Broad absorption lines (BALs) in quasar spectra identify high-velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. The variability of BALs ...can help us understand the structure, evolution and basic physical properties of the outflows. Here we report on our first results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2 < z < 2.9, focusing on C ivλ1549 BAL variability in two different time intervals: 4-9 months (short term) and 3.8-7.7 yr (long term) in the quasar rest frame. We find that 39 per cent (7/18) of the quasars varied in the short-term data, whereas 65 per cent (15/23) varied in the long-term data, with a larger typical change in strength in the long-term data. The variability occurs typically in only portions of the BAL troughs. The components at higher outflow velocities are more likely to vary than those at lower velocities, and weaker BALs are more likely to vary than stronger BALs. The fractional change in BAL strength correlates inversely with the strength of the BAL feature, but does not correlate with the outflow velocity. Both the short-term and long-term data indicate the same trends. The observed behaviour is most readily understood as a result of the movement of clouds across the continuum source. If the crossing speeds do not exceed the local Keplerian velocity, then the observed short-term variations imply that the absorbers are <6 pc from the central quasar.
This is the second in a series of papers aiming to test how the mass (M
BH), accretion rate (Ṁ) and spin (a
*) of supermassive black holes (SMBHs) determine the observed properties of type I active ...galactic nuclei (AGN). Our project utilizes a sample of 39 unobscured AGN at z ≃ 1.55 observed by Very Large Telescope/X-Shooter, selected to map a large range in M
BH and L/L
Edd and covers the most prominent UV–optical (broad) emission lines, including Hα, Hβ, Mg ii λ2798 and C iv λ1549. This paper focuses on single-epoch, ‘virial’ M
BH determinations from broad emission lines and examines the implications of different continuum modelling approaches in line width measurements. We find that using a local power-law continuum instead of a physically motivated thin disc continuum leads to only slight underestimation of the full width at half-maximum (FWHM) of the lines and the associated M
BH(FWHM). However, the line dispersion σline and associated M
BH(σline) are strongly affected by the continuum placement and provides less reliable mass estimates than FWHM-based methods. Our analysis shows that Hα, Hβ and Mg ii can be safely used for virial M
BH estimation. The C iv line, on the other hand, is not reliable in the majority of the cases; this may indicate that the gas emitting this line is not virialized. While Hα and Hβ show very similar line widths, the mean FWHM(Mg ii) is about 30 per cent narrower than FWHM(Hβ). We confirm several recent suggestions to improve the accuracy in C iv-based mass estimates, relying on other UV emission lines. Such improvements do not reduce the scatter between C iv-based and Balmer-line-based mass estimates.
The physics of active super massive black holes (BHs) is governed by their mass (M...), spin (a*), and accretion rate (M). This work is the first in a series of papers with the aim of testing how ...these parameters determine the observable attributes of active galactic nuclei (AGN). We have selected a sample in a narrow redshift range, centred on z ~ 1.55, that covers a wide range in M... and M, and are observing them with X-shooter, covering rest wavelengths ~1200-9800 A. The current work covers 30 such objects and focuses on the origin of the AGN spectral energy distribution (SED). After estimating M... and M ... based on each observed SED, we use thin accretion disc (AD) models and a Bayesian analysis to fit the observed SEDs in our sample. We are able to fit 22/30 of the SEDs. Out of the remaining eight SEDs, three can be fit by the thin AD model by correcting the observed SED for reddening within the host galaxy and four can be fit by adding a disc wind to the model. In four of these eight sources, Milky Way-type extinction, with the strong 2175 A feature, provides the best reddening correction. The distribution in spin parameter covers the entire range, from -1 to 0.998, and the most massive BHs have spin parameters greater than 0.7. This is consistent with the 'spin-up' model of BH evolution. Altogether, these results indicate that thin ADs are indeed the main power houses of AGN, and earlier claims to the contrary are likely affected by variability and a limited observed wavelength range. (ProQuest: ... denotes formulae/symbols omitted.)
