Iv Broad Absorption Line Research Articles

O iii] emission in z ≈ 2 quasars with and without broad absorption lines

ABSTRACT Understanding the links between different phases of outflows from active galactic nuclei is a key goal in extragalactic astrophysics. Here, we compare [O iii] $\lambda \lambda$4960, 5008 outflow signatures in quasars with and without broad absorption lines (BALs), aiming to test how the broad absorption troughs seen in the rest-frame ultraviolet are linked to the narrow line region outflows seen in the rest-frame optical. We present new near-infrared spectra from Magellan/FIRE that cover [O iii] in 12 quasars with $2.1\lt z\lt 2.3$, selected to have strong outflow signatures in C iv$\lambda$1550. Combining with data from the literature, we build a sample of 73 BAL, 115 miniBAL, and 125 non-BAL quasars with $1.5\lt z\lt 2.6$. The strength and velocity width of [O iii] correlate strongly with the C iv emission properties, but no significant difference is seen in the [O iii] emission-line properties between the BALs, non-BALs, and miniBALs once the dependence on C iv emission is taken into account. A weak correlation is observed between the velocities of C iv BALs and [O iii] emission, which is accounted for by the fact that both outflow signatures correlate with the underlying C iv emission properties. Our results add to the growing evidence that BALs and non-BALs are drawn from the same parent population and are consistent with a scenario wherein BAL troughs are intermittent tracers of persistent quasar outflows, with a part of such outflow becoming optically thick along our line of sight for sporadic periods of time within which BALs are observed.

The SDSS-V Black Hole Mapper Reverberation Mapping Project: C iv Broad Absorption Line Acceleration in the Quasar SBS 1408+544

We present the results of an investigation of a highly variable C iv broad absorption line (BAL) feature in spectra of the quasar SBS 1408+544 (z = 2.337) that shows a significant shift in velocity over time. This source was observed as a part of the Sloan Digital Sky Survey (SDSS) Reverberation Mapping project and the SDSS-V Black Hole Mapper Reverberation Mapping project, and has been included in two previous studies, both of which identified significant variability in a high-velocity C iv BAL on timescales of just a few days in the quasar rest frame. Using ∼130 spectra acquired over 8 yr of spectroscopic monitoring with SDSS, we have determined that this BAL is not only varying in strength, but is also systematically shifting to higher velocities. Using cross-correlation methods, we measure the velocity shifts (and corresponding acceleration) of the BAL over a wide range of timescales, measuring an overall velocity shift of Δv=−683−84+89 km s−1 over the 8 yr monitoring period. This corresponds to an average rest-frame acceleration of a = 1.04 −0.13+0.14 cm s−2, though the magnitude of the acceleration on shorter timescales is not constant throughout. We place our measurements in the context of BAL-acceleration models and examine various possible causes of the observed velocity shift.

Time variability of ultra-fast BAL outflows using SALT: C iv absorption depth based analysis

ABSTRACT We probe the small-scale absorption line variability using absorption depth based analysis of a sample of 64 ultra-fast outflow (UFO) C iv broad absorption line (BAL) quasars monitored using the Southern African Large Telescope. We confirm the strong monotonic increase in the strength of variability with increasing outflow velocity. We identify regions inside the BAL trough for each source where the normalized flux difference between two epochs is >0.1 for a velocity width ≥500 km s−1 (called ‘variable regions’). We find that the total number of variable regions increases with the time interval probed and the number of BALs showing variable regions almost doubles from short (<2 yr) to long (>2 yr) time-scales. We study the distributions of variable region properties such as its velocity width, depth, and location. These regions typically occupy a few-tenths of the entire width of the BAL. Their widths are found to increase with increasing time-scales having typical widths of ∼2000 km s−1 for Δt > 2 yr. However, their absolute velocity with respect to zem and their relative position within the BAL profile remain random irrespective of the time-scale probed. The equivalent width variations of the BALs are strongly dependent on the size and depth of the variable regions but are little dependent on their total number. Finally, we find that ∼17 per cent of the UFO BALs show uncorrelated variability within the BAL trough.

