By performing Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA), astronomers at the University of Illinois at Urbana-Champaign and elsewhere have investigated a quasar known as SDSS J0823+2418. The study, published June 6 on the arXiv preprint server, sheds important light on the true nature of this quasar.
Los cuásares u objetos cuasi-estelares (QSO) son núcleos galácticos activos (AGN) de muy alta luminosidad, que emiten radiación electromagnética observable en longitudes de onda de radio, infrarrojo, visible, ultravioleta y rayos X. Se encuentran entre los objetos más brillantes y distantes del universo conocido, y sirven como herramientas fundamentales para numerosos estudios en astrofísica y cosmología. Por ejemplo, los cuásares se han utilizado para investigar la estructura a gran escala del universo y la era de la reionización. También mejoraron nuestra comprensión de la dinámica de los agujeros negros supermasivos y el medio intergaláctico.
With a redshift of 1.81, SDSS J0823+2418 is a peculiar source, the nature of which is still uncertain. Previous observations have suggested that it may be a dual quasar or a single quasar gravitationally lensed from a foreground galaxy. One of the methods that could be helpful in verifying these two hypotheses is varstrometry.
“Varstrometry is based on variable fluctuations in the position of the astrometric centroid of an unresolved source during a series of observations. Such a signature may indicate the presence of two separate sources with intrinsic photometric variability, making it possible to compile samples of candidate dual quasars into kiloparsec-large-scale physical separations,” writes Arran C. Gross, lead author of the study.
The SDSS J0823+2418 image shows it to consist of two sources, labeled “N” and “S”, separated by approximately 0.64 arcseconds. Previous studies detected differences in the flows at a given wavelength between the two sources. This would suggest that SDSS J0823+2418 is composed of two unique sources that form a dual quasar system. However, the researchers noted that if the flux ratio is constant as a function of wavelength, then the difference could be due to wavelength-independent lens magnification.
The new study found consistent flux ratios (around 1.25-1.45) between N and S sources in optical, near-infrared, ultraviolet, and radio bands and thus spectral power distributions (SEDs). similar, suggesting strong gravitational lensing. This is confirmed by posterior lens modeling, which shows that the best fit positions and magnitudes of the image decomposition are consistent with the strong lens scenario.