arXiv subjects

XueGuang Zhang

Publications and source records attributed to XueGuang Zhang.

At least 19 recordsLinked to original sources

arXiv2025

AGN-Driven Biconical Outflows as the Origin of the Double-Peaked [O~{\sc iii}] doublet in SDSS J134733.36+121724.27

In this manuscript, we recheck the spectroscopic properties of SDSS J134733.36+121724.27 (4C+12.50), confirming the presence of the double-peaked [O~{\sc iii}]$λ\lambda4959,5007$Å doublet and a broad H$α$. The former likely results from AGN-driven biconical outflows, while the absence of a broad H$β$ supports a classification of the source as a Type-1.9 AGN. We analyze its high-quality Sloan Digital Sky Survey (SDSS) optical spectrum after robustly subtracting host galaxy and AGN continuum contributions through a simple stellar population fitting method employing 39 templates and a power-law continuum. Each narrow line of the [O~{\sc iii}]$λ\lambda4959,5007$Å doublet is better described by two Gaussian components (blue-shifted and red-shifted) than by a single Gaussian, as confirmed by the F-test. Broad components are included for both H$α$ and H$β$, but only H$α$ reveals a significant detection, further supported by a comparison between the SDSS spectrum and that previously reported. These results support that the object is highly consistent with a Type-1.9 AGN classification, and the double-peaked [O~{\sc iii}] profiles are most likely produced by AGN-driven biconical outflows rather than by a rotating narrow-line region or a dual AGN merger system. Additional observations are still needed to strengthen these conclusions.

astro-ph.GA↗

arXiv2025

A gravitational acceleration model to explain the double-peaked narrow emission lines shifted in the same direction

In this manuscript, we propose, for the first time, an oversimplified but potentially effective gravitational acceleration model to interpret the double-peaked narrow emission lines (DPNELs) shifted in the same direction. We adopt the framework of a merging kpc-scale dual-core system in an elliptical orbit, which has an emission-line galaxy with clear narrow line regions (NLRs) merging with a companion galaxy lacking emission line features. Due to gravitational forces induced by both galaxies on the NLRs, the accelerations of the far-side and near-side NLR components may share the same vector direction when projected along the line-of-sight, leading the velocities of the observed DPNELs to shift in the same direction. Our simulations indicate that the probability of producing double-peaked features shifted in the same direction reaches 5.81% in merging kpc-scale dual core systems containing emission-line galaxies. Besides the expected results from our proposed model, we identify a unique galaxy SDSS J001050.52-103246.6, whose apparent DPNELs shifted in the same direction can be plausibly explained by the gravitational acceleration model. This proposed model provides a new path to explain DPNELs shifted in the same direction in the scenario that the two galaxies align along the line-of-sight in kpc-scale dual-core systems.

astro-ph.GA↗

arXiv2025

An improved Seyfert-LINER classification line in the [N~{\sc ii}] BPT diagram

In this manuscript, an improved Seyfert-LINER classification line (= S-L line) is proposed in the [N~{\sc ii}] BPT diagram, based on a sample of 47,968 low redshift narrow emission line galaxies from SDSS DR16, motivated by different S-L lines reported in the [N~{\sc ii}] BPT diagram through different methods. The method proposed by Kewley et al. in 2006 is firstly applied, however, the method cannot lead to an accepted S-L line in the [N~{\sc ii}] BPT diagram. Meanwhile, the S-L lines proposed by Schawinski et al. in 2007 and Cid Fernandes et al. in 2010 in the [N~{\sc ii}] BPT diagram are different from each other. Therefore, it is meaningful to check which proposed S-L line is better or to determine an improved one in the [N~{\sc ii}] BPT diagram by a new method. In this manuscript, Seyferts and LINERs that have already been classified in the [S~{\sc ii}] and/or [O~{\sc i}] BPT diagrams can be visualized in the [N~{\sc ii}] BPT diagram, leading the intersection boundary of the two contour maps to be considered as the S-L line in the [N~{\sc ii}] BPT diagram. Rather than the previously proposed S-L lines, the new S-L line can lead to more efficient and harmonious classifications of Seyferts and LINERs, especially in the composite galaxy region, in the [N~{\sc ii}] BPT diagram. Furthermore, based on the discussed S-L lines, the number ratio of Type-2 Seyferts to Type-2 LINERs differs significantly from that of Type-1 Seyferts to Type-1 LINERs in the [N~{\sc ii}] BPT diagram, suggesting that about 90$\%$ of Type-2 LINERs are non-AGN-related objects, true Type-2 AGNs, or objects exhibiting both Seyfert and LINER characteristics.