Time variability of ultra fast BAL outflows using SALT: C iv equivalent width analysis

ABSTRACT We study the time variability (over ≤7.3 yr) of ultra fast outflows (UFOs) detected in a sample of 64 C iv broad absorption line (BAL) quasars (with 80 distinct BAL components) monitored using the Southern African Large Telescope. By comparing the properties of the quasar in our sample with those of a control sample of non-BAL quasars, we show that the distributions of black hole mass are different and the bolometric luminosities and optical photometric variations of UFO BAL quasars are slightly smaller compared to that of non-BAL quasars. The detection fraction of C iv equivalent width (W) variability (∼95 per cent), the fractional variability amplitude $\left(\frac{\Delta W}{W}\right)$ and the fraction of ‘highly variable’ BAL (i.e. $\big|$$\frac{\Delta W}{W}$$\big|$ > 0.67) components (∼33 per cent) are higher in our sample compared to the general BAL population. The scatter in $\frac{\Delta W}{W}$ and the fraction of ‘highly variable’ BALs increase with the time-scale probed. The $\frac{\Delta W}{W}$ distribution is asymmetric at large time scales. We attribute this to the BAL strengthening time-scales being shorter than the weakening time-scales. The BAL variability amplitude correlates strongly with the BAL properties compared to the quasar properties. BALs with low W, high-velocity, shallow profiles, and low-velocity width tend to show more variability. When multiple BAL components are present, a correlated variability is seen between low- and high-velocity components with the latter showing a larger amplitude variations. We find an anticorrelation between the fractional variations in the continuum flux and W. While this suggests photoionization induced variability, the scatter in continuum flux is much smaller than that of W.

MALS SALT-NOT Survey of MIR-selected Powerful Radio-bright AGN at 0 < z < 3.5

We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased sample of powerful radio-bright (>200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median z = 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δi = 0.6 mag) and redder (Δ(g−i) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar population detected in optical surveys. About 20% of the sources are narrow-line AGN (NLAGN)–65% of these, at z < 0.5 are galaxies without strong nuclear emission, and 10% at z > 1.9, have emission line ratios similar to radio galaxies. The farthest NLAGN in our sample is M1513-2524 (z em = 3.132), and the largest radio source (size ∼330 kpc) is M0909-3133 (z em = 0.884). We discuss in detail 110 AGN at 1.9 < z < 3.5. Despite representing the radio loudest quasars (median R = 3685), their Eddington ratios are similar to the Sloan Digital Sky Survey quasars having lower R. We detect four C iv broad-absorption line (BAL) QSOs, all among AGN with least R, and highest black hole masses and Eddington ratios. The BAL detection rate (%) is consistent with that seen in extremely powerful (L 1.4GHz > 1025 W Hz−1) quasars. Using optical light curves, radio polarization, and γ-ray detections, we identify seven high-probability BL Lacertae objects. We also summarize the full MALS footprint to search for H i 21 cm and OH 18 cm lines at z < 2.

The Farthest Quasar Mini-Broad Absorption Line Outflow from Its Central Source: Very Large Telescope/UVES Observation of SDSS J0242+0049

Abstract We analyze Very Large Telescope/UVES observations of the quasar SDSS J024221.87+004912.6. We identify four absorption outflow systems: a C iv broad absorption line (BAL) at v ≈ −18,000 km s−1 and three narrower low-ionization systems with centroid velocities ranging from –1200 to –3500 km s−1. These outflows show similar physical attributes to the [O iii] outflows studied by Liu et al. (2013). We find that two of the systems are energetic enough to contribute to active galactic nucleus feedback, with one system reaching above 5% of the quasar’s Eddington luminosity. We also find that this system is at a distance of 67 kpc away from the quasar, the farthest detected mini-BAL absorption outflow from its central source to date. In addition, we examine the time-variability of the BAL and find that its velocity monotonically increases, while the trough itself becomes shallower over time.

