X-ray Properties of Radio-Selected Dual Active Galactic Nuclei

Merger simulations predict that tidally induced gas inflows can trigger kpc-scale dual active galactic nuclei (dAGN) in heavily obscured environments. Previously with the Very Large Array, we have confirmed four dAGN with redshifts between $0.04 < z < 0.22$ and projected separations between 4.3 and 9.2 kpc in the SDSS Stripe 82 field. Here, we present $Chandra$ X-ray observations that spatially resolve these dAGN and compare their multi-wavelength properties to those of single AGN from the literature. We detect X-ray emission from six of the individual merger components and obtain upper limits for the remaining two. Combined with previous radio and optical observations, we find that our dAGN have properties similar to nearby low-luminosity AGN, and they agree well with the black hole fundamental plane relation. There are three AGN-dominated X-ray sources, whose X-ray hardness-ratio derived column densities show that two are unobscured and one is obscured. The low obscured fraction suggests these dAGN are no more obscured than single AGN, in contrast to the predictions from simulations. These three sources show an apparent X-ray deficit compared to their mid-infrared continuum and optical [OIII] line luminosities, suggesting higher levels of obscuration, in tension with the hardness-ratio derived column densities. Enhanced mid-infrared and [OIII] luminosities from star formation may explain this deficit. There is ambiguity in the level of obscuration for the remaining five components since their hardness ratios may be affected by non-nuclear X-ray emissions, or are undetected altogether. They require further observations to be fully characterized.Comment: 11 pages, 5 figures, Accepted for publication in the Astrophysical Journa

Testing the Radio-Selection Method of Dual Active Galactic Nuclei in the Stripe 82 Field

We test the merger-induced dual active galactic nuclei (dAGN) paradigm using a sample of 35 radio galaxy pairs from the SDSS Stripe 82 field. Using Keck optical spectroscopy, we confirm 21 pairs have consistent redshifts, constituting kinematic pairs; the remaining 14 pairs are line-of-sight projections. We classify the optical spectral signatures via emission line ratios, equivalent widths, and excess of radio power above star-formation predicted outputs. We find 6 galaxies are classified as LINERs and 7 are AGN/starburst composites. Most of the LINERs are retired galaxies, while the composites likely have AGN contribution. All of the kinematic pairs exhibit radio power more than 10$\times$ above the level expected from just star-formation, suggestive of a radio AGN contribution. We also analyze high-resolution (0.3") imaging at 6 GHz from the NSF's Karl G. Jansky Very Large Array for 17 of the kinematic pairs. We find 6 pairs (2 new, 4 previously known) host two separate radio cores, confirming their status as dAGNs. The remaining 11 pairs contain single AGNs, with most exhibiting prominent jets/lobes overlapping their companion. Our final census indicates a dAGN duty cycle slightly higher than predictions of purely stochastic fueling, although a larger sample (potentially culled from VLASS) is needed to fully address the dAGN fraction. We conclude that while dAGNs in the Stripe 82 field are rare, the merger process plays some role in their triggering and it facilitates low to moderate levels of accretion.Comment: 26 pages, 10 figures, resubmitted to ApJ after addressing referee report, supplemental figures/data to be included in online journa

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

We report Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) deep IR (F160W) imaging of SDSS J1608+2716. This system, located at a redshift of $z=2.575$, was recently reported as a triple quasar candidate with subarcsecond separations ($\sim0.25''$) based on selection from Gaia astrometry and follow-up Keck adaptive optics-assisted integral field unit spectroscopy. Our new HST deep IR imaging reveals the presence of a fourth point-like component located $\sim0.9''$ away from the triple system. Additionally, we detect an edge-on disk galaxy located in between the four point sources, which appears to be in the process of merging with a fainter companion galaxy. The entire system exhibits a characteristic cusp structure in the context of strong gravitational lensing, and the observed image configuration can be successfully reproduced using a lens model based on a singular isothermal ellipsoid mass profile. These findings indicate that this system is a quadruply lensed quasar. Our results highlight the challenges associated with identifying dual/multiple quasars on $\sim$kpc scales at high redshifts, and emphasize the crucial role of deep, high-resolution IR imaging in robustly confirming such systems.Comment: 9 pages, 3 figures, submitted to ApJ

