Dynamics of Galactic Disks and Mergers at z ~ 1.6: Spatially Resolved Spectroscopy with Keck Laser Guide Star Adaptive Optics
Abstract
We present 0".2 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 r_(1/2) = 2.9 kpc and an average dereddened star formation rate of 22 M⊙ 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 ν(p) = 185 km s^(–1) is achieved within 1.0 kpc. The majority of observed velocity dispersions (σ ~ 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 (σ_(obs) ≳ 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 (≾0".2), 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.
Additional Information
© 2009 The American Astronomical Society. Received 2008 June 20; accepted 2009 April 29; published 2009 June 11. The authors acknowledge the dedicated members of the Keck Observatory staff, particularly Marcos van Dam, Jim Lyke, Randy Campbell, and Al Conrad, who helped greatly with the success of our observations. Our referee offered interesting insight and beneficial suggestions. We would like to thank the generous funding from the Center of Adaptive Optics which supported this research program. Data presented herein were obtained at W.M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by generous financial support of the W.M. Keck Foundation. The authors recognize and acknowledge the significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this "heiau" mountain.Attached Files
Published - Wright2009p4801Astrophys_J.pdf
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Additional details
- Eprint ID
- 15665
- Resolver ID
- CaltechAUTHORS:20090908-091007755
- W. M. Keck Foundation
- Created
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2009-09-15Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field