Finding binary active galactic nuclei by the centroid shift in imaging surveys

Liu, Yuan

doi:10.1051/0004-6361/201526266

Cited by 11 publications

(13 citation statements)

References 27 publications

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“…In this paper, we have introduced a new technique varstrometry, based on the ideas proposed in Shen (2012) and Liu (2015) where astrometric jitter induced by intrinsic photometric variability in unresolved offcenter sources can be used to constrain the pair separation. A particular application of this technique is to identify sub-kpc dual and off-nucleus AGN with masprecision astrometry.…”

Section: Discussionmentioning

confidence: 99%

Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA): Methodology and Initial Results with Gaia DR2

Hwang

Shen

Zakamska

et al. 2020

ApJ

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Gaia's milli-arcsec (mas) astrometric precision allows systematic identification of optically-selected sub-kpc dual active galactic nuclei (AGN), off-nucleus AGN, and small-scale lensed quasars by 'varstrometry' -where variability-induced astrometric jitter, i.e., temporal displacements of photocenter in unresolved sources, can be reasonably well detected or constrained. This approach extends systematic searches for small-scale ( mas) dual and off-nucleus AGN to poorly explored regime between ∼ 10 pc and ∼ 1 kpc, with Gaia's full sky coverage and depth to G ∼ 21. We outline the general principles of this method and calculate the expected astrometric signals from the full time series of photocenter measurements and light curves. We demonstrate the feasibility of varstrometry by using Gaia DR2 data on a sample of variable pre-main sequence stars with known close companions. We find that extended host galaxies have a significant impact on the accuracy of astrometric and photometric variability in Gaia DR2, a situation to be improved in future Gaia releases. Using spectroscopically confirmed SDSS quasars, we present several examples of candidate sub-kpc off-nucleus or dual AGN selected from Gaia DR2. We discuss the merits and limitations of this method and follow-up strategy for promising candidates. We highlight Gaia's potential of systematically discovering and characterizing the sub-kpc off-nucleus and dual AGN population in the entire optical sky.

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Section: Discussionmentioning

confidence: 99%

Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA): Methodology and Initial Results with Gaia DR2

Hwang

Shen

Zakamska

et al. 2020

ApJ

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“…Using the varstrometry technique (Paper I, also see Wielen 1996;Shen 2012;Liu 2015) and Gaia DR2 data, we have constrained the population of sub-kpc-scale, offnucleus AGN among low-redshift (0.3 < z < 0.8) AGN. We find that low-redshift AGN are well-centered to < 1 kpc, < 500 pc and < 100 pc for 99%, 90% and 40% of the population, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…The same idea was applied to identify variable binary stars (e.g., Wielen 1996;Pourbaix et al 2003), in which the method was dubbed 'variability-induced movers' (VIMs). First extragalactic applications of this technique include Shen (2012) on constraining the sizes of the broad-line region and torus in quasars, and Liu (2015) on identifying dual AGN.…”

Section: Introductionmentioning

confidence: 99%

Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): How Well Centered Are Low-z AGN?

Shen

Hwang

Zakamska

et al. 2019

ApJL

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Off-nucleus active galactic nuclei (AGN) can be signposts of inspiraling supermassive black holes (SMBHs) on galactic scales, or accreting SMBHs recoiling after the coalescence of a SMBH binary or slingshot from three-body interactions. Because of the stochastic variability of AGN, the measured photocenter of an unresolved AGN-host system will display astrometric jitter that depends on the off-nucleus distance of the AGN, the total photometric variability of the system, and the AGN-host contrast. Here we use the precision astrometry from Gaia DR2 to constrain the off-nucleus population of a low-redshift (0.3 < z < 0.8) sample of unobscured broad-line AGN drawn from the SDSS with significant host contribution and photometric variability. We find that Gaia DR2 already provides strong constraints on the projected off-nucleus distance in the sub-kpc regime at these redshifts: 99%, 90% and 40% of AGN must be well-centered to < 1 kpc, < 500 pc and < 100 pc, respectively. Limiting the sample to the most variable subset constrains > 99% of AGN to be well-centered below 500 parsec. These results suggest that genuine off-nucleus AGN (offset by > a few hundred pc) must be rare at low redshift. Future Gaia releases of time series of photocenter and flux measurements, improved treatments for extended sources and longer baselines will further tighten these constraints, and enable a systematic full-sky search for rare off-nucleus AGN on ∼ 10 − 1000 pc scales.

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“…Direct imaging confirmation for most of these sub-pc binary candidates is not feasible even with very long baseline interferometry in radio due to strict angular resolution requirement. Shen et al (2019) and Hwang et al (2020) have proposed a new astrometric technique, varstrometry, with Gaia data (Gaia Collaboration et al 2018) to discover close (sub-arcsecond) dual/lensed quasars (also see Liu 2015;Springer & Ofek 2021). It takes advantage of the ubiquitous quasar variability, which in dual or lensed quasars results in an astrometric noise signature when the asynchronous variability from the two quasars causes centroid jitters in the unresolved system.…”

Section: Introductionmentioning

confidence: 99%

Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): Hubble Space Telescope Discovers Double Quasars

Chen,

Hwang,

Shen

et al. 2021

Preprint

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Dual supermassive black holes (SMBHs) at ∼ kpc scales are the progenitor population of SMBH mergers and play an important role in understanding the pairing and dynamical evolution of massive black holes in galaxy mergers. Because of the stringent resolution requirement and the apparent rareness of these small-separation pairs, there are scarce observational constraints on this population, with few confirmed dual SMBHs at < 10 kpc separations at z > 1. Here we present results from a pilot search for kpc-scale dual quasars selected with Gaia Data release 2 (DR2) astrometry and followed up with Hubble Space Telescope (HST) Wide Field Camera 3 dual-band (F475W and F814W) snapshot imaging. Our targets are quasars primarily selected with the varstrometry technique, i.e., light centroid jitter caused by asynchronous variability from both members in an unresolved quasar pair, supplemented by sub-arcsec pairs already resolved by Gaia DR2. We find an overall high fraction of HST-resolved pairs among the varstrometry-selected quasars (unresolved in Gaia DR2), ∼ 30−50%, increasing toward high redshift (∼ 60 − 80% at z > 1.5). We discuss the nature of the 43 resolved sub-arcsec pairs based on HST and supplementary data. A substantial fraction (∼ 40%) of these pairs are likely physical quasar pairs or gravitationally lensed quasars. We also discover a triple quasar candidate and a quadruply lensed quasar, which is among the smallest-separation quadruple lenses. These results provide important guidelines to improve varstrometry selection and follow-up confirmation of ∼ kpc-scale dual SMBHs at high redshift.

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Finding binary active galactic nuclei by the centroid shift in imaging surveys

Cited by 11 publications

References 27 publications

Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA): Methodology and Initial Results with Gaia DR2

Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA): Methodology and Initial Results with Gaia DR2

Varstrometry for Off-nucleus and Dual Sub-Kpc AGN (VODKA): How Well Centered Are Low-z AGN?

Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): Hubble Space Telescope Discovers Double Quasars

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