2008/06/30 by R. E. Ryan Jr., R. E. Ryan, Jr., S. H. Cohen +3
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Einstein radius #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gravitational lens #Lens (geology) #Quasar #RADIUS #Redshift #Strong gravitational lensing #astro-ph
paper · pdf · doi:10.1086/592077
5 pages, 3 figures (1 color), accepted to ApJ. Made minor changes and fixed typos
arxiv created 2008/07/17 · openalex publication_date 2008/11/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 z arc = 2.48 −0.05 +0.14 . We present lens models with an Einstein radius of R E = 1.3'' which contains a mass of M dyn = 10 12 ± 0.5 M ☉ , where the uncertainty reflects the range of possible lens redshifts. The putative lens is not detected to J lim = 22.0 mag and H lim = 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 M dyn / L B ≳ 10 M ☉ L ☉ −1 for A V = 1 mag, and this lower limit could be as high as 30 M ☉ L ☉ −1 for A V = 0 mag. Since the radio source is optically unidentified ( V lim = 25.5 mag) and has a radio flux of S 1.4 GHz = 33 mJy, it is likely a massive early-type galaxy which hosts a radio-loud AGN at 0.8 ≲ z radio ≲ 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.