astro-ph.GA↗

arXiv2025

Optical QPOs with dual periodicities 1103days and 243days in the blue quasar SDSS J100438.8+151056

This manuscript investigates the possible existence of a binary supermassive black holes (BSMBH) system in the blue quasar SDSS J100438.8+151056 (=SDSS J1004+1510) at z=0.219 based on the detection of robust optical QPOs. We determine QPOs using multiple analysis methods applied to the CSS-V, ZTFg/r band light curves, and additionally, combined with the characteristics of broad emission lines and explores potential mechanisms for the QPOs, including jet and disk precession models. Two distinct periodicities, $1103\pm260$days and $243\pm29$days, are identified in the ZTF g/r-band light curves with confidence level exceeding $5σ$, through four different techniques. Meanwhile, the $1103\pm260$days periodicity is also clearly detected in the CSS V-band light curve. The optical periodicities suggest a BSMBH system candidate in SDSS J1004+1510, with an estimated total virial BH mass of $(1.13\pm0.14)\times10^8 M_{\odot}$ and a space separation of $0.0053\pm0.0016$pc for the periodicity of $1103\pm260$days. The second periodicity of $243\pm29$days could be attributed to harmonic oscillations, considering $(1103\pm260)/(243\pm29)\sim4.54\pm0.47$ with large scatters. However, if the periodicity of $243\pm29$days was from an independent QPO, a triple BH system candidate on sub-pc scale could be probably expected, with space separations of $0.00036\pm0.00004$pc between a close BSMBH system and of $0.0053\pm0.0016$pc between the BSMBH system and the third BH, after considering similar BH mass of the third BH as the total mass of the central BSMBH. These findings strongly demonstrate that combined light curves from the different sky survey projects can lead to more reliable QPOs candidates to be detected, and also indicate higher quality light curves could be helpful to find probably potential QPOs with multiple periodicities leading to rare detections of candidates for sub-pc triple BH systems.

astro-ph.GA↗

arXiv2025

The orbital kinematics of kpc-scale dual-core systems with double-peaked narrow emission lines

In this manuscript, based on SDSS photometry and spectroscopy, a method is proposed to test the hypothesis that the orbital kinematics of kpc-scale dual-core systems can lead to double-peaked narrow emission lines (DPNELs), through analyzing a sample of seven kpc-scale dual-core systems by comparing the upper limits of their orbital velocities (calculated using total stellar mass and projected distance) with the velocity separation of DPNELs (peak separation). To determine accurate total stellar masses, GALFIT is applied to consider the effects of the overlapping components on the photometric images to obtain accurate magnitudes. Then, based on the correlation between absolute Petrosian magnitudes and total stellar masses, the individual masses of the galaxies are determined. Therefore, the maximum orbital velocities can be calculated by combining the projected distance. Meanwhile, the peak separation can be accurately measured after subtracting the pPXF determined host galaxy contributions. Finally, four objects exhibit peak separations almost consistent with their respective maximum orbital velocities under the assumption of a circular orbit, while the remaining three objects display peak separations larger than the maximum orbital velocities. A larger sample will be given later to further test whether DPNELs can arise from kpc-scale dual-core systems.

astro-ph.GA↗

arXiv2025

A central TDE candidate detected through spectroscopic continuum emission properties in a SDSS blue quasar

