Internal Kinematics and Stellar Populations of the Poststarburst+AGN Galaxy SDSS J230743.41+152558.4

We present the first 3D spectroscopic observations of a nearby HI 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 disc (v_circ = 300km/s) with a positive age gradient (0.6 to 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 disc 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 a LINER or AGN. 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.
accepted for publication by Astrophysical Journal Letters, 9 pages, 4 figures