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arXiv · 0907.4145

COSMOS 5921+0638: Characterization and analysis of a new strong gravitationally lensed AGN

T. Anguita·C. Faure·J. -P. Kneib·J. Wambsganss·C. Knobel·A. M. Koekemoer·M. Limousin
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Abstract

[abridged] We present VLT/FORS1 spectroscopic follow-up observations and HST/WFPC2 imaging of the system COSMOS 5921+0638, which exhibits quadruply lensed images and a perfect Einstein ring. We investigate the nature of COSMOS 5921+0638 by studying its photometric, spectroscopic and physical properties. We completed both an environmental analysis and detailed analytical and grid-based mass modeling of the system. We measured the redshifts of the lensing galaxy in COSMOS 5921+0638 (z_l=0.551+/-0.001) and 9 additional galaxies in the field (5 of them at z~0.35). The redshift of the lensed source was inferred by identifying a candidate Lya line at z_s=3.14+/-0.05. The mass modeling reveals the requirement of a small external shear (gamma=0.038), which is slightly larger than the lensing contribution expected by galaxy groups along the line-of-sight (kappa_groups~0.01 and gamma_groups~0.005). The estimated time-delays between the different images are of the order of hours to half a week and the total magnification of the background source is mu~150. The measured mass-to-light ratio of the lensing galaxy within the Einstein ring is M/L_B~8.5+/-1.6. Our analysis indicates that the ring and point-like structures in COSMOS 5921+0638 consist of a lensed high redshift galaxy hosting a low luminosity AGN (LLAGN). Flux ratio anomalies observed in the lensed AGN images are probably due to microlensing by stars in the lensing galaxy and/or a combination of static phenomena. Because of its short time-delays and the possibility of microlensing, COSMOS 5921+0638 is a promising laboratory for future studies of LLAGNs.

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T. Anguita, C. Faure, J. -P. Kneib, J. Wambsganss, C. Knobel, A. M. Koekemoer, M. Limousin. 2009-11-19. COSMOS 5921+0638: Characterization and analysis of a new strong gravitationally lensed AGN. https://doi.org/10.1051/0004-6361/200912091

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