X-ray Properties of Radio-Selected Dual Active Galactic Nuclei

Merger simulations predict that tidally induced gas inflows can trigger kiloparsec-scale dual active galactic nuclei (dAGN) in heavily obscured environments. Previously, with the Very Large Array, we have confirmed four dAGN with redshifts between 0.04 < z < 0.22 and projected separations between 4.3 and 9.2 kpc in the Sloan Digital Sky Survey Stripe 82 field. Here, we present Chandra X-ray observations that spatially resolve these dAGN and compare their multiwavelength properties to those of single AGN from the literature. We detect X-ray emission from six of the individual merger components and obtain upper limits for the remaining two. Combined with previous radio and optical observations, we find that our dAGN have properties similar to nearby low-luminosity AGN, and they agree with the black hole fundamental plane relation well. There are three AGN-dominated X-ray sources, whose X-ray hardness-ratio derived column densities show that two are unobscured and one is obscured. The low obscured fraction suggests these dAGN are no more obscured than single AGN, in contrast to the predictions from simulations. These three sources show an apparent X-ray deficit compared to their mid-infrared continuum and optical [O iii] line luminosities, suggesting higher levels of obscuration, in tension with the hardness-ratio derived column densities. Enhanced mid-infrared and [O iii] luminosities from star formation may explain this deficit. There is ambiguity in the level of obscuration for the remaining five components because their hardness ratios may be affected by nonnuclear X-ray emissions, or are undetected altogether. They require further observations to be fully characterized

SDSS-IV MaNGA: Galaxy Pair Fraction and Correlated Active Galactic Nuclei

We have identified 105 galaxy pairs at z ~ 0.04 with the MaNGA integral-field spectroscopic data. The pairs have projected separations between 1 kpc and 30 kpc, and are selected to have radial velocity offsets less than 600 km/s and stellar mass ratio between 0.1 and 1. The pair fraction increases with both the physical size of the integral-field unit and the stellar mass, consistent with theoretical expectations. We provide the best-fit analytical function of the pair fraction and find that ~3% of M* galaxies are in close pairs. For both isolated galaxies and paired galaxies, active galactic nuclei (AGN) are selected using emission-line ratios and H_alpha equivalent widths measured inside apertures at a fixed physical size. We find AGNs in ~24% of the paired galaxies and binary AGNs in ~13% of the pairs. To account for the selection biases in both the pair sample and the MaNGA sample, we compare the AGN comoving volume densities with those expected from the mass- and redshift-dependent AGN fractions. We find a strong (~5x) excess of binary AGNs over random pairing and a mild (~20%) deficit of single AGNs. The binary AGN excess increases from ~2x to ~6x as the projected separation decreases from 10-30 kpc to 1-10 kpc. Our results indicate that pairing of galaxies preserves the AGN duty cycle in individual galaxies but increases the population of binary AGNs through correlated activities. We suggest tidally-induced galactic-scale shocks and AGN cross-ionization as two plausible channels to produce low-luminosity narrow-line-selected binary AGNs.Comment: ApJ in press. Matched to accepted version. The pair catalog is provided in the Appendi

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

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

We report Hubble Space Telescope (HST) Wide Field Camera 3 deep IR (F160W) imaging of SDSS J1608+2716. This system, located at a redshift of z = 2.575, was recently reported as a triple-quasar candidate with subarcsecond separations (∼0.″25) based on selection from Gaia astrometry and follow-up Keck adaptive optics–assisted integral field unit spectroscopy. Our new HST deep IR imaging reveals the presence of a fourth point-like component located ∼0.″9 away from the triple system. Additionally, we detect an edge-on disk galaxy located in between the four point sources. The entire system exhibits a characteristic cusp structure in the context of strong gravitational lensing, and the observed image configuration can be successfully reproduced using a lens model based on a singular isothermal ellipsoid mass profile. These findings indicate that this system is a quadruply lensed quasar. Our results highlight the challenges associated with identifying dual/multiple quasars on ∼kiloparsec scales at high redshifts and emphasize the crucial role of deep, high-resolution IR imaging in robustly confirming such systems