Gemini Speckle Imaging of Dual Quasar Candidates

We observed the candidate dual quasar )21220026 with speckle interferometric imaging at the Gemini-North Observatory. Result s of our one-hour high resolution 'Alopeke imaging observation agree with and confirm Hubble Space Telescope imaging of the pair separated at ~0'.1 5. These observations show that sub-arcsec dual quasar candidates as faint as r ~ 19 can be observed and detected using speckle imaging at Gemini. "Do not go where the path may lead, go instead where there is no path and leave a tra il."


Introduction and Observations
The population of ~kpc-scale dual supermassive black holes (SMBHs) at z > 1 is poorly explored given the stringent requirement on spat ia l resolution (Shen et al . .2Q21). Faint candidate dua l quasars (wit h both SMBHs being act ive) are usua lly selecte d with ind irect methods and resolved/confirmed with high-resolution observations with Hubble Space Telescope (HST) (Chen et al.~-Ground-based, nearly d iffraction-limited optical imaging will open a new venue to the confirmation and detailed studies of high-z d ual quasars, which in turn will improve our und erstanding of this e lusive population.
We used one-hour of engineering t ime to observe the dual quasar candidate J2122-0026 (Chen et al. .2Q21) on 2021 August 8 UT using the 'Alopeke speckle instrument mounted on the 8 m Gemini-North telescope located on Maunakea, Hl....6..'Alopeke (Scott & Howell .aQ.1. §,) uses a dichroic t o split the optical light at 674 nm and obtains simultaneous blue and red images wit h two EMCCD detectors. The observations reported herein were obtained using SDSS rand i filters at an airmass between 1.0 and 1.09 with seeing of Q1_145 and in dark t ime.
The speckle o bservation consisted of a total on-source time of 45 minutes bracketed by observations of the point-spread function (PSF) standard star HR 8199. Speckle imaging collects many 60 ms images which are then subjected to Fourier analysis a nd used to search fo r close compa nions, dete rmine their properties, and provide reconstructed high resolution images (Howell et al. 2Qll). Observations of HR 8199 consisted of 3 sets of 1000 60 ms images with an EMCCD gain near O whi le the r ~ 19 quasar J2122-0026 observations used 45 sets of 1000 60 ms images and an EMCCD gain of 1000. The HR 8199 (V = 5.5) observations obtained through the broad -band SDSS filters, even at EM gain = 0, contained a ghost due to internal reflections within the instrument. This ghost raised the speckle image background in a non-symmetric manner, producing a low-level ghost in the Fourier output and obscuring the companion image from detection. Thus, in reducing the data, we used 'Alopeke a rchival speckle images of HR 7040 in the blue and HR 7086 in the re d observed at a irmass 1.02 on 2021 June 26 UT and using our sta ndard narrow band fil te rs. In futu re observatio ns of this type, we would reduce the integration time/frame for the bright standard star observed in the SDSS filters.

Discussion
Footnotes References IOP L. ¥ '-1 1 <IIUU='t l <11'-'-A'-'-11'-1 1 ' ->'-'-" '=' Ul l <11'-1 11=1 1 1 , Vt '-''-'->'-1 ¥ U .,VII UIIU <1 1'-' " ''-''-->'-1"<.l ' U"VII \ _,_. _, , V I <I ll.> quasar pair, allowed us to d irectly o bseive t he dual QSO pair, t he purpose of this experiment was to subject the target to speckle int erferometric analysis. Speckle obseivations would allow us to resolve close quasar pairs as fa int as m ~ 18-19 and as close as the diffract ion limit of Gemini (~20 mas) limit not possible with other telescopes. Speckle imaging of sources bright er t han r ~ 15 can be done in bright time, with seein g of less than 1' 2, and with airmass values below 1.4. However, in order to obtain speckle imaging for faint targets such as J2 122, certain observing conditions are req uired. The observations were performed in dark t ime, the seeing was excellent (~0~15), and the airmass remained between 1.0 and 1.09. The total integration time required for the target depends on these conditions but will be close to 45-60 minutes for sources with similar total bright ness  and magnitud e contrast t o J2122. Note that in speckle interferometry, the detection contrast is proportional to 1/seeing 2 while t he angular resolution is unaffected. This is in contrast to IR/AO in which t he final image resolution is affected by the nat ive seeing.
J2122 is the first dual quasar candidate observed by 'Alopeke and the faintest target ever observed by speckle interferometry. Earlier speckle interferometry imaging observations for quasars, even with 6 m telescopes, were limited to brighter (m ~ 16) targets (e.g., Hege et a l. llfil). The raw data and final reduced data products are available at the Gemini archive.
We wish to thank the Gemini Director fo r the allocation of engineering time (GN-2021A-ENG-191)