In this manuscript, properties of spectroscopic continuum emissions are considered to detect potential tidal disruption event (TDE) candidates among SDSS quasars. After considering the simple blackbody photosphere model applied to describe quasar continuum emissions with parameters of blackbody temperature $T_{BB}$ and blackbody radius $R_{BB}$, SDSS quasars and reported optical TDEs occupy distinct regions in the space of $T_{BB}$ and $R_{BB}$. Then, through the dependence of $R_{BB}$ on $T_{BB}$ for SDSS quasars, 402 outliers in SDSS Stripe82 region can be collected. Among the 402 outliers, the SDSS J2308 at $z=1.16$ is mainly considered, due to its SDSS spectrum observed around the peak brightness of the light curves. With the 7.2-year-long light curves described by theoretical TDE model, the determined $T_{BB}$ and $R_{BB}$ through its spectroscopic continuum emissions are consistent with the TDE model determined values, to support the central TDE. Moreover, considering simulated results on continuum emissions of SDSS quasars around $z\sim1.16$, confidence level higher than 4$σ$ can be confirmed that the continuum emissions of SDSS J2308 are not related to normal quasars. Furthermore, accepted CAR process to simulate intrinsic AGN variability, the confidence level higher than $3σ$ can be confirmed that the long-term light curves of SDSS J2308 are related to a central TDE. Jointed the probabilities through both spectroscopic and photometric simulations, the confidence level higher than $5σ$ can be confirmed to support the central TDE in SDSS J2308.

astro-ph.GA↗

arXiv2024

Optical QPOs with 550 day periodicity in the reverberation mapped broad line quasar PG 1411+442

In this manuscript, optical quasi-periodic oscillations (QPOs) with 550 day periodicity related to a candidate of sub-pc binary black hole (BBH) system are reported in the reverberation mapped broad line quasar PG 1411+442 but with different line profile of broad H$α$ from that of broad H$β$ in its rms spectrum. First, considering sine function to describe the 18.8years-long light curves from the CSS, ASAS-SN and ZTF, 550days periodicity can be confirmed with confidence level higher than 5$σ$. Second, the stable 550days optical QPOs can be re-confirmed with confidence levels higher than 5$σ$ by the Generalized Lomb-Scargle periodogram, the sine-like phase-folded light curves and the WWZ technique determined power maps. Third, based on simulated light curves by CAR process, confidence level higher than $3.5σ$ can be confirmed for the optical QPOs not related to intrinsic AGN variability. Moreover, considering spatial separation of central two BH accreting systems smaller than expected sizes of broad emission line regions (BLRs), central total BH mass higher than $10^6{\rm M_\odot}$ could lead to few effects of supposed BBH systems on estimated virial BH masses. Meanwhile, disk precession is not preferred due to the similar estimated sizes of optical and NUV emission regions, and jet precession can be ruled out due to PG 1411+442 as a radio quiet quasar. The results strongly indicate it would be practicable by applying very different line profiles of broad Balmer emission lines to detect candidates of BBH systems in normal broad line AGN in the near future.

astro-ph.GA↗

arXiv2024

Mass evolution of broad line regions to explain the luminosity variability of broad H$α$ in the TDE ASASSN-14li

In this manuscript, an oversimplified model is proposed for the first time to explain the different variability trends in the observed broad H$α$ emission line luminosity $L_{Hα}(t)$ and in the TDE model determined bolometric luminosity $L_{bol}(t)$ in the known TDE ASASSN-14li. Considering broad emission line regions (BLRs) lying into central accretion disk related to accreted materials onto central black hole in TDEs, mass evolution $M_{BLRs}(t)$ of central BLRs can be determined by the maximum mass $M_{BLRs,0}$ of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of Broad Balmer emission line luminosity on mass of BLRs, the mass evolution $M_{BLRs}(t)$ of central BLRs can be applied to describe the observed $L_{Hα}(t)$. Although the proposed model is oversimplified with only one free model parameter $M_{BLRs,0}$, the model with $M_{BLRs,0}\sim0.02{\rm M_\odot}$ can be applied to well describe the observed $L_{Hα}(t)$ in the TDE ASASSN-14li. Meanwhile, the oversimplified model can also be applied to roughly describe the observed $L_{Hα}(t)$ in the TDE ASASSN-14ae. The reasonable descriptions to the observed $L_{Hα}(t)$ in ASASSN-14li and ASASSN-14ae indicate the oversimplified model with only one free model parameter is probably efficient enough to describe mass evolutions of $M_{BLRs}$ related to central accreted debris in TDEs.

