The kinematics of morphologically selected z∼2 galaxies in the Goods-North field

We present near-IR spectra of Halpha emission from 13 galaxies at z similar to 2 in the Great Observatories Origins Deep Survey - North (GOODS-N) field. The galaxies were selected primarily because they appear to have elongated morphologies, and slits were aligned with the major axes ( as determined from the rest-frame UVemission) of 11 of the 13. If the galaxies are elongated because they are highly inclined, alignment of the slit and major axis should maximize the observed velocity and reveal velocity shear, if present. In spite of this alignment, we see spatially resolved velocity shear in only two galaxies. We show that the seeing makes a large difference in the observed velocity spread of a tilted emission line, and use this information to place limits on the velocity spread of the ionized gas of the galaxies in the sample: we find that all 13 have v(0.5) less than or equal to 110 km s(-1), where v(0.5) is the velocity shear ( half of the velocity range of a tilted emission line) that would be observed under our best seeing conditions of similar to0.5. When combined with previous work, our data also indicate that aligning the slit along the major axis does not increase the probability of observing a tilted emission line. We then focus on the one-dimensional velocity dispersion sigma, which is much less affected by the seeing, and see that the elongated subsample exhibits a significantly lower velocity dispersion than galaxies selected at random from our total Halpha sample, not higher as one might have expected. We also see some evidence that the elongated galaxies are less reddened than those randomly selected using only UV colors. Both of these results are contrary to what would be expected if the elongated galaxies were highly inclined disks. It is at least as likely that the galaxies' elongated morphologies are due to merging subunits.