Improved selection of extremely red quasars with boxy C iv lines in BOSS

ABSTRACT Extremely red quasars (ERQs) are an interesting sample of quasars in the Baryon Oscillation Spectroscopic Sample (BOSS) in the redshift range of 2.0–3.4 and have extreme red colours of i − W3 ≥ 4.6. Core ERQs have strong C iv emission lines with rest equivalent width of ≥100 Å. Many core ERQs also have C iv line profiles with peculiar boxy shapes which distinguish them from normal blue quasars. We show, using a combination of kernel density estimation and local outlier factor analyses on a space of the i − W3 colour, C iv rest equivalent width and line kurtosis, that core ERQs likely represent a separate population rather than a smooth transition between normal blue quasars and the quasars in the tail of the colour-REW distribution. We apply our analyses to find new criteria for selecting ERQs in this 3D parameter space. Our final selection produces 133 quasars, which are three times more likely to have a visually verified C iv broad absorption line feature than the previous core ERQ sample. We further show that our newly selected sample are extreme objects in the intersection of the WISE AGN catalogue with the MILLIQUAS quasar catalogue in the colour–colour space of (W1 − W2, W2 − W3). This paper validates an improved selection method for red quasars which can be applied to future data sets such as the quasar catalogue from the Dark Energy Spectroscopic Instrument.

Correlated time variability of multicomponent high-velocity outflows in J162122.54+075808.4

ABSTRACT We present a detailed analysis of time variability of two distinct C iv broad absorption line (BAL) components seen in the spectrum of J162122.54+075808.4 (zem = 2.1394) using observations from SDSS, NTT, and SALT taken at seven different epochs spanning about 15 yr. The blue-BAL component (with an ejection velocity, $v_{\rm e}\sim 37\, 500$ km s−1) is an emerging absorption that shows equivalent width variations and kinematic shifts consistent with acceleration. The red-BAL component ($v_{\rm e} \sim 15\, 400$ km s−1) is a three-component absorption. One of the components is emerging and subsequently disappearing. The two other components show kinematic shifts consistent with acceleration coupled with equivalent width variability. Interestingly, we find the kinematic shifts and equivalent width variability of the blue- and red-BAL components to be correlated. While the C iv emission-line flux varies by more than 17 per cent during our monitoring period, the available light curves (covering rest frame 1300–2300 Å) do not show more than a 0.1 mag variability in the continuum. This suggests that the variations in the ionizing flux are larger than that of the near-ultraviolet flux. However, the correlated variability seen between different BAL components cannot be explained solely by photoionization models without structural changes. In the framework of disc wind models, any changes in the radial profiles of density and/or velocity triggered either by disc instabilities or by changes in the ionizing radiation can explain our observations. High-resolution spectroscopic monitoring of J1621+0758 is important to understand the physical conditions of the absorbing gas and thereby to constrain the parameters of disc wind models.

Appearance versus disappearance of broad absorption line troughs in quasars

ABSTRACT We present a new set of 84 broad absorption line (BAL) quasars (1.7 &amp;lt; zem &amp;lt; 4.4) exhibiting an appearance of C iv BAL troughs over 0.3–4.8 rest-frame years by comparing the Sloan Digital Sky Survey Data Release (SDSSDR)-7, SDSSDR-12, and SDSSDR-14 quasar catalogues. We contrast the nature of BAL variability in this appearing BAL quasar sample with a disappearing BAL quasar sample studied in the literature by comparing the quasar’s intrinsic, BAL trough, and continuum parameters between the two samples. We find that appearing BAL quasars have relatively higher redshift and smaller probed time-scales as compared to the disappearing BAL quasars. To mitigate the effect of any redshift bias, we created control samples of appearing and disappearing BAL quasars that have similar redshift distribution. We find that the appearing BAL quasars are relatively brighter and have shallower and wider BAL troughs compared to the disappearing BAL sample. The distribution of quasar continuum variability parameters between the two samples is clearly separated, with the appearance of the BAL troughs being accompanied by the dimming of the continuum and vice versa. Spectral index variations in the two samples also point to the anticorrelation between the BAL trough and continuum variations consistent with the ‘bluer when brighter’ trend in quasars. We show that the intrinsic dust model is less likely to be a favourable scenario in explaining BAL appearance/disappearance. Our analysis suggests that the extreme variations of BAL troughs like BAL appearance/disappearance are mainly driven by changes in the ionization conditions of the absorbing gas.

