arXiv subjects

Yu-Yang Songsheng

Publications and source records attributed to Yu-Yang Songsheng.

31 records · Page 2Linked to original sources

arXiv2022

Spectroastrometry and Reverberation Mapping: the Mass and Geometric Distance of the Supermassive Black Hole in the Quasar 3C 273

The quasar 3C 273 has been observed with infrared spectroastrometry (SA) on broad Pa$α$ line and optical reverberation mapping (RM) on 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 of $\log\,(D_{\rm A}/{\rm Mpc}) = 2.83_{-0.28}^{+0.32}$ and SMBH mass of $\log\,(M_\bullet/M_\odot)=9.06_{-0.27}^{+0.21}$, which agrees 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 mass and distance of AGNs even though SA and RM observations are undertaken with different emission lines and/or in different periods.

astro-ph.GA↗

arXiv2021

Search for Continuous Gravitational Wave Signals in Pulsar Timing Residuals: A New Scalable Approach with Diffusive Nested Sampling

Detecting continuous nanohertz gravitational waves (GWs) generated by individual close binaries of supermassive black holes (CB-SMBHs) is one of the primary objectives of pulsar timing arrays (PTAs). The detection sensitivity is slated to increase significantly as the number of well-timed millisecond pulsars will increase by more than an order of magnitude with the advent of next-generation radio telescopes. Currently, the Bayesian analysis pipeline using parallel tempering Markov chain Monte Carlo has been applied in multiple studies for CB-SMBH searches, but it may be challenged by the high dimensionality of the parameter space for future large-scale PTAs. One solution is to reduce the dimensionality by maximizing or marginalizing over uninformative parameters semi-analytically, but it is not clear whether this approach can be extended to more complex signal models without making overly simplified assumptions. Recently, the method of diffusive nested (DNest) sampling shown the capability of coping with high dimensionality and multimodality effectively in Bayesian analysis. In this paper, we apply DNest to search for continuous GWs in simulated pulsar timing residuals and find that it performs well in terms of accuracy, robustness, and efficiency for a PTA including $\mathcal{O}(10^2)$ pulsars. DNest also allows a simultaneous search of multiple sources elegantly, which demonstrates its scalability and general applicability. Our results show that it is convenient and also high beneficial to include DNest in current toolboxes of PTA analysis.

astro-ph.IM↗

arXiv2021

Reverberation Mapping of Two Luminous Quasars: the Broad-line Region Structure and Black Hole Mass

We report the results of a multi-year spectroscopic and photometric monitoring campaign of two luminous quasars, PG~0923+201 and PG~1001+291, both located at the high-luminosity end of the broad-line region (BLR) size-luminosity relation with optical luminosities above $10^{45}~{\rm erg~s^{-1}}$. PG~0923+201 is for the first time monitored, and PG~1001+291 was previously monitored but our campaign has a much longer temporal baseline. We detect time lags of variations of the broad H$β$, H$γ$, Fe {\sc ii} lines with respect to those of the 5100~Å continuum. The velocity-resolved delay map of H$β$ in PG~0923+201 indicates a complicated structure with a mix of Keplerian disk-like motion and outflow, and the map of H$β$ in PG~1001+291 shows a signature of Keplerian disk-like motion. Assuming a virial factor of $f_{\rm BLR}=1$ and FWHM line widths, we measure the black hole mass to be $118_{-16}^{+11}\times 10^7 M_{\odot}$ for PG~0923+201 and $3.33_{-0.54}^{+0.62}\times 10^7 M_{\odot}$ for PG~1001+291. Their respective accretion rates are estimated to be $0.21_{-0.07}^{+0.06} \times L_{\rm Edd}\,c^{-2}$ and $679_{-227}^{+259}\times L_{\rm Edd}\,c^{-2}$, indicating that PG~0923+201 is a sub-Eddington accretor and PG~1001+291 is a super-Eddington accretor. While the H$β$ time lag of PG~0923+201 agrees with the size-luminosity relation, the time lag of PG~1001+291 shows a significant deviation, confirming that in high-luminosity AGN the BLR size depends on both luminosity and Eddington ratio. Black hole mass estimates from single AGN spectra will be over-estimated at high luminosities and redshifts if this effect is not taken into account.

astro-ph.GA↗

arXiv2021

Geometric Distances of Quasars Measured by Spectroastrometry and Reverberation Mapping:Monte Carlo Simulations

Recently, GRAVITY onboard the Very Large Telescope Interferometer (VLTI) first spatially resolved the structure of the quasar 3C 273 with an unprecedented resolution of $\sim 10μ$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 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 $\gtrsim 10^{\circ}$ and opening angles $\lesssim 40^{\circ}$ 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 $0.1^{\circ}$ per baseline for targets with magnitudes $K \lesssim 11.5$, the SARM campaign can constrain $H_0$ to an uncertainty of $2\%$ by observing $60$ targets.

