B2114+022: a distant radio source gravitationally lensed by a starburst galaxy
4 Given the constraint provided by the shape of the spectrum of the sum of the components shown in Fig. 3, all four components must either have flat spectra or a low-frequency turnover.
3 Compact Symmetric Objects (CSOs) also have two flat spectrum components but they have typical separations around 10 mas, not ∼1 arcsec.
2 iraf (Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.
1 The faint feature visible in Fig. 1 near the radio component D arises from a single bad pixel which we also see in NICMOS images of the lens systems B1600+434 and MG0414+054.
Abstract
We have discovered a radio source (B2114+022) with a unique structure during the course of the JVAS gravitational lens survey. VLA, MERLIN, VLBA and MERLIN+EVN radio maps reveal four compact components, in a configuration unlike that of any known lens system, or, for that matter, any of the ∼15 000 radio sources in the JVAS and CLASS surveys. Three of the components are within 0.3 arcsec of each other while the fourth is separated from the group by 2.4 arcsec. The widest separation pair of components have similar radio structures and spectra. The other pair also have similar properties. This latter pair have spectra which peak at ∼5 GHz. Their surface brightnesses are much lower than expected for synchrotron self-absorbed components.
Ground-based and Hubble Space Telescope optical observations show two galaxies (z=0.3157 and 0.5883) separated by 1.25 arcsec. The lower redshift galaxy has a post-starburst spectrum and lies close to, but not coincident with, the compact group of three radio components. No optical or infrared emission is detected from any of the radio components down to I=25 and H=23. We argue that the most likely explanation of the B2114+022 system is that the post-starburst galaxy, assisted by the second galaxy, lenses a distant radio source producing the two wide-separation images. The other two radio components are then associated with the post-starburst galaxy. The combination of the angular sizes of these components, their radio spectra and their location with respect to their host galaxy still remains puzzling.
