Abstract
Pairs of supermassive black holes (SMBHs) at different stages are the natural results of galaxy mergers in the hierarchical framework of galaxy formation and evolution. However, ...identification of close binaries of SMBHs (CB-SMBHs) with sub-parsec separations in observations are still elusive. Recently, unprecedented spatial resolutions achieved by GRAVITY/GRAVITY+ on board the Very Large Telescope Interferometer through spectroastrometry (SA) provide new opportunities to resolve CB-SMBHs. Differential phase curves of CB-SMBHs with two independent broad-line regions (BLRs) are found to have distinguished characteristic structures from a single BLR. Once the CB-SMBH evolves to the stage where BLRs merge to form a circumbinary BLR, it will hopefully be resolved by the pulsar timing array in the near future as sources of nanohertz gravitational waves. In this work, we use a parameterized model for circumbinary BLRs to calculate line profiles and differential phase curves for SA observations. We show that both profiles and phase curves exhibit asymmetries caused by the Doppler boosting effect of accretion disks around individual black holes, depending on the orbital parameters of the binary and geometries of the BLR. We also generate mock SA data using the model and then recover orbital parameters by fitting the mock data. Degeneracies between parameters contribute greatly to uncertainties of parameters but can be eased through joint analysis of multiple-epoch SA observations and reverberation mappings.
Abstract
We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2 m telescope from 2017 July to 2020 February. Significant ...variations in the fluxes of the continuum and broad emission lines, including H
β
and He
ii
, were observed in the first and third years, and clear time lags between them are measured. The broad H
β
line profile consists of two Gaussian components: an intermediate-width H
with an FWHM of 1964 ± 18
and another very broad H
with an FWHM of 7570 ± 83
. H
has long time lags of ∼40–60 days in the rest frame, while H
shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of ∼30–50 days at the core of the broad H
β
line and roughly zero lags at the wings. H
has a redshift of ∼400
, which seems to be stable for nearly 30 yr by comparing with archived spectra, and may originate from an infall. The rms spectrum of H
shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. Both the double-peaked profile and the near-zero lag suggest that H
comes from a region associated with the part of the accretion disk that emits the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag measured for the total H
β
line, and a virial factor of 1.5, we obtain a virial mass of
for the central black hole in this quasar.
In the present paper, we explore opportunities of applying the GRAVITY at the Very Large Telescope Interferometer with unprecedented spatial resolution to identify close binaries of supermassive ...black holes (CB-SMBHs) in active galactic nuclei (AGNs). Each supermassive black hole is assumed to be separately surrounded by its own broad-line regions (BLRs) composed of clouds with virialized motion. Composition of the binary orbital motion and the virial motion of clouds in each BLR determines the projected velocity fields and hence differential phase curves, which are obviously different from that of a single BLR. We calculate emission line profiles and differential phase curves of CB-SMBHs for the GRAVITY. For the simplest case, in which angular momenta of two BLRs and orbital motion are parallel, a phase plateau generally appears in the phase curves. For other combinations of the angular momentum, the plateau is replaced by new peaks and valleys variously depending on the situation. Given a combination, phase curves are also sensitive to changes of parameters of CB-SMBHs. All these features are easily distinguished from the well-known S-shaped phase curves of a single BLR, so that the GRAVITY is expected to reveal signals of CB-SMBH from candidates of AGNs. With joint analysis of observations of reverberation-mapping campaigns, we can reliably identify CB-SMBHs, and measure their orbital parameters in the meanwhile. This independent measurement of the orbital parameters also has implications to analysis of pulsar timing array observations for properties of low-frequency gravitational waves in future.