astro-ph.GA↗

arXiv2020

Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129

We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2m telescope from July 2017 to February 2020. 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$β_{\rm IC}$ with a full width at half-maximum (FWHM) of 1964$\pm$18 $\rm km~s^{-1}$ and another very broad H$β_{\rm VBC}$ with a FWHM of 7570$\pm$83 $\rm km~s^{-1}$. H$β_{\rm IC}$ has long time lags of $\sim$40--60 days in the rest frame, while H$β_{\rm VBC}$ shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of $\sim$30--50 days at the core of the broad H$β$ line and roughly zero lags at the wings. H$β_{\rm IC}$ has a redshift of $\sim$400 $\rm km~s^{-1}$ which seems to be stable for nearly 30 years by comparing with archived spectra, and may originate from an infall. The root mean square (rms) spectrum of H$β_{\rm VBC}$ 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$β_{\rm VBC}$ comes from a region associated with the part of the accretion disc 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 $2.89_{-0.69}^{+0.60} \times10^7 M_{\odot}$ for the central black hole in this quasar.

astro-ph.GA↗

arXiv2020

Differential interferometry of close binary of supermassive black holes in an elliptical configuration

The Very Large Telescope Interferometer (VLTI), and the Extremely Large Telescope (ELT) will be a robust astrophysics suite offering the opportunity of probing the structure and dynamics of CB-SMBH at high spectral and angular resolution. Here, we explore and illustrate the application of differential interferometry on unresolved the CB-SMBH systems in elliptical orbital configurations and a single SMBH with clouds in elliptical orbital motion. Photocenter displacements between each SMBH and regions in their disc-like broad line regions (BLR) appear as small interferometric differential phase variability. To investigate the application of interferometric phases for the detection of CB-SMBH systems, we simulate a series of differential interferometry signatures, based on our model comprising ensembles of clouds surrounding each of supermassive black hole in a CB-SMBH. Setting model to the parameters of a single SMBH with elliptical cloud motion, we also calculated a series of differential interferometry observables for this case. We found various deviations from the canonical S-shaped of CB-SMBH phases profile for elliptically configured CB-SMBH systems. The amplitude and specific shape of the interferometry observables depend on orbital configurations of the CB-SMBH system. We get distinctive results when considering antialigned angular momenta of cloud orbits regarding total CB-SMBH angular momentum. Some simulated spectral lines from our model closely resemble observations of Pa αline got from near-infrared AGN surveys. We found differences between differential phases zoo of a single SMBH and CB-SMBH systems. The differential phases zoo for a single SMBH comprises deformed S shape. We also showed how their differential phase shape, amplitude, and slope evolve with various sets of cloud orbital parameters and observer position.

astro-ph.GA↗

arXiv2020

A parallax distance to 3C 273 through spectroastrometry and reverberation mapping

Distance measurements for extragalactic objects are a fundamental problem in astronomy and cosmology. In the era of precision cosmology, we urgently need better measurements of cosmological distances to observationally test the increasing $H_{0}$ tension of the Hubble constant measured from different tools. Using spectroastrometry, GRAVITY at The Very Large Telescope Interferometer successfully revealed the structure, kinematics and angular sizes of the broad-line region (BLR) of 3C 273 with an unprecedentedly high spatial resolution. Fortunately, reverberation mapping (RM) of active galactic nuclei (AGNs) reliably provides linear sizes of their BLRs. Here we report a joint analysis of spectroastrometry and RM observations to measure AGN distances. We apply this analysis to 3C 273 observed by both GRAVITY and an RM campaign,and find an angular distance of $551.5_{-78.7}^{+97.3}\, {\rm Mpc}$ and $H_{0}=71.5_{-10.6}^{+11.9}\,{\rm km\,s^{-1}\,Mpc^{-1}}$. Advantages of the analysis are 1) its pure geometrical measurements and 2) it simultaneously yields mass of the central black hole in the BLR. Moreover, we can conveniently repeat measurements of selected AGNs to efficiently reduce the statistical and systematic errors. Future observations of a reasonably sized sample ($\sim 30$ AGNs) will provide distances of the AGNs and hence a new way of measuring $H_{0}$ with a high precision $\left(\lesssim 3\%\right)$ to test the $H_{0}$ tension.

astro-ph.CO↗

arXiv2019

Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei. II. Atlas of two-dimensional transfer functions

