Spectral energy distributions of candidate periodically variable quasars: testing the binary black hole hypothesis

Guo, Hengxiao; Liu, Xin; Zafar, T.; Liao, Wei‐Ting

doi:10.1093/mnras/stz3566

Cited by 16 publications

(9 citation statements)

References 168 publications

(226 reference statements)

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“…All four candidate periodic quasars show similar SEDs (within 3σ) to those of the control quasars. Guo et al (2020) have studied the SEDs of the periodic quasar candidates discovered by Graham et al (2015a) and Charisi et al (2016). They have found that the SEDs of periodic quasar candidates from the CRTS and PTF studies are consistent with those of the control quasars.…”

Section: Spectral Energy Distributionmentioning

confidence: 89%

Candidate Periodically Variable Quasars from the Dark Energy Survey and the Sloan Digital Sky Survey

Chen

Liu

Liao

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Periodically variable quasars have been suggested as close binary supermassive black holes. We present a systematic search for periodic light curves in 625 spectroscopically confirmed quasars with a median redshift of 1.8 in a 4.6 deg2 overlapping region of the Dark Energy Survey Supernova (DES-SN) fields and the Sloan Digital Sky Survey Stripe 82 (SDSS-S82). Our sample has a unique 20-year long multi-color (griz) light curve enabled by combining DES-SN Y6 observations with archival SDSS-S82 data. The deep imaging allows us to search for periodic light curves in less luminous quasars (down to r ∼23.5 mag) powered by less massive black holes (with masses ≳ 108.5M⊙) at high redshift for the first time. We find five candidates with significant (at >99.74% single-frequency significance in at least two bands with a global p-value of ∼7 × 10−4–3× 10−3 accounting for the look-elsewhere effect) periodicity with observed periods of ∼3–5 years (i.e., 1–2 years in rest frame) having ∼4–6 cycles spanned by the observations. If all five candidates are periodically variable quasars, this translates into a detection rate of ${\sim }0.8^{+0.5}_{-0.3}$% or ${\sim }1.1^{+0.7}_{-0.5}$ quasar per deg2. Our detection rate is 4–80 times larger than those found by previous searches using shallower surveys over larger areas. This discrepancy is likely caused by differences in the quasar populations probed and the survey data qualities. We discuss implications on the future direct detection of low-frequency gravitational waves. Continued photometric monitoring will further assess the robustness and characteristics of these candidate periodic quasars to determine their physical origins.

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Section: Spectral Energy Distributionmentioning

confidence: 89%

Candidate Periodically Variable Quasars from the Dark Energy Survey and the Sloan Digital Sky Survey

Chen

Liu

Liao

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…To estimate the host-galaxy stellar mass (see Section 3.2 below for details), we queried the archival SED data for DES J0218−0430 using the Vizier tool 5 within 3 arcsec following the procedures of Guo et al (2020a). We adopt measurements from large systematic surveys to focus on a more homogeneous data set.…”

Section: Multiwavelength Observationsmentioning

confidence: 99%

Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability

Guo¹,

Burke²,

Liu³

et al. 2020

Monthly Notices of the Royal Astronomical Society

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ABSTRACT We report the identification of a low-mass active galactic nucleus (AGN), DES J0218−0430, in a redshift z = 0.823 galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218−0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning over 6 yr. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg ii and broad H β lines, confirming its nature as a broad-line AGN. Archival XMM–Newton X-ray observations suggest an intrinsic hard X-ray luminosity of $L_{{\rm 2-12\, keV}}\approx 7.6\pm 0.4\times 10^{43}$ erg s−1, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H β from SDSS spectrum, we estimate a virial black hole (BH) mass of M• ≈ 106.43–106.72 M⊙ (with the error denoting the systematic uncertainty from different calibrations), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift > 0.4 detected in optical. We estimate the host galaxy stellar mass to be M* ≈ 1010.5 ± 0.3 M⊙ based on modelling the multiwavelength spectral energy distribution. DES J0218−0430 extends the M•–M* relation observed in luminous AGNs at z ∼ 1 to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory.

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“…a lower limit of ∼10% for the other candidate periodic quasars from the literature which are radio-loud (𝑅 >10). Guo et al (2020) has carried out a multi-wavelength SED study for the previous candidate periodic quasars from the CRTS and the PTF. These authors find a tentatively higher fraction of radio-loud quasars compared to the control sample of ordinary quasars matched in redshift and luminosity.…”

Section: Comparison To Previous Candidate Periodic Quasarsmentioning

confidence: 99%

Very Large Array imaging rules out precessing radio jets in three DES$-$SDSS-selected candidate periodic quasars

Chen,

Liu,

Liao

et al. 2021

Preprint

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Periodic quasars have been suggested as candidates for hosting binary supermassive black holes (SMBHs), although alternative scenarios remain possible to explain the optical light curve periodicity. To test the alternative hypothesis of precessing radio jet, we present deep 6 GHz radio imaging conducted with NSF's Karl G. Jansky Very Large Array (VLA) in its C configuration for the three candidate periodic quasars, DES J024703.24−010032.0, DES J024944.66−000036.8, and DES J025214.67−002813.7. Our targets were selected based on their optical variability using 20-yr long multi-color light curves from the Dark Energy Survey (DES) and the Sloan Digital Sky Survey (SDSS). The new VLA observations show that all three periodic quasars are radio-quiet with the radio loudness parameters measured to be 𝑅 ≡ 𝑓 6 cm / 𝑓 2500 of ∼1.0-1.8 and the 𝑘-corrected luminosities 𝜈𝐿 𝜈 [6 GHz] of ∼5-21 × 10 39 erg s −1 . They are in stark contrast to previously known periodic quasars proposed as binary SMBH candidates such as the blazar OJ 287 and PG1302−102. Our results rule out optical emission contributed from precessing radio jets as the origin of the optical periodicity in the three DES-SDSS-selected candidate periodic quasars. Future continued optical monitoring and complementary multi-wavelength observations are still needed to further test the binary SMBH hypothesis as well as other competing scenarios to explain the optical periodicity.

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Spectral energy distributions of candidate periodically variable quasars: testing the binary black hole hypothesis

Cited by 16 publications

References 168 publications

Candidate Periodically Variable Quasars from the Dark Energy Survey and the Sloan Digital Sky Survey

Candidate Periodically Variable Quasars from the Dark Energy Survey and the Sloan Digital Sky Survey

Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability

Very Large Array imaging rules out precessing radio jets in three DES$-$SDSS-selected candidate periodic quasars

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