Close binaries of supermassive black holes (CB-SMBHs) with separations of 0.1 pc as the final stage of galaxy mergers are sources of low-frequency gravitational waves; however, they are still elusive ...observationally because they are not spatially resolved. Fortunately, reverberation as echoes of broad emission lines to ionizing continuum conveys invaluable information on the dynamics of broad-line regions (BLRs) governed by SMBHs in the central regions of active galactic nuclei (AGNs). In this paper, we demonstrate how to compose the hybrid two-dimensional transfer functions (TFs) of binary BLRs around the CB-SMBHs in AGNs, providing an opportunity for identifying them from reverberation mapping (RM) data. It is found that there are variation-coupling effects in the TFs arising from the coupling of CB-SMBH light curves in the Fourier space. We provide semi-analytical formulations of the TFs for kinematic maps of the gas. For cases with the simplest variation-coupling effects, we make calculations for several BLR models and reveal significant distinctions from those of single active black holes. In principle, the difference is caused by the orbital motion of the CB-SMBH systems. In order to search for CB-SMBHs in time-domain space, selection of target candidates should focus on local AGNs with Hβ double-peaked profiles and weaker near-infrared emission. High-fidelity RM campaigns of monitoring the targets in future will provide opportunities to reveal these kinematic signatures of the CB-SMBHs and hence measurements of their orbital parameters.
Abstract
We test the potential of Bayesian synthesis of upcoming multi-instrument data to extract orbital parameters and individual light curves of close binary supermassive black holes (CB-SMBH) ...with subparsec separations. Next-generation interferometers, will make possible the observation of astrometric wobbles in CB-SMBH. Combining them with periodic variable time-domain data from surveys like the Vera C. Rubin Legacy Survey of Space and Time, allows for more information on CB-SMBH candidates compared to standalone observational methods. Our method reliably determines binary parameters and component fluxes from binary total flux across long-term, intermediate, and short-term binary dynamics and observational configurations, assuming 10 annual observations, even in short period “q-accrete” objects. Expected CB-SMBH astrometric wobbles constructed from binary dynamical parameters might serve in refining observational strategies for CB-SMBH. Combination of inferred mass ratio, light curves of binary components, and observed photocenter wobbles can be a proxy for the activity states of CB-SMBH components.
Abstract
In this work, we present the first results of the long-term high-cadence spectroscopic monitoring of 15 PG quasars with relatively strong Fe
ii
emission, as a part of a broader reverberation ...mapping campaign performed using the Calar Alto Observatory’s 2.2 m telescope. The
V
-band, 5100 Å continuum, and H
β
broad emission line light curves are measured for a set of quasars for periods ranging from dozens to more than a hundred epochs between 2017 May and 2020 July. Accurate time lags between the variations of the H
β
broad-line fluxes and the optical continuum strength are obtained for all 15 quasars, ranging from
17.0
−
3.2
+
2.5
to
95.9
−
23.9
+
7.1
days in the rest frame. The virial masses of the central supermassive black holes are derived for all 15 quasars, ranging between
0.50
−
0.19
+
0.18
and
19.17
−
2.73
+
2.98
in units of 10
7
M
⊙
. For 11 of the objects in our sample, this is the first reverberation analysis to be published. Of the rest, two objects have been the subject of previous reverberation studies, but we determine time lags for these that are only half as long as those found in the earlier investigations, which had only been able to sample much more sparsely. The remaining two objects have previously been monitored with high sampling rates. Our results here are consistent with the earlier findings, in the sense that the time lag and the line width vary inversely, consistent with virialization.
Abstract
The quasar 3C 273 has been observed with infrared spectroastrometry (SA) of the broad Pa
α
line and optical reverberation mapping (RM) of the broad H
β
line. SA delivers information about ...the angular size and structure of the Pa
α
broad-line region (BLR), while RM delivers information about the physical size and structure of the H
β
BLR. Based on the fact that the two BLRs share the mass of the supermassive black hole (SMBH) and viewing inclination, a combination of SA and velocity-resolved RM (SARM) thereby allows us to simultaneously determine the SMBH mass and geometric distance through dynamically modeling the two BLRs. We construct a suite of dynamical models with different geometric configurations and apply a Bayesian approach to obtain the parameter inferences. Overall the obtained masses and distances are insensitive to specific BLR configurations but more or less depend on parameterizations of the vertical distributions. The most probable model, chosen in light of the Bayes factor, yields an angular-size distance
log
(
D
A
/
Mpc
)
=
2.83
−
0.28
+
0.32
and an SMBH mass
log
(
M
•
/
M
⊙
)
=
9.06
−
0.27
+
0.21
, which agree with the relationships between SMBH masses and bulge properties. The BLRs have an inclination of
5
−
1
+
1
degrees, consistent with that of the large-scale jet in 3C 273. Our approach reinforces the capability of SARM analysis to measure SMBH masses and distances of active galactic nuclei and quasars even though SA and RM observations are undertaken with different emission lines and/or in different periods.
