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2871. CIV and SiIV broad absorption line troughs in SDSS
ID:
ivo://CDS.VizieR/J/ApJ/777/168
Title:
CIV and SiIV broad absorption line troughs in SDSS
Short Name:
J/ApJ/777/168
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed investigation of the variability of 428 CIV and 235 SiIV broad absorption line (BAL) troughs identified in multi-epoch observations of 291 quasars by the Sloan Digital Sky Survey-I/II/III. These observations primarily sample rest-frame timescales of 1-3.7yr over which significant rearrangement of the BAL wind is expected. We derive a number of observational results on, e.g., the frequency of BAL variability, the velocity range over which BAL variability occurs, the primary observed form of BAL-trough variability, the dependence of BAL variability upon timescale, the frequency of BAL strengthening versus weakening, correlations between BAL variability and BAL-trough profiles, relations between CIV and SiIV BAL variability, coordinated multi-trough variability, and BAL variations as a function of quasar properties. We assess implications of these observational results for quasar winds. Our results support models where most BAL absorption is formed within an order-of-magnitude of the wind-launching radius, although a significant minority of BAL troughs may arise on larger scales. We estimate an average lifetime for a BAL trough along our line-of-sight of a few thousand years. BAL disappearance and emergence events appear to be extremes of general BAL variability, rather than being qualitatively distinct phenomena. We derive the parameters of a random-walk model for BAL EW variability, finding that this model can acceptably describe some key aspects of EW variability. The coordinated trough variability of BAL quasars with multiple troughs suggests that changes in "shielding gas" may play a significant role in driving general BAL variability.
2872. CIV BAL disappearance in SDSS QSOs
ID:
ivo://CDS.VizieR/J/A+A/616/A114
Title:
CIV BAL disappearance in SDSS QSOs
Short Name:
J/A+A/616/A114
Date:
21 Oct 2021
Publisher:
CDS
Description:
Broad absorption lines (BALs) in the spectra of quasi-stellar objects (QSOs) originate from outflowing winds along our line of sight; winds are thought to originate from the inner regions of the QSO accretion disk, close to the central supermassive black hole (SMBH). These winds likely play a role in galaxy evolution and are responsible for aiding the accretion mechanism onto the SMBH. Several works have shown that BAL equivalent widths can change on typical timescales from months to years; such variability is generally attributed to changes in the covering factor (due to rotation and/or changes in the wind structure) and/or in the ionization level of the gas. We investigate BAL variability, focusing on BAL disappearance. We analyze multi-epoch spectra of more than 1500 QSOs - the largest sample ever used for such a study - observed by different programs from the Sloan Digital Sky Survey-I/II/III (SDSS-I/II/III), and search for disappearing CIV BALs. The spectra cover a rest-frame time baseline ranging from 0.28 to 4.9yr; the source redshifts range from 1.68 to 4.27. We detect 73 disappearing BALs in the spectra of 67 unique sources. This corresponds to 3.9% of BALs disappearing within 4.9yr (rest frame), and 5.1% of our BAL QSOs exhibit at least one disappearing BAL within 4.9yr (rest frame). We estimate the average lifetime of a BAL along our line of sight (~=80-100yr), which appears consistent with the accretion disk orbital time at distances where winds are thought to originate. We inspect various properties of the disappearing BAL sample and compare them to the corresponding properties of our main sample. We also investigate the existence of a correlation in the variability of multiple troughs in the same spectrum, and find it persistent at large velocity offsets between BAL pairs, suggesting that a mechanism extending on a global scale is necessary to explain the phenomenon. We select a more reliable sample of disappearing BALs on the basis of some criteria adopted in a previous publication, where a subset of our current sample was analyzed, and compare the findings from the two works, obtaining generally consistent results.
