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arXiv · 1406.3351

The Nature of Extreme Emission Line Galaxies at z=1-2: Kinematics and Metallicities from Near-Infrared Spectroscopy

Michael V. Maseda·Arjen van der Wel·Hans-Walter Rix·Elisabete da Cunha·Camilla Pacifici·Ivelina Momcheva·Gabriel B. Brammer·Sharon E. Meidt·Marijn Franx·Pieter van Dokkum·Mattia Fumagalli·Eric F. Bell·Henry C. Ferguson·Natascha M. Förster-Schreiber·Anton M. Koekemoer·David C. Koo·Britt F. Lundgren·Danilo Marchesini·Erica J. Nelson·Shannon G. Patel·Rosalind E. Skelton·Amber N. Straughn·Jonathan R. Trump·Katherine E. Whitaker
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Abstract

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* = 10^8 - 10^9 M_sun) galaxies undergoing intense starburst episodes (M*/SFR ~ 10-100 Myr). The sample is selected by [O III] or H{\alpha} 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]/H{\beta} line ratio is high (> 5) and [N II]/H{\alpha} is always significantly below unity, which suggests a low gas-phase metallicity. We are able to determine gas-phase metallicities for 7 of our objects using various strong-line methods, with values in the range 0.05-0.30 Z_sun and with a median of 0.15 Z_sun; for 3 of these objects we detect [O III]{\lambda}4363 which allows for a direct constraint on the metallicity. The velocity dispersion, as measured from the nebular emission lines, is typically ~50 km/s. Combined with the observed star-forming activity, the Jeans and Toomre stability criteria imply that the gas fraction must be large (> 2/3), consistent with the difference between our dynamical and stellar mass estimates. The implied gas depletion time scale (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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Michael V. Maseda, Arjen van der Wel, Hans-Walter Rix, Elisabete da Cunha, Camilla Pacifici, Ivelina Momcheva, Gabriel B. Brammer, Sharon E. Meidt, Marijn Franx, Pieter van Dokkum, Mattia Fumagalli, Eric F. Bell, Henry C. Ferguson, Natascha M. Förster-Schreiber, Anton M. Koekemoer, David C. Koo, Britt F. Lundgren, Danilo Marchesini, Erica J. Nelson, Shannon G. Patel, Rosalind E. Skelton, Amber N. Straughn, Jonathan R. Trump, Katherine E. Whitaker. 2014-06-12. The Nature of Extreme Emission Line Galaxies at z=1-2: Kinematics and Metallicities from Near-Infrared Spectroscopy. https://doi.org/10.1088/0004-637x%2F791%2F1%2F17

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