Spatially resolved medium resolution spectroscopy of an interacting E+A (post-starburst) system with the Subaru Telescope

Abstract

ABSTRACT We have performed spatially resolved medium resolution long-slit spectroscopy of a nearby E+A (post-starburst) galaxy system, SDSS J161330.18+510335.5, with the FOCAS spectrograph mounted on the Subaru Telescope. This E+A galaxy has an obvious companion galaxy 14 kpc in front with the velocity difference of 61.8 km s-1. Both galaxies have obviously disturbed morphology. Thus, this E+A system provides us with a perfect opportunity to investigate the relation between the post-starburst phenomena and galaxy-galaxy interaction. We have found that the Hδ equivalent width (EW) of the E+A galaxy is greater than 7 Å galaxy wide (8.5 kpc) with no significant spatial variation. The E+A galaxy has a weak [O iii] emission (EW ∼ 1 Å) offset by ∼2.6 kpc from the peak of the Balmer absorption lines. We detected a rotational velocity in the companion galaxy of >175 km s-1. The progenitor of the companion may have been a rotationally supported, but yet passive S0 galaxy. We did not detect significant rotation on the E+A galaxy. A metallicity estimate based on the r - H colour suggests Z = 0.008 and 0.02, for the E+A and the companion galaxies, respectively. Assuming these metallicity estimates, the age of the E+A galaxy after quenching the star formation is estimated to be 100-500 Myr, with its centre having a slightly younger stellar population. The companion galaxy is estimated to have an older stellar population of >2 Gyr of age with no significant spatial variation. These findings are inconsistent with a simple picture where the dynamical interaction creates infall of the gas reservoir that causes the central starburst/post-starburst. Instead, our results present an important example where the galaxy-galaxy interaction can trigger a galaxy-wide post-starburst phenomenon. © 2008 RAS.