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.

A Kinematic Shift of the C iv Broad Absorption Line in Quasar SDSS J120819.29+035559.4

Abstract We report the kinematic shift of the C iv broad absorption line (BAL) in quasar SDSS J120819.29+035559.4 (hereafter J1208+0355). This quasar shows two BAL systems, including a blue component of system A at ∼23,500 km s−1 that shows a kinematic shift of 1166 ± 65 km s−1, and a red component of system B at ∼7000 km s−1 that can be decomposed into several narrow absorption lines (NALs). First, we confirm that the most likely cause for the equivalent width variations of the absorption lines (at least for system B) in J1208+0355 is the ionization change scenario as a response to the changes in the ionization continuum according to the following observational factors: (1) coordinated multiple absorption lines strengthening; (2) the continuum flux shows an obvious weakening. Second, we find line-locking phenomena from the blended NALs within system B, indicating that these outflow clouds are driven by a radiative force caused by resonance lines. The above two research aspects convincingly reveal that the BAL outflows of J1208+0355 are affected by the background radiation energy. Therefore, we infer that the kinematic shift shown in system A may be produced by actual line-of-sight acceleration of the outflow clouds, which is driven by radiation pressure from the background light source.

Correlations between the Variation of the Ionizing Continuum and Broad Absorption Lines in Individual Quasars

Abstract We discover the significant (significance level of &gt;99%) correlations between the fractional variation of the ionizing continuum and that of the C iv and/or Si iv broad absorption lines (BALs) in each of 21 BAL quasars that have at least five-epoch observations from the Sloan Digital Sky Survey-I/II/III. This result reveals that the fluctuation of the ionizing continuum is the driver of most of these BAL variations. Among them, 17 show negative correlations and the other 4 positive correlations, which agrees with the prediction of photoionization models that absorption line variability response to ionization changes is not monotonic. Eight quasars out of 21 examples have been observed at least 30 times on rest-frame timescales as short as a few days, which reveals that changes in the incident ionizing continuum can cause BAL variability even in such a short period of time. In addition, we find that most of the 21 quasars show larger variation amplitude in Si iv than C iv, which reveals the ubiquity of saturation in these BALs (at least for C iv BALs).

Narrow Absorption Lines Complex. III. Gradual Transition from Type S to Type N Broad Absorption Line

Abstract We study the relationship between the broad absorption lines (BALs) that can be decomposed into multiple narrow absorption lines and those that cannot (hereafter Type N and Type S BAL, respectively), based on the analysis of three BAL systems (systems A, B, and C) in two-epoch spectra of quasar SDSS J113009.40+495247.9 (hereafter J1130+4952). As the velocity decreases (from systems A to C), these three BAL systems show a gradual transition from Type S to Type N BAL, and their equivalent widths (EWs) and profile shapes vary in a regular way. We ascribe the absorption line variability in J1130+4952 to the ionization change as a response to the fluctuation of the ionizing continuum based on several factors: (1) coordinated EW strengthening over a wide range in systems A and B, (2) the system B shows an obvious change in Si iv but no significant change in C iv BAL, and (3) asynchronized variability between the continuum and absorption lines. Based on the analysis of the variation mechanism, location, ionization state, and structure of systems A, B, and C, we hold the view that the Type S and Type N BALs in J1130+4952 probe the same clumped outflow, with the Type S BALs originating from the inner part of the outflow with a relatively higher ionization state, smaller column density, and more clumpy structures, while the Type N BALs originate from the outer part of the outflow with relatively lower ionization state, larger column density, and fewer clumpy structures.

