Study of the Lynx-Cancer void galaxies-V. The extremely isolated galaxy
  UGC4722
  We present a detailed study of the extremely isolated Sdm galaxy UGC4722 (M_B
= -17.4) located in the nearby Lynx-Cancer void. UGC4722 is a member of the
catalogue of isolated galaxies, and has also been identified as one of the most
isolated galaxies in the Local Supercluster. Optical images of the galaxy
however show that it has a peculiar morphology with an elongated ~ 14 kpc long
plume. New observations with the Russian 6-m telescope (BTA) and the Giant
Metrewave Radio Telescope (GMRT) of the ionised and neutral gas in UGC4722
reveal the second component responsible for the disturbed morphology of the
system. This is a small, almost completely destroyed, very gas-rich dwarf (M_B
= -15.2, M_HI/L_B ~4.3). We estimate the oxygen abundance for both galaxies to
be 12+log(O/H) ~ 7.5-7.6, which is 2-3 times lower than what is expected from
the luminosity-metallicity relation for similar galaxies in denser
environments. The ugr colours of the plume derived from Sloan Digital Sky
Survey (SDSS) images are consistent with a simple stellar population with a
post starburst age of 0.45-0.5 Gyr. This system hence appears to be the first
known case of a minor merger with a prominent tidal feature consisting of a
young stellar population.