Broad absorption lines (BALs) in quasar spectra identify high-velocity outflows that might exist in all quasars and could play a major role in feedback to galaxy evolution. The viability of BAL ...outflows as a feedback mechanism depends on their kinetic energies, as derived from the outflow velocities, column densities, and distances from the central quasar. We estimate these quantities for the quasar, Q1413+1143 (redshift z
e
= 2.56), aided by the first detection of P v λλ1118, 1128 BAL variability in a quasar. In particular, P v absorption at velocities where the C iv trough does not reach zero intensity implies that the C iv BAL is saturated and the absorber only partially covers the background continuum source (with characteristic size <0.01 pc). With the assumption of solar abundances, we estimate that the total column density in the BAL outflow is log N
H ≳ 22.3 cm−2. Variability in the P v and saturated C iv BALs strongly disfavours changes in the ionization as the cause of the BAL variability, but supports models with high column density BAL clouds moving across our lines of sight. The observed variability time of 1.6 yr in the quasar rest frame indicates crossing speeds >750 km s−1 and a radial distance from the central black hole of ≲ 3.5 pc, if the crossing speeds are Keplerian. The total outflow mass is ∼4100 M⊙, the kinetic energy ∼4 × 1054 erg, and the ratio of the outflow kinetic energy luminosity to the quasar bolometric luminosity is ∼0.02 (at the minimum column density and maximum distance), which might be sufficient for important feedback to the quasar's host galaxy.
This is the third paper in a series describing the spectroscopic properties of a sample of 39 AGN at z ∼ 1.5, selected to cover a large range in black hole mass (M
BH) and Eddington ratio (L/L
Edd). ...In this paper, we continue the analysis of the VLT/X-shooter observations of our sample with the addition of nine new sources. We use an improved Bayesian procedure, which takes into account intrinsic reddening, and improved M
BH estimates, to fit thin accretion disc (AD) models to the observed spectra and constrain the spin parameter (a
*) of the central black holes. We can fit 37 out of 39 AGN with the thin AD model, and for those with satisfactory fits, we obtain constraints on the spin parameter of the BHs, with the constraints becoming generally less well defined with decreasing BH mass. Our spin parameter estimates range from ∼−0.6 to maximum spin for our sample, and our results are consistent with the ‘spin-up’ scenario of BH spin evolution. We also discuss how the results of our analysis vary with the inclusion of non-simultaneous GALEX photometry in our thin AD fitting. Simultaneous spectra covering the rest-frame optical through far-UV are necessary to definitively test the thin AD theory and obtain the best constraints on the spin parameter.
Broad absorption lines (BALs) in quasar spectra are prominent signatures of high-velocity outflows, which might be present in all quasars and could be a major contributor to feedback to galaxy ...evolution. Studying the variability in these BALs allows us to further our understanding of the structure, evolution and basic physical properties of the outflows. This is the third paper in a series on a monitoring programme of 24 luminous BAL quasars at redshifts 1.2 < z < 2.9. We focus here on the time-scales of variability in C iv λ1549 BALs in our full multi-epoch sample, which covers time-scales from 0.02 to 8.7 yr in the quasar rest frame. Our sample contains up to 13 epochs of data per quasar, with an average of seven epochs per quasar. We find that both the incidence and the amplitude of variability are greater across longer time-scales. Part of our monitoring programme specifically targeted half of these BAL quasars at rest-frame time-scales ≤2 months. This revealed variability down to the shortest time-scales we probe (8-10 d). Observed variations in only portions of BAL troughs or in lines that are optically thick suggest that at least some of these changes are caused by clouds (or some type of outflow substructures) moving across our lines of sight. In this crossing cloud scenario, the variability times constrain both the crossing speeds and the absorber locations. Specific results also depend on the emission and absorption geometries. We consider a range of geometries and use Keplerian rotational speeds to derive a general relationship between the variability times, crossing speeds and outflow locations. Typical variability times of the order of ∼1 yr indicate crossing speeds of a few thousand km s−1 and radial distances ∼1 pc from the central black hole. However, the most rapid BAL changes occurring in 8-10 d require crossing speeds of 17 000-84 000 km s−1 and radial distances of only 0.001-0.02 pc. These speeds are similar to or greater than the observed radial outflow speeds, and the inferred locations are within the nominal radius of the broad emission-line region.
