An initial analysis of a strongly-lensed QSOs candidate identified by LAMOST

TL;DR

This paper reports an initial analysis of a candidate strongly-lensed quasar system identified from LAMOST data, suggesting it may be a gravitational lens based on spectral and positional similarities, and estimating lensing parameters.

Contribution

It presents the first detailed analysis of a candidate lensed quasar system from LAMOST, including spectral comparison and lensing mass estimation.

Findings

Components A and B have similar redshifts and spectra, indicating possible lensing.

A nearby galaxy group may act as the lensing mass.

Estimated Einstein mass is 1.46 x 10^{11} M_sun.

Abstract

From 2011 to 2021, LAMOST has released a total of 76,167 quasar data. We try to search for gravitationally lensed QSOs by limiting coordinate differences and redshift differences of these QSOs. The name, brightness, spectrum, photometry and other information of each QSO will be visually checked carefully. Special attention should be paid to check whether there are groups of galaxies, gravitationally lensed arcs, Einstein crosses, or Einstein rings near the QSOs. Through careful selection, we select LAMOST J160603.01+290050.8 (A) and LAMOST J160602.81+290048.7 (B) as a candidate and perform an initial analysis. The component A and B are 3.36 arc seconds apart and they display blue during photometric observations. The redshift values of component A and B are 0.2\% different, their Gaia$\_$g values are 1.3\% different, and their ugriz values are 1.0\% or less different. For the spectra covering from 3,690 {\AA} to 9,100 {\AA}, the emission lines of C\,II, Mg, H\,$\gamma$, O\,III, and H\,$\beta$ are present for both component A and B and the ratio of flux(B) to flux(A) from LAMOST is basically a constant, around 2.2. We accidentally find a galaxy group near the component A and B. If the center of dark matter in the galaxy group is at the center between component A and B, the component A and B are probably gravitationally lensed QSOs. We estimate that the Einstein mass is 1.46 $\times$ $10^{11}$ $M_{\odot}$ and the total mass of the lens is 1.34 $\times$ $10^{13}$ $M_{\odot}$. The deflection angle is 1.97 arc seconds at positions A and B and the velocity dispersion is 261\,$km\,s^{-1}$. Theoretically, this candidate could be a pair of fold images of a strong lensing system by a galaxy group, and we will investigate the possibility when the redshifts of nearby galaxies are available.