2008ApJ...688...43R -
Astrophys. J., 688, 43-47 (2008/November-3)
Is the optically unidentified radio source FIRST J121839.7+295325 a dark lens?.
RYAN R.E.Jr, COHEN S.H., WINDHORST R.A., KEETON C.R. and VEACH T.J.
Abstract (from CDS):
We present evidence that the optically unidentified radio source FIRST J121839.7+295325 may be strongly lensing a background galaxy. We estimate the redshift of the assumed gravitational arc, discovered in parallel imaging with HST, from MMT-Blue Channel spectroscopy to be zarc=2.48+0.14–0.05. We present lens models with an Einstein radius of RE=1.3" which contains a mass of Mdyn=1012±0.5 M☉, where the uncertainty reflects the range of possible lens redshifts. The putative lens is not detected to Jlim=22.0 mag and Hlim=20.7 mag in our MMT-SWIRC imaging. Using the flux limits from WFPC2 and SWIRC, we estimate that the dynamical mass-to-light ratio of J121839.7+295325 is Mdyn/LB≳10 M☉L–1☉ for AV=1 mag, and this lower limit could be as high as 30 M☉ L–1☉ for AV=0 mag. Since the radio source is optically unidentified (Vlim=25.5 mag) and has a radio flux of S1.4GHz=33 mJy, it is likely a massive early-type galaxy which hosts a radio-loud AGN at 0.8≲zradio≲1.5. However, the present data cannot uniquely determine the mass-to-light ratio of the lensing galaxy, and hence the possibility that this system may be a reasonably dark lens is not ruled out.
Abstract Copyright:
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Journal keyword(s):
Cosmology: Dark Matter - galaxies: individual (FIRST J121839.7+295325) - Cosmology: Gravitational Lensing
Simbad objects:
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