This paper presents new images and spectroscopic observations of NGC 34
(Mrk 938) obtained with the du Pont 2.5-m and Baade 6.5-m telescopes at
Las Campanas, plus photometry of an archival V image obtained with
Hubble Space Telescope.
This MV = -21.6 galaxy has often been classified as a Seyfert 2, yet
recently published infrared spectra suggest a dominant central starburst.
We find that the galaxy features a single nucleus, a main spheroid
containing a blue central disk and much outer fine structure, and tidal
tails indicative of two former disk galaxies.
At present these galaxies appear to have completed merging.
The remnant 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 star clusters, of which 87 have
absolute magnitudes -10.0 ≥ MV ≥ -15.4.
Five clusters with available spectra have ages in the range 0.1-1.0 Gyr
and photometric masses of 2x106 ≤ M ≤ 2x107M(sun);
they are gravitationally bound young globulars.
(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
suggesting that its optical light is dominated by a ~400 Myr old
poststarburst population.
And (3), the center of NGC 34 drives a strong outflow of cool, neutral gas,
as revealed by broad blueshifted Na I D-lines.
The center-of-line velocity of this gas is -620 km/s, while the
maximum detected outflow velocity reaches -1050 km/s.
Assessing all available evidence, we suggest that NGC 34 stems from two
recently merged gas-rich disk galaxies with an estimated mass
ratio of 1/3 ≤ m/M ≤ 2/3.
The remnant seems to have first experienced a galaxy-wide starburst that
then shrank to its current central and obscured state.
The strong gaseous outflow came last.