astro-ph.GA↗

arXiv2024

SDSS J222428.53+261423.2: unique emission lines properties unveil a sub-kiloparsec dual AGN candidate

In this paper, we presented a detailed analysis of the Sloan Digital Sky Survey optical spectrum of a new sub-kpc scale dual AGN candidate SDSS J222428.53+261423.2 (=SDSS J2224). The target is one of the few AGNs with all the optical narrow emission lines characterized by double-peaked profiles and with peak separations in velocity units of about 930 km/s. If the double-peaked narrow emission lines (DPNELs) are due to a dual AGN in \obj, the estimated physical separation between the two cores is about 500 pc. Meanwhile, three alternative explanations are also discussed in this paper, however, we can not find solid evidence to completely rule them out. Our results support the presence of a sub-kpc dual AGN with DPNELs in all lines, indicating a key episode of galaxy merging evolution at sub-kpc scale.

astro-ph.GA↗

arXiv2024

To test $R_{NLRs}~-~L_{O3}$ relation for narrow emission line regions of AGN through low redshift Type-2 AGN in SDSS

Sizes of narrow emission line regions (NLRs) of AGN could be estimated by [O~{\sc iii}] line luminosity $L_{O3}$ through the known $R_{NLRs}-L_{O3}$ empirical relations. Unfortunately, it is not convenient to test the $R_{NLRs}-L_{O3}$ empirical relations through structure properties of spatially resolved NLRs of large samples of AGN. In this manuscript, a method is proposed to test the $R_{NLRs}-L_{O3}^{\sim0.25}$ empirical relations for AGN NLRs through SDSS Type-2 AGN having few orientation effects on NLRs sizes expected by AGN unified model, after considering sizes $R_{fib}$ of SDSS fiber covered regions. Comparing $R_{fib}$ and $R_{NLRs}$ estimated by $L_{O3}$, Type-2 AGN with $R_{fib}>R_{NLRs}$ (Sample-II) and with $R_{fib}<R_{NLRs}$ (Sample-I) should have different physical properties of NLRs. Accepted electron density gradients in AGN NLRs, statistically higher electron densities (traced by lower flux ratio $R_{S2}$ of [S~{\sc ii}]$\lambda6717$Å~ to [S~{\sc ii}]$\lambda6731$Å) could be expected for the Type-2 AGN in the Sample-I. Then, through the collected 1062 SDSS Type-2 AGN in the Sample-I and 3658 SDSS Type-2 AGN in the Sample-II, statistically lower $R_{S2}$ for the Type-2 AGN in the Sample-I can be confirmed with confidence level higher than 5$σ$, even after considering necessary effects. Therefore, the results in this manuscript can provide strong clues to support that the reported $R_{NLRs}~\propto~L_{O3}^{0.25}$ empirical relation is preferred to estimate NLRs sizes of SDSS AGN through SDSS fiber spectroscopic results, and also to support the commonly expected electron density gradients in AGN NLRs.

astro-ph.GA↗

arXiv2024

Different dependence of narrow H$α$ line luminosity on optical continuum luminosity between starforming galaxies and Type-2 AGN: globally negative AGN feedback in local Type-2 AGN?

