Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21342421h&link_type=abstract
American Astronomical Society, AAS Meeting #213, #424.21; Bulletin of the American Astronomical Society, Vol. 41, p.249
Astronomy and Astrophysics
Astronomy
1
Scientific paper
We present Keck NIRSPEC rest-frame optical spectra for three lensed galaxies: the recently discovered Cosmic Horseshoe (z = 2.38), the Clone (z = 2.00), and LRG 3-817 (z = 2.26). Gravitational lensing allows for high S/N spectra, providing an unusually detailed view of the physical conditions in these objects. A full complement of high signal-to-noise rest-frame optical lines are measured, spanning from rest-frame 3600 to 6800 Å, including robust detections of H-gamma, [SII]λ6717,6732, and in one instance [NeIII]λ3869. Line ratios from these strong lines allow us to deduce the physical conditions in these objects. Due to the large set of line measurements, metallicities have been calculated with a variety of indicators, which span a range of subsolar values of 12+log(O/H) = 8.3 - 8.6. From the [SII] line ratio, electron densities are high ( 1000 cm-3) compared to local galaxies, and from the [OIII]/[OII] line ratio, calculated ionization parameters are also high (log(q) = 7.6 - 8.0) compared to the local population. A comparison of the Balmer lines allowed us to measure dust reddening coefficients. Variations in the line ratios between the different lensed images are also observed, indicating that the spectra are probing different regions of the lensed galaxy. Current lensing models for the Cosmic Horseshoe and the Clone allow us to correct the measured H-alpha luminosity and calculated star formation rate, which appear to be fairly typical for star-forming galaxies at z 2. The Cosmic Horseshoe and Clone occupy positions on the emission-line diagnostic diagram of [OIII]/Hβ vs. [NII]/Hα offset from the locations of z 0 galaxies. Building on previous similar results at z 2, these measurements provide further evidence (at high S/N) that star-forming regions are significantly different in high-redshift galaxies, compared to what is observed locally.
Allam Sahar S.
Hainline Kevin
Pettini Marco
Shapley Alice
Tucker Douglas L.
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