Spatially Offset Active Galactic Nuclei. I. Selection and Spectroscopic Properties

Abstract

We present a sample of 18optically selected and X-ray-detected spatially offset active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS). In ninesystems, the X-ray active galactic nucleus (AGN) is spatially offset from the galactic stellar core that is located within the 3″ diameter SDSS spectroscopic fiber. In 11systems, the X-ray AGN is spatially offset from a stellar core that is located outside the fiber, with an overlap of two. To build the sample, we cross-matched Type II AGNs selected from the SDSS galaxy catalog with archival Chandra imaging and employed our custom astrometric and registration procedure. The projected angular (physical) offsets span a range of 0 6 (0.8 kpc) to 17 4 (19.4 kpc), with a median value of 2 7 (4.6 kpc). The offset nature of an AGN is an unambiguous signature of a galaxy merger, and these systems can be used to study the properties of AGNs in galaxy mergers without the biases introduced by morphological merger selection techniques. In this paper (Paper I), we use our sample to assess the kinematics of AGN photoionized gas in galaxy mergers. We find that spectroscopic offset AGN selection may be up to -+ 89 16 7 % incomplete due to small projected velocity offsets. We also find that the magnitude of the velocity offsets are generally larger than expected if our spatial selection introduces a bias toward face-on orbits, suggesting the presence of complex kinematics in the emission line gas of AGNs in galaxy mergers.

Galactic-scale Feedback Observed in the 3C 298 Quasar Host Galaxy

“…The offset between the dynamical center of the second disk and the secondary outflow is on the order of 3 kpc. We note that this is a typical separation that is found between the stellar centroid and AGN location in local late-stage mergers (Liu et al 2013b;Comerford et al 2015;Barrows et al 2016). We infer that the 3C 298 system likely has two massive galaxies with distinct rotating disks that are currently experiencing a close passage, where their galactic nuclei and SMBHs have yet to merge.…”

Buried AGNs in Advanced Mergers: Mid-infrared Color Selection as a Dual AGN Candidate Finder

“…We note that due to insufficient counts, coupled with the fact the exact location of the galaxy nuclei is uncertain in the advanced mergers in our sample (see SDSS images in Figure 1), it is impossible to quantify any possible spatial offsets between the positions of the detected Chandra sources and the actual galactic nuclei. It is therefore not possible to determine using these observations alone if some of the mergers host offset AGNs, another unambiguous signature of a galaxy merger that can probe AGN triggering through galaxy interactions (Barrows et al 2016(Barrows et al , 2017. We note that for sources within the 2′ of the boresight, the absolute accuracy of source locations on the ACIS-S chip has a 90% uncertainty radius of  0.…”

THE ORIGIN OF DOUBLE-PEAKED NARROW LINES IN ACTIVE GALACTIC NUCLEI. II. KINEMATIC CLASSIFICATIONS FOR THE POPULATION AT z < 0.1

“…The VLA observations are complementary to the optical longslit data and together they can fully constrain 1 Spatially-resolved imaging of X-ray sources (e.g., Komossa et al 2003;Mazzarella et al 2012;Barrows et al 2016) that are coincident with emission-line peaks can also confirm the presence of dual AGNs. In this paper series we focus on radio observations as a method for confirming dual AGNs.…”