Correlation between the ionizing continuum and the variable C iv broad absorption line in multi-epoch observations of SDSS J141007.74+541203.3

Abstract Correlations between the variations of quasar absorption lines and the ionizing continuum have been confirmed recently in systematic studies. However, no convincing individual case is reported. We present a statistical analysis of the variable C iv broad absorption line (BAL) in the quasar SDSS J141007.74+541203.3, which has been observed with 44 epochs by the Sloan Digital Sky Survey Data Release 14. Grier et al. have concluded that the most likely cause of the variability of the BAL in SDSS J141007.74+541203.3 is a rapid response to changes in the incident ionizing continuum. In this paper, we confirm the anticorrelation between the equivalent width of BALs and the flux of the continuum based on the spectra of this quasar, which show significant variations. This serves as further independent evidence for the conclusions of Grier et al.

Variability of Low-ionization Broad Absorption-line Quasars Based on Multi-epoch Spectra from the Sloan Digital Sky Survey

Abstract We present absorption variability results for 134 bona fide Mg ii broad absorption-line (BAL) quasars at 0.46 ≲ z ≲ 2.3 covering days to ∼10 yr in the rest frame. We use multiple-epoch spectra from the Sloan Digital Sky Survey, which has delivered the largest such BAL variability sample ever studied. Mg ii-BAL identifications and related measurements are compiled and presented in a catalog. We find a remarkable time-dependent asymmetry in the equivalent width (EW) variation from the sample, such that weakening troughs outnumber strengthening troughs, the first report of such a phenomenon in BAL variability. Our investigations of the sample further reveal that (i) the frequency of BAL variability is significantly lower (typically by a factor of 2) than that in high-ionization BALQSO samples, (ii) Mg ii-BAL absorbers tend to have relatively high optical depths and small covering factors along our line of sight, (iii) there is no significant EW-variability correlation between Mg ii troughs at different velocities in the same quasar, and (iv) the EW-variability correlation between Mg ii and Al iii BALs is significantly stronger than that between Mg ii and C iv BALs at the same velocities. These observational results can be explained by a combined transverse-motion/ionization-change scenario, where transverse motions likely dominate the strengthening BALs while ionization changes and/or other mechanisms dominate the weakening BALs.

The Sloan Digital Sky Survey Reverberation Mapping Project: Systematic Investigations of Short-timescale C IV Broad Absorption Line Variability

Abstract We systematically investigate short-timescale (&lt;10 day rest-frame) C iv broad absorption-line (BAL) variability to constrain quasar-wind properties and provide insights into BAL-variability mechanisms in quasars. We employ data taken by the Sloan Digital Sky Survey Reverberation Mapping project, as the rapid cadence of these observations provides a novel opportunity to probe BAL variability on shorter rest-frame timescales than have previously been explored. In a sample of 27 quasars with a median of 58 spectral epochs per quasar, we have identified 15 quasars ( %), 19 of 37 C iv BAL troughs ( %), and 54 of 1460 epoch pairs (3.7% ± 0.5%) that exhibit significant C iv BAL equivalent-width variability on timescales of less than 10 days in the quasar rest frame. These frequencies indicate that such variability is common among quasars and BALs, though somewhat rare among epoch pairs. Thus, models describing BALs and their behavior must account for variability on timescales down to less than a day in the quasar rest frame. We also examine a variety of spectral characteristics and find that, in some cases, BAL variability is best described by ionization-state changes, while other cases are more consistent with changes in covering fraction or column density. We adopt a simple model to constrain the density and radial distance of two outflows appearing to vary by ionization-state changes, yielding outflow density lower limits consistent with previous work.

