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arXiv · 1004.4318

LBT/LUCIFER Observations of the z~2 Lensed Galaxy J0900+2234

Fuyan Bian·Xiaohui Fan·Jill Bechtold·Ian D. McGreer·Dennis W. Just·David J. Sand·Richard F. Green·David Thompson·Chien Y. Peng·Walter Seifert·Nancy Ageorges·Marcus Juette·Volker Knierim·Peter Buschkamp
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Abstract

We present rest-frame optical images and spectra of the gravitationally lensed, star-forming galaxy J0900+2234 (z=2.03). The observations were performed with the newly commissioned LUCIFER1 near-infrared instrument mounted on the Large Binocular Telescope (LBT). We fit lens models to the rest-frame optical images and find the galaxy has an intrinsic effective radius of 7.4 kpc with a lens magnification factor of about 5 for the A and B components. We also discovered a new arc belonging to another lensed high-z source galaxy, which makes this lens system a potential double Einstein ring system. Using the high S/N rest-frame optical spectra covering H+K band, we detected Hbeta, OIII, Halpha, NII and SII emission lines. Detailed physical properties of this high-z galaxy were derived. The extinction towards the ionized HII regions (E_g(B-V)) is computed from the flux ratio of Halpha and Hbeta and appears to be much higher than that towards stellar continuum (E_s(B-V)), derived from the optical and NIR broad band photometry fitting. The metallicity was estimated using N2 and O3N2 indices. It is in the range of 1/5-1/3 solar abundance, which is much lower than the typical z~2 star-forming galaxies. From the flux ratio of SII 6717 and 6732, we found that the electron number density of the HII regions in the high-z galaxy were >1000 cm^-3, consistent with other z~2 galaxies but much higher than that in local HII regions. The star-formation rate was estimated via the Halpha luminosity, after correction for the lens magnification, to be about 365\pm69 Msun/yr. Combining the FWHM of Halpha emission lines and the half-light radius, we found the dynamical mass of the lensed galaxy is 5.8\pm0.9x10^10 Msun. The gas mass is 5.1\pm1.1x10^10~Msun from the H\alpha flux surface density by using global Kennicutt-Schmidt Law, indicating a very high gas fraction of 0.79\pm0.19 in J0900+2234.

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Fuyan Bian, Xiaohui Fan, Jill Bechtold, Ian D. McGreer, Dennis W. Just, David J. Sand, Richard F. Green, David Thompson, Chien Y. Peng, Walter Seifert, Nancy Ageorges, Marcus Juette, Volker Knierim, Peter Buschkamp. 2010-04-25. LBT/LUCIFER Observations of the z~2 Lensed Galaxy J0900+2234. https://doi.org/10.1088/0004-637x/725/2/1877

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