Search for quasar pairs with Gaia astrometric data III. Confirmation of 16 dual quasars and 36 projected quasars

Abstract

Dual quasars separated at kiloparsec scale are widely regarded as precursors to binary supermassive black holes and offer a key insight into the dynamical evolution of galaxy mergers. Our series of studies focus on searching for dual quasars by using a selection strategy of zero proper motion and zero parallax to isolate quasar candidates near known ones and by follow-up spectroscopy of the candidates. This paper, the third in the series, reports the spectroscopic confirmations of our quasar pair candidates primarily based on the data of the DESI DR1. We newly identified 16 dual quasars and 36 projected quasars. The redshifts of the 16 dual quasars range from 0.609 to 2.758, with a median of 1.46. One notable system, J0023+0417, exhibits nearly identical spectral features in the two members and shows evidence of a potential foreground galaxy, making it a high-confidence strong gravitational lensing system. The redshift of the 36 projected quasars are from 0.377 to 3.399, with a median of 1.663. Among them, four have projected distances below 30 kpc, offering valuable opportunities to probe the circumgalactic medium (CGM) of the foreground host galaxy through absorption lines.

Figures (6)

• Figure 1: DESI-LS DR9 pseudo-color cutout images and spectra of the 16 dual quasars. Blue and red circles mark the known and unknown quasars from MGQPC, respectively. The system name is shown at the top, while the labels on the left indicate the Gaia G-band magnitude (G), the average redshift ($\langle z \rangle$), the transverse distance ($\langle r_p \rangle$, in units of kpc), the angular separation (Sep, in units of arcsecond), and the radial velocity difference ($|\Delta v_r|$, in units of km/s) between the two quasars. The size of each image is 30$^{\prime\prime}$$\times$ 30$^{\prime\prime}$, with north up and east to the left. Spectral colors match those used in the images. Black dashed lines represent major quasar emission lines.
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• Figure 2: Cutout images and spectra of 36 projected quasars. All pseudo-color images are from DESI-LS DR9. The blue and red circle markings, image size, orientation, and the presentation of spectra are consistent with those in Figure \ref{['DQspec']}. $r_{p,\mathrm{min}}$ is the projected distance of the background quasar (higher redshift) relative to the foreground quasar (lower redshift).
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