2873. 188 CIV BAL QSOs from SDSS DR7
ID:
ivo://CDS.VizieR/J/MNRAS/454/3962
Title:
188 CIV BAL QSOs from SDSS DR7
Short Name:
J/MNRAS/454/3962
Date:
21 Oct 2021
Publisher:
CDS
Description:
The variability of broad absorption lines (BALs) is investigated for a sample of 188 BAL quasars (QSOs) (z>1.7) with at least two epoch observations from the Sloan Digital Sky Survey Data Release 7, covering a time-scale of about 0.001-3yr in the rest frame. Considering only the longest time-scale between epochs for each QSO, 73 variable regions in the CIV BAL troughs are detected for 43 BAL QSOs. The proportion of BAL QSOs showing variable regions increases with longer time-interval than about 1 yr in the rest frame. The velocity width of variable regions is narrow compared to the BAL-trough outflow velocity. For 43 BAL QSOs with variable regions, it is found that there is a medium strong correlation between the variation of the continuum luminosity at 1500{AA} and the variation of the spectral index. With respect to the total 188 QSOs, a larger proportion of BAL QSOs with variable regions appears bluer during their brighter phases, which implies that the origin of BAL variable regions is related to the central accretion process. For 43 BAL QSOs with variable regions, it is possible that there is a negative medium strong correlation between the absolute variation of the equivalent width and the Mgii-based black hole mass, and a medium strong correlation between the maximum outflow velocity of variable regions and the Eddington ratio. These results imply a connection between the BAL-trough variation and the central accretion process.
2874. C IV BAL troughs properties in quasars
ID:
ivo://CDS.VizieR/J/ApJ/791/88
Title:
C IV BAL troughs properties in quasars
Short Name:
J/ApJ/791/88
Date:
21 Oct 2021
Publisher:
CDS
Description:
We consider how the profile and multi-year variability properties of a large sample of C IV Broad Absorption Line (BAL) troughs change when BALs from Si IV and/or Al III are present at corresponding velocities, indicating that the line of sight intercepts at least some lower ionization gas. We derive a number of observational results for C IV BALs separated according to the presence or absence of accompanying lower ionization transitions, including measurements of composite profile shapes, equivalent width (EW), characteristic velocities, composite variation profiles, and EW variability. We also measure the correlations between EW and fractional-EW variability for C IV, Si IV, and Al III. Our measurements reveal the basic correlated changes between ionization level, kinematics, and column density expected in accretion-disk wind models; e.g., lines of sight including lower ionization material generally show deeper and broader C IV troughs that have smaller minimum velocities and that are less variable. Many C IV BALs with no accompanying Si IV or Al III BALs may have only mild or no saturation.
2875. CIV broad abs. line SDSS QSO obs. with Gemini
ID:
ivo://CDS.VizieR/J/ApJ/862/22
Title:
CIV broad abs. line SDSS QSO obs. with Gemini
Short Name:
J/ApJ/862/22
Date:
21 Oct 2021
Publisher:
CDS
Description:
We isolate a set of quasars that exhibit emergent CIV broad absorption lines (BALs) in their spectra by comparing spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 and the SDSS/BOSS Data Releases 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. We find an emergence rate consistent with the previously reported disappearance rate of BAL quasars given the relative numbers of non-BAL and BAL quasars in the SDSS. We find that candidate newly emerged BALs are preferentially drawn from among BALs with smaller balnicity indices, shallower depths, larger velocities, and smaller widths. Within two rest-frame years (average) after a BAL has emerged, we find it equally likely to continue increasing in equivalent width in an observation 6 months later (average) as it is to start decreasing. From the time separations between our observations, we conclude that the coherence timescale of BALs is less than 100 rest-frame days. We observe coordinated variability among pairs of troughs in the same quasar, likely due to clouds at different velocities responding to the same changes in ionizing flux, and the coordination is stronger if the velocity separation between the two troughs is smaller. We speculate that the latter effect may be due to clouds having on average lower densities at higher velocities owing to mass conservation in an accelerating flow, causing the absorbing gas in those clouds to respond on different timescales to the same ionizing flux variations.
2876. CIV candidates
ID:
ivo://CDS.VizieR/J/ApJ/708/868
Title:
CIV candidates
Short Name:
J/ApJ/708/868
Date:
21 Oct 2021
Publisher:
CDS
Description:
We surveyed the Hubble Space Telescope UV spectra of 49 low-redshift quasars for z<1 CIV candidates, relying solely on the characteristic wavelength separation of the doublet. After consideration of the defining traits of CIV doublets (e.g., consistent line profiles, other associated transitions, etc.), we defined a sample of 38 definite (group G=1) and five likely (G=2) doublets with rest equivalent widths W_r_ for both lines detected at >=3{sigma}_W_r__. We conducted Monte Carlo completeness tests to measure the unblocked redshift ({Delta}z) and co-moving path length ({Delta}X) over which we were sensitive to CIV doublets of a range of equivalent widths and column densities. Using the power-law model of f(N(C^+3^)), we measured the C^+3^ mass density relative to the critical density: {Omega}_C^+3^_=(6.20^+1.82^_-1.52_)x10^-8^ for 13<=logN(C^+3^)<=15.