Most large galaxies harbor supermassive black holes (SMBHs) in their centers, and galaxies merge. Consequently, binary SMBHs should be common in galactic nuclei. However, close binaries of SMBH (CB-SMBHs) with sub-parsec separation cannot be imaged directly using current facilities. Some indirect signatures, such as periodic signals in light curves and double peaks in emission-line profile, have been used to find CB-SMBH candidates, but ambiguities still exist and no definitive conclusions can be made. We have recently proposed a new method focusing on kinematic signatures that can be derived from reverberation mapping of CB-SMBHs, one that offers a promising avenue to address this important problem. In this paper, we calculated models for a wide range of parameters, but BLRs of two BHs are close but still not merged. The purpose of this supplementary paper is to provide an atlas of two-dimensional transfer functions of CB-SMBHs with a wide range of orbital and geometrical parameters to aid more efficient identification of CB-SMBH candidates in reverberation mapping data.

astro-ph.GA↗

arXiv2019

Differential Interferometric Signatures of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei

In the present paper, we explore opportunities of applying the GRAVITY at the Very Large Telescope Interferometry (VLTI) with unprecedented spatial resolution to identify close binaries of supermassive black holes (CB-SMBHs) in active galactic nuclei (AGNs). Each SMBH is assumed to be separately surrounded by their 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 where angular momentums 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 situations. 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 (PTA) observations for properties of low-frequency gravitational waves in future.

astro-ph.GA↗

arXiv2018

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. VIII. Structure of the Broad-Line Region and Mass of the Central Black Hole in Mrk 142

This is the eighth in a series of papers reporting on a large reverberation mapping campaign to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). We employ the recently developed dynamical modeling approach for broad-line regions (BLRs) based on the method of Pancoast et al. to analyze the reverberation mapping dataset 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 of BLR clouds, non-linear 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 mass of the central BH. We apply three BLR models with different prescriptions of BLR clouds 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 $\log (M_\bullet/M_\odot)=6.23_{-0.45}^{+0.26}$, resulting in a virial factor of $\log f=-0.36_{-0.54}^{+0.33}$ for the full width at half maximum of the H$β$ line measured from the mean spectrum. The virial factors for the other measures of the H$β$ line width are also presented.

astro-ph.GA↗

arXiv2018

Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei

Close binaries of supermassive black holes (CB-SMBHs) with separations of $\lesssim 0.1$pc as the final stage of galaxy mergers are sources of low frequency gravitational waves (GW), 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 of the dynamics of broad-line regions (BLRs) governed by supermassive black holes in the central regions of active galactic nuclei (AGNs). In this paper, we demonstrate how to composite the hybrid 2-dimensional transfer functions of binary BLRs around the CB-SMBHs in AGNs, providing an opportunity of identifying them from reverberation mapping (RM) data. It is found that there are variation-coupling effects in the transfer functions, arising from the coupling of CB-SMBH light curves in the Fourier space. We provide semi-analytical formulations of the transfer functions 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 H$β$ 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 for measurements of their orbital parameters.

astro-ph.GA↗

arXiv2017

Tidally disrupted dusty clumps as the origin of broad emission lines in active galactic nuclei

Type 1 active galactic nuclei display broad emission lines, regarded as arising from photoionized gas moving in the gravitational potential of a supermassive black hole. The origin of this broad-line region gas is unresolved so far, however. Another component is the dusty torus beyond the broad-line region, likely an assembly of discrete clumps that can hide the region from some viewing angles and make them observationally appear as Type 2 objects. Here we report that these clumps moving within the dust sublimation radius, like the molecular cloud G2 discovered in the Galactic center, will be tidally disrupted by the hole, resulting in some gas becoming bound at smaller radii while other gas is ejected and returns to the torus. The clumps fulfill necessary conditions to be photoionized. Specific dynamical components of tidally disrupted clumps include spiral-in gas as inflow, circularized gas, and ejecta as outflow. We calculate various profiles of emission lines from these clouds, and find they generally agree with H$β$ profiles of Palomar-Green quasars. We find that asymmetry, shape and shift of the profiles strongly depend on [O III], luminosity, which we interpret as a proxy of dusty torus angles. Tidally disrupted clumps from the torus may represent the source of the broad-line region gas.

astro-ph.GA↗

arXiv2017

Measuring black hole mass of type I active galactic nuclei by spectropolarimetry

Black hole (BH) mass of Type I active galactic nuclei (AGN) can be measured or estimated through either reverberation mapping (RM) or empirical $R-L$ relation, however, both of them suffer from uncertainties of the virial factor ($f_{\rm BLR}$), thus limiting the measurement accuracy. In this letter, we make an effort to investigate $f_{\rm BLR}$ through polarised spectra of the broad-line regions (BLR) arisen from electrons in the equatorial plane. Given the BLR composed of discrete clouds with Keplerian velocity around the central BH, we simulate a large number of spectra of total and polarised flux with wide ranges of parameters of the BLR model and equatorial scatters. We find that the $f_{\rm BLR}$-distribution of polarised spectra is much narrower than that of total ones. This provides a way of n accurately estimating BH mass from single spectropolarimetric observations of type I AGN whose equatorial scatters are identified.

astro-ph.GA↗