The Rest-Frame Optical Spectrum of MS 1512-CB58

April 2000 • 2000ApJ...533L..65T

Authors • Teplitz, Harry I. • McLean, Ian S. • Becklin, E. E. • Figer, Donald F. • Gilbert, Andrea M. • Graham, James R. • Larkin, James E. • Levenson, N. A. • Wilcox, Mavourneen K.

Abstract • Moderate-resolution, near-IR spectroscopy of MS 1512-cB58 is presented, obtained during commissioning of the near-infrared spectrometer (NIRSPEC) on the Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground cluster MS 1512+36 makes it the best candidate for detailed study of the rest-frame optical properties of Lyman-break galaxies. In 80 minutes of on-source integration, we have detected Hα, [N II] λλ6583, 6548, [O I] λ6300, He I λ5876, [O III] λλ5007, 4959, Hβ, Hγ, [O II] λ3727, and a strong continuum signal in the range of 1.29-2.46 μm. A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in contrast to the z=2.7233 calculated from UV observations of interstellar absorption lines. Using the Balmer line ratios, we find an extinction of E(B-V) = 0.27. Using the line strengths, we infer a star formation rate (SFR) of 620+/-18 M_solar yr^-1 (H₀=75, q₀=0.1, and Λ=0), which is a factor of 2 higher than that measured from narrowband imaging observations of the galaxy but is a factor of almost 4 lower than the SFR inferred from the UV continuum luminosity. The width of the Balmer lines yields a mass of M_vir=1.2x10¹⁰ M_solar. We find that the oxygen abundance is 1/3 solar, in good agreement with other estimates of the metallicity. However, we infer a high nitrogen abundance, which may argue for the presence of an older stellar population. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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Harry Teplitz

Senior Scientist