In this manuscript, clues are provided to support globally negative AGN feedback on star formation in the host galaxies of the local low-redshift SDSS Type-2 AGN, based on the different dependence of narrow H$α$ line luminosity $L_{Hα}$ on optical continuum luminosity $λL_{cont}$ between the starforming galaxies and the Type-2 AGN. Through the measured $L_{Hα}$ and $λL_{cont}$ in SDSS starforming galaxies, there is a strong linear correlation between $λL_{cont}$ and $L_{Hα}$, accepted as a standard correlation without effects of AGN activity. Meanwhile, considering apparent contributions of AGN activity to narrow H$α$ line emissions in the Type-2 AGN, the correlation between $λL_{cont}$ and $L_{Hα}$ in the SDSS Type-2 AGN leads to statistically lower $L_{Hα}$ in the Type-2 AGN than in the starforming galaxies, with significance level higher than 5$σ$, even after considering necessary effects (including effects of host galaxy properties), leading to accepted conclusion on the globally negative AGN feedback in the local Type-2 AGN. Meanwhile, properties of Dn(4000) and H$δ_A$ can provide indirect clues to support the globally negative AGN feedback in the local Type-2 AGN, due to older stellar ages in the Type-2 AGN. Moreover, it is interesting to expect more than 50\% narrow H$α$ emissions globally suppressed in the host galaxies of the Type-2 AGN relative to the starforming galaxies. The results not only support globally negative AGN feedback in the local Type-2 AGN, but also show further clues on the quantification of suppressions of star formation by the globally negative AGN feedback.

astro-ph.GA↗

arXiv2024

A candidate for central tidal disruption event in the broad line AGN SDSS J1605 with double-peaked broad H$β$

In this letter, motivated by double-peaked broad Balmer emission lines probably related to tidal disruption events (TDEs), a potential TDE candidate is reported in SDSS J160536+134838 (=SDSS J1605) at $z\sim0.44$ having quasar-like spectrum but with double-peaked broad H$β$. The long-term CSS light curve can be naturally described by a main-sequence star of $2.82_{-0.19}^{+0.20}{\rm M_\odot}$ disrupted by the central black hole (BH) of $144_{-21}^{+26}\times10^6{\rm M_\odot}$ in SDSS J1605. Meanwhile, the ASAS-SN light curves afterwards show none apparent trend variability, indicating the bright CSS flare in SDSS J1605 unique and different enough from variability of normal AGN. Furthermore, there is a consistency between the TDE model determined sizes of debris with the sizes of emission regions for the double-peaked broad H$β$ described by the accretion disk model, supporting the disk-like BLRs probably related to a central TDE in SDSS J1605. And the virial BH mass $\sim$7 times higher than the TDE model determined value can be naturally explained by R-L relation determined BLRs sizes very larger than the actual distance of emission regions related to TDEs debris in SDSS J1605. Although no clear conclusion on double-peaked broad lines absolutely related to TDEs, the results here provide clues to detect potential TDEs in AGN with double-peaked broad lines.

astro-ph.GA↗

arXiv2024

Very blue-shifted broad H$α$ in a low redshift Type-1.9 AGN: a disk emitter or a recoiling black hole scenario

In this manuscript, very blue-shifted broad H$α$ with shifted velocity $\sim$2200km/s is reported in the low redshift Type-1.9 AGN SDSS J1052+1036. Blue-shifted broad emission lines may arise due to the presence of a rotating gas disk around central black hole (BH), but may also be a signature of rare phenomena such as gravitational wave recoil of a supermassive BH (rSMBH) or the presence of a binary BH (BBH) system. Here, due to larger shifted velocity of stronger and wider blue-shifted broad H$α$, the BBH system is disfavoured. Meanwhile, if this object contained a rSMBH, intrinsic obscuration with E(B-V)$\le$0.6 should lead to a detectable broad H$β$, indicating the rSMBH scenario not preferred. We find that the blue-shifted broad H$α$ can be well explained by emission from an AGN disk, indicating that SDSS J1052+1036 is likely a disk-emitting AGN. In order to determine which scenario, a rSMBH or a disk emitter, is more preferred, a re-observed spectrum in 2025 can provide robust clues, with a disk emitter probably leading to clear variations of peak positions, peak separations and/or peak intensity ratios in broad H$α$, but with a rSMBH scenario probably leading to no variations of peak separations in broad H$α$.

