Remnant of a "Wet" Merger: NGC 34 and Its Young Massive Clusters, Young Stellar Disk, and Strong Gaseous Outflow

This paper presents new images and spectroscopy of NGC 34 (Mrk 938) obtainedwith the du Pont 2.5-m and Baade 6.5-m telescopes at Las Campanas, plusphotometry of an HST archival V image. This Mv = -21.6 galaxy has often beenclassified as a Seyfert 2, yet recently published infrared spectra suggest adominant central starburst. We find that the galaxy features a single nucleus,a main spheroid containing a blue central disk, and tidal tails indicative oftwo former disk galaxies. These galaxies appear to have completed merging. Theremnant shows three clear optical signs that the merger was gas-rich ("wet")and accompanied by a starburst: (1) It sports a rich system of young starclusters, of which 87 have absolute magnitudes -10.0 > Mv > -15.4. Fiveclusters with available spectra have ages in the range 0.1-1.0 Gyr, photometricmasses between 2x10^6 and 2x10^7 Msun, and are gravitationally bound youngglobulars. (2) The blue central disk appears to be young. It is exponential,can be traced to >10 kpc radius, and has a smooth structure and colors suggest-ing a dominant, ~400 Myr old poststarburst population. And (3), the center ofNGC 34 drives a strong outflow of cool, neutral gas, as revealed by broadblueshifted Na I D lines. The mean outflow velocity of this gas is -620 km/s,while the maximum velocity reaches -1050 km/s. We suggest that NGC 34 stemsfrom two recently merged gas-rich disk galaxies with an estimated mass ratiobetween 1/3 and 2/3. The remnant seems to have first experienced a galaxy-widestarburst that then shrank to its current central and obscured state. Thestrong gaseous outflow came last. (Abridged)Comment: 26 pages, 18 figures, 8 tables (emulateapj). Accepted for publication in The Astronomical Journal, Vol. 133. Figs. 1, 2, 3, & 5 degraded to reduce file size