The physics of active super massive black holes (BHs) is governed by their mass (M_BH), spin (a_*), and accretion rate (M). This work is the first in a series of papers with the aim of testing how ...these parameters determine the observable attributes of active galactic nuclei (AGN). We have selected a sample in a narrow redshift range, centred on z similar to 1.55, that covers a wide range in M_BH and M, and are observing them with X-shooter, covering rest wavelengths similar to 1200-9800 A. The current work covers 30 such objects and focuses on the origin of the AGN spectral energy distribution (SED). After estimating M_BH and M based on each observed SED, we use thin accretion disc (AD) models and a Bayesian analysis to fit the observed SEDs in our sample. We are able to fit 22/30 of the SEDs. Out of the remaining eight SEDs, three can be fit by the thin AD model by correcting the observed SED for reddening within the host galaxy and four can be fit by adding a disc wind to the model. In four of these eight sources, Milky Way-type extinction, with the strong 2175 A feature, provides the best reddening correction. The distribution in spin parameter covers the entire range, from -1 to 0.998, and the most massive BHs have spin parameters greater than 0.7. This is consistent with the 'spin-up' model of BH evolution. Altogether, these results indicate that thin ADs are indeed the main power houses of AGN, and earlier claims to the contrary are likely affected by variability and a limited observed wavelength range.
Broad absorption lines (BALs) in quasar spectra indicate high-velocity outflows that may be present in all quasars and could be an important contributor to feedback to their host galaxies. ...Variability studies of BALs help illuminate the structure, evolution and basic physical properties of the outflows. Here we present further results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2 < z < 2.9. We directly compare the variabilities in the Civλ1549 and Siivλ1400 absorption to try to ascertain the cause(s) of the variability. We find that Siiv BALs are more likely to vary than Civ BALs. When looking at flow speeds >-20000kms-1, 47per cent of quasars exhibited Siiv variability while 31per cent exhibited Civ variability. Furthermore, 50per cent of the variable Siiv regions did not have corresponding Civ variability at the same velocities, while nearly all occurrences of Civ variability had corresponding changes in Siiv. We do not find any correlation between the absolute change in strength in Civ and in Siiv, but the fractional change in strength tends to be greater in Siiv than in Civ. When both Civ and Siiv varied, those changes always occurred in the same sense (either getting weaker or stronger). We also include our full data set so far in this paper, which includes up to 10 epochs of data per quasar. The multi-epoch data show that the BAL changes were not generally monotonic across the full 5-8yr time span of our observations, suggesting that the characteristic time-scale for significant line variations, and (perhaps) for structural changes in the outflows, is less than a few years. Coordinated variabilities between absorption regions at different velocities in individual quasars seem to favour changing ionization of the outflowing gas as the cause of the observed BAL variability. However, variability in limited portions of broad troughs fits naturally in a scenario where movements of individual clouds, or substructures in the flow, across our lines of sight cause the absorption to vary. The actual situation may be a complex mixture of changing ionization and cloud movements. Further discussion of the implications of variability, e.g. in terms of the size and location of the outflowing gas, will be presented in a forthcoming paper. PUBLICATION ABSTRACT
Abstract
Quasar outflows have long been recognized as potential contributors to the co-evolution between supermassive black holes (SMBHs) and their host galaxies. The role of outflows in active ...galactic nucleus (AGN) feedback processes can be better understood by placing observational constraints on wind locations and kinetic energies. We utilize broad absorption line (BAL) variability to investigate the properties of a sample of 71 BAL quasars with P v broad absorption. The presence of P v BALs indicates that other BALs like C iv are saturated, such that variability in those lines favours clouds crossing the line of sight. We use these constraints with measurements of BAL variability to estimate outflow locations and energetics. Our data set consists of multiple-epoch spectra from the Sloan Digital Sky Survey and MDM Observatory. We detect significant (4σ) BAL variations from 10 quasars in our sample over rest-frame time-scales between ≤0.2–3.8 yr. Our derived distances for the 10 variable outflows are nominally ≲ 1–10 pc from the SMBH using the transverse-motion scenario, and ≲ 100–1000 pc from the central source using ionization-change considerations. These distances, in combination with the estimated high outflow column densities (i.e. NH ≳ 1022 cm−2), yield outflow kinetic luminosities between ∼ 0.001 and 1 times the bolometric luminosity of the quasar, indicating that many absorber energies within our sample are viable for AGN feedback.
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