astro-ph.GA↗

arXiv2023

Unobscured central broad line regions in Type-1.9 AGN SDSS J1241+2602

In this manuscript, strong evidence is reported to support unobscured broad line regions (BLRs) in Type-1.9 AGN SDSS J1241+2602 with reliable broad H$α$ but no broad H$β$. Commonly, disappearance of broad H$β$ can be explained by the AGN unified model expected heavily obscured BLRs in Type-1.9 AGN. Here, based on properties of two kinds of BH masses, the virial BH mass and the BH mass through the \msig relation, an independent method is proposed to test whether are there unobscured central BLRs in a Type-1.9 AGN. By the reliable measurement of stellar velocity dispersion about 110$\pm$12km/s through the host galaxy absorption features in \obj, the BH mass through the \msig relation is consistent with the virial BH mass $(3.43\pm1.25)\times10^7{\rm M_\odot}$ determined through properties of the observed broad H$α$ without considering effects of obscurations in SDSS J1241+2602. Meanwhile, if considering heavily obscured BLRs in SDSS J1241+2602, the reddening corrected virial BH mass is tens of times larger than the \msig expected value, leading SDSS J1241+2602 to be an outlier in the \msig space with confidence level higher than $5σ$. Therefore, the unobscured BLRs are preferred in the Type-1.9 AGN SDSS J1241+2602. The results indicate that it is necessary to check whether unobscured central BLRs are common in Type-1.9 AGN, when to test the AGN unified model of AGN by properties of Type-1.9 AGN.

astro-ph.GA↗

arXiv2023

SDSS J1619 with blue-shifted broad components in H$α$ and in [O~{\sc iii}] having similar line width and velocity shifts: a recoiling SMBH candidate?

In this Letter, we report a potential candidate of recoiling supermassive black hole (rSMBH) in SDSS J1619 based on similar velocity shifts and line widths of the blue-shifted broad components in H$α$ and [O~{\sc iii}] doublet. The measured line width ratio between blue-shifted broad H$α$ and broad [O~{\sc iii}] line is 1.06, if compared with common values around 5.12 for normal Type-1 AGN, indicating different properties of the blue-shifted broad components in SDSS J1619 from those of normal QSOs. The virial BH mass $M_{BHr}$ derived from the broad H$α$ is consistent with the mass expected from the M_{BH}-σrelation. The similar velocity shifts and line widths of the blue-shifted broad components in H$α$ and [O~{\sc iii}] and the virial BH mass derived from the H$α$ broad line emissions that is consistent with the mass expected from the M_{BH}-σ~ relation, can be explained by a rSMBH scenario. Besides the rSMBH scenario, either the similar line widths of the blue-shifted broad components in H$α$ and in [O~{\sc iii}] or the consistency between the virial BH mass and the mass expected from the M_{BH}-σ~ relation cannot be explained by the other proposed models in SDSS J1619.

astro-ph.GA↗

arXiv2023

Interesting Clues to Detect Hidden Tidal Disruption Events in Active Galactic Nuclei

In the manuscript, effects of Tidal Disruption Events (TDEs) are estimated on long-term AGN variability, to provide interesting clues to detect probable hidden TDEs in normal broad line AGN with apparent intrinsic variability which overwhelm the TDEs expected variability features, after considering the unique TDEs expected variability patterns. Based on theoretical TDEs expected variability plus AGN intrinsic variability randomly simulated by Continuous AutoRegressive process, long-term variability properties with and without TDEs contributions are well analyzed in AGN. Then, interesting effects of TDEs can be determined on long-term observed variability of AGN. First, more massive BHs, especially masses larger than $10^7{\rm M_\odot}$, can lead to more sensitive and positive dependence of $τ_{TN}$ on $R_{TN}$, with $τ_{TN}$ as variability timescale ratio of light curves with TDEs contributions to intrinsic light curves without TDEs contributions, and $R_{TN}$ as ratio of peak intensity of TDEs expected variability to the mean intensity of intrinsic AGN variability without TDEs contributions. Second, stronger TDEs contributions $R_{TN}$ can lead to $τ_{TN}$ quite larger than 5. Third, for intrinsic AGN variability having longer variability timescales, TDEs contributions will lead $τ_{TN}$ to be increased more slowly. The results actually provide an interesting forward-looking method to detect probable hidden TDEs in normal broad line AGN, due to quite different variability properties, especially different DRW/CAR process expected variability timescales, in different epochs, especially in normal broad line AGN with shorter intrinsic variability timescales and with BH masses larger than $10^7{\rm M_\odot}$.

