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外文期刊>The Astrophysical journal
>THE NATURE OF EXTREME EMISSION LINE GALAXIES AT z = 1-2: KINEMATICS AND METALLICITIES FROM NEAR-INFRARED SPECTROSCOPY*
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THE NATURE OF EXTREME EMISSION LINE GALAXIES AT z = 1-2: KINEMATICS AND METALLICITIES FROM NEAR-INFRARED SPECTROSCOPY*
We present near-infrared spectroscopy of a sample of 22 Extreme Emission Line Galaxies at redshifts 1.3 z 2.3, confirming that these are low-mass (M = 108-109 M ☉) galaxies undergoing intense starburst episodes (M /SFR ~ 10-100?Myr). The sample is selected by [O III] or Hα emission line flux and equivalent width using near-infrared grism spectroscopy from the 3D-HST survey. High-resolution NIR spectroscopy is obtained with LBT/LUCI and VLT/X-SHOOTER. The [O III]/Hβ line ratio is high ( 5) and [N II]/Hα is always significantly below unity, which suggests a low gas-phase metallicity. We are able to determine gas-phase metallicities for seven of our objects using various strong-line methods, with values in the range 0.05-0.30 Z ☉ and with a median of 0.15 Z ☉; for three of these objects we detect [O III] λ4363, which allows for a direct constraint on the metallicity. The velocity dispersion, as measured from the nebular emission lines, is typically ~50 km s–1. Combined with the observed star-forming activity, the Jeans and Toomre stability criteria imply that the gas fraction must be large (f gas 2/3), consistent with the difference between our dynamical and stellar mass estimates. The implied gas depletion timescale (several hundred Myr) is substantially longer than the inferred mass-weighted ages (~50?Myr), which further supports the emerging picture that most stars in low-mass galaxies form in short, intense bursts of star formation.
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