A search for the optical/IR counterpart of the probable Einstein ring source 1830–211

Abstract

We report the results of deep optical and IR imaging, astrometry and spectroscopy of the recently identified, probable Einstein ring source 1830–211. While no definitive counterpart has been identified, several faint objects have been found in the proximity of the radio positions. The brightest object (∼ 20 mag in the red) is nearly coincident with the North-eastern (NE) component of the radio source; however, it has been identified spectroscopically as a foreground M star. Its presence will make the optical or IR identification of the north-eastern radio component very difficult. The object previously proposed as the possible counterpart by Subrahmanyan et al. is probably too far from the radio position to be a viable candidate, as are the other two faint, nearby objects, with typical R or I magnitudes ∼21–23. There is a possible marginal IR detection of an object nearly coincident with the South-western (SW) radio component; its existence needs to be checked by IR imaging in subarcsecond seeing conditions. The follow-up spectroscopy will be extremely difficult, due to the faintness of the possible identifications and the crowding. If previous estimates of the galactic extinction along this line of sight are correct, then 1830–211 is optically very faint and the lensing galaxy is likely to be at a redshift of at least a few tenths.