variation of C iv BALs in Phenomenon I to the saturation effects. Nonetheless, these absorbers are not very optically thick in Si iv and the ionization changes in response to continuum variations could be the main driver of their variations. Finally, we find that the saturation effect on BAL variability can explain many phenomena of BAL variations that have been reported before.

The Correlated Variations of Narrow Absorption Lines and Quasar Continuum

Abstract We assemble 207 variable quasars from the Sloan Digital Sky Survey, all with at least 3 observations, to analyze C iv narrow absorption doublets, and obtain 328 C iv narrow absorption line systems. We find that 19 out of 328 C iv narrow absorption line systems were changed by on timescales from 15.9 to 1477 days at rest-frame. Among the 19 obviously variable C iv systems, we find that (1) 14 systems have relative velocities and 4 systems have , where c is the speed of light; (2) 13 systems are accompanied by other variable C iv systems; (3) 9 systems were changed continuously during multiple observations; and (4) 1 system with 16,862 km s−1 was enhanced by in 0.67 day at rest-frame. The variations of absorption lines are inversely correlated with the changes in the ionizing continuum. We also find that large variations of C iv narrow absorption lines are form differently over a short timescale.

Discovery of Variable Hydrogen Balmer Absorption Lines with Inverse Decrement in PG 1411+442

Abstract We present new optical spectra of the well-known broad absorption line (BAL) quasar PG 1411+442, using the DBSP spectrograph at the Palomar 200 inch telescope in 2014 and 2017 and the YFOSC spectrograph at the Lijiang 2.4 m telescope in 2015. A blueshifted narrow absorption line system is clearly revealed in 2014 and 2015 consisting of hydrogen Balmer series and metastable He i lines. The velocity of these lines is similar to the centroid velocity of the UV BALs, suggesting that both originate from the outflow. The Balmer lines vary significantly between the two observations and vanished in 2017. They were also absent in the archived spectra obtained before 2001. The variation is thought to be driven by photoionization change. Besides, the absorption lines show inversed Balmer decrement, i.e., the apparent optical depths of higher-order Balmer absorption lines are larger than those of lower-order lines, which is inconsistent with the oscillator strengths of the transitions. We suggest that such anomalous line ratios can be naturally explained by the thermal structure of a background accretion disk, which allows the obscured part of the disk to contribute differently to the continuum flux at different wavelengths. High-resolution spectroscopic and photometric monitoring would be very useful to probe the structure of the accretion disk as well as the geometry and physical conditions of the outflow.

Nature and statistical properties of quasar associated absorption systems in the XQ-100 Legacy Survey

We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyze the spectra of 100 quasars with 3.5 < z$\rm_{em}$ < 4.5, observed with X-shooter/VLT in the context of the XQ-100 Legacy Survey. We detect a $\sim$ 8 $\sigma$ excess in the number density of absorbers within 10,000 km/s of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km/s cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10,000 km/s when also weak absorbers (equivalent width < 0.2 \AA) are considered. We infer NV is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 percent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by CII) along the line of sight associated with the quasar host galaxy, in contrast with what is observed in the transverse direction.

MONITORING THE VARIABILITY OF INTRINSIC ABSORPTION LINES IN QUASAR SPECTRA, ,

We have monitored 12 intrinsic narrow absorption lines (NALs) in five quasars and seven mini-broad absorption lines (mini-BALs) in six quasars for a period of 4-12 years (1-3.5 years in the quasar rest-frame). We present the observational data and the conclusions that follow immediately from them, as a prelude to a more detailed analysis. We found clear variability in the equivalent widths (EWs) of the mini-BAL systems but no easily discernible changes in their profiles. We did not detect any variability in the NAL systems nor in narrow components that are often located at the center of mini-BAL profiles. Variations in mini-BAL EWs are larger at longer time intervals, reminiscent of the trend seen in variable broad absorption lines. If we assume that the observed variations result from changes in the ionization state of the mini-BAL gas, we infer lower limits to the gas density $\sim$ 10$^3$-10$^5$ cm$^{-3}$ and upper limits on the distance of the absorbers from the central engine of order a few kpc. Motivated by the observed variability properties, we suggest that mini-BALs can vary because of fluctuations of the ionizing continuum or changes in partial coverage while NALs can vary primarily because of changes in partial coverage.

THE PHYSICAL CONDITIONS OF THE INTRINSIC N V NARROW ABSORPTION LINE SYSTEMS OF THREE QUASARS

We employ detailed photoionization models to infer the physical conditions of intrinsic narrow absorption line systems found in high resolution spectra of three quasars at z=2.6-3.0. We focus on a family of intrinsic absorbers characterized by N V lines that are strong relative to the Ly-alpha lines. The inferred physical conditions are similar for the three intrinsic N V absorbers, with metallicities greater than 10 times the solar value (assuming a solar abundance pattern), and with high ionization parameters (log U ~ 0). Thus, we conclude that the unusual strength of the N V lines results from a combination of partial coverage, a high ionization state, and high metallicity. We consider whether dilution of the absorption lines by flux from the broad-emission line region can lead us to overestimate the metallicities and we find that this is an unlikely possibility. The high abundances that we infer are not surprising in the context of scenarios in which metal enrichment takes place very early on in massive galaxies. We estimate that the mass outflow rate in the absorbing gas (which is likely to have a filamentary structure) is less than a few solar masses per year under the most optimistic assumptions, although it may be embedded in a much hotter, more massive outflow.

