New multiple AGN systems with subarcsec separation: Confirmation of candidates selected via the novel GMP method

Abstract

The existence of multiple active galactic nuclei (AGNs) at small projected distances on the sky is due to either the presence of multiple, inspiraling supermassive black holes, or to gravitational lensing of a single AGN. Both phenomena allow us to address important astrophysical and cosmological questions. However, few kiloparsec-separation multiple AGNs are currently known. Recently, the newly developed Gaia multi-peak (GMP) method provided numerous new candidate members of these populations. We present spatially resolved, integral-field spectroscopy of a sample of four GMP-selected multiple AGN candidates. In all of these systems, we detect two or more components with subarcsec separations. We find that two of the systems are dual AGNs, one is either an intrinsic triple or a lensed dual AGN, while the last system is a chance alignment of an AGN and a star. Our observations double the number of confirmed multiple AGNs at projected separations below 7 kpc at z > 0.5, present the first detection of a possible triple AGN in a single galaxy at z > 0.5, and successfully test the GMP method as a novel technique to discover previously unknown multiple AGNs.

Varstrometry for Off-nucleus and Dual Subkiloparsec AGN (VODKA). SDSS J1608+2716: A Subarcsecond Quadruply Lensed Quasar at z = 2.575

“…In general, the system consists of an edge-on disklike galaxy G1 with a central bulge as described by q ∼ 0.3 and n ∼ 4.0. Its total magnitude is ∼20.8 mag from our fitting, which is ∼3 times fainter in surface brightness than C, placing it just below the Keck detection limit in Ciurlo et al (2023). The disk of G1 exhibits a classic U-type warped morphology, which cannot be appropriately described by a smooth Sérsic profile, as indicated by the black curve in Figure 1.…”

“…One extended component G1 appears to be an edge-on disklike galaxy located between A, B, C, and D, while G2 exhibits extended emissions in the outskirts but is outshined by the point source D in the central region. The Keck AO-assisted IFU spectrum in Ciurlo et al (2023), which had a FOV of 1 6 × 3 2 that covers D and G2, did not report any signals detected at their positions. Nor was a foreground lens detected in Ciurlo et al (2023), leading the authors to conclude that A, B, and C is most likely to be a bona fide triple-quasar system.…”

“…The Keck AO-assisted IFU spectrum in Ciurlo et al (2023), which had a FOV of 1 6 × 3 2 that covers D and G2, did not report any signals detected at their positions. Nor was a foreground lens detected in Ciurlo et al (2023), leading the authors to conclude that A, B, and C is most likely to be a bona fide triple-quasar system. Our deep HST observation with a larger FOV shows that the image configuration closely resembles a classical cusp structure for a quadruply lensed quasar, with the putative foreground lens clearly detected between the four source images.…”

“…In this paper, we focus on SDSS J160829.23+271626.7 (hereafter SDSS J1608+2716 for short), which is a spectroscopically confirmed type 1 (i.e., broad-line) quasar at z = 2.575 (Dawson et al 2013). It has been recently reported as a close-separation triple-quasar candidate based on adaptive optics (AO)-assisted Keck integral field spectroscopy (IFU; Ciurlo et al 2023), originally selected as a GMP source (Mannucci et al 2022). The Keck observations unambiguously revealed the presence of three distinct components with separations of ∼0 25 (∼2 kpc), each emitting a broad Hα line with FWHM of ∼5000 km s −1 .…”

“…Notably, two components display similar line profiles, while the third component exhibits slight differences in both line width and centroid. The nondetection of a foreground lens in the AO data makes it a promising candidate for a genuine triple-quasar system although the possibility of lensing cannot be ruled out based on the shallow Keck imaging (Ciurlo et al 2023).…”