astro-ph.HE↗

arXiv2023

A sub-pc BBH system in SDSS J1609+1756 through optical QPOs in ZTF light curves

Optical quasi-periodic oscillations (QPOs) are the most preferred signs of sub-pc binary black hole (BBH) systems in AGN. In this manuscript, robust optical QPOs are reported in quasar SDSS J1609+1756 at $z=0.347$. In order to detect reliable optical QPOs, four different methods are applied to analyze the 4.45 years-long ZTF g/r/i-band light curves of SDSS J1609+1756, direct fitting results by sine function, Generalized Lomb-Scargle periodogram, Auto-Cross Correlation Function and Weighted Wavelet Z-transform method. The Four different methods can lead to well determined reliable optical QPOs with periodicities $\sim340$ days with confidence levels higher than 5$σ$, to guarantee the robustness of the optical QPOs in SDSS J1609+1756. Meanwhile, based on simulated light curves through CAR process to trace intrinsic AGN activities, confidence level higher than $3σ$ can be confirmed that the optical QPOs are not mis-detected in intrinsic AGN activities, re-confirming the robust optical QPOs and strongly indicating a central sub-pc BBH system in SDSS J1609+1756. Furthermore, based on apparent red-shifted shoulders in broad Balmer emission lines in SDSS J1609+1756, space separation of the expected central BBH system can be estimated to be smaller than $107\pm60$ light-days, accepted upper limit of total BH mass $\sim(1.03\pm0.22)\times10^8{\rm M_\odot}$. Therefore, to detect and report BBH system expected optical QPOs with periodicities around 1 year is efficiently practicable through ZTF light curves, and combining with peculiar broad line emission features, further clues should be given on space separations of BBH systems in broad line AGN in the near future.

astro-ph.GA↗

arXiv2023

A candidate of binary black hole system in AGN with broad Balmer emission lines having quite different line widths

In the manuscript, a candidate of sub-pc binary black hole (BBH) system is reported in SDSS J1257+2023 through different properties of broad Balmer emission lines. After subtractions of host galaxy contributions, Gaussian functions are applied to measure emission lines in SDSS J1257+2023, leading line width (second moment) 760${\rm km/s}$ of broad H$β$ to be 0.69 times of line width 1100${\rm km/s}$ of broad H$α$, quite different from normal line width ratio 1.1 of broad H$β$ to broad H$α$ in quasars. The quite broader component in broad H$α$ in SDSS J1257+2023 can be confirmed with confidence level higher than $5σ$ through F-test technique, through different model functions applied to measure emission lines. The broad Balmer emission lines having different line widths can be naturally explained by a BBH system with different obscurations on central two independent BLRs. Meanwhile, through ZTF light curves and corresponding phase folded light curves well described by sinusoidal function, BBH system expected optical QPOs can be detected with periodicity about 1000days, confirmed with confidence level higher than $3σ$ by Generalized Lomb-Scargle periodogram. And through CAR process simulated light curves, confidence level higher than $2σ$ can be determined to support the optical QPOs in SDSS J1257+2023 not from intrinsic AGN activities, although the ZTF light curves have short time durations. Moreover, through oversimplified BBH system simulated results, studying different broad Balmer lines as signs of BBH systems in normal quasars with flux ratios around 4 of broad H$α$ to broad H$β$ could be done in near future.

astro-ph.GA↗