SDSS J1004+4112
SDSS J1004+4112 is a gravitationally-lensed quasar located in the constellation of Leo Minor. It has a redshift of 1.73 indicating a light-travel time distance of 10 billion light-years. This object was first discovered by a team of astronomers in December 2003.
Description
SDSS J1004+4112 is classified a quadruple imaged quasar with a separation of 14.62 arcseconds. When imaged, it is separated into four components and lensed by a foreground galaxy cluster located at a redshift of 0.68 based on follow-up imaging observations by Subaru Telescope, making this the first known object lensed by a cluster. A fifth image was discovered by astronomers based on a detection of a faint source located inside of the brightest cluster galaxy in the cluster. Further observations also showed there are seven other imaged galaxies behind SDSS J1004+4112 and the cluster, one of them located at 3.332.Astronomers have found SDSS J1004+4112 displays multiple time delays. Based on optical monitoring data results by J. Fohlmeister, the time delay between the A and B components were calculated as 38.4 ± 2.0 days with B as the leading component. Later in 2008, Fohlmeister would measure the time delays again and found the C component has a time-delay of 2.3 years while also refining the time delay value of A and B components as 40.6 ± 1.8 days. An estimate of 2457 days was found for the D component lagging behind C, making this the longest known measured time delay. Astronomers also noted the A and B components showed evidence of microlensing with flux ratios switching from 0.44 ± 0.01 magnitude to 0.29 ± 0.01 magnitude and vice versa.
Spectroscopy observations conducted in 2004 showed the quasar's spectra shows emission lines differences between the lens images. When probed, the A component displayed signs of strong enhancement in the emission line wing of its ionization lines, indicating the evidence of microlensing of the broad emission line region. A 28-day long amplification period was recorded for the emission lines of the A component.
A study published in 2019 has showed, the four components of SDSS J1004+4112 display polarization. Based on spectroscopy and polarimetric observations, astronomers noted the A and B components have a polarization angle of 40-50° while the polarization angle for the C and D components is 140°. They also noted the D component displays a significant fraction of polarization variability.
The quasar is found to display X-ray emission from the lens images based on Chandra X-ray observations and has a supermassive black hole mass of 108.4 ± 0.2 Mʘ based on a magnesium emission line width. There are also detections of both redshifted and blueshifted lines from the quasar with the quasar's half-light radius of the accretion disk estimated as RE = light-days.