TESTING THE POSSIBLE INTRINSIC ORIGIN OF THE EXCESS VERY STRONG Mg II ABSORBERS ALONG GAMMA-RAY BURST LINES-OF-SIGHT

The startling discovery of Prochter et al. (2006) that the frequency of very strong (W_r(2796)>1 A) MgII absorbers along gamma-ray burst (GRB) lines of sight ([dN/dz]_{GRB} = 0.90) is more than three times the frequency along quasar lines of sight ([dN/dz]_{QSO} = 0.24), over similar redshift ranges, has yet to be understood. We reconsider the possibility that the excess of very strong MgII absorbers toward GRBs is intrinsic either to the GRBs themselves or to their immediate environment, and associated with bulk outflows with velocities as large as v_{max} ~ 0.3c. In order to examine this hypothesis, we accumulate a sample of 27 W_r(2796) > 1 A absorption systems found toward 81 quasars, and compare their properties to those of 9 W_r(2796)>1 A absorption systems found toward 6 GRBs; all systems have been observed at high spectral resolution (R = 45,000) using the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. We make multiple comparisons of the absorber properties across the two populations, testing for differences in metallicity, ionization state, abundance patterns, dust abundance, kinematics, and phase structure. We find no significant differences between the two absorber populations using any of these metrics, implying that, if the excess absorbers toward GRB lines of sight are indeed intrinsic, they must be produced in a process which has strong similarities to the processes yielding strong MgII systems in association with intervening galaxies. Although this may seem a priori unlikely, given the high outflow velocities required for any intrinsic model, we note that the same conclusion was reached, recently, with respect to the narrow absorption line systems seen in some quasars.

A Survey for NvAbsorption atz ≈ zGRBin GRB Afterglow Spectra: Clues to Gas Near the Progenitor Star

We survey N V absorption in the afterglow spectra of long-duration gamma-ray bursts (GRBs) with the intent to study highly ionized gas in the galaxies hosting these events. We identify a high incidence (6/7) of spectra exhibiting N V gas with z ≈ zGRB, and the majority show large column densities N(N+ 4) 1014 cm −2. With one exception, the observed line profiles are kinematically cold; i.e., they are narrow and have small velocity offset (δ v 20 km s−1) from absorption lines associated with neutral gas. In addition, the N V absorption has similar velocity to that of the UV-pumped fine-structure lines, indicating that these high ions are located within ≈1 kpc of the GRB afterglow. These characteristics are unlike those for N V gas detected in the halo/disk of the Milky Way or along sight lines through high-z damped Lyα systems but resemble the narrow absorption line systems associated with quasars and some high-z starbursts. We demonstrate that GRB afterglows photoionize nitrogen to N+4 at r ≈ 10 pc. This process can produce N V absorption with characteristics resembling the majority of our sample, and we argue that it is the principal mechanism for N+4 along GRB sight lines. Therefore, the observations provide a snapshot of the physical conditions at this distance. In this scenario, the observations imply that the progenitor's stellar wind is confined to r 103 cm −3) environments, typical of molecular clouds. The observations, therefore, primarily constrain the physical conditions—metallicity, density, velocity fields—of the gas within the (former) molecular cloud region surrounding the GRB.

EUV spectral energy distribution of quasars restored from associated absorbers

(abridged) Aims. To reconstruct the spectral shape of the quasar ionizing radiation in the extreme-UV range (1Ryd <= E < 10Ryd) from the analysis of narrow absorption lines (NAL) of the associated systems. Methods. Computational technique for inverse spectroscopic problems - Monte Carlo Inversion augmented by procedure of the spectral shape recovering and modified to account for the incomplete coverage of the light source. Results. The ionizing spectra responsible for the ionization structure of the NAL systems require an intensity depression at E > 4Ryd which is attributed to the HeII Lyman continuum opacity (tau^HeII_c ~ 1). A most likely source of this opacity is a quasar accretion disk wind. The corresponding column density of HI in the wind is estimated as a few times 10^16 cm^-2. This amount of neutral hydrogen should cause a weak continuum depression at lamb <= 912A (rest-frame), and a broad and shallow absorption in HI Ly-alpha. If metallicity of the wind is high enough, other resonance lines of OVI, NeVI-NeVIII, etc. are expected. In the analyzed QSO spectra we do observe broad (stretching over 1000s km/s) and shallow (tau << 1) absorption troughs of HI Ly-alpha and OVI 1031,1037A...

Strong Narrow FeiiEmission Lines in the Quasar SDSS J102839.11+450009.4

We report identification of SDSS J102839.11+450009.4 as a peculiarly interesting quasar. It shows very prominent narrow emission lines (NELs) in Fe II that are remarkably different from the broad Fe II multiplets commonly observed in quasars and Seyfert 1 galaxies. The Fe II NEL spectrum is dominated in the UV by transitions to the low-lying ground levels with even parity, and by forbidden transitions in the optical, suggesting its formation in a warm collisionally ionized low density medium. Comparison with photoionization models suggests that fluorescence of Fe II by a soft continuum is probably also important in explaining the intensity ratios within the Fe II NEL multiplets and that of Fe II to S II λ4047 NELs. The Fe II NELs have similar widths to other NELs, including [O III] and [O II], but are blueshifted by ~170 km s−1 with respect to the redshift of the latter, which we take to be the systemic redshift of the quasar. In addition to the unusual Fe II NELs, the SDSS spectrum also reveals narrow absorption lines (NALs) in Hβ, Hγ, Hδ, He I λλ3889, 3189, 2946, 2830, and Mg II λλ2796, 2803. We identify two Mg II NAL systems blueshifted by 1200 and 670 km s−1, respectively. The redshift of the lower velocity Mg II NAL system is consistent with that of the Balmer and He I NALs. The observed He I NALs require a hydrogen column density of >1020 cm−2 in an H II region. Very few quasars show absorption in He I lines, and even fewer in Balmer lines. The unique spectral properties make this quasar a promising probe of the formation of Fe II emission lines and outflows, and the possible relation between the two.