2877. CIV column densities in z<2.5 QSOs
ID:
ivo://CDS.VizieR/J/MNRAS/401/2715
Title:
CIV column densities in z<2.5 QSOs
Short Name:
J/MNRAS/401/2715
Date:
21 Oct 2021
Publisher:
CDS
Description:
The cosmic evolution of the metal content of the intergalactic medium puts stringent constraints on the properties of galactic outflows and on the nature of UV background. In this paper, we present a new measure of the redshift evolution of the mass density of CIV, {OMEGA}_CIV_, in the interval 1.5~<z~<4 based on a sample of more than 1500 CIV lines with column densities 10^12^~<N(CIV)~<10^15^cm^-2^. This sample more than doubles the absorption redshift path covered in the range z<2.5 by previous samples. The result shows a significant increase of {OMEGA}_CIV_ towards the lower redshifts at variance with the previously pictured constant behaviour.
2878. CIV NAL systems from SDSS-DR14 quasar spectra
ID:
ivo://CDS.VizieR/J/ApJS/239/23
Title:
CIV NAL systems from SDSS-DR14 quasar spectra
Short Name:
J/ApJS/239/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for CIV{lambda}{lambda}1548,1551 narrow absorption doublets in spectral data from the blue wing {upsilon}r=30000km/s until the red wing of CIV{lambda}1549 emission lines. We have obtained 21239 CIV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from {Delta}MJD=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 {upsilon}r~2000km/s and gently extends to a larger offset velocity. There are 110 variable C IV NALs with {upsilon}r>12000km/s. 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.
2879. CIV narrow absorption line systems in SDSS-DR14
ID:
ivo://CDS.VizieR/J/ApJS/236/39
Title:
CIV narrow absorption line systems in SDSS-DR14
Short Name:
J/ApJS/236/39
Date:
21 Oct 2021
Publisher:
CDS
Description:
We assemble 207 variable quasars from the Sloan Digital Sky Survey, all with at least 3 observations, to analyze CIV narrow absorption doublets, and obtain 328 CIV narrow absorption line systems. We find that 19 out of 328 CIV narrow absorption line systems were changed by |{Delta}W_r_^{lambda}1548^|>=3{sigma}_{Delta}Wr_^{lambda}1548^ on timescales from 15.9 to 1477 days at rest-frame. Among the 19 obviously variable CIV systems, we find that (1) 14 systems have relative velocities {upsilon}_r_>0.01c and 4 systems have {upsilon}_r_>0.1c, where c is the speed of light; (2) 13 systems are accompanied by other variable CIV systems; (3) 9 systems were changed continuously during multiple observations; and (4) 1 system with {upsilon}_r_=16862km/s was enhanced by {Delta}W_r_^{lambda}1548^=2.7{sigma}_{Delta}Wr_^{lambda}1548^ 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 CIV narrow absorption lines are form differently over a short timescale.
2880. CIV QSO absorption systems
ID:
ivo://CDS.VizieR/J/A+A/283/759
Title:
CIV QSO absorption systems
Short Name:
J/A+A/283/759
Date:
21 Oct 2021
Publisher:
CDS
Description:
High spectral resolution (FWHM = 0.6 or 0.35 {AA}) were obtained for six high redshift QSOs, z_em_ > 2.2, containing lines from 31 metal-rich absorption line systems amongst which 20 Civ doublets split in subcomponents with velocity differences within a system smaller than 400 km.s^-1^. Our survey has been combined with published data at similar resolution and the resulting sample comprises 35 systems, 23 of which are splitted in a total of 87 subcomponents. The mean redshift of the sample is <z> = 2.65. The observations were carried out at the F/8 Cassegrain focus of the 3.6m telescope at la Silla, between 1984 and 1989.

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