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

• Published in: arXiv.org 2010-11
• Main Authors: Bian, Fuyan, Fan, Xiaohui, Bechtold, Jill, McGreer, Ian D, Just, Dennis W, Sand, David J, Green, Richard F, Thompson, David, Peng, Chien Y, Seifert, Walter, Ageorges, Nancy, Juette, Marcus, Knierim, Volker, Buschkamp, Peter
• Format: Article
• Language: English
• Subjects: Abundance; Astronomical models; Density; Emission; Flux; Galaxies; Infrared instruments; Lenses; Luminosity; Metallicity; Photometry; Physical properties; Rest; Star formation; Stars & galaxies
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1004.4318

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.