Deceleration of C iv and Si iv Broad Absorption Lines in X-Ray Bright Quasar SDSS-J092345+512710

Abstract We report a synchronized kinematic shift of C iv and Si iv broad absorption lines (BAL) in a high-ionization, radio-loud, and X-ray bright quasar SDSS-J092345+512710 (at ∼ 2.1627). This quasar shows two broad absorption components (blue component at v ∼ 14,000 km s−1, and red component at v ∼ 4000 km s−1 with respect to the quasars systemic redshift). The absorption profiles of C iv and Si iv BAL of the blue component show a decrease in outflow velocity with an average deceleration rate of cm s−2 and cm s−2 over a rest-frame time span of 4.15 yr. We do not see any acceleration-like signature in the red component. This is consistent with dramatic variabilities usually seen at high velocities. During our monitoring period the quasar has shown no strong continuum variability. We suggest the observed variability could be related to the time dependent changes in disk wind parameters like launching radius, initial flow velocity, or mass outflow rate.

Broad Absorption Line Disappearance/Emergence in Multiple Ions in a Weak Emission-line Quasar

Abstract We report the discovery of the disappearance of Mg ii, Al iii, C iv, and Si iv broad absorption lines (BALs) at the same velocity (0.07c), accompanied by a new C iv BAL emerging at a higher velocity (up to 0.11c), in the quasar J0827+4252 at z = 2.038. This is the first report of BAL disappearance (i) over Mg ii, Al iii, C iv, and Si iv ions and (ii) in a weak emission-line quasar (WLQ). The discovery is based on four spectra from the Sloan Digital Sky Survey and one follow-up spectrum from Hobby–Eberly Telescope/Low-Resolution Spectrograph-2. The simultaneous C iv BAL disappearance and emergence at different velocities, together with no variations in the Catalina Real-Time Transient Survey light curve, indicate that ionization changes in the absorbing material are unlikely to cause the observed BAL variability. Our analyses reveal that transverse motion is the most likely dominant driver of the BAL disappearance/emergence. Given the presence of mildly relativistic BAL outflows and an apparently large C iv emission-line blueshift that is likely associated with strong bulk outflows in this WLQ, J0827+4252 provides a notable opportunity to study extreme quasar winds and their potential in expelling material from inner to large-scale regions.

The Discovery of a Luminous Broad Absorption Line Quasar at a Redshift of 7.02

Abstract Despite extensive efforts, to date only two quasars have been found at z &gt; 7, due to a combination of low spatial density and high contamination from more ubiquitous Galactic cool dwarfs in quasar selection. This limits our current knowledge of the super-massive black hole growth mechanism and reionization history. In this Letter, we report the discovery of a luminous quasar at z = 7.021, DELS J003836.10–152723.6 (hereafter J0038–1527), selected using photometric data from Dark Energy Spectroscopic Instrument Legacy Imaging Survey, Pan-STARRS1 (PS1) imaging Survey, as well as Wide-field Infrared Survey Explore mid-infrared all-sky survey. With an absolute magnitude of M 1450 = –27.1 and bolometric luminosity of L Bol = 5.6 × 1013 L ⊙, J0038–1527 is the most luminous quasar known at z &gt; 7. Deep optical to near-infrared spectroscopic observations suggest that J0038–1527 hosts a 1.3 billion solar mass black hole accreting at the Eddington limit, with an Eddington ratio of 1.25 ± 0.19. The C iv broad emission line of J0038–1527 is blueshifted by more than 3000 km s−1 relative to the quasar systemic redshift. More detailed investigations of the high-quality spectra reveal three extremely high-velocity C iv broad absorption lines with velocity from 0.08 to 0.14 times the speed of light and total “balnicity” index of more than 5000 km s−1, suggesting the presence of relativistic outflows. J0038–1527 is the first quasar found at the epoch of reionization with such strong outflows, and therefore provides a unique laboratory to investigate active galactic nuclei feedback on the formation and growth of the most massive galaxies in the early universe.

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.