Abstract
Recently, GRAVITY on board the Very Large Telescope Interferometer (VLTI) first spatially resolved the structure of the quasar 3C 273 with an unprecedented resolution of ∼10
μ
as. A new ...method of measuring parallax distances has been successfully applied to the quasar through joint analysis of spectroastrometry (SA) and reverberation mapping (RM) observation of its broad-line region (BLR). The uncertainty of this SA and RM (SARM) measurement is about 16% from real data, showing its great potential as a powerful tool for precision cosmology. In this paper, we carry out detailed analyses of mock data to study impacts of data qualities of SA observations on distance measurements and establish a quantitative relationship between statistical uncertainties of distances and relative errors of differential phases. We employ a circular disk model of the BLR for the SARM analysis. We show that SARM analyses of observations generally generate reliable quasar distances, even for relatively poor SA measurements with error bars of 40% at peaks of phases. Inclinations and opening angles of BLRs are the major parameters governing distance uncertainties. It is found that BLRs with inclinations ≳10° and opening angles ≲40° are the most reliable regimes from SARM analysis for distance measurements. Through analysis of a mock sample of AGNs generated by quasar luminosity functions, we find that if the GRAVITY/GRAVITY+ can achieve a phase error of 0.°1 per baseline for targets with magnitudes
K
≲ 11.5, the SARM campaign can constrain
H
0
to an uncertainty of 2% by observing 60 targets.
This is the eighth in a series of papers reporting on a large reverberation mapping (RM) campaign to measure black hole (BH) mass in active galactic nuclei with high accretion rates. We employ the ...recently developed dynamical modeling approach for broad-line regions (BLRs) based on the method of Pancoast et al. to analyze the RM data set of Mrk 142 observed in the first monitoring season. In this approach, continuum variations are reconstructed using a damped random walk process, and BLR structure is delineated using a flexible disk-like geometry, in which BLR clouds move around the central BH with Keplerian orbits or inflow/outflow motion. The approach also includes the possibilities of anisotropic emission from BLR clouds, nonlinear response of the line emission to the continuum, and different long-term trends in the continuum and emission-line variations. We implement the approach in a Bayesian framework that is apt for parallel computation and use a Markov chain Monte Carlo technique to recover the parameters and uncertainties for the modeling, including the mass of the central BH. We apply three BLR models with different prescriptions of BLR cloud distributions and find that the best model for fitting the data of Mrk 142 is a two-zone BLR model, consistent with the theoretical BLR model surrounding slim accretion disks. The best model yields a BH mass of , resulting in a virial factor of for the full width at half maximum of the Hβ line measured from the mean spectrum. The virial factors for the other measures of the Hβ line width are also presented.
Abstract
Strong iron lines are a common feature of the optical spectra of active galactic nuclei (AGNs) and quasars from
z
∼ 6−7 to the local universe, and Fe/Mg ratios do not show cosmic evolution. ...During active episodes, accretion disks surrounding supermassive black holes (SMBHs) inevitably form stars in the self-gravitating part, and these stars accrete with high accretion rates. In this paper, we investigate the population evolution of accretion-modified stars (AMSs) to produce iron and magnesium in AGNs. The AMSs, as a new type of star, are allowed to have any metallicity but without significant loss from stellar winds, since the winds are choked by the dense medium of the disks and return to the core stars. Mass functions of the AMS population show a pile-up or cutoff pile-up shape in top-heavy or top-dominant forms if the stellar winds are strong, consistent with the narrow range of supernovae (SNe) explosions driven by the known pair-instability. This provides an efficient way to produce metals. Meanwhile, SN explosions support an inflated disk as a dusty torus. Furthermore, the evolving top-heavy initial mass functions lead to bright luminosity in infrared bands in dusty regions. This contributes a new component in infrared bands, which is independent of the emissions from the central part of accretion disks, appearing as a long-term trending of the NIR continuum compared to optical variations. Moreover, the model can be further tested through reverberation mapping of emission lines, including LIGO/LISA detections of gravitational waves and signatures from spatially resolved observations of GRAVITY+/VLTI.
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