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Title:
Dynamics of Galactic Disks and Mergers at z ~ 1.6: Spatially Resolved Spectroscopy with Keck Laser Guide Star Adaptive Optics
Authors:
Wright, Shelley A.; Larkin, James E.; Law, David R.; Steidel, Charles C.; Shapley, Alice E.; Erb, Dawn K.
Affiliation:
AA(Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA ), AB(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA ), AC(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA ), AD(California Institute of Technology, MS 105-24, Pasadena, CA 91125, USA ), AE(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA ), AF(Department of Physics, University of California, Santa Barbara, CA 93106, USA )
Publication:
The Astrophysical Journal, Volume 699, Issue 1, pp. 421-440 (2009). (ApJ Homepage)
Publication Date:
07/2009
Origin:
IOP
ApJ Keywords:
galaxies: evolution, galaxies: high-redshift, galaxies: kinematics and dynamics, infrared: galaxies
DOI:
10.1088/0004-637X/699/1/421
Bibliographic Code:
2009ApJ...699..421W

Abstract

We present 0farcs2 resolution near-infrared integral field spectroscopy of Hα emission from six star-forming galaxies at z ~ 1.6 (a look-back time of ~9.6 Gyr). These observations were obtained with OSIRIS using the Keck Laser Guide Star Adaptive Optics system. All sources have a compact spatial extent of ~1'', with an average half-light radius of \overline{r} 1/2 = 2.9 kpc and an average dereddened star formation rate of 22 M sun yr-1. Based on Hα kinematics we find that these six galaxies are dynamically distinguishable, and we classify them as either irregular/merger or disk candidate systems. We find three systems (HDF-BX1287, HDF-BX1315, and Q1623-BX491) with varying geometries and dynamical properties. Three galaxies (HDF-BMZ1299, Q2343-BX344, and Q2343-BM145) are well fitted by an inclined-disk model with low-velocity residuals (20 to 46 km s-1). An average plateau velocity of \overline{v_{p}} = 185 km s-1 is achieved within 1.0 kpc. The majority of observed velocity dispersions (\overline{\sigma } ~ 88 km s-1) can be explained by the residual seeing halo, and are not intrinsic to our sources. However, one irregular and one disk candidate have high-velocity dispersions (σobs gsim 200 km s-1) that cannot be solely explained by beam smearing. For two disk candidates, we detect [N II] emission and are able to map the [N II]/Hα ratio on kiloparsec scales. In both cases, [N II] emission is more concentrated than Hα emission (lsim0farcs2), and peak ratios are best explained by the presence of an active galactic nucleus (AGN). These are among the weakest known AGNs at high redshift; however their emission is strong enough to impact high-redshift metallicity studies that use nebular ratios. All disk candidates have likely to be completed only a few orbital periods, and if left unperturbed are excellent candidates to become present-day spiral galaxies.
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