INTERNAL KINEMATICS AND STELLAR POPULATIONS OF THE POSTSTARBURST GALAXY SDSS J230743.41+152558.4

We present the first 3D-spectroscopic observations of a nearby H I detected poststarburst, or E+A, galaxy, SDSS J230743.41+152558.4, obtained with the VIMOS IFU spectrograph at ESO VLT. Using the NBURSTS full spectral fitting technique, we derive maps of stellar kinematics, age, and metallicity out to 2-3 half-light radii. Our analysis reveals a large-scale rapidly rotating disk (v circ = 300 km s-1) with a positive age gradient (0.6-1.5 Gyr), and a very metal-rich central region ([Fe/H] = +0.25 dex). If a merger or interaction is responsible for triggering the starburst, the presence of this undisturbed disk suggests a minor merger with a gas-rich satellite as the most plausible option, rather than a disruptive major merger. We find spectroscopic evidence for the presence of an active galactic nucleus. This is an important clue to the feedback mechanism that truncated the starburst. The presently observed quiescent phase may well be a temporary episode in the galaxy's life. SDSS J230743.41+152558.4 is gas-rich and may restart forming stars, again